libgo: update to Go1.18beta2

gotools/
	* Makefile.am (go_cmd_cgo_files): Add ast_go118.go
	(check-go-tool): Copy golang.org/x/tools directories.
	* Makefile.in: Regenerate.

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/384695

37 files changed, 2507 insertions, 250 deletions

diff --git a/libgo/go/golang.org/x/tools/cover/profile.go b/libgo/go/golang.org/x/tools/cover/profile.go
index 57195774cea..47a9a541164 100644
--- a/libgo/go/golang.org/x/tools/cover/profile.go
+++ b/libgo/go/golang.org/x/tools/cover/profile.go
@@ -10,6 +10,7 @@ import (
 	"bufio"
 	"errors"
 	"fmt"
+	"io"
 	"math"
 	"os"
 	"sort"
@@ -45,14 +46,18 @@ func ParseProfiles(fileName string) ([]*Profile, error) {
 		return nil, err
 	}
 	defer pf.Close()
+	return ParseProfilesFromReader(pf)
+}
 
-	files := make(map[string]*Profile)
-	buf := bufio.NewReader(pf)
+// ParseProfilesFromReader parses profile data from the Reader and
+// returns a Profile for each source file described therein.
+func ParseProfilesFromReader(rd io.Reader) ([]*Profile, error) {
 	// First line is "mode: foo", where foo is "set", "count", or "atomic".
 	// Rest of file is in the format
 	//	encoding/base64/base64.go:34.44,37.40 3 1
 	// where the fields are: name.go:line.column,line.column numberOfStatements count
-	s := bufio.NewScanner(buf)
+	files := make(map[string]*Profile)
+	s := bufio.NewScanner(rd)
 	mode := ""
 	for s.Scan() {
 		line := s.Text()
diff --git a/libgo/go/golang.org/x/tools/go/analysis/internal/facts/imports.go b/libgo/go/golang.org/x/tools/go/analysis/internal/facts/imports.go
index 34740f48e04..ade0cc6fab4 100644
--- a/libgo/go/golang.org/x/tools/go/analysis/internal/facts/imports.go
+++ b/libgo/go/golang.org/x/tools/go/analysis/internal/facts/imports.go
@@ -4,7 +4,11 @@
 
 package facts
 
-import "go/types"
+import (
+	"go/types"
+
+	"golang.org/x/tools/internal/typeparams"
+)
 
 // importMap computes the import map for a package by traversing the
 // entire exported API each of its imports.
@@ -42,9 +46,20 @@ func importMap(imports []*types.Package) map[string]*types.Package {
 			// nop
 		case *types.Named:
 			if addObj(T.Obj()) {
+				// TODO(taking): Investigate why the Underlying type is not added here.
 				for i := 0; i < T.NumMethods(); i++ {
 					addObj(T.Method(i))
 				}
+				if tparams := typeparams.ForNamed(T); tparams != nil {
+					for i := 0; i < tparams.Len(); i++ {
+						addType(tparams.At(i))
+					}
+				}
+				if targs := typeparams.NamedTypeArgs(T); targs != nil {
+					for i := 0; i < targs.Len(); i++ {
+						addType(targs.At(i))
+					}
+				}
 			}
 		case *types.Pointer:
 			addType(T.Elem())
@@ -60,6 +75,11 @@ func importMap(imports []*types.Package) map[string]*types.Package {
 		case *types.Signature:
 			addType(T.Params())
 			addType(T.Results())
+			if tparams := typeparams.ForSignature(T); tparams != nil {
+				for i := 0; i < tparams.Len(); i++ {
+					addType(tparams.At(i))
+				}
+			}
 		case *types.Struct:
 			for i := 0; i < T.NumFields(); i++ {
 				addObj(T.Field(i))
@@ -72,6 +92,17 @@ func importMap(imports []*types.Package) map[string]*types.Package {
 			for i := 0; i < T.NumMethods(); i++ {
 				addObj(T.Method(i))
 			}
+			for i := 0; i < T.NumEmbeddeds(); i++ {
+				addType(T.EmbeddedType(i)) // walk Embedded for implicits
+			}
+		case *typeparams.Union:
+			for i := 0; i < T.Len(); i++ {
+				addType(T.Term(i).Type())
+			}
+		case *typeparams.TypeParam:
+			if addObj(T.Obj()) {
+				addType(T.Constraint())
+			}
 		}
 	}
 
diff --git a/libgo/go/golang.org/x/tools/go/analysis/passes/asmdecl/asmdecl.go b/libgo/go/golang.org/x/tools/go/analysis/passes/asmdecl/asmdecl.go
index 34c7a36234d..3997ac861df 100644
--- a/libgo/go/golang.org/x/tools/go/analysis/passes/asmdecl/asmdecl.go
+++ b/libgo/go/golang.org/x/tools/go/analysis/passes/asmdecl/asmdecl.go
@@ -51,6 +51,11 @@ type asmArch struct {
 	bigEndian bool
 	stack     string
 	lr        bool
+	// retRegs is a list of registers for return value in register ABI (ABIInternal).
+	// For now, as we only check whether we write to any result, here we only need to
+	// include the first integer register and first floating-point register. Accessing
+	// any of them counts as writing to result.
+	retRegs []string
 	// calculated during initialization
 	sizes    types.Sizes
 	intSize  int
@@ -79,8 +84,8 @@ type asmVar struct {
 var (
 	asmArch386      = asmArch{name: "386", bigEndian: false, stack: "SP", lr: false}
 	asmArchArm      = asmArch{name: "arm", bigEndian: false, stack: "R13", lr: true}
-	asmArchArm64    = asmArch{name: "arm64", bigEndian: false, stack: "RSP", lr: true}
-	asmArchAmd64    = asmArch{name: "amd64", bigEndian: false, stack: "SP", lr: false}
+	asmArchArm64    = asmArch{name: "arm64", bigEndian: false, stack: "RSP", lr: true, retRegs: []string{"R0", "F0"}}
+	asmArchAmd64    = asmArch{name: "amd64", bigEndian: false, stack: "SP", lr: false, retRegs: []string{"AX", "X0"}}
 	asmArchMips     = asmArch{name: "mips", bigEndian: true, stack: "R29", lr: true}
 	asmArchMipsLE   = asmArch{name: "mipsle", bigEndian: false, stack: "R29", lr: true}
 	asmArchMips64   = asmArch{name: "mips64", bigEndian: true, stack: "R29", lr: true}
@@ -139,7 +144,7 @@ var (
 	asmSP        = re(`[^+\-0-9](([0-9]+)\(([A-Z0-9]+)\))`)
 	asmOpcode    = re(`^\s*(?:[A-Z0-9a-z_]+:)?\s*([A-Z]+)\s*([^,]*)(?:,\s*(.*))?`)
 	ppc64Suff    = re(`([BHWD])(ZU|Z|U|BR)?$`)
-	abiSuff      = re(`^(.+)<ABI.+>$`)
+	abiSuff      = re(`^(.+)<(ABI.+)>$`)
 )
 
 func run(pass *analysis.Pass) (interface{}, error) {
@@ -187,6 +192,7 @@ Files:
 		var (
 			fn                 *asmFunc
 			fnName             string
+			abi                string
 			localSize, argSize int
 			wroteSP            bool
 			noframe            bool
@@ -197,18 +203,22 @@ Files:
 		flushRet := func() {
 			if fn != nil && fn.vars["ret"] != nil && !haveRetArg && len(retLine) > 0 {
 				v := fn.vars["ret"]
+				resultStr := fmt.Sprintf("%d-byte ret+%d(FP)", v.size, v.off)
+				if abi == "ABIInternal" {
+					resultStr = "result register"
+				}
 				for _, line := range retLine {
-					pass.Reportf(analysisutil.LineStart(tf, line), "[%s] %s: RET without writing to %d-byte ret+%d(FP)", arch, fnName, v.size, v.off)
+					pass.Reportf(analysisutil.LineStart(tf, line), "[%s] %s: RET without writing to %s", arch, fnName, resultStr)
 				}
 			}
 			retLine = nil
 		}
-		trimABI := func(fnName string) string {
+		trimABI := func(fnName string) (string, string) {
 			m := abiSuff.FindStringSubmatch(fnName)
 			if m != nil {
-				return m[1]
+				return m[1], m[2]
 			}
-			return fnName
+			return fnName, ""
 		}
 		for lineno, line := range lines {
 			lineno++
@@ -275,11 +285,12 @@ Files:
 						// log.Printf("%s:%d: [%s] cannot check cross-package assembly function: %s is in package %s", fname, lineno, arch, fnName, pkgPath)
 						fn = nil
 						fnName = ""
+						abi = ""
 						continue
 					}
 				}
 				// Trim off optional ABI selector.
-				fnName := trimABI(fnName)
+				fnName, abi = trimABI(fnName)
 				flag := m[3]
 				fn = knownFunc[fnName][arch]
 				if fn != nil {
@@ -307,6 +318,7 @@ Files:
 				flushRet()
 				fn = nil
 				fnName = ""
+				abi = ""
 				continue
 			}
 
@@ -337,6 +349,15 @@ Files:
 				haveRetArg = true
 			}
 
+			if abi == "ABIInternal" && !haveRetArg {
+				for _, reg := range archDef.retRegs {
+					if strings.Contains(line, reg) {
+						haveRetArg = true
+						break
+					}
+				}
+			}
+
 			for _, m := range asmSP.FindAllStringSubmatch(line, -1) {
 				if m[3] != archDef.stack || wroteSP || noframe {
 					continue
diff --git a/libgo/go/golang.org/x/tools/go/analysis/passes/composite/composite.go b/libgo/go/golang.org/x/tools/go/analysis/passes/composite/composite.go
index 4c3ac6647f6..d3670aca97a 100644
--- a/libgo/go/golang.org/x/tools/go/analysis/passes/composite/composite.go
+++ b/libgo/go/golang.org/x/tools/go/analysis/passes/composite/composite.go
@@ -14,6 +14,7 @@ import (
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/analysis/passes/inspect"
 	"golang.org/x/tools/go/ast/inspector"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 const Doc = `check for unkeyed composite literals
@@ -67,41 +68,61 @@ func run(pass *analysis.Pass) (interface{}, error) {
 			// skip whitelisted types
 			return
 		}
-		under := typ.Underlying()
-		for {
-			ptr, ok := under.(*types.Pointer)
-			if !ok {
-				break
+		var structuralTypes []types.Type
+		switch typ := typ.(type) {
+		case *typeparams.TypeParam:
+			terms, err := typeparams.StructuralTerms(typ)
+			if err != nil {
+				return // invalid type
 			}
-			under = ptr.Elem().Underlying()
-		}
-		if _, ok := under.(*types.Struct); !ok {
-			// skip non-struct composite literals
-			return
-		}
-		if isLocalType(pass, typ) {
-			// allow unkeyed locally defined composite literal
-			return
+			for _, term := range terms {
+				structuralTypes = append(structuralTypes, term.Type())
+			}
+		default:
+			structuralTypes = append(structuralTypes, typ)
 		}
+		for _, typ := range structuralTypes {
+			under := deref(typ.Underlying())
+			if _, ok := under.(*types.Struct); !ok {
+				// skip non-struct composite literals
+				continue
+			}
+			if isLocalType(pass, typ) {
+				// allow unkeyed locally defined composite literal
+				continue
+			}
 
-		// check if the CompositeLit contains an unkeyed field
-		allKeyValue := true
-		for _, e := range cl.Elts {
-			if _, ok := e.(*ast.KeyValueExpr); !ok {
-				allKeyValue = false
-				break
+			// check if the CompositeLit contains an unkeyed field
+			allKeyValue := true
+			for _, e := range cl.Elts {
+				if _, ok := e.(*ast.KeyValueExpr); !ok {
+					allKeyValue = false
+					break
+				}
 			}
-		}
-		if allKeyValue {
-			// all the composite literal fields are keyed
+			if allKeyValue {
+				// all the composite literal fields are keyed
+				continue
+			}
+
+			pass.ReportRangef(cl, "%s composite literal uses unkeyed fields", typeName)
 			return
 		}
-
-		pass.ReportRangef(cl, "%s composite literal uses unkeyed fields", typeName)
 	})
 	return nil, nil
 }
 
+func deref(typ types.Type) types.Type {
+	for {
+		ptr, ok := typ.(*types.Pointer)
+		if !ok {
+			break
+		}
+		typ = ptr.Elem().Underlying()
+	}
+	return typ
+}
+
 func isLocalType(pass *analysis.Pass, typ types.Type) bool {
 	switch x := typ.(type) {
 	case *types.Struct:
@@ -112,6 +133,8 @@ func isLocalType(pass *analysis.Pass, typ types.Type) bool {
 	case *types.Named:
 		// names in package foo are local to foo_test too
 		return strings.TrimSuffix(x.Obj().Pkg().Path(), "_test") == strings.TrimSuffix(pass.Pkg.Path(), "_test")
+	case *typeparams.TypeParam:
+		return strings.TrimSuffix(x.Obj().Pkg().Path(), "_test") == strings.TrimSuffix(pass.Pkg.Path(), "_test")
 	}
 	return false
 }
diff --git a/libgo/go/golang.org/x/tools/go/analysis/passes/copylock/copylock.go b/libgo/go/golang.org/x/tools/go/analysis/passes/copylock/copylock.go
index c4ebf785710..350dc4e0fec 100644
--- a/libgo/go/golang.org/x/tools/go/analysis/passes/copylock/copylock.go
+++ b/libgo/go/golang.org/x/tools/go/analysis/passes/copylock/copylock.go
@@ -17,6 +17,7 @@ import (
 	"golang.org/x/tools/go/analysis/passes/inspect"
 	"golang.org/x/tools/go/analysis/passes/internal/analysisutil"
 	"golang.org/x/tools/go/ast/inspector"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 const Doc = `check for locks erroneously passed by value
@@ -145,7 +146,7 @@ func checkCopyLocksCallExpr(pass *analysis.Pass, ce *ast.CallExpr) {
 func checkCopyLocksFunc(pass *analysis.Pass, name string, recv *ast.FieldList, typ *ast.FuncType) {
 	if recv != nil && len(recv.List) > 0 {
 		expr := recv.List[0].Type
-		if path := lockPath(pass.Pkg, pass.TypesInfo.Types[expr].Type); path != nil {
+		if path := lockPath(pass.Pkg, pass.TypesInfo.Types[expr].Type, nil); path != nil {
 			pass.ReportRangef(expr, "%s passes lock by value: %v", name, path)
 		}
 	}
@@ -153,7 +154,7 @@ func checkCopyLocksFunc(pass *analysis.Pass, name string, recv *ast.FieldList, t
 	if typ.Params != nil {
 		for _, field := range typ.Params.List {
 			expr := field.Type
-			if path := lockPath(pass.Pkg, pass.TypesInfo.Types[expr].Type); path != nil {
+			if path := lockPath(pass.Pkg, pass.TypesInfo.Types[expr].Type, nil); path != nil {
 				pass.ReportRangef(expr, "%s passes lock by value: %v", name, path)
 			}
 		}
@@ -199,12 +200,12 @@ func checkCopyLocksRangeVar(pass *analysis.Pass, rtok token.Token, e ast.Expr) {
 	if typ == nil {
 		return
 	}
-	if path := lockPath(pass.Pkg, typ); path != nil {
+	if path := lockPath(pass.Pkg, typ, nil); path != nil {
 		pass.Reportf(e.Pos(), "range var %s copies lock: %v", analysisutil.Format(pass.Fset, e), path)
 	}
 }
 
-type typePath []types.Type
+type typePath []string
 
 // String pretty-prints a typePath.
 func (path typePath) String() string {
@@ -215,7 +216,7 @@ func (path typePath) String() string {
 			fmt.Fprint(&buf, " contains ")
 		}
 		// The human-readable path is in reverse order, outermost to innermost.
-		fmt.Fprint(&buf, path[n-i-1].String())
+		fmt.Fprint(&buf, path[n-i-1])
 	}
 	return buf.String()
 }
@@ -234,16 +235,57 @@ func lockPathRhs(pass *analysis.Pass, x ast.Expr) typePath {
 			return nil
 		}
 	}
-	return lockPath(pass.Pkg, pass.TypesInfo.Types[x].Type)
+	return lockPath(pass.Pkg, pass.TypesInfo.Types[x].Type, nil)
 }
 
 // lockPath returns a typePath describing the location of a lock value
 // contained in typ. If there is no contained lock, it returns nil.
-func lockPath(tpkg *types.Package, typ types.Type) typePath {
+//
+// The seenTParams map is used to short-circuit infinite recursion via type
+// parameters.
+func lockPath(tpkg *types.Package, typ types.Type, seenTParams map[*typeparams.TypeParam]bool) typePath {
 	if typ == nil {
 		return nil
 	}
 
+	if tpar, ok := typ.(*typeparams.TypeParam); ok {
+		if seenTParams == nil {
+			// Lazily allocate seenTParams, since the common case will not involve
+			// any type parameters.
+			seenTParams = make(map[*typeparams.TypeParam]bool)
+		}
+		if seenTParams[tpar] {
+			return nil
+		}
+		seenTParams[tpar] = true
+		terms, err := typeparams.StructuralTerms(tpar)
+		if err != nil {
+			return nil // invalid type
+		}
+		for _, term := range terms {
+			subpath := lockPath(tpkg, term.Type(), seenTParams)
+			if len(subpath) > 0 {
+				if term.Tilde() {
+					// Prepend a tilde to our lock path entry to clarify the resulting
+					// diagnostic message. Consider the following example:
+					//
+					//  func _[Mutex interface{ ~sync.Mutex; M() }](m Mutex) {}
+					//
+					// Here the naive error message will be something like "passes lock
+					// by value: Mutex contains sync.Mutex". This is misleading because
+					// the local type parameter doesn't actually contain sync.Mutex,
+					// which lacks the M method.
+					//
+					// With tilde, it is clearer that the containment is via an
+					// approximation element.
+					subpath[len(subpath)-1] = "~" + subpath[len(subpath)-1]
+				}
+				return append(subpath, typ.String())
+			}
+		}
+		return nil
+	}
+
 	for {
 		atyp, ok := typ.Underlying().(*types.Array)
 		if !ok {
@@ -252,6 +294,17 @@ func lockPath(tpkg *types.Package, typ types.Type) typePath {
 		typ = atyp.Elem()
 	}
 
+	ttyp, ok := typ.Underlying().(*types.Tuple)
+	if ok {
+		for i := 0; i < ttyp.Len(); i++ {
+			subpath := lockPath(tpkg, ttyp.At(i).Type(), seenTParams)
+			if subpath != nil {
+				return append(subpath, typ.String())
+			}
+		}
+		return nil
+	}
+
 	// We're only interested in the case in which the underlying
 	// type is a struct. (Interfaces and pointers are safe to copy.)
 	styp, ok := typ.Underlying().(*types.Struct)
@@ -263,7 +316,7 @@ func lockPath(tpkg *types.Package, typ types.Type) typePath {
 	// is a sync.Locker, but a value is not. This differentiates
 	// embedded interfaces from embedded values.
 	if types.Implements(types.NewPointer(typ), lockerType) && !types.Implements(typ, lockerType) {
-		return []types.Type{typ}
+		return []string{typ.String()}
 	}
 
 	// In go1.10, sync.noCopy did not implement Locker.
@@ -272,15 +325,15 @@ func lockPath(tpkg *types.Package, typ types.Type) typePath {
 	if named, ok := typ.(*types.Named); ok &&
 		named.Obj().Name() == "noCopy" &&
 		named.Obj().Pkg().Path() == "sync" {
-		return []types.Type{typ}
+		return []string{typ.String()}
 	}
 
 	nfields := styp.NumFields()
 	for i := 0; i < nfields; i++ {
 		ftyp := styp.Field(i).Type()
-		subpath := lockPath(tpkg, ftyp)
+		subpath := lockPath(tpkg, ftyp, seenTParams)
 		if subpath != nil {
-			return append(subpath, typ)
+			return append(subpath, typ.String())
 		}
 	}
 
diff --git a/libgo/go/golang.org/x/tools/go/analysis/passes/ctrlflow/ctrlflow.go b/libgo/go/golang.org/x/tools/go/analysis/passes/ctrlflow/ctrlflow.go
index 51600ffc7eb..73746d6f04d 100644
--- a/libgo/go/golang.org/x/tools/go/analysis/passes/ctrlflow/ctrlflow.go
+++ b/libgo/go/golang.org/x/tools/go/analysis/passes/ctrlflow/ctrlflow.go
@@ -187,7 +187,11 @@ func (c *CFGs) callMayReturn(call *ast.CallExpr) (r bool) {
 		return false // panic never returns
 	}
 
-	// Is this a static call?
+	// Is this a static call? Also includes static functions
+	// parameterized by a type. Such functions may or may not
+	// return depending on the parameter type, but in some
+	// cases the answer is definite. We let ctrlflow figure
+	// that out.
 	fn := typeutil.StaticCallee(c.pass.TypesInfo, call)
 	if fn == nil {
 		return true // callee not statically known; be conservative
diff --git a/libgo/go/golang.org/x/tools/go/analysis/passes/ifaceassert/ifaceassert.go b/libgo/go/golang.org/x/tools/go/analysis/passes/ifaceassert/ifaceassert.go
index fd2285332cc..30130f63ea6 100644
--- a/libgo/go/golang.org/x/tools/go/analysis/passes/ifaceassert/ifaceassert.go
+++ b/libgo/go/golang.org/x/tools/go/analysis/passes/ifaceassert/ifaceassert.go
@@ -51,6 +51,12 @@ func assertableTo(v, t types.Type) *types.Func {
 	if V == nil || T == nil {
 		return nil
 	}
+
+	// Mitigations for interface comparisons and generics.
+	// TODO(https://github.com/golang/go/issues/50658): Support more precise conclusion.
+	if isParameterized(V) || isParameterized(T) {
+		return nil
+	}
 	if f, wrongType := types.MissingMethod(V, T, false); wrongType {
 		return f
 	}
diff --git a/libgo/go/golang.org/x/tools/go/analysis/passes/ifaceassert/parameterized.go b/libgo/go/golang.org/x/tools/go/analysis/passes/ifaceassert/parameterized.go
new file mode 100644
index 00000000000..1285ecf1367
--- /dev/null
+++ b/libgo/go/golang.org/x/tools/go/analysis/passes/ifaceassert/parameterized.go
@@ -0,0 +1,112 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+package ifaceassert
+
+import (
+	"go/types"
+
+	"golang.org/x/tools/internal/typeparams"
+)
+
+// isParameterized reports whether typ contains any of the type parameters of tparams.
+//
+// NOTE: Adapted from go/types/infer.go. If that is exported in a future release remove this copy.
+func isParameterized(typ types.Type) bool {
+	w := tpWalker{
+		seen: make(map[types.Type]bool),
+	}
+	return w.isParameterized(typ)
+}
+
+type tpWalker struct {
+	seen map[types.Type]bool
+}
+
+func (w *tpWalker) isParameterized(typ types.Type) (res bool) {
+	// detect cycles
+	if x, ok := w.seen[typ]; ok {
+		return x
+	}
+	w.seen[typ] = false
+	defer func() {
+		w.seen[typ] = res
+	}()
+
+	switch t := typ.(type) {
+	case nil, *types.Basic: // TODO(gri) should nil be handled here?
+		break
+
+	case *types.Array:
+		return w.isParameterized(t.Elem())
+
+	case *types.Slice:
+		return w.isParameterized(t.Elem())
+
+	case *types.Struct:
+		for i, n := 0, t.NumFields(); i < n; i++ {
+			if w.isParameterized(t.Field(i).Type()) {
+				return true
+			}
+		}
+
+	case *types.Pointer:
+		return w.isParameterized(t.Elem())
+
+	case *types.Tuple:
+		n := t.Len()
+		for i := 0; i < n; i++ {
+			if w.isParameterized(t.At(i).Type()) {
+				return true
+			}
+		}
+
+	case *types.Signature:
+		// t.tparams may not be nil if we are looking at a signature
+		// of a generic function type (or an interface method) that is
+		// part of the type we're testing. We don't care about these type
+		// parameters.
+		// Similarly, the receiver of a method may declare (rather then
+		// use) type parameters, we don't care about those either.
+		// Thus, we only need to look at the input and result parameters.
+		return w.isParameterized(t.Params()) || w.isParameterized(t.Results())
+
+	case *types.Interface:
+		for i, n := 0, t.NumMethods(); i < n; i++ {
+			if w.isParameterized(t.Method(i).Type()) {
+				return true
+			}
+		}
+		terms, err := typeparams.InterfaceTermSet(t)
+		if err != nil {
+			panic(err)
+		}
+		for _, term := range terms {
+			if w.isParameterized(term.Type()) {
+				return true
+			}
+		}
+
+	case *types.Map:
+		return w.isParameterized(t.Key()) || w.isParameterized(t.Elem())
+
+	case *types.Chan:
+		return w.isParameterized(t.Elem())
+
+	case *types.Named:
+		list := typeparams.NamedTypeArgs(t)
+		for i, n := 0, list.Len(); i < n; i++ {
+			if w.isParameterized(list.At(i)) {
+				return true
+			}
+		}
+
+	case *typeparams.TypeParam:
+		return true
+
+	default:
+		panic(t) // unreachable
+	}
+
+	return false
+}
diff --git a/libgo/go/golang.org/x/tools/go/analysis/passes/nilfunc/nilfunc.go b/libgo/go/golang.org/x/tools/go/analysis/passes/nilfunc/nilfunc.go
index cd42c9897f2..e4c66df6d6d 100644
--- a/libgo/go/golang.org/x/tools/go/analysis/passes/nilfunc/nilfunc.go
+++ b/libgo/go/golang.org/x/tools/go/analysis/passes/nilfunc/nilfunc.go
@@ -14,6 +14,7 @@ import (
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/analysis/passes/inspect"
 	"golang.org/x/tools/go/ast/inspector"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 const Doc = `check for useless comparisons between functions and nil
@@ -59,6 +60,12 @@ func run(pass *analysis.Pass) (interface{}, error) {
 			obj = pass.TypesInfo.Uses[v]
 		case *ast.SelectorExpr:
 			obj = pass.TypesInfo.Uses[v.Sel]
+		case *ast.IndexExpr, *typeparams.IndexListExpr:
+			// Check generic functions such as "f[T1,T2]".
+			x, _, _, _ := typeparams.UnpackIndexExpr(v)
+			if id, ok := x.(*ast.Ident); ok {
+				obj = pass.TypesInfo.Uses[id]
+			}
 		default:
 			return
 		}
diff --git a/libgo/go/golang.org/x/tools/go/analysis/passes/printf/printf.go b/libgo/go/golang.org/x/tools/go/analysis/passes/printf/printf.go
index 822820f06e9..dee37d78ae0 100644
--- a/libgo/go/golang.org/x/tools/go/analysis/passes/printf/printf.go
+++ b/libgo/go/golang.org/x/tools/go/analysis/passes/printf/printf.go
@@ -25,6 +25,7 @@ import (
 	"golang.org/x/tools/go/analysis/passes/internal/analysisutil"
 	"golang.org/x/tools/go/ast/inspector"
 	"golang.org/x/tools/go/types/typeutil"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 func init() {
@@ -452,8 +453,15 @@ func stringConstantArg(pass *analysis.Pass, call *ast.CallExpr, idx int) (string
 	if idx >= len(call.Args) {
 		return "", false
 	}
-	arg := call.Args[idx]
-	lit := pass.TypesInfo.Types[arg].Value
+	return stringConstantExpr(pass, call.Args[idx])
+}
+
+// stringConstantExpr returns expression's string constant value.
+//
+// ("", false) is returned if expression isn't a string
+// constant.
+func stringConstantExpr(pass *analysis.Pass, expr ast.Expr) (string, bool) {
+	lit := pass.TypesInfo.Types[expr].Value
 	if lit != nil && lit.Kind() == constant.String {
 		return constant.StringVal(lit), true
 	}
@@ -490,7 +498,7 @@ func printfNameAndKind(pass *analysis.Pass, call *ast.CallExpr) (fn *types.Func,
 		_, ok = isPrint[strings.ToLower(fn.Name())]
 	}
 	if ok {
-		if fn.Name() == "Errorf" {
+		if fn.FullName() == "fmt.Errorf" {
 			kind = KindErrorf
 		} else if strings.HasSuffix(fn.Name(), "f") {
 			kind = KindPrintf
@@ -513,7 +521,12 @@ func printfNameAndKind(pass *analysis.Pass, call *ast.CallExpr) (fn *types.Func,
 func isFormatter(typ types.Type) bool {
 	// If the type is an interface, the value it holds might satisfy fmt.Formatter.
 	if _, ok := typ.Underlying().(*types.Interface); ok {
-		return true
+		// Don't assume type parameters could be formatters. With the greater
+		// expressiveness of constraint interface syntax we expect more type safety
+		// when using type parameters.
+		if !typeparams.IsTypeParam(typ) {
+			return true
+		}
 	}
 	obj, _, _ := types.LookupFieldOrMethod(typ, false, nil, "Format")
 	fn, ok := obj.(*types.Func)
@@ -555,7 +568,7 @@ func checkPrintf(pass *analysis.Pass, kind Kind, call *ast.CallExpr, fn *types.F
 	format, idx := formatString(pass, call)
 	if idx < 0 {
 		if false {
-			pass.Reportf(call.Lparen, "can't check non-constant format in call to %s", fn.Name())
+			pass.Reportf(call.Lparen, "can't check non-constant format in call to %s", fn.FullName())
 		}
 		return
 	}
@@ -563,7 +576,7 @@ func checkPrintf(pass *analysis.Pass, kind Kind, call *ast.CallExpr, fn *types.F
 	firstArg := idx + 1 // Arguments are immediately after format string.
 	if !strings.Contains(format, "%") {
 		if len(call.Args) > firstArg {
-			pass.Reportf(call.Lparen, "%s call has arguments but no formatting directives", fn.Name())
+			pass.Reportf(call.Lparen, "%s call has arguments but no formatting directives", fn.FullName())
 		}
 		return
 	}
@@ -577,7 +590,7 @@ func checkPrintf(pass *analysis.Pass, kind Kind, call *ast.CallExpr, fn *types.F
 		if format[i] != '%' {
 			continue
 		}
-		state := parsePrintfVerb(pass, call, fn.Name(), format[i:], firstArg, argNum)
+		state := parsePrintfVerb(pass, call, fn.FullName(), format[i:], firstArg, argNum)
 		if state == nil {
 			return
 		}
@@ -589,8 +602,9 @@ func checkPrintf(pass *analysis.Pass, kind Kind, call *ast.CallExpr, fn *types.F
 			anyIndex = true
 		}
 		if state.verb == 'w' {
-			if kind != KindErrorf {
-				pass.Reportf(call.Pos(), "%s call has error-wrapping directive %%w, which is only supported by Errorf", state.name)
+			switch kind {
+			case KindNone, KindPrint, KindPrintf:
+				pass.Reportf(call.Pos(), "%s does not support error-wrapping directive %%w", state.name)
 				return
 			}
 			if anyW {
@@ -621,7 +635,7 @@ func checkPrintf(pass *analysis.Pass, kind Kind, call *ast.CallExpr, fn *types.F
 	if maxArgNum != len(call.Args) {
 		expect := maxArgNum - firstArg
 		numArgs := len(call.Args) - firstArg
-		pass.ReportRangef(call, "%s call needs %v but has %v", fn.Name(), count(expect, "arg"), count(numArgs, "arg"))
+		pass.ReportRangef(call, "%s call needs %v but has %v", fn.FullName(), count(expect, "arg"), count(numArgs, "arg"))
 	}
 }
 
@@ -833,8 +847,9 @@ func okPrintfArg(pass *analysis.Pass, call *ast.CallExpr, state *formatState) (o
 	}
 
 	// Could current arg implement fmt.Formatter?
+	// Skip check for the %w verb, which requires an error.
 	formatter := false
-	if state.argNum < len(call.Args) {
+	if v.typ != argError && state.argNum < len(call.Args) {
 		if tv, ok := pass.TypesInfo.Types[call.Args[state.argNum]]; ok {
 			formatter = isFormatter(tv.Type)
 		}
@@ -870,8 +885,12 @@ func okPrintfArg(pass *analysis.Pass, call *ast.CallExpr, state *formatState) (o
 			return
 		}
 		arg := call.Args[argNum]
-		if !matchArgType(pass, argInt, nil, arg) {
-			pass.ReportRangef(call, "%s format %s uses non-int %s as argument of *", state.name, state.format, analysisutil.Format(pass.Fset, arg))
+		if reason, ok := matchArgType(pass, argInt, arg); !ok {
+			details := ""
+			if reason != "" {
+				details = " (" + reason + ")"
+			}
+			pass.ReportRangef(call, "%s format %s uses non-int %s%s as argument of *", state.name, state.format, analysisutil.Format(pass.Fset, arg), details)
 			return false
 		}
 	}
@@ -888,12 +907,16 @@ func okPrintfArg(pass *analysis.Pass, call *ast.CallExpr, state *formatState) (o
 		pass.ReportRangef(call, "%s format %s arg %s is a func value, not called", state.name, state.format, analysisutil.Format(pass.Fset, arg))
 		return false
 	}
-	if !matchArgType(pass, v.typ, nil, arg) {
+	if reason, ok := matchArgType(pass, v.typ, arg); !ok {
 		typeString := ""
 		if typ := pass.TypesInfo.Types[arg].Type; typ != nil {
 			typeString = typ.String()
 		}
-		pass.ReportRangef(call, "%s format %s has arg %s of wrong type %s", state.name, state.format, analysisutil.Format(pass.Fset, arg), typeString)
+		details := ""
+		if reason != "" {
+			details = " (" + reason + ")"
+		}
+		pass.ReportRangef(call, "%s format %s has arg %s of wrong type %s%s", state.name, state.format, analysisutil.Format(pass.Fset, arg), typeString, details)
 		return false
 	}
 	if v.typ&argString != 0 && v.verb != 'T' && !bytes.Contains(state.flags, []byte{'#'}) {
@@ -949,7 +972,7 @@ func recursiveStringer(pass *analysis.Pass, e ast.Expr) (string, bool) {
 	}
 	if id, ok := e.(*ast.Ident); ok {
 		if pass.TypesInfo.Uses[id] == sig.Recv() {
-			return method.Name(), true
+			return method.FullName(), true
 		}
 	}
 	return "", false
@@ -1044,40 +1067,39 @@ func checkPrint(pass *analysis.Pass, call *ast.CallExpr, fn *types.Func) {
 		if sel, ok := call.Args[0].(*ast.SelectorExpr); ok {
 			if x, ok := sel.X.(*ast.Ident); ok {
 				if x.Name == "os" && strings.HasPrefix(sel.Sel.Name, "Std") {
-					pass.ReportRangef(call, "%s does not take io.Writer but has first arg %s", fn.Name(), analysisutil.Format(pass.Fset, call.Args[0]))
+					pass.ReportRangef(call, "%s does not take io.Writer but has first arg %s", fn.FullName(), analysisutil.Format(pass.Fset, call.Args[0]))
 				}
 			}
 		}
 	}
 
 	arg := args[0]
-	if lit, ok := arg.(*ast.BasicLit); ok && lit.Kind == token.STRING {
-		// Ignore trailing % character in lit.Value.
+	if s, ok := stringConstantExpr(pass, arg); ok {
+		// Ignore trailing % character
 		// The % in "abc 0.0%" couldn't be a formatting directive.
-		s := strings.TrimSuffix(lit.Value, `%"`)
+		s = strings.TrimSuffix(s, "%")
 		if strings.Contains(s, "%") {
 			m := printFormatRE.FindStringSubmatch(s)
 			if m != nil {
-				pass.ReportRangef(call, "%s call has possible formatting directive %s", fn.Name(), m[0])
+				pass.ReportRangef(call, "%s call has possible formatting directive %s", fn.FullName(), m[0])
 			}
 		}
 	}
 	if strings.HasSuffix(fn.Name(), "ln") {
 		// The last item, if a string, should not have a newline.
 		arg = args[len(args)-1]
-		if lit, ok := arg.(*ast.BasicLit); ok && lit.Kind == token.STRING {
-			str, _ := strconv.Unquote(lit.Value)
-			if strings.HasSuffix(str, "\n") {
-				pass.ReportRangef(call, "%s arg list ends with redundant newline", fn.Name())
+		if s, ok := stringConstantExpr(pass, arg); ok {
+			if strings.HasSuffix(s, "\n") {
+				pass.ReportRangef(call, "%s arg list ends with redundant newline", fn.FullName())
 			}
 		}
 	}
 	for _, arg := range args {
 		if isFunctionValue(pass, arg) {
-			pass.ReportRangef(call, "%s arg %s is a func value, not called", fn.Name(), analysisutil.Format(pass.Fset, arg))
+			pass.ReportRangef(call, "%s arg %s is a func value, not called", fn.FullName(), analysisutil.Format(pass.Fset, arg))
 		}
 		if methodName, ok := recursiveStringer(pass, arg); ok {
-			pass.ReportRangef(call, "%s arg %s causes recursive call to %s method", fn.Name(), analysisutil.Format(pass.Fset, arg), methodName)
+			pass.ReportRangef(call, "%s arg %s causes recursive call to %s method", fn.FullName(), analysisutil.Format(pass.Fset, arg), methodName)
 		}
 	}
 }
diff --git a/libgo/go/golang.org/x/tools/go/analysis/passes/printf/types.go b/libgo/go/golang.org/x/tools/go/analysis/passes/printf/types.go
index 6a5fae44f46..270e917c809 100644
--- a/libgo/go/golang.org/x/tools/go/analysis/passes/printf/types.go
+++ b/libgo/go/golang.org/x/tools/go/analysis/passes/printf/types.go
@@ -5,45 +5,60 @@
 package printf
 
 import (
+	"fmt"
 	"go/ast"
 	"go/types"
 
 	"golang.org/x/tools/go/analysis"
-	"golang.org/x/tools/go/analysis/passes/internal/analysisutil"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 var errorType = types.Universe.Lookup("error").Type().Underlying().(*types.Interface)
 
-// matchArgType reports an error if printf verb t is not appropriate
-// for operand arg.
+// matchArgType reports an error if printf verb t is not appropriate for
+// operand arg.
 //
-// typ is used only for recursive calls; external callers must supply nil.
-//
-// (Recursion arises from the compound types {map,chan,slice} which
-// may be printed with %d etc. if that is appropriate for their element
-// types.)
-func matchArgType(pass *analysis.Pass, t printfArgType, typ types.Type, arg ast.Expr) bool {
-	return matchArgTypeInternal(pass, t, typ, arg, make(map[types.Type]bool))
-}
-
-// matchArgTypeInternal is the internal version of matchArgType. It carries a map
-// remembering what types are in progress so we don't recur when faced with recursive
-// types or mutually recursive types.
-func matchArgTypeInternal(pass *analysis.Pass, t printfArgType, typ types.Type, arg ast.Expr, inProgress map[types.Type]bool) bool {
+// If arg is a type parameter, the verb t must be appropriate for every type in
+// the type parameter type set.
+func matchArgType(pass *analysis.Pass, t printfArgType, arg ast.Expr) (reason string, ok bool) {
 	// %v, %T accept any argument type.
 	if t == anyType {
-		return true
+		return "", true
 	}
+
+	typ := pass.TypesInfo.Types[arg].Type
 	if typ == nil {
-		// external call
-		typ = pass.TypesInfo.Types[arg].Type
-		if typ == nil {
-			return true // probably a type check problem
-		}
+		return "", true // probably a type check problem
 	}
 
+	m := &argMatcher{t: t, seen: make(map[types.Type]bool)}
+	ok = m.match(typ, true)
+	return m.reason, ok
+}
+
+// argMatcher recursively matches types against the printfArgType t.
+//
+// To short-circuit recursion, it keeps track of types that have already been
+// matched (or are in the process of being matched) via the seen map. Recursion
+// arises from the compound types {map,chan,slice} which may be printed with %d
+// etc. if that is appropriate for their element types, as well as from type
+// parameters, which are expanded to the constituents of their type set.
+//
+// The reason field may be set to report the cause of the mismatch.
+type argMatcher struct {
+	t      printfArgType
+	seen   map[types.Type]bool
+	reason string
+}
+
+// match checks if typ matches m's printf arg type. If topLevel is true, typ is
+// the actual type of the printf arg, for which special rules apply. As a
+// special case, top level type parameters pass topLevel=true when checking for
+// matches among the constituents of their type set, as type arguments will
+// replace the type parameter at compile time.
+func (m *argMatcher) match(typ types.Type, topLevel bool) bool {
 	// %w accepts only errors.
-	if t == argError {
+	if m.t == argError {
 		return types.ConvertibleTo(typ, errorType)
 	}
 
@@ -51,65 +66,122 @@ func matchArgTypeInternal(pass *analysis.Pass, t printfArgType, typ types.Type,
 	if isFormatter(typ) {
 		return true
 	}
+
 	// If we can use a string, might arg (dynamically) implement the Stringer or Error interface?
-	if t&argString != 0 && isConvertibleToString(pass, typ) {
+	if m.t&argString != 0 && isConvertibleToString(typ) {
+		return true
+	}
+
+	if typ, _ := typ.(*typeparams.TypeParam); typ != nil {
+		// Avoid infinite recursion through type parameters.
+		if m.seen[typ] {
+			return true
+		}
+		m.seen[typ] = true
+		terms, err := typeparams.StructuralTerms(typ)
+		if err != nil {
+			return true // invalid type (possibly an empty type set)
+		}
+
+		if len(terms) == 0 {
+			// No restrictions on the underlying of typ. Type parameters implementing
+			// error, fmt.Formatter, or fmt.Stringer were handled above, and %v and
+			// %T was handled in matchType. We're about to check restrictions the
+			// underlying; if the underlying type is unrestricted there must be an
+			// element of the type set that violates one of the arg type checks
+			// below, so we can safely return false here.
+
+			if m.t == anyType { // anyType must have already been handled.
+				panic("unexpected printfArgType")
+			}
+			return false
+		}
+
+		// Only report a reason if typ is the argument type, otherwise it won't
+		// make sense. Note that it is not sufficient to check if topLevel == here,
+		// as type parameters can have a type set consisting of other type
+		// parameters.
+		reportReason := len(m.seen) == 1
+
+		for _, term := range terms {
+			if !m.match(term.Type(), topLevel) {
+				if reportReason {
+					if term.Tilde() {
+						m.reason = fmt.Sprintf("contains ~%s", term.Type())
+					} else {
+						m.reason = fmt.Sprintf("contains %s", term.Type())
+					}
+				}
+				return false
+			}
+		}
 		return true
 	}
 
 	typ = typ.Underlying()
-	if inProgress[typ] {
-		// We're already looking at this type. The call that started it will take care of it.
+	if m.seen[typ] {
+		// We've already considered typ, or are in the process of considering it.
+		// In case we've already considered typ, it must have been valid (else we
+		// would have stopped matching). In case we're in the process of
+		// considering it, we must avoid infinite recursion.
+		//
+		// There are some pathological cases where returning true here is
+		// incorrect, for example `type R struct { F []R }`, but these are
+		// acceptable false negatives.
 		return true
 	}
-	inProgress[typ] = true
+	m.seen[typ] = true
 
 	switch typ := typ.(type) {
 	case *types.Signature:
-		return t == argPointer
+		return m.t == argPointer
 
 	case *types.Map:
-		return t == argPointer ||
-			// Recur: map[int]int matches %d.
-			(matchArgTypeInternal(pass, t, typ.Key(), arg, inProgress) && matchArgTypeInternal(pass, t, typ.Elem(), arg, inProgress))
+		if m.t == argPointer {
+			return true
+		}
+		// Recur: map[int]int matches %d.
+		return m.match(typ.Key(), false) && m.match(typ.Elem(), false)
 
 	case *types.Chan:
-		return t&argPointer != 0
+		return m.t&argPointer != 0
 
 	case *types.Array:
 		// Same as slice.
-		if types.Identical(typ.Elem().Underlying(), types.Typ[types.Byte]) && t&argString != 0 {
+		if types.Identical(typ.Elem().Underlying(), types.Typ[types.Byte]) && m.t&argString != 0 {
 			return true // %s matches []byte
 		}
 		// Recur: []int matches %d.
-		return matchArgTypeInternal(pass, t, typ.Elem(), arg, inProgress)
+		return m.match(typ.Elem(), false)
 
 	case *types.Slice:
 		// Same as array.
-		if types.Identical(typ.Elem().Underlying(), types.Typ[types.Byte]) && t&argString != 0 {
+		if types.Identical(typ.Elem().Underlying(), types.Typ[types.Byte]) && m.t&argString != 0 {
 			return true // %s matches []byte
 		}
-		if t == argPointer {
+		if m.t == argPointer {
 			return true // %p prints a slice's 0th element
 		}
 		// Recur: []int matches %d. But watch out for
 		//	type T []T
 		// If the element is a pointer type (type T[]*T), it's handled fine by the Pointer case below.
-		return matchArgTypeInternal(pass, t, typ.Elem(), arg, inProgress)
+		return m.match(typ.Elem(), false)
 
 	case *types.Pointer:
 		// Ugly, but dealing with an edge case: a known pointer to an invalid type,
 		// probably something from a failed import.
-		if typ.Elem().String() == "invalid type" {
-			if false {
-				pass.Reportf(arg.Pos(), "printf argument %v is pointer to invalid or unknown type", analysisutil.Format(pass.Fset, arg))
-			}
+		if typ.Elem() == types.Typ[types.Invalid] {
 			return true // special case
 		}
 		// If it's actually a pointer with %p, it prints as one.
-		if t == argPointer {
+		if m.t == argPointer {
 			return true
 		}
 
+		if typeparams.IsTypeParam(typ.Elem()) {
+			return true // We don't know whether the logic below applies. Give up.
+		}
+
 		under := typ.Elem().Underlying()
 		switch under.(type) {
 		case *types.Struct: // see below
@@ -118,19 +190,31 @@ func matchArgTypeInternal(pass *analysis.Pass, t printfArgType, typ types.Type,
 		case *types.Map: // see below
 		default:
 			// Check whether the rest can print pointers.
-			return t&argPointer != 0
+			return m.t&argPointer != 0
 		}
-		// If it's a top-level pointer to a struct, array, slice, or
+		// If it's a top-level pointer to a struct, array, slice, type param, or
 		// map, that's equivalent in our analysis to whether we can
 		// print the type being pointed to. Pointers in nested levels
 		// are not supported to minimize fmt running into loops.
-		if len(inProgress) > 1 {
+		if !topLevel {
 			return false
 		}
-		return matchArgTypeInternal(pass, t, under, arg, inProgress)
+		return m.match(under, false)
 
 	case *types.Struct:
-		return matchStructArgType(pass, t, typ, arg, inProgress)
+		// report whether all the elements of the struct match the expected type. For
+		// instance, with "%d" all the elements must be printable with the "%d" format.
+		for i := 0; i < typ.NumFields(); i++ {
+			typf := typ.Field(i)
+			if !m.match(typf.Type(), false) {
+				return false
+			}
+			if m.t&argString != 0 && !typf.Exported() && isConvertibleToString(typf.Type()) {
+				// Issue #17798: unexported Stringer or error cannot be properly formatted.
+				return false
+			}
+		}
+		return true
 
 	case *types.Interface:
 		// There's little we can do.
@@ -142,7 +226,7 @@ func matchArgTypeInternal(pass *analysis.Pass, t printfArgType, typ types.Type,
 		switch typ.Kind() {
 		case types.UntypedBool,
 			types.Bool:
-			return t&argBool != 0
+			return m.t&argBool != 0
 
 		case types.UntypedInt,
 			types.Int,
@@ -156,35 +240,32 @@ func matchArgTypeInternal(pass *analysis.Pass, t printfArgType, typ types.Type,
 			types.Uint32,
 			types.Uint64,
 			types.Uintptr:
-			return t&argInt != 0
+			return m.t&argInt != 0
 
 		case types.UntypedFloat,
 			types.Float32,
 			types.Float64:
-			return t&argFloat != 0
+			return m.t&argFloat != 0
 
 		case types.UntypedComplex,
 			types.Complex64,
 			types.Complex128:
-			return t&argComplex != 0
+			return m.t&argComplex != 0
 
 		case types.UntypedString,
 			types.String:
-			return t&argString != 0
+			return m.t&argString != 0
 
 		case types.UnsafePointer:
-			return t&(argPointer|argInt) != 0
+			return m.t&(argPointer|argInt) != 0
 
 		case types.UntypedRune:
-			return t&(argInt|argRune) != 0
+			return m.t&(argInt|argRune) != 0
 
 		case types.UntypedNil:
 			return false
 
 		case types.Invalid:
-			if false {
-				pass.Reportf(arg.Pos(), "printf argument %v has invalid or unknown type", analysisutil.Format(pass.Fset, arg))
-			}
 			return true // Probably a type check problem.
 		}
 		panic("unreachable")
@@ -193,7 +274,7 @@ func matchArgTypeInternal(pass *analysis.Pass, t printfArgType, typ types.Type,
 	return false
 }
 
-func isConvertibleToString(pass *analysis.Pass, typ types.Type) bool {
+func isConvertibleToString(typ types.Type) bool {
 	if bt, ok := typ.(*types.Basic); ok && bt.Kind() == types.UntypedNil {
 		// We explicitly don't want untyped nil, which is
 		// convertible to both of the interfaces below, as it
@@ -228,19 +309,3 @@ func hasBasicType(pass *analysis.Pass, x ast.Expr, kind types.BasicKind) bool {
 	b, ok := t.(*types.Basic)
 	return ok && b.Kind() == kind
 }
-
-// matchStructArgType reports whether all the elements of the struct match the expected
-// type. For instance, with "%d" all the elements must be printable with the "%d" format.
-func matchStructArgType(pass *analysis.Pass, t printfArgType, typ *types.Struct, arg ast.Expr, inProgress map[types.Type]bool) bool {
-	for i := 0; i < typ.NumFields(); i++ {
-		typf := typ.Field(i)
-		if !matchArgTypeInternal(pass, t, typf.Type(), arg, inProgress) {
-			return false
-		}
-		if t&argString != 0 && !typf.Exported() && isConvertibleToString(pass, typf.Type()) {
-			// Issue #17798: unexported Stringer or error cannot be properly formatted.
-			return false
-		}
-	}
-	return true
-}
diff --git a/libgo/go/golang.org/x/tools/go/analysis/passes/shift/shift.go b/libgo/go/golang.org/x/tools/go/analysis/passes/shift/shift.go
index 1f3df07ccd1..e968f27b403 100644
--- a/libgo/go/golang.org/x/tools/go/analysis/passes/shift/shift.go
+++ b/libgo/go/golang.org/x/tools/go/analysis/passes/shift/shift.go
@@ -14,11 +14,14 @@ import (
 	"go/ast"
 	"go/constant"
 	"go/token"
+	"go/types"
+	"math"
 
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/analysis/passes/inspect"
 	"golang.org/x/tools/go/analysis/passes/internal/analysisutil"
 	"golang.org/x/tools/go/ast/inspector"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 const Doc = "check for shifts that equal or exceed the width of the integer"
@@ -93,9 +96,36 @@ func checkLongShift(pass *analysis.Pass, node ast.Node, x, y ast.Expr) {
 	if t == nil {
 		return
 	}
-	size := 8 * pass.TypesSizes.Sizeof(t)
-	if amt >= size {
+	var structuralTypes []types.Type
+	switch t := t.(type) {
+	case *typeparams.TypeParam:
+		terms, err := typeparams.StructuralTerms(t)
+		if err != nil {
+			return // invalid type
+		}
+		for _, term := range terms {
+			structuralTypes = append(structuralTypes, term.Type())
+		}
+	default:
+		structuralTypes = append(structuralTypes, t)
+	}
+	sizes := make(map[int64]struct{})
+	for _, t := range structuralTypes {
+		size := 8 * pass.TypesSizes.Sizeof(t)
+		sizes[size] = struct{}{}
+	}
+	minSize := int64(math.MaxInt64)
+	for size := range sizes {
+		if size < minSize {
+			minSize = size
+		}
+	}
+	if amt >= minSize {
 		ident := analysisutil.Format(pass.Fset, x)
-		pass.ReportRangef(node, "%s (%d bits) too small for shift of %d", ident, size, amt)
+		qualifier := ""
+		if len(sizes) > 1 {
+			qualifier = "may be "
+		}
+		pass.ReportRangef(node, "%s (%s%d bits) too small for shift of %d", ident, qualifier, minSize, amt)
 	}
 }
diff --git a/libgo/go/golang.org/x/tools/go/analysis/passes/stdmethods/stdmethods.go b/libgo/go/golang.org/x/tools/go/analysis/passes/stdmethods/stdmethods.go
index 64a28ac0b97..cc9497179da 100644
--- a/libgo/go/golang.org/x/tools/go/analysis/passes/stdmethods/stdmethods.go
+++ b/libgo/go/golang.org/x/tools/go/analysis/passes/stdmethods/stdmethods.go
@@ -61,7 +61,7 @@ var Analyzer = &analysis.Analyzer{
 // we let it go. But if it does have a fmt.ScanState, then the
 // rest has to match.
 var canonicalMethods = map[string]struct{ args, results []string }{
-	"As": {[]string{"interface{}"}, []string{"bool"}}, // errors.As
+	"As": {[]string{"any"}, []string{"bool"}}, // errors.As
 	// "Flush": {{}, {"error"}}, // http.Flusher and jpeg.writer conflict
 	"Format":        {[]string{"=fmt.State", "rune"}, []string{}},                      // fmt.Formatter
 	"GobDecode":     {[]string{"[]byte"}, []string{"error"}},                           // gob.GobDecoder
@@ -194,7 +194,9 @@ func matchParams(pass *analysis.Pass, expect []string, actual *types.Tuple, pref
 func matchParamType(expect string, actual types.Type) bool {
 	expect = strings.TrimPrefix(expect, "=")
 	// Overkill but easy.
-	return typeString(actual) == expect
+	t := typeString(actual)
+	return t == expect ||
+		(t == "any" || t == "interface{}") && (expect == "any" || expect == "interface{}")
 }
 
 var errorType = types.Universe.Lookup("error").Type().Underlying().(*types.Interface)
diff --git a/libgo/go/golang.org/x/tools/go/analysis/passes/stringintconv/string.go b/libgo/go/golang.org/x/tools/go/analysis/passes/stringintconv/string.go
index 7a005901e84..e41de809de1 100644
--- a/libgo/go/golang.org/x/tools/go/analysis/passes/stringintconv/string.go
+++ b/libgo/go/golang.org/x/tools/go/analysis/passes/stringintconv/string.go
@@ -10,10 +10,12 @@ import (
 	"fmt"
 	"go/ast"
 	"go/types"
+	"strings"
 
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/analysis/passes/inspect"
 	"golang.org/x/tools/go/ast/inspector"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 const Doc = `check for string(int) conversions
@@ -36,6 +38,35 @@ var Analyzer = &analysis.Analyzer{
 	Run:      run,
 }
 
+// describe returns a string describing the type typ contained within the type
+// set of inType. If non-empty, inName is used as the name of inType (this is
+// necessary so that we can use alias type names that may not be reachable from
+// inType itself).
+func describe(typ, inType types.Type, inName string) string {
+	name := inName
+	if typ != inType {
+		name = typeName(typ)
+	}
+	if name == "" {
+		return ""
+	}
+
+	var parentheticals []string
+	if underName := typeName(typ.Underlying()); underName != "" && underName != name {
+		parentheticals = append(parentheticals, underName)
+	}
+
+	if typ != inType && inName != "" && inName != name {
+		parentheticals = append(parentheticals, "in "+inName)
+	}
+
+	if len(parentheticals) > 0 {
+		name += " (" + strings.Join(parentheticals, ", ") + ")"
+	}
+
+	return name
+}
+
 func typeName(typ types.Type) string {
 	if v, _ := typ.(interface{ Name() string }); v != nil {
 		return v.Name()
@@ -54,6 +85,11 @@ func run(pass *analysis.Pass) (interface{}, error) {
 	inspect.Preorder(nodeFilter, func(n ast.Node) {
 		call := n.(*ast.CallExpr)
 
+		if len(call.Args) != 1 {
+			return
+		}
+		arg := call.Args[0]
+
 		// Retrieve target type name.
 		var tname *types.TypeName
 		switch fun := call.Fun.(type) {
@@ -65,62 +101,119 @@ func run(pass *analysis.Pass) (interface{}, error) {
 		if tname == nil {
 			return
 		}
-		target := tname.Name()
 
-		// Check that target type T in T(v) has an underlying type of string.
-		T, _ := tname.Type().Underlying().(*types.Basic)
-		if T == nil || T.Kind() != types.String {
-			return
+		// In the conversion T(v) of a value v of type V to a target type T, we
+		// look for types T0 in the type set of T and V0 in the type set of V, such
+		// that V0->T0 is a problematic conversion. If T and V are not type
+		// parameters, this amounts to just checking if V->T is a problematic
+		// conversion.
+
+		// First, find a type T0 in T that has an underlying type of string.
+		T := tname.Type()
+		ttypes, err := structuralTypes(T)
+		if err != nil {
+			return // invalid type
 		}
-		if s := T.Name(); target != s {
-			target += " (" + s + ")"
+
+		var T0 types.Type // string type in the type set of T
+
+		for _, tt := range ttypes {
+			u, _ := tt.Underlying().(*types.Basic)
+			if u != nil && u.Kind() == types.String {
+				T0 = tt
+				break
+			}
 		}
 
-		// Check that type V of v has an underlying integral type that is not byte or rune.
-		if len(call.Args) != 1 {
+		if T0 == nil {
+			// No target types have an underlying type of string.
 			return
 		}
-		v := call.Args[0]
-		vtyp := pass.TypesInfo.TypeOf(v)
-		V, _ := vtyp.Underlying().(*types.Basic)
-		if V == nil || V.Info()&types.IsInteger == 0 {
-			return
+
+		// Next, find a type V0 in V that has an underlying integral type that is
+		// not byte or rune.
+		V := pass.TypesInfo.TypeOf(arg)
+		vtypes, err := structuralTypes(V)
+		if err != nil {
+			return // invalid type
 		}
-		switch V.Kind() {
-		case types.Byte, types.Rune, types.UntypedRune:
-			return
+
+		var V0 types.Type // integral type in the type set of V
+
+		for _, vt := range vtypes {
+			u, _ := vt.Underlying().(*types.Basic)
+			if u != nil && u.Info()&types.IsInteger != 0 {
+				switch u.Kind() {
+				case types.Byte, types.Rune, types.UntypedRune:
+					continue
+				}
+				V0 = vt
+				break
+			}
 		}
 
-		// Retrieve source type name.
-		source := typeName(vtyp)
-		if source == "" {
+		if V0 == nil {
+			// No source types are non-byte or rune integer types.
 			return
 		}
-		if s := V.Name(); source != s {
-			source += " (" + s + ")"
+
+		convertibleToRune := true // if true, we can suggest a fix
+		for _, t := range vtypes {
+			if !types.ConvertibleTo(t, types.Typ[types.Rune]) {
+				convertibleToRune = false
+				break
+			}
+		}
+
+		target := describe(T0, T, tname.Name())
+		source := describe(V0, V, typeName(V))
+
+		if target == "" || source == "" {
+			return // something went wrong
 		}
+
 		diag := analysis.Diagnostic{
 			Pos:     n.Pos(),
 			Message: fmt.Sprintf("conversion from %s to %s yields a string of one rune, not a string of digits (did you mean fmt.Sprint(x)?)", source, target),
-			SuggestedFixes: []analysis.SuggestedFix{
+		}
+
+		if convertibleToRune {
+			diag.SuggestedFixes = []analysis.SuggestedFix{
 				{
 					Message: "Did you mean to convert a rune to a string?",
 					TextEdits: []analysis.TextEdit{
 						{
-							Pos:     v.Pos(),
-							End:     v.Pos(),
+							Pos:     arg.Pos(),
+							End:     arg.Pos(),
 							NewText: []byte("rune("),
 						},
 						{
-							Pos:     v.End(),
-							End:     v.End(),
+							Pos:     arg.End(),
+							End:     arg.End(),
 							NewText: []byte(")"),
 						},
 					},
 				},
-			},
+			}
 		}
 		pass.Report(diag)
 	})
 	return nil, nil
 }
+
+func structuralTypes(t types.Type) ([]types.Type, error) {
+	var structuralTypes []types.Type
+	switch t := t.(type) {
+	case *typeparams.TypeParam:
+		terms, err := typeparams.StructuralTerms(t)
+		if err != nil {
+			return nil, err
+		}
+		for _, term := range terms {
+			structuralTypes = append(structuralTypes, term.Type())
+		}
+	default:
+		structuralTypes = append(structuralTypes, t)
+	}
+	return structuralTypes, nil
+}
diff --git a/libgo/go/golang.org/x/tools/go/analysis/passes/testinggoroutine/testinggoroutine.go b/libgo/go/golang.org/x/tools/go/analysis/passes/testinggoroutine/testinggoroutine.go
index d2b9a5640d9..7ea8f77e335 100644
--- a/libgo/go/golang.org/x/tools/go/analysis/passes/testinggoroutine/testinggoroutine.go
+++ b/libgo/go/golang.org/x/tools/go/analysis/passes/testinggoroutine/testinggoroutine.go
@@ -11,6 +11,7 @@ import (
 	"golang.org/x/tools/go/analysis/passes/inspect"
 	"golang.org/x/tools/go/analysis/passes/internal/analysisutil"
 	"golang.org/x/tools/go/ast/inspector"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 const Doc = `report calls to (*testing.T).Fatal from goroutines started by a test.
@@ -119,11 +120,44 @@ func typeIsTestingDotTOrB(expr ast.Expr) (string, bool) {
 	return varTypeName, ok
 }
 
+// goStmtFunc returns the ast.Node of a call expression
+// that was invoked as a go statement. Currently, only
+// function literals declared in the same function, and
+// static calls within the same package are supported.
+func goStmtFun(goStmt *ast.GoStmt) ast.Node {
+	switch fun := goStmt.Call.Fun.(type) {
+	case *ast.IndexExpr, *typeparams.IndexListExpr:
+		x, _, _, _ := typeparams.UnpackIndexExpr(fun)
+		id, _ := x.(*ast.Ident)
+		if id == nil {
+			break
+		}
+		if id.Obj == nil {
+			break
+		}
+		if funDecl, ok := id.Obj.Decl.(ast.Node); ok {
+			return funDecl
+		}
+	case *ast.Ident:
+		// TODO(cuonglm): improve this once golang/go#48141 resolved.
+		if fun.Obj == nil {
+			break
+		}
+		if funDecl, ok := fun.Obj.Decl.(ast.Node); ok {
+			return funDecl
+		}
+	case *ast.FuncLit:
+		return goStmt.Call.Fun
+	}
+	return goStmt.Call
+}
+
 // checkGoStmt traverses the goroutine and checks for the
 // use of the forbidden *testing.(B, T) methods.
 func checkGoStmt(pass *analysis.Pass, goStmt *ast.GoStmt) {
+	fn := goStmtFun(goStmt)
 	// Otherwise examine the goroutine to check for the forbidden methods.
-	ast.Inspect(goStmt, func(n ast.Node) bool {
+	ast.Inspect(fn, func(n ast.Node) bool {
 		selExpr, ok := n.(*ast.SelectorExpr)
 		if !ok {
 			return true
@@ -147,7 +181,11 @@ func checkGoStmt(pass *analysis.Pass, goStmt *ast.GoStmt) {
 			return true
 		}
 		if typeName, ok := typeIsTestingDotTOrB(field.Type); ok {
-			pass.ReportRangef(selExpr, "call to (*%s).%s from a non-test goroutine", typeName, selExpr.Sel)
+			var fnRange analysis.Range = goStmt
+			if _, ok := fn.(*ast.FuncLit); ok {
+				fnRange = selExpr
+			}
+			pass.ReportRangef(fnRange, "call to (*%s).%s from a non-test goroutine", typeName, selExpr.Sel)
 		}
 		return true
 	})
diff --git a/libgo/go/golang.org/x/tools/go/analysis/passes/tests/tests.go b/libgo/go/golang.org/x/tools/go/analysis/passes/tests/tests.go
index 8232276186a..2c878824966 100644
--- a/libgo/go/golang.org/x/tools/go/analysis/passes/tests/tests.go
+++ b/libgo/go/golang.org/x/tools/go/analysis/passes/tests/tests.go
@@ -8,12 +8,15 @@ package tests
 
 import (
 	"go/ast"
+	"go/token"
 	"go/types"
+	"regexp"
 	"strings"
 	"unicode"
 	"unicode/utf8"
 
 	"golang.org/x/tools/go/analysis"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 const Doc = `check for common mistaken usages of tests and examples
@@ -42,10 +45,10 @@ func run(pass *analysis.Pass) (interface{}, error) {
 				// Ignore non-functions or functions with receivers.
 				continue
 			}
-
 			switch {
 			case strings.HasPrefix(fn.Name.Name, "Example"):
-				checkExample(pass, fn)
+				checkExampleName(pass, fn)
+				checkExampleOutput(pass, fn, f.Comments)
 			case strings.HasPrefix(fn.Name.Name, "Test"):
 				checkTest(pass, fn, "Test")
 			case strings.HasPrefix(fn.Name.Name, "Benchmark"):
@@ -108,7 +111,59 @@ func lookup(pkg *types.Package, name string) []types.Object {
 	return ret
 }
 
-func checkExample(pass *analysis.Pass, fn *ast.FuncDecl) {
+// This pattern is taken from /go/src/go/doc/example.go
+var outputRe = regexp.MustCompile(`(?i)^[[:space:]]*(unordered )?output:`)
+
+type commentMetadata struct {
+	isOutput bool
+	pos      token.Pos
+}
+
+func checkExampleOutput(pass *analysis.Pass, fn *ast.FuncDecl, fileComments []*ast.CommentGroup) {
+	commentsInExample := []commentMetadata{}
+	numOutputs := 0
+
+	// Find the comment blocks that are in the example. These comments are
+	// guaranteed to be in order of appearance.
+	for _, cg := range fileComments {
+		if cg.Pos() < fn.Pos() {
+			continue
+		} else if cg.End() > fn.End() {
+			break
+		}
+
+		isOutput := outputRe.MatchString(cg.Text())
+		if isOutput {
+			numOutputs++
+		}
+
+		commentsInExample = append(commentsInExample, commentMetadata{
+			isOutput: isOutput,
+			pos:      cg.Pos(),
+		})
+	}
+
+	// Change message based on whether there are multiple output comment blocks.
+	msg := "output comment block must be the last comment block"
+	if numOutputs > 1 {
+		msg = "there can only be one output comment block per example"
+	}
+
+	for i, cg := range commentsInExample {
+		// Check for output comments that are not the last comment in the example.
+		isLast := (i == len(commentsInExample)-1)
+		if cg.isOutput && !isLast {
+			pass.Report(
+				analysis.Diagnostic{
+					Pos:     cg.pos,
+					Message: msg,
+				},
+			)
+		}
+	}
+}
+
+func checkExampleName(pass *analysis.Pass, fn *ast.FuncDecl) {
 	fnName := fn.Name.Name
 	if params := fn.Type.Params; len(params.List) != 0 {
 		pass.Reportf(fn.Pos(), "%s should be niladic", fnName)
@@ -116,6 +171,9 @@ func checkExample(pass *analysis.Pass, fn *ast.FuncDecl) {
 	if results := fn.Type.Results; results != nil && len(results.List) != 0 {
 		pass.Reportf(fn.Pos(), "%s should return nothing", fnName)
 	}
+	if tparams := typeparams.ForFuncType(fn.Type); tparams != nil && len(tparams.List) > 0 {
+		pass.Reportf(fn.Pos(), "%s should not have type params", fnName)
+	}
 
 	if fnName == "Example" {
 		// Nothing more to do.
@@ -182,6 +240,12 @@ func checkTest(pass *analysis.Pass, fn *ast.FuncDecl, prefix string) {
 		return
 	}
 
+	if tparams := typeparams.ForFuncType(fn.Type); tparams != nil && len(tparams.List) > 0 {
+		// Note: cmd/go/internal/load also errors about TestXXX and BenchmarkXXX functions with type parameters.
+		// We have currently decided to also warn before compilation/package loading. This can help users in IDEs.
+		pass.Reportf(fn.Pos(), "%s has type parameters: it will not be run by go test as a %sXXX function", fn.Name.Name, prefix)
+	}
+
 	if !isTestSuffix(fn.Name.Name[len(prefix):]) {
 		pass.Reportf(fn.Pos(), "%s has malformed name: first letter after '%s' must not be lowercase", fn.Name.Name, prefix)
 	}
diff --git a/libgo/go/golang.org/x/tools/go/analysis/passes/unmarshal/unmarshal.go b/libgo/go/golang.org/x/tools/go/analysis/passes/unmarshal/unmarshal.go
index 92b37caff9f..5129048a076 100644
--- a/libgo/go/golang.org/x/tools/go/analysis/passes/unmarshal/unmarshal.go
+++ b/libgo/go/golang.org/x/tools/go/analysis/passes/unmarshal/unmarshal.go
@@ -14,6 +14,7 @@ import (
 	"golang.org/x/tools/go/analysis/passes/inspect"
 	"golang.org/x/tools/go/ast/inspector"
 	"golang.org/x/tools/go/types/typeutil"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 const Doc = `report passing non-pointer or non-interface values to unmarshal
@@ -85,7 +86,7 @@ func run(pass *analysis.Pass) (interface{}, error) {
 
 		t := pass.TypesInfo.Types[call.Args[argidx]].Type
 		switch t.Underlying().(type) {
-		case *types.Pointer, *types.Interface:
+		case *types.Pointer, *types.Interface, *typeparams.TypeParam:
 			return
 		}
 
diff --git a/libgo/go/golang.org/x/tools/go/analysis/passes/unusedresult/unusedresult.go b/libgo/go/golang.org/x/tools/go/analysis/passes/unusedresult/unusedresult.go
index bececee7e93..06747ba72b9 100644
--- a/libgo/go/golang.org/x/tools/go/analysis/passes/unusedresult/unusedresult.go
+++ b/libgo/go/golang.org/x/tools/go/analysis/passes/unusedresult/unusedresult.go
@@ -17,6 +17,7 @@ import (
 	"golang.org/x/tools/go/analysis/passes/inspect"
 	"golang.org/x/tools/go/analysis/passes/internal/analysisutil"
 	"golang.org/x/tools/go/ast/inspector"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 // TODO(adonovan): make this analysis modular: export a mustUseResult
@@ -70,6 +71,11 @@ func run(pass *analysis.Pass) (interface{}, error) {
 			return // a conversion, not a call
 		}
 
+		x, _, _, _ := typeparams.UnpackIndexExpr(fun)
+		if x != nil {
+			fun = x // If this is generic function or method call, skip the instantiation arguments
+		}
+
 		selector, ok := fun.(*ast.SelectorExpr)
 		if !ok {
 			return // neither a method call nor a qualified ident
diff --git a/libgo/go/golang.org/x/tools/go/analysis/unitchecker/unitchecker.go b/libgo/go/golang.org/x/tools/go/analysis/unitchecker/unitchecker.go
index 323282136fb..393954a238b 100644
--- a/libgo/go/golang.org/x/tools/go/analysis/unitchecker/unitchecker.go
+++ b/libgo/go/golang.org/x/tools/go/analysis/unitchecker/unitchecker.go
@@ -51,6 +51,7 @@ import (
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/analysis/internal/analysisflags"
 	"golang.org/x/tools/go/analysis/internal/facts"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 // A Config describes a compilation unit to be analyzed.
@@ -233,6 +234,8 @@ func run(fset *token.FileSet, cfg *Config, analyzers []*analysis.Analyzer) ([]re
 		Scopes:     make(map[ast.Node]*types.Scope),
 		Selections: make(map[*ast.SelectorExpr]*types.Selection),
 	}
+	typeparams.InitInstanceInfo(info)
+
 	pkg, err := tc.Check(cfg.ImportPath, fset, files, info)
 	if err != nil {
 		if cfg.SucceedOnTypecheckFailure {
diff --git a/libgo/go/golang.org/x/tools/go/ast/astutil/enclosing.go b/libgo/go/golang.org/x/tools/go/ast/astutil/enclosing.go
index 6b7052b892c..a5c6d6d4fa0 100644
--- a/libgo/go/golang.org/x/tools/go/ast/astutil/enclosing.go
+++ b/libgo/go/golang.org/x/tools/go/ast/astutil/enclosing.go
@@ -11,6 +11,8 @@ import (
 	"go/ast"
 	"go/token"
 	"sort"
+
+	"golang.org/x/tools/internal/typeparams"
 )
 
 // PathEnclosingInterval returns the node that encloses the source
@@ -294,8 +296,8 @@ func childrenOf(n ast.Node) []ast.Node {
 
 	case *ast.FieldList:
 		children = append(children,
-			tok(n.Opening, len("(")),
-			tok(n.Closing, len(")")))
+			tok(n.Opening, len("(")), // or len("[")
+			tok(n.Closing, len(")"))) // or len("]")
 
 	case *ast.File:
 		// TODO test: Doc
@@ -322,6 +324,9 @@ func childrenOf(n ast.Node) []ast.Node {
 			children = append(children, n.Recv)
 		}
 		children = append(children, n.Name)
+		if tparams := typeparams.ForFuncType(n.Type); tparams != nil {
+			children = append(children, tparams)
+		}
 		if n.Type.Params != nil {
 			children = append(children, n.Type.Params)
 		}
@@ -371,8 +376,13 @@ func childrenOf(n ast.Node) []ast.Node {
 
 	case *ast.IndexExpr:
 		children = append(children,
-			tok(n.Lbrack, len("{")),
-			tok(n.Rbrack, len("}")))
+			tok(n.Lbrack, len("[")),
+			tok(n.Rbrack, len("]")))
+
+	case *typeparams.IndexListExpr:
+		children = append(children,
+			tok(n.Lbrack, len("[")),
+			tok(n.Rbrack, len("]")))
 
 	case *ast.InterfaceType:
 		children = append(children,
@@ -581,6 +591,8 @@ func NodeDescription(n ast.Node) string {
 		return "decrement statement"
 	case *ast.IndexExpr:
 		return "index expression"
+	case *typeparams.IndexListExpr:
+		return "index list expression"
 	case *ast.InterfaceType:
 		return "interface type"
 	case *ast.KeyValueExpr:
diff --git a/libgo/go/golang.org/x/tools/go/ast/astutil/rewrite.go b/libgo/go/golang.org/x/tools/go/ast/astutil/rewrite.go
index cf72ea990bd..6d9ca23e2b0 100644
--- a/libgo/go/golang.org/x/tools/go/ast/astutil/rewrite.go
+++ b/libgo/go/golang.org/x/tools/go/ast/astutil/rewrite.go
@@ -9,6 +9,8 @@ import (
 	"go/ast"
 	"reflect"
 	"sort"
+
+	"golang.org/x/tools/internal/typeparams"
 )
 
 // An ApplyFunc is invoked by Apply for each node n, even if n is nil,
@@ -251,6 +253,10 @@ func (a *application) apply(parent ast.Node, name string, iter *iterator, n ast.
 		a.apply(n, "X", nil, n.X)
 		a.apply(n, "Index", nil, n.Index)
 
+	case *typeparams.IndexListExpr:
+		a.apply(n, "X", nil, n.X)
+		a.applyList(n, "Indices")
+
 	case *ast.SliceExpr:
 		a.apply(n, "X", nil, n.X)
 		a.apply(n, "Low", nil, n.Low)
diff --git a/libgo/go/golang.org/x/tools/go/ast/inspector/typeof.go b/libgo/go/golang.org/x/tools/go/ast/inspector/typeof.go
index b6b00cf2e1e..11f4fc369a0 100644
--- a/libgo/go/golang.org/x/tools/go/ast/inspector/typeof.go
+++ b/libgo/go/golang.org/x/tools/go/ast/inspector/typeof.go
@@ -9,7 +9,11 @@ package inspector
 // The initial map-based implementation was too slow;
 // see https://go-review.googlesource.com/c/tools/+/135655/1/go/ast/inspector/inspector.go#196
 
-import "go/ast"
+import (
+	"go/ast"
+
+	"golang.org/x/tools/internal/typeparams"
+)
 
 const (
 	nArrayType = iota
@@ -47,6 +51,7 @@ const (
 	nImportSpec
 	nIncDecStmt
 	nIndexExpr
+	nIndexListExpr
 	nInterfaceType
 	nKeyValueExpr
 	nLabeledStmt
@@ -164,6 +169,8 @@ func typeOf(n ast.Node) uint64 {
 		return 1 << nIncDecStmt
 	case *ast.IndexExpr:
 		return 1 << nIndexExpr
+	case *typeparams.IndexListExpr:
+		return 1 << nIndexListExpr
 	case *ast.InterfaceType:
 		return 1 << nInterfaceType
 	case *ast.KeyValueExpr:
diff --git a/libgo/go/golang.org/x/tools/go/types/objectpath/objectpath.go b/libgo/go/golang.org/x/tools/go/types/objectpath/objectpath.go
index cffd7acbee7..7e96fc234e5 100644
--- a/libgo/go/golang.org/x/tools/go/types/objectpath/objectpath.go
+++ b/libgo/go/golang.org/x/tools/go/types/objectpath/objectpath.go
@@ -23,10 +23,12 @@ package objectpath
 
 import (
 	"fmt"
+	"go/types"
+	"sort"
 	"strconv"
 	"strings"
 
-	"go/types"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 // A Path is an opaque name that identifies a types.Object
@@ -57,12 +59,16 @@ type Path string
 // - The only PO operator is Package.Scope.Lookup, which requires an identifier.
 // - The only OT operator is Object.Type,
 //   which we encode as '.' because dot cannot appear in an identifier.
-// - The TT operators are encoded as [EKPRU].
-// - The OT operators are encoded as [AFMO];
+// - The TT operators are encoded as [EKPRUTC];
+//   one of these (TypeParam) requires an integer operand,
+//   which is encoded as a string of decimal digits.
+// - The TO operators are encoded as [AFMO];
 //   three of these (At,Field,Method) require an integer operand,
 //   which is encoded as a string of decimal digits.
 //   These indices are stable across different representations
 //   of the same package, even source and export data.
+//   The indices used are implementation specific and may not correspond to
+//   the argument to the go/types function.
 //
 // In the example below,
 //
@@ -89,17 +95,19 @@ const (
 	opType = '.' // .Type()		  (Object)
 
 	// type->type operators
-	opElem       = 'E' // .Elem()		(Pointer, Slice, Array, Chan, Map)
-	opKey        = 'K' // .Key()		(Map)
-	opParams     = 'P' // .Params()		(Signature)
-	opResults    = 'R' // .Results()	(Signature)
-	opUnderlying = 'U' // .Underlying()	(Named)
+	opElem       = 'E' // .Elem()		        (Pointer, Slice, Array, Chan, Map)
+	opKey        = 'K' // .Key()		        (Map)
+	opParams     = 'P' // .Params()		      (Signature)
+	opResults    = 'R' // .Results()	      (Signature)
+	opUnderlying = 'U' // .Underlying()	    (Named)
+	opTypeParam  = 'T' // .TypeParams.At(i) (Named, Signature)
+	opConstraint = 'C' // .Constraint()     (TypeParam)
 
 	// type->object operators
-	opAt     = 'A' // .At(i)		(Tuple)
-	opField  = 'F' // .Field(i)		(Struct)
-	opMethod = 'M' // .Method(i)		(Named or Interface; not Struct: "promoted" names are ignored)
-	opObj    = 'O' // .Obj()		(Named)
+	opAt     = 'A' // .At(i)		 (Tuple)
+	opField  = 'F' // .Field(i)	 (Struct)
+	opMethod = 'M' // .Method(i) (Named or Interface; not Struct: "promoted" names are ignored)
+	opObj    = 'O' // .Obj()		 (Named, TypeParam)
 )
 
 // The For function returns the path to an object relative to its package,
@@ -190,10 +198,15 @@ func For(obj types.Object) (Path, error) {
 	// 3. Not a package-level object.
 	//    Reject obviously non-viable cases.
 	switch obj := obj.(type) {
+	case *types.TypeName:
+		if _, ok := obj.Type().(*typeparams.TypeParam); !ok {
+			// With the exception of type parameters, only package-level type names
+			// have a path.
+			return "", fmt.Errorf("no path for %v", obj)
+		}
 	case *types.Const, // Only package-level constants have a path.
-		*types.TypeName, // Only package-level types have a path.
-		*types.Label,    // Labels are function-local.
-		*types.PkgName:  // PkgNames are file-local.
+		*types.Label,   // Labels are function-local.
+		*types.PkgName: // PkgNames are file-local.
 		return "", fmt.Errorf("no path for %v", obj)
 
 	case *types.Var:
@@ -245,6 +258,12 @@ func For(obj types.Object) (Path, error) {
 				return Path(r), nil
 			}
 		} else {
+			if named, _ := T.(*types.Named); named != nil {
+				if r := findTypeParam(obj, typeparams.ForNamed(named), path); r != nil {
+					// generic named type
+					return Path(r), nil
+				}
+			}
 			// defined (named) type
 			if r := find(obj, T.Underlying(), append(path, opUnderlying)); r != nil {
 				return Path(r), nil
@@ -270,8 +289,12 @@ func For(obj types.Object) (Path, error) {
 		// Inspect declared methods of defined types.
 		if T, ok := o.Type().(*types.Named); ok {
 			path = append(path, opType)
-			for i := 0; i < T.NumMethods(); i++ {
-				m := T.Method(i)
+			// Note that method index here is always with respect
+			// to canonical ordering of methods, regardless of how
+			// they appear in the underlying type.
+			canonical := canonicalize(T)
+			for i := 0; i < len(canonical); i++ {
+				m := canonical[i]
 				path2 := appendOpArg(path, opMethod, i)
 				if m == obj {
 					return Path(path2), nil // found declared method
@@ -313,6 +336,9 @@ func find(obj types.Object, T types.Type, path []byte) []byte {
 		}
 		return find(obj, T.Elem(), append(path, opElem))
 	case *types.Signature:
+		if r := findTypeParam(obj, typeparams.ForSignature(T), path); r != nil {
+			return r
+		}
 		if r := find(obj, T.Params(), append(path, opParams)); r != nil {
 			return r
 		}
@@ -353,10 +379,30 @@ func find(obj types.Object, T types.Type, path []byte) []byte {
 			}
 		}
 		return nil
+	case *typeparams.TypeParam:
+		name := T.Obj()
+		if name == obj {
+			return append(path, opObj)
+		}
+		if r := find(obj, T.Constraint(), append(path, opConstraint)); r != nil {
+			return r
+		}
+		return nil
 	}
 	panic(T)
 }
 
+func findTypeParam(obj types.Object, list *typeparams.TypeParamList, path []byte) []byte {
+	for i := 0; i < list.Len(); i++ {
+		tparam := list.At(i)
+		path2 := appendOpArg(path, opTypeParam, i)
+		if r := find(obj, tparam, path2); r != nil {
+			return r
+		}
+	}
+	return nil
+}
+
 // Object returns the object denoted by path p within the package pkg.
 func Object(pkg *types.Package, p Path) (types.Object, error) {
 	if p == "" {
@@ -381,10 +427,13 @@ func Object(pkg *types.Package, p Path) (types.Object, error) {
 	type hasElem interface {
 		Elem() types.Type
 	}
-	// abstraction of *types.{Interface,Named}
-	type hasMethods interface {
-		Method(int) *types.Func
-		NumMethods() int
+	// abstraction of *types.{Named,Signature}
+	type hasTypeParams interface {
+		TypeParams() *typeparams.TypeParamList
+	}
+	// abstraction of *types.{Named,TypeParam}
+	type hasObj interface {
+		Obj() *types.TypeName
 	}
 
 	// The loop state is the pair (t, obj),
@@ -401,7 +450,7 @@ func Object(pkg *types.Package, p Path) (types.Object, error) {
 		// Codes [AFM] have an integer operand.
 		var index int
 		switch code {
-		case opAt, opField, opMethod:
+		case opAt, opField, opMethod, opTypeParam:
 			rest := strings.TrimLeft(suffix, "0123456789")
 			numerals := suffix[:len(suffix)-len(rest)]
 			suffix = rest
@@ -466,14 +515,32 @@ func Object(pkg *types.Package, p Path) (types.Object, error) {
 		case opUnderlying:
 			named, ok := t.(*types.Named)
 			if !ok {
-				return nil, fmt.Errorf("cannot apply %q to %s (got %s, want named)", code, t, t)
+				return nil, fmt.Errorf("cannot apply %q to %s (got %T, want named)", code, t, t)
 			}
 			t = named.Underlying()
 
+		case opTypeParam:
+			hasTypeParams, ok := t.(hasTypeParams) // Named, Signature
+			if !ok {
+				return nil, fmt.Errorf("cannot apply %q to %s (got %T, want named or signature)", code, t, t)
+			}
+			tparams := hasTypeParams.TypeParams()
+			if n := tparams.Len(); index >= n {
+				return nil, fmt.Errorf("tuple index %d out of range [0-%d)", index, n)
+			}
+			t = tparams.At(index)
+
+		case opConstraint:
+			tparam, ok := t.(*typeparams.TypeParam)
+			if !ok {
+				return nil, fmt.Errorf("cannot apply %q to %s (got %T, want type parameter)", code, t, t)
+			}
+			t = tparam.Constraint()
+
 		case opAt:
 			tuple, ok := t.(*types.Tuple)
 			if !ok {
-				return nil, fmt.Errorf("cannot apply %q to %s (got %s, want tuple)", code, t, t)
+				return nil, fmt.Errorf("cannot apply %q to %s (got %T, want tuple)", code, t, t)
 			}
 			if n := tuple.Len(); index >= n {
 				return nil, fmt.Errorf("tuple index %d out of range [0-%d)", index, n)
@@ -495,20 +562,21 @@ func Object(pkg *types.Package, p Path) (types.Object, error) {
 		case opMethod:
 			hasMethods, ok := t.(hasMethods) // Interface or Named
 			if !ok {
-				return nil, fmt.Errorf("cannot apply %q to %s (got %s, want interface or named)", code, t, t)
+				return nil, fmt.Errorf("cannot apply %q to %s (got %T, want interface or named)", code, t, t)
 			}
-			if n := hasMethods.NumMethods(); index >= n {
+			canonical := canonicalize(hasMethods)
+			if n := len(canonical); index >= n {
 				return nil, fmt.Errorf("method index %d out of range [0-%d)", index, n)
 			}
-			obj = hasMethods.Method(index)
+			obj = canonical[index]
 			t = nil
 
 		case opObj:
-			named, ok := t.(*types.Named)
+			hasObj, ok := t.(hasObj)
 			if !ok {
-				return nil, fmt.Errorf("cannot apply %q to %s (got %s, want named)", code, t, t)
+				return nil, fmt.Errorf("cannot apply %q to %s (got %T, want named or type param)", code, t, t)
 			}
-			obj = named.Obj()
+			obj = hasObj.Obj()
 			t = nil
 
 		default:
@@ -522,3 +590,28 @@ func Object(pkg *types.Package, p Path) (types.Object, error) {
 
 	return obj, nil // success
 }
+
+// hasMethods is an abstraction of *types.{Interface,Named}. This is pulled up
+// because it is used by methodOrdering, which is in turn used by both encoding
+// and decoding.
+type hasMethods interface {
+	Method(int) *types.Func
+	NumMethods() int
+}
+
+// canonicalize returns a canonical order for the methods in a hasMethod.
+func canonicalize(hm hasMethods) []*types.Func {
+	count := hm.NumMethods()
+	if count <= 0 {
+		return nil
+	}
+	canon := make([]*types.Func, count)
+	for i := 0; i < count; i++ {
+		canon[i] = hm.Method(i)
+	}
+	less := func(i, j int) bool {
+		return canon[i].Id() < canon[j].Id()
+	}
+	sort.Slice(canon, less)
+	return canon
+}
diff --git a/libgo/go/golang.org/x/tools/go/types/typeutil/callee.go b/libgo/go/golang.org/x/tools/go/types/typeutil/callee.go
index 38f596daf9e..90b3ab0e21c 100644
--- a/libgo/go/golang.org/x/tools/go/types/typeutil/callee.go
+++ b/libgo/go/golang.org/x/tools/go/types/typeutil/callee.go
@@ -9,13 +9,29 @@ import (
 	"go/types"
 
 	"golang.org/x/tools/go/ast/astutil"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 // Callee returns the named target of a function call, if any:
 // a function, method, builtin, or variable.
+//
+// Functions and methods may potentially have type parameters.
 func Callee(info *types.Info, call *ast.CallExpr) types.Object {
+	fun := astutil.Unparen(call.Fun)
+
+	// Look through type instantiation if necessary.
+	isInstance := false
+	switch fun.(type) {
+	case *ast.IndexExpr, *typeparams.IndexListExpr:
+		// When extracting the callee from an *IndexExpr, we need to check that
+		// it is a *types.Func and not a *types.Var.
+		// Example: Don't match a slice m within the expression `m[0]()`.
+		isInstance = true
+		fun, _, _, _ = typeparams.UnpackIndexExpr(fun)
+	}
+
 	var obj types.Object
-	switch fun := astutil.Unparen(call.Fun).(type) {
+	switch fun := fun.(type) {
 	case *ast.Ident:
 		obj = info.Uses[fun] // type, var, builtin, or declared func
 	case *ast.SelectorExpr:
@@ -28,11 +44,18 @@ func Callee(info *types.Info, call *ast.CallExpr) types.Object {
 	if _, ok := obj.(*types.TypeName); ok {
 		return nil // T(x) is a conversion, not a call
 	}
+	// A Func is required to match instantiations.
+	if _, ok := obj.(*types.Func); isInstance && !ok {
+		return nil // Was not a Func.
+	}
 	return obj
 }
 
-// StaticCallee returns the target (function or method) of a static
-// function call, if any. It returns nil for calls to builtins.
+// StaticCallee returns the target (function or method) of a static function
+// call, if any. It returns nil for calls to builtins.
+//
+// Note: for calls of instantiated functions and methods, StaticCallee returns
+// the corresponding generic function or method on the generic type.
 func StaticCallee(info *types.Info, call *ast.CallExpr) *types.Func {
 	if f, ok := Callee(info, call).(*types.Func); ok && !interfaceMethod(f) {
 		return f
diff --git a/libgo/go/golang.org/x/tools/go/types/typeutil/map.go b/libgo/go/golang.org/x/tools/go/types/typeutil/map.go
index c7f75450064..490ee904a62 100644
--- a/libgo/go/golang.org/x/tools/go/types/typeutil/map.go
+++ b/libgo/go/golang.org/x/tools/go/types/typeutil/map.go
@@ -11,6 +11,8 @@ import (
 	"fmt"
 	"go/types"
 	"reflect"
+
+	"golang.org/x/tools/internal/typeparams"
 )
 
 // Map is a hash-table-based mapping from types (types.Type) to
@@ -211,11 +213,29 @@ func (m *Map) KeysString() string {
 // Call MakeHasher to create a Hasher.
 type Hasher struct {
 	memo map[types.Type]uint32
+
+	// ptrMap records pointer identity.
+	ptrMap map[interface{}]uint32
+
+	// sigTParams holds type parameters from the signature being hashed.
+	// Signatures are considered identical modulo renaming of type parameters, so
+	// within the scope of a signature type the identity of the signature's type
+	// parameters is just their index.
+	//
+	// Since the language does not currently support referring to uninstantiated
+	// generic types or functions, and instantiated signatures do not have type
+	// parameter lists, we should never encounter a second non-empty type
+	// parameter list when hashing a generic signature.
+	sigTParams *typeparams.TypeParamList
 }
 
 // MakeHasher returns a new Hasher instance.
 func MakeHasher() Hasher {
-	return Hasher{make(map[types.Type]uint32)}
+	return Hasher{
+		memo:       make(map[types.Type]uint32),
+		ptrMap:     make(map[interface{}]uint32),
+		sigTParams: nil,
+	}
 }
 
 // Hash computes a hash value for the given type t such that
@@ -273,17 +293,62 @@ func (h Hasher) hashFor(t types.Type) uint32 {
 		if t.Variadic() {
 			hash *= 8863
 		}
+
+		// Use a separate hasher for types inside of the signature, where type
+		// parameter identity is modified to be (index, constraint). We must use a
+		// new memo for this hasher as type identity may be affected by this
+		// masking. For example, in func[T any](*T), the identity of *T depends on
+		// whether we are mapping the argument in isolation, or recursively as part
+		// of hashing the signature.
+		//
+		// We should never encounter a generic signature while hashing another
+		// generic signature, but defensively set sigTParams only if h.mask is
+		// unset.
+		tparams := typeparams.ForSignature(t)
+		if h.sigTParams == nil && tparams.Len() != 0 {
+			h = Hasher{
+				// There may be something more efficient than discarding the existing
+				// memo, but it would require detecting whether types are 'tainted' by
+				// references to type parameters.
+				memo: make(map[types.Type]uint32),
+				// Re-using ptrMap ensures that pointer identity is preserved in this
+				// hasher.
+				ptrMap:     h.ptrMap,
+				sigTParams: tparams,
+			}
+		}
+
+		for i := 0; i < tparams.Len(); i++ {
+			tparam := tparams.At(i)
+			hash += 7 * h.Hash(tparam.Constraint())
+		}
+
 		return hash + 3*h.hashTuple(t.Params()) + 5*h.hashTuple(t.Results())
 
+	case *typeparams.Union:
+		return h.hashUnion(t)
+
 	case *types.Interface:
+		// Interfaces are identical if they have the same set of methods, with
+		// identical names and types, and they have the same set of type
+		// restrictions. See go/types.identical for more details.
 		var hash uint32 = 9103
+
+		// Hash methods.
 		for i, n := 0, t.NumMethods(); i < n; i++ {
-			// See go/types.identicalMethods for rationale.
 			// Method order is not significant.
 			// Ignore m.Pkg().
 			m := t.Method(i)
 			hash += 3*hashString(m.Name()) + 5*h.Hash(m.Type())
 		}
+
+		// Hash type restrictions.
+		terms, err := typeparams.InterfaceTermSet(t)
+		// if err != nil t has invalid type restrictions.
+		if err == nil {
+			hash += h.hashTermSet(terms)
+		}
+
 		return hash
 
 	case *types.Map:
@@ -293,13 +358,22 @@ func (h Hasher) hashFor(t types.Type) uint32 {
 		return 9127 + 2*uint32(t.Dir()) + 3*h.Hash(t.Elem())
 
 	case *types.Named:
-		// Not safe with a copying GC; objects may move.
-		return uint32(reflect.ValueOf(t.Obj()).Pointer())
+		hash := h.hashPtr(t.Obj())
+		targs := typeparams.NamedTypeArgs(t)
+		for i := 0; i < targs.Len(); i++ {
+			targ := targs.At(i)
+			hash += 2 * h.Hash(targ)
+		}
+		return hash
+
+	case *typeparams.TypeParam:
+		return h.hashTypeParam(t)
 
 	case *types.Tuple:
 		return h.hashTuple(t)
 	}
-	panic(t)
+
+	panic(fmt.Sprintf("%T: %v", t, t))
 }
 
 func (h Hasher) hashTuple(tuple *types.Tuple) uint32 {
@@ -311,3 +385,57 @@ func (h Hasher) hashTuple(tuple *types.Tuple) uint32 {
 	}
 	return hash
 }
+
+func (h Hasher) hashUnion(t *typeparams.Union) uint32 {
+	// Hash type restrictions.
+	terms, err := typeparams.UnionTermSet(t)
+	// if err != nil t has invalid type restrictions. Fall back on a non-zero
+	// hash.
+	if err != nil {
+		return 9151
+	}
+	return h.hashTermSet(terms)
+}
+
+func (h Hasher) hashTermSet(terms []*typeparams.Term) uint32 {
+	var hash uint32 = 9157 + 2*uint32(len(terms))
+	for _, term := range terms {
+		// term order is not significant.
+		termHash := h.Hash(term.Type())
+		if term.Tilde() {
+			termHash *= 9161
+		}
+		hash += 3 * termHash
+	}
+	return hash
+}
+
+// hashTypeParam returns a hash of the type parameter t, with a hash value
+// depending on whether t is contained in h.sigTParams.
+//
+// If h.sigTParams is set and contains t, then we are in the process of hashing
+// a signature, and the hash value of t must depend only on t's index and
+// constraint: signatures are considered identical modulo type parameter
+// renaming.
+//
+// Otherwise the hash of t depends only on t's pointer identity.
+func (h Hasher) hashTypeParam(t *typeparams.TypeParam) uint32 {
+	if h.sigTParams != nil {
+		i := t.Index()
+		if i >= 0 && i < h.sigTParams.Len() && t == h.sigTParams.At(i) {
+			return 9173 + 2*h.Hash(t.Constraint()) + 3*uint32(i)
+		}
+	}
+	return h.hashPtr(t.Obj())
+}
+
+// hashPtr hashes the pointer identity of ptr. It uses h.ptrMap to ensure that
+// pointers values are not dependent on the GC.
+func (h Hasher) hashPtr(ptr interface{}) uint32 {
+	if hash, ok := h.ptrMap[ptr]; ok {
+		return hash
+	}
+	hash := uint32(reflect.ValueOf(ptr).Pointer())
+	h.ptrMap[ptr] = hash
+	return hash
+}
diff --git a/libgo/go/golang.org/x/tools/internal/lsp/fuzzy/input.go b/libgo/go/golang.org/x/tools/internal/lsp/fuzzy/input.go
index ac377035ec6..c1038163f1a 100644
--- a/libgo/go/golang.org/x/tools/internal/lsp/fuzzy/input.go
+++ b/libgo/go/golang.org/x/tools/internal/lsp/fuzzy/input.go
@@ -27,23 +27,23 @@ const (
 // RuneRoles detects the roles of each byte rune in an input string and stores it in the output
 // slice. The rune role depends on the input type. Stops when it parsed all the runes in the string
 // or when it filled the output. If output is nil, then it gets created.
-func RuneRoles(str string, reuse []RuneRole) []RuneRole {
+func RuneRoles(candidate []byte, reuse []RuneRole) []RuneRole {
 	var output []RuneRole
-	if cap(reuse) < len(str) {
-		output = make([]RuneRole, 0, len(str))
+	if cap(reuse) < len(candidate) {
+		output = make([]RuneRole, 0, len(candidate))
 	} else {
 		output = reuse[:0]
 	}
 
 	prev, prev2 := rtNone, rtNone
-	for i := 0; i < len(str); i++ {
-		r := rune(str[i])
+	for i := 0; i < len(candidate); i++ {
+		r := rune(candidate[i])
 
 		role := RNone
 
 		curr := rtLower
-		if str[i] <= unicode.MaxASCII {
-			curr = runeType(rt[str[i]] - '0')
+		if candidate[i] <= unicode.MaxASCII {
+			curr = runeType(rt[candidate[i]] - '0')
 		}
 
 		if curr == rtLower {
@@ -58,7 +58,7 @@ func RuneRoles(str string, reuse []RuneRole) []RuneRole {
 			if prev == rtUpper {
 				// This and previous characters are both upper case.
 
-				if i+1 == len(str) {
+				if i+1 == len(candidate) {
 					// This is last character, previous was also uppercase -> this is UCTail
 					// i.e., (current char is C): aBC / BC / ABC
 					role = RUCTail
@@ -118,11 +118,26 @@ func LastSegment(input string, roles []RuneRole) string {
 	return input[start+1 : end+1]
 }
 
-// ToLower transforms the input string to lower case, which is stored in the output byte slice.
+// fromChunks copies string chunks into the given buffer.
+func fromChunks(chunks []string, buffer []byte) []byte {
+	ii := 0
+	for _, chunk := range chunks {
+		for i := 0; i < len(chunk); i++ {
+			if ii >= cap(buffer) {
+				break
+			}
+			buffer[ii] = chunk[i]
+			ii++
+		}
+	}
+	return buffer[:ii]
+}
+
+// toLower transforms the input string to lower case, which is stored in the output byte slice.
 // The lower casing considers only ASCII values - non ASCII values are left unmodified.
 // Stops when parsed all input or when it filled the output slice. If output is nil, then it gets
 // created.
-func ToLower(input string, reuse []byte) []byte {
+func toLower(input []byte, reuse []byte) []byte {
 	output := reuse
 	if cap(reuse) < len(input) {
 		output = make([]byte, len(input))
@@ -130,7 +145,7 @@ func ToLower(input string, reuse []byte) []byte {
 
 	for i := 0; i < len(input); i++ {
 		r := rune(input[i])
-		if r <= unicode.MaxASCII {
+		if input[i] <= unicode.MaxASCII {
 			if 'A' <= r && r <= 'Z' {
 				r += 'a' - 'A'
 			}
diff --git a/libgo/go/golang.org/x/tools/internal/lsp/fuzzy/matcher.go b/libgo/go/golang.org/x/tools/internal/lsp/fuzzy/matcher.go
index 16a643097de..265cdcf1604 100644
--- a/libgo/go/golang.org/x/tools/internal/lsp/fuzzy/matcher.go
+++ b/libgo/go/golang.org/x/tools/internal/lsp/fuzzy/matcher.go
@@ -51,8 +51,12 @@ type Matcher struct {
 	lastCandidateLen     int // in bytes
 	lastCandidateMatched bool
 
-	// Here we save the last candidate in lower-case. This is basically a byte slice we reuse for
-	// performance reasons, so the slice is not reallocated for every candidate.
+	// Reusable buffers to avoid allocating for every candidate.
+	//  - inputBuf stores the concatenated input chunks
+	//  - lowerBuf stores the last candidate in lower-case
+	//  - rolesBuf stores the calculated roles for each rune in the last
+	//    candidate.
+	inputBuf [MaxInputSize]byte
 	lowerBuf [MaxInputSize]byte
 	rolesBuf [MaxInputSize]RuneRole
 }
@@ -72,7 +76,7 @@ func NewMatcher(pattern string) *Matcher {
 
 	m := &Matcher{
 		pattern:      pattern,
-		patternLower: ToLower(pattern, nil),
+		patternLower: toLower([]byte(pattern), nil),
 	}
 
 	for i, c := range m.patternLower {
@@ -88,7 +92,7 @@ func NewMatcher(pattern string) *Matcher {
 		m.patternShort = m.patternLower
 	}
 
-	m.patternRoles = RuneRoles(pattern, nil)
+	m.patternRoles = RuneRoles([]byte(pattern), nil)
 
 	if len(pattern) > 0 {
 		maxCharScore := 4
@@ -102,10 +106,15 @@ func NewMatcher(pattern string) *Matcher {
 // This is not designed for parallel use. Multiple candidates must be scored sequentially.
 // Returns a score between 0 and 1 (0 - no match, 1 - perfect match).
 func (m *Matcher) Score(candidate string) float32 {
+	return m.ScoreChunks([]string{candidate})
+}
+
+func (m *Matcher) ScoreChunks(chunks []string) float32 {
+	candidate := fromChunks(chunks, m.inputBuf[:])
 	if len(candidate) > MaxInputSize {
 		candidate = candidate[:MaxInputSize]
 	}
-	lower := ToLower(candidate, m.lowerBuf[:])
+	lower := toLower(candidate, m.lowerBuf[:])
 	m.lastCandidateLen = len(candidate)
 
 	if len(m.pattern) == 0 {
@@ -174,7 +183,7 @@ func (m *Matcher) MatchedRanges() []int {
 	return ret
 }
 
-func (m *Matcher) match(candidate string, candidateLower []byte) bool {
+func (m *Matcher) match(candidate []byte, candidateLower []byte) bool {
 	i, j := 0, 0
 	for ; i < len(candidateLower) && j < len(m.patternLower); i++ {
 		if candidateLower[i] == m.patternLower[j] {
@@ -192,7 +201,7 @@ func (m *Matcher) match(candidate string, candidateLower []byte) bool {
 	return true
 }
 
-func (m *Matcher) computeScore(candidate string, candidateLower []byte) int {
+func (m *Matcher) computeScore(candidate []byte, candidateLower []byte) int {
 	pattLen, candLen := len(m.pattern), len(candidate)
 
 	for j := 0; j <= len(m.pattern); j++ {
diff --git a/libgo/go/golang.org/x/tools/internal/lsp/fuzzy/symbol.go b/libgo/go/golang.org/x/tools/internal/lsp/fuzzy/symbol.go
new file mode 100644
index 00000000000..df9fbd51410
--- /dev/null
+++ b/libgo/go/golang.org/x/tools/internal/lsp/fuzzy/symbol.go
@@ -0,0 +1,236 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package fuzzy
+
+import (
+	"unicode"
+)
+
+// SymbolMatcher implements a fuzzy matching algorithm optimized for Go symbols
+// of the form:
+//  example.com/path/to/package.object.field
+//
+// Knowing that we are matching symbols like this allows us to make the
+// following optimizations:
+//  - We can incorporate right-to-left relevance directly into the score
+//    calculation.
+//  - We can match from right to left, discarding leading bytes if the input is
+//    too long.
+//  - We just take the right-most match without losing too much precision. This
+//    allows us to use an O(n) algorithm.
+//  - We can operate directly on chunked strings; in many cases we will
+//    be storing the package path and/or package name separately from the
+//    symbol or identifiers, so doing this avoids allocating strings.
+//  - We can return the index of the right-most match, allowing us to trim
+//    irrelevant qualification.
+//
+// This implementation is experimental, serving as a reference fast algorithm
+// to compare to the fuzzy algorithm implemented by Matcher.
+type SymbolMatcher struct {
+	// Using buffers of length 256 is both a reasonable size for most qualified
+	// symbols, and makes it easy to avoid bounds checks by using uint8 indexes.
+	pattern     [256]rune
+	patternLen  uint8
+	inputBuffer [256]rune   // avoid allocating when considering chunks
+	roles       [256]uint32 // which roles does a rune play (word start, etc.)
+	segments    [256]uint8  // how many segments from the right is each rune
+}
+
+const (
+	segmentStart uint32 = 1 << iota
+	wordStart
+	separator
+)
+
+// NewSymbolMatcher creates a SymbolMatcher that may be used to match the given
+// search pattern.
+//
+// Currently this matcher only accepts case-insensitive fuzzy patterns.
+//
+// An empty pattern matches no input.
+func NewSymbolMatcher(pattern string) *SymbolMatcher {
+	m := &SymbolMatcher{}
+	for _, p := range pattern {
+		m.pattern[m.patternLen] = unicode.ToLower(p)
+		m.patternLen++
+		if m.patternLen == 255 || int(m.patternLen) == len(pattern) {
+			// break at 255 so that we can represent patternLen with a uint8.
+			break
+		}
+	}
+	return m
+}
+
+// Match looks for the right-most match of the search pattern within the symbol
+// represented by concatenating the given chunks, returning its offset and
+// score.
+//
+// If a match is found, the first return value will hold the absolute byte
+// offset within all chunks for the start of the symbol. In other words, the
+// index of the match within strings.Join(chunks, ""). If no match is found,
+// the first return value will be -1.
+//
+// The second return value will be the score of the match, which is always
+// between 0 and 1, inclusive. A score of 0 indicates no match.
+func (m *SymbolMatcher) Match(chunks []string) (int, float64) {
+	// Explicit behavior for an empty pattern.
+	//
+	// As a minor optimization, this also avoids nilness checks later on, since
+	// the compiler can prove that m != nil.
+	if m.patternLen == 0 {
+		return -1, 0
+	}
+
+	// First phase: populate the input buffer with lower-cased runes.
+	//
+	// We could also check for a forward match here, but since we'd have to write
+	// the entire input anyway this has negligible impact on performance.
+
+	var (
+		inputLen  = uint8(0)
+		modifiers = wordStart | segmentStart
+	)
+
+input:
+	for _, chunk := range chunks {
+		for _, r := range chunk {
+			if r == '.' || r == '/' {
+				modifiers |= separator
+			}
+			// optimization: avoid calls to unicode.ToLower, which can't be inlined.
+			l := r
+			if r <= unicode.MaxASCII {
+				if 'A' <= r && r <= 'Z' {
+					l = r + 'a' - 'A'
+				}
+			} else {
+				l = unicode.ToLower(r)
+			}
+			if l != r {
+				modifiers |= wordStart
+			}
+			m.inputBuffer[inputLen] = l
+			m.roles[inputLen] = modifiers
+			inputLen++
+			if m.roles[inputLen-1]&separator != 0 {
+				modifiers = wordStart | segmentStart
+			} else {
+				modifiers = 0
+			}
+			// TODO: we should prefer the right-most input if it overflows, rather
+			//       than the left-most as we're doing here.
+			if inputLen == 255 {
+				break input
+			}
+		}
+	}
+
+	// Second phase: find the right-most match, and count segments from the
+	// right.
+
+	var (
+		pi    = uint8(m.patternLen - 1) // pattern index
+		p     = m.pattern[pi]           // pattern rune
+		start = -1                      // start offset of match
+		rseg  = uint8(0)
+	)
+	const maxSeg = 3 // maximum number of segments from the right to count, for scoring purposes.
+
+	for ii := inputLen - 1; ; ii-- {
+		r := m.inputBuffer[ii]
+		if rseg < maxSeg && m.roles[ii]&separator != 0 {
+			rseg++
+		}
+		m.segments[ii] = rseg
+		if p == r {
+			if pi == 0 {
+				start = int(ii)
+				break
+			}
+			pi--
+			p = m.pattern[pi]
+		}
+		// Don't check ii >= 0 in the loop condition: ii is a uint8.
+		if ii == 0 {
+			break
+		}
+	}
+
+	if start < 0 {
+		// no match: skip scoring
+		return -1, 0
+	}
+
+	// Third phase: find the shortest match, and compute the score.
+
+	// Score is the average score for each character.
+	//
+	// A character score is the multiple of:
+	//   1. 1.0 if the character starts a segment, .8 if the character start a
+	//      mid-segment word, otherwise 0.6. This carries over to immediately
+	//      following characters.
+	//   2. For the final character match, the multiplier from (1) is reduced to
+	//     .8 if the next character in the input is a mid-segment word, or 0.6 if
+	//      the next character in the input is not a word or segment start. This
+	//      ensures that we favor whole-word or whole-segment matches over prefix
+	//      matches.
+	//   3. 1.0 if the character is part of the last segment, otherwise
+	//      1.0-.2*<segments from the right>, with a max segment count of 3.
+	//
+	// This is a very naive algorithm, but it is fast. There's lots of prior art
+	// here, and we should leverage it. For example, we could explicitly consider
+	// character distance, and exact matches of words or segments.
+	//
+	// Also note that this might not actually find the highest scoring match, as
+	// doing so could require a non-linear algorithm, depending on how the score
+	// is calculated.
+
+	pi = 0
+	p = m.pattern[pi]
+
+	const (
+		segStreak  = 1.0
+		wordStreak = 0.8
+		noStreak   = 0.6
+		perSegment = 0.2 // we count at most 3 segments above
+	)
+
+	streakBonus := noStreak
+	totScore := 0.0
+	for ii := uint8(start); ii < inputLen; ii++ {
+		r := m.inputBuffer[ii]
+		if r == p {
+			pi++
+			p = m.pattern[pi]
+			// Note: this could be optimized with some bit operations.
+			switch {
+			case m.roles[ii]&segmentStart != 0 && segStreak > streakBonus:
+				streakBonus = segStreak
+			case m.roles[ii]&wordStart != 0 && wordStreak > streakBonus:
+				streakBonus = wordStreak
+			}
+			finalChar := pi >= m.patternLen
+			// finalCost := 1.0
+			if finalChar && streakBonus > noStreak {
+				switch {
+				case ii == inputLen-1 || m.roles[ii+1]&segmentStart != 0:
+					// Full segment: no reduction
+				case m.roles[ii+1]&wordStart != 0:
+					streakBonus = wordStreak
+				default:
+					streakBonus = noStreak
+				}
+			}
+			totScore += streakBonus * (1.0 - float64(m.segments[ii])*perSegment)
+			if finalChar {
+				break
+			}
+		} else {
+			streakBonus = noStreak
+		}
+	}
+
+	return start, totScore / float64(m.patternLen)
+}
diff --git a/libgo/go/golang.org/x/tools/internal/typeparams/common.go b/libgo/go/golang.org/x/tools/internal/typeparams/common.go
new file mode 100644
index 00000000000..1222764b6a3
--- /dev/null
+++ b/libgo/go/golang.org/x/tools/internal/typeparams/common.go
@@ -0,0 +1,79 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package typeparams contains common utilities for writing tools that interact
+// with generic Go code, as introduced with Go 1.18.
+//
+// Many of the types and functions in this package are proxies for the new APIs
+// introduced in the standard library with Go 1.18. For example, the
+// typeparams.Union type is an alias for go/types.Union, and the ForTypeSpec
+// function returns the value of the go/ast.TypeSpec.TypeParams field. At Go
+// versions older than 1.18 these helpers are implemented as stubs, allowing
+// users of this package to write code that handles generic constructs inline,
+// even if the Go version being used to compile does not support generics.
+//
+// Additionally, this package contains common utilities for working with the
+// new generic constructs, to supplement the standard library APIs. Notably,
+// the StructuralTerms API computes a minimal representation of the structural
+// restrictions on a type parameter. In the future, this API may be available
+// from go/types.
+//
+// See the example/README.md for a more detailed guide on how to update tools
+// to support generics.
+package typeparams
+
+import (
+	"go/ast"
+	"go/token"
+	"go/types"
+)
+
+// UnpackIndexExpr extracts data from AST nodes that represent index
+// expressions.
+//
+// For an ast.IndexExpr, the resulting indices slice will contain exactly one
+// index expression. For an ast.IndexListExpr (go1.18+), it may have a variable
+// number of index expressions.
+//
+// For nodes that don't represent index expressions, the first return value of
+// UnpackIndexExpr will be nil.
+func UnpackIndexExpr(n ast.Node) (x ast.Expr, lbrack token.Pos, indices []ast.Expr, rbrack token.Pos) {
+	switch e := n.(type) {
+	case *ast.IndexExpr:
+		return e.X, e.Lbrack, []ast.Expr{e.Index}, e.Rbrack
+	case *IndexListExpr:
+		return e.X, e.Lbrack, e.Indices, e.Rbrack
+	}
+	return nil, token.NoPos, nil, token.NoPos
+}
+
+// PackIndexExpr returns an *ast.IndexExpr or *ast.IndexListExpr, depending on
+// the cardinality of indices. Calling PackIndexExpr with len(indices) == 0
+// will panic.
+func PackIndexExpr(x ast.Expr, lbrack token.Pos, indices []ast.Expr, rbrack token.Pos) ast.Expr {
+	switch len(indices) {
+	case 0:
+		panic("empty indices")
+	case 1:
+		return &ast.IndexExpr{
+			X:      x,
+			Lbrack: lbrack,
+			Index:  indices[0],
+			Rbrack: rbrack,
+		}
+	default:
+		return &IndexListExpr{
+			X:       x,
+			Lbrack:  lbrack,
+			Indices: indices,
+			Rbrack:  rbrack,
+		}
+	}
+}
+
+// IsTypeParam reports whether t is a type parameter.
+func IsTypeParam(t types.Type) bool {
+	_, ok := t.(*TypeParam)
+	return ok
+}
diff --git a/libgo/go/golang.org/x/tools/internal/typeparams/enabled_go117.go b/libgo/go/golang.org/x/tools/internal/typeparams/enabled_go117.go
new file mode 100644
index 00000000000..18212390e19
--- /dev/null
+++ b/libgo/go/golang.org/x/tools/internal/typeparams/enabled_go117.go
@@ -0,0 +1,12 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !go1.18
+// +build !go1.18
+
+package typeparams
+
+// Enabled reports whether type parameters are enabled in the current build
+// environment.
+const Enabled = false
diff --git a/libgo/go/golang.org/x/tools/internal/typeparams/enabled_go118.go b/libgo/go/golang.org/x/tools/internal/typeparams/enabled_go118.go
new file mode 100644
index 00000000000..d67148823c4
--- /dev/null
+++ b/libgo/go/golang.org/x/tools/internal/typeparams/enabled_go118.go
@@ -0,0 +1,15 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build go1.18
+// +build go1.18
+
+package typeparams
+
+// Note: this constant is in a separate file as this is the only acceptable
+// diff between the <1.18 API of this package and the 1.18 API.
+
+// Enabled reports whether type parameters are enabled in the current build
+// environment.
+const Enabled = true
diff --git a/libgo/go/golang.org/x/tools/internal/typeparams/normalize.go b/libgo/go/golang.org/x/tools/internal/typeparams/normalize.go
new file mode 100644
index 00000000000..090f142a5f3
--- /dev/null
+++ b/libgo/go/golang.org/x/tools/internal/typeparams/normalize.go
@@ -0,0 +1,216 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package typeparams
+
+import (
+	"errors"
+	"fmt"
+	"go/types"
+	"os"
+	"strings"
+)
+
+//go:generate go run copytermlist.go
+
+const debug = false
+
+var ErrEmptyTypeSet = errors.New("empty type set")
+
+// StructuralTerms returns a slice of terms representing the normalized
+// structural type restrictions of a type parameter, if any.
+//
+// Structural type restrictions of a type parameter are created via
+// non-interface types embedded in its constraint interface (directly, or via a
+// chain of interface embeddings). For example, in the declaration
+//  type T[P interface{~int; m()}] int
+// the structural restriction of the type parameter P is ~int.
+//
+// With interface embedding and unions, the specification of structural type
+// restrictions may be arbitrarily complex. For example, consider the
+// following:
+//
+//  type A interface{ ~string|~[]byte }
+//
+//  type B interface{ int|string }
+//
+//  type C interface { ~string|~int }
+//
+//  type T[P interface{ A|B; C }] int
+//
+// In this example, the structural type restriction of P is ~string|int: A|B
+// expands to ~string|~[]byte|int|string, which reduces to ~string|~[]byte|int,
+// which when intersected with C (~string|~int) yields ~string|int.
+//
+// StructuralTerms computes these expansions and reductions, producing a
+// "normalized" form of the embeddings. A structural restriction is normalized
+// if it is a single union containing no interface terms, and is minimal in the
+// sense that removing any term changes the set of types satisfying the
+// constraint. It is left as a proof for the reader that, modulo sorting, there
+// is exactly one such normalized form.
+//
+// Because the minimal representation always takes this form, StructuralTerms
+// returns a slice of tilde terms corresponding to the terms of the union in
+// the normalized structural restriction. An error is returned if the
+// constraint interface is invalid, exceeds complexity bounds, or has an empty
+// type set. In the latter case, StructuralTerms returns ErrEmptyTypeSet.
+//
+// StructuralTerms makes no guarantees about the order of terms, except that it
+// is deterministic.
+func StructuralTerms(tparam *TypeParam) ([]*Term, error) {
+	constraint := tparam.Constraint()
+	if constraint == nil {
+		return nil, fmt.Errorf("%s has nil constraint", tparam)
+	}
+	iface, _ := constraint.Underlying().(*types.Interface)
+	if iface == nil {
+		return nil, fmt.Errorf("constraint is %T, not *types.Interface", constraint.Underlying())
+	}
+	return InterfaceTermSet(iface)
+}
+
+// InterfaceTermSet computes the normalized terms for a constraint interface,
+// returning an error if the term set cannot be computed or is empty. In the
+// latter case, the error will be ErrEmptyTypeSet.
+//
+// See the documentation of StructuralTerms for more information on
+// normalization.
+func InterfaceTermSet(iface *types.Interface) ([]*Term, error) {
+	return computeTermSet(iface)
+}
+
+// UnionTermSet computes the normalized terms for a union, returning an error
+// if the term set cannot be computed or is empty. In the latter case, the
+// error will be ErrEmptyTypeSet.
+//
+// See the documentation of StructuralTerms for more information on
+// normalization.
+func UnionTermSet(union *Union) ([]*Term, error) {
+	return computeTermSet(union)
+}
+
+func computeTermSet(typ types.Type) ([]*Term, error) {
+	tset, err := computeTermSetInternal(typ, make(map[types.Type]*termSet), 0)
+	if err != nil {
+		return nil, err
+	}
+	if tset.terms.isEmpty() {
+		return nil, ErrEmptyTypeSet
+	}
+	if tset.terms.isAll() {
+		return nil, nil
+	}
+	var terms []*Term
+	for _, term := range tset.terms {
+		terms = append(terms, NewTerm(term.tilde, term.typ))
+	}
+	return terms, nil
+}
+
+// A termSet holds the normalized set of terms for a given type.
+//
+// The name termSet is intentionally distinct from 'type set': a type set is
+// all types that implement a type (and includes method restrictions), whereas
+// a term set just represents the structural restrictions on a type.
+type termSet struct {
+	complete bool
+	terms    termlist
+}
+
+func indentf(depth int, format string, args ...interface{}) {
+	fmt.Fprintf(os.Stderr, strings.Repeat(".", depth)+format+"\n", args...)
+}
+
+func computeTermSetInternal(t types.Type, seen map[types.Type]*termSet, depth int) (res *termSet, err error) {
+	if t == nil {
+		panic("nil type")
+	}
+
+	if debug {
+		indentf(depth, "%s", t.String())
+		defer func() {
+			if err != nil {
+				indentf(depth, "=> %s", err)
+			} else {
+				indentf(depth, "=> %s", res.terms.String())
+			}
+		}()
+	}
+
+	const maxTermCount = 100
+	if tset, ok := seen[t]; ok {
+		if !tset.complete {
+			return nil, fmt.Errorf("cycle detected in the declaration of %s", t)
+		}
+		return tset, nil
+	}
+
+	// Mark the current type as seen to avoid infinite recursion.
+	tset := new(termSet)
+	defer func() {
+		tset.complete = true
+	}()
+	seen[t] = tset
+
+	switch u := t.Underlying().(type) {
+	case *types.Interface:
+		// The term set of an interface is the intersection of the term sets of its
+		// embedded types.
+		tset.terms = allTermlist
+		for i := 0; i < u.NumEmbeddeds(); i++ {
+			embedded := u.EmbeddedType(i)
+			if _, ok := embedded.Underlying().(*TypeParam); ok {
+				return nil, fmt.Errorf("invalid embedded type %T", embedded)
+			}
+			tset2, err := computeTermSetInternal(embedded, seen, depth+1)
+			if err != nil {
+				return nil, err
+			}
+			tset.terms = tset.terms.intersect(tset2.terms)
+		}
+	case *Union:
+		// The term set of a union is the union of term sets of its terms.
+		tset.terms = nil
+		for i := 0; i < u.Len(); i++ {
+			t := u.Term(i)
+			var terms termlist
+			switch t.Type().Underlying().(type) {
+			case *types.Interface:
+				tset2, err := computeTermSetInternal(t.Type(), seen, depth+1)
+				if err != nil {
+					return nil, err
+				}
+				terms = tset2.terms
+			case *TypeParam, *Union:
+				// A stand-alone type parameter or union is not permitted as union
+				// term.
+				return nil, fmt.Errorf("invalid union term %T", t)
+			default:
+				if t.Type() == types.Typ[types.Invalid] {
+					continue
+				}
+				terms = termlist{{t.Tilde(), t.Type()}}
+			}
+			tset.terms = tset.terms.union(terms)
+			if len(tset.terms) > maxTermCount {
+				return nil, fmt.Errorf("exceeded max term count %d", maxTermCount)
+			}
+		}
+	case *TypeParam:
+		panic("unreachable")
+	default:
+		// For all other types, the term set is just a single non-tilde term
+		// holding the type itself.
+		if u != types.Typ[types.Invalid] {
+			tset.terms = termlist{{false, t}}
+		}
+	}
+	return tset, nil
+}
+
+// under is a facade for the go/types internal function of the same name. It is
+// used by typeterm.go.
+func under(t types.Type) types.Type {
+	return t.Underlying()
+}
diff --git a/libgo/go/golang.org/x/tools/internal/typeparams/termlist.go b/libgo/go/golang.org/x/tools/internal/typeparams/termlist.go
new file mode 100644
index 00000000000..10857d504c4
--- /dev/null
+++ b/libgo/go/golang.org/x/tools/internal/typeparams/termlist.go
@@ -0,0 +1,172 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Code generated by copytermlist.go DO NOT EDIT.
+
+package typeparams
+
+import (
+	"bytes"
+	"go/types"
+)
+
+// A termlist represents the type set represented by the union
+// t1 ∪ y2 ∪ ... tn of the type sets of the terms t1 to tn.
+// A termlist is in normal form if all terms are disjoint.
+// termlist operations don't require the operands to be in
+// normal form.
+type termlist []*term
+
+// allTermlist represents the set of all types.
+// It is in normal form.
+var allTermlist = termlist{new(term)}
+
+// String prints the termlist exactly (without normalization).
+func (xl termlist) String() string {
+	if len(xl) == 0 {
+		return "∅"
+	}
+	var buf bytes.Buffer
+	for i, x := range xl {
+		if i > 0 {
+			buf.WriteString(" ∪ ")
+		}
+		buf.WriteString(x.String())
+	}
+	return buf.String()
+}
+
+// isEmpty reports whether the termlist xl represents the empty set of types.
+func (xl termlist) isEmpty() bool {
+	// If there's a non-nil term, the entire list is not empty.
+	// If the termlist is in normal form, this requires at most
+	// one iteration.
+	for _, x := range xl {
+		if x != nil {
+			return false
+		}
+	}
+	return true
+}
+
+// isAll reports whether the termlist xl represents the set of all types.
+func (xl termlist) isAll() bool {
+	// If there's a 𝓤 term, the entire list is 𝓤.
+	// If the termlist is in normal form, this requires at most
+	// one iteration.
+	for _, x := range xl {
+		if x != nil && x.typ == nil {
+			return true
+		}
+	}
+	return false
+}
+
+// norm returns the normal form of xl.
+func (xl termlist) norm() termlist {
+	// Quadratic algorithm, but good enough for now.
+	// TODO(gri) fix asymptotic performance
+	used := make([]bool, len(xl))
+	var rl termlist
+	for i, xi := range xl {
+		if xi == nil || used[i] {
+			continue
+		}
+		for j := i + 1; j < len(xl); j++ {
+			xj := xl[j]
+			if xj == nil || used[j] {
+				continue
+			}
+			if u1, u2 := xi.union(xj); u2 == nil {
+				// If we encounter a 𝓤 term, the entire list is 𝓤.
+				// Exit early.
+				// (Note that this is not just an optimization;
+				// if we continue, we may end up with a 𝓤 term
+				// and other terms and the result would not be
+				// in normal form.)
+				if u1.typ == nil {
+					return allTermlist
+				}
+				xi = u1
+				used[j] = true // xj is now unioned into xi - ignore it in future iterations
+			}
+		}
+		rl = append(rl, xi)
+	}
+	return rl
+}
+
+// If the type set represented by xl is specified by a single (non-𝓤) term,
+// structuralType returns that type. Otherwise it returns nil.
+func (xl termlist) structuralType() types.Type {
+	if nl := xl.norm(); len(nl) == 1 {
+		return nl[0].typ // if nl.isAll() then typ is nil, which is ok
+	}
+	return nil
+}
+
+// union returns the union xl ∪ yl.
+func (xl termlist) union(yl termlist) termlist {
+	return append(xl, yl...).norm()
+}
+
+// intersect returns the intersection xl ∩ yl.
+func (xl termlist) intersect(yl termlist) termlist {
+	if xl.isEmpty() || yl.isEmpty() {
+		return nil
+	}
+
+	// Quadratic algorithm, but good enough for now.
+	// TODO(gri) fix asymptotic performance
+	var rl termlist
+	for _, x := range xl {
+		for _, y := range yl {
+			if r := x.intersect(y); r != nil {
+				rl = append(rl, r)
+			}
+		}
+	}
+	return rl.norm()
+}
+
+// equal reports whether xl and yl represent the same type set.
+func (xl termlist) equal(yl termlist) bool {
+	// TODO(gri) this should be more efficient
+	return xl.subsetOf(yl) && yl.subsetOf(xl)
+}
+
+// includes reports whether t ∈ xl.
+func (xl termlist) includes(t types.Type) bool {
+	for _, x := range xl {
+		if x.includes(t) {
+			return true
+		}
+	}
+	return false
+}
+
+// supersetOf reports whether y ⊆ xl.
+func (xl termlist) supersetOf(y *term) bool {
+	for _, x := range xl {
+		if y.subsetOf(x) {
+			return true
+		}
+	}
+	return false
+}
+
+// subsetOf reports whether xl ⊆ yl.
+func (xl termlist) subsetOf(yl termlist) bool {
+	if yl.isEmpty() {
+		return xl.isEmpty()
+	}
+
+	// each term x of xl must be a subset of yl
+	for _, x := range xl {
+		if !yl.supersetOf(x) {
+			return false // x is not a subset yl
+		}
+	}
+	return true
+}
diff --git a/libgo/go/golang.org/x/tools/internal/typeparams/typeparams_go117.go b/libgo/go/golang.org/x/tools/internal/typeparams/typeparams_go117.go
new file mode 100644
index 00000000000..5fd3fc35156
--- /dev/null
+++ b/libgo/go/golang.org/x/tools/internal/typeparams/typeparams_go117.go
@@ -0,0 +1,192 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !go1.18
+// +build !go1.18
+
+package typeparams
+
+import (
+	"go/ast"
+	"go/token"
+	"go/types"
+)
+
+func unsupported() {
+	panic("type parameters are unsupported at this go version")
+}
+
+// IndexListExpr is a placeholder type, as type parameters are not supported at
+// this Go version. Its methods panic on use.
+type IndexListExpr struct {
+	ast.Expr
+	X       ast.Expr   // expression
+	Lbrack  token.Pos  // position of "["
+	Indices []ast.Expr // index expressions
+	Rbrack  token.Pos  // position of "]"
+}
+
+// ForTypeSpec returns an empty field list, as type parameters on not supported
+// at this Go version.
+func ForTypeSpec(*ast.TypeSpec) *ast.FieldList {
+	return nil
+}
+
+// ForFuncType returns an empty field list, as type parameters are not
+// supported at this Go version.
+func ForFuncType(*ast.FuncType) *ast.FieldList {
+	return nil
+}
+
+// TypeParam is a placeholder type, as type parameters are not supported at
+// this Go version. Its methods panic on use.
+type TypeParam struct{ types.Type }
+
+func (*TypeParam) Index() int             { unsupported(); return 0 }
+func (*TypeParam) Constraint() types.Type { unsupported(); return nil }
+func (*TypeParam) Obj() *types.TypeName   { unsupported(); return nil }
+
+// TypeParamList is a placeholder for an empty type parameter list.
+type TypeParamList struct{}
+
+func (*TypeParamList) Len() int          { return 0 }
+func (*TypeParamList) At(int) *TypeParam { unsupported(); return nil }
+
+// TypeList is a placeholder for an empty type list.
+type TypeList struct{}
+
+func (*TypeList) Len() int          { return 0 }
+func (*TypeList) At(int) types.Type { unsupported(); return nil }
+
+// NewTypeParam is unsupported at this Go version, and panics.
+func NewTypeParam(name *types.TypeName, constraint types.Type) *TypeParam {
+	unsupported()
+	return nil
+}
+
+// SetTypeParamConstraint is unsupported at this Go version, and panics.
+func SetTypeParamConstraint(tparam *TypeParam, constraint types.Type) {
+	unsupported()
+}
+
+// NewSignatureType calls types.NewSignature, panicking if recvTypeParams or
+// typeParams is non-empty.
+func NewSignatureType(recv *types.Var, recvTypeParams, typeParams []*TypeParam, params, results *types.Tuple, variadic bool) *types.Signature {
+	if len(recvTypeParams) != 0 || len(typeParams) != 0 {
+		panic("signatures cannot have type parameters at this Go version")
+	}
+	return types.NewSignature(recv, params, results, variadic)
+}
+
+// ForSignature returns an empty slice.
+func ForSignature(*types.Signature) *TypeParamList {
+	return nil
+}
+
+// RecvTypeParams returns a nil slice.
+func RecvTypeParams(sig *types.Signature) *TypeParamList {
+	return nil
+}
+
+// IsComparable returns false, as no interfaces are type-restricted at this Go
+// version.
+func IsComparable(*types.Interface) bool {
+	return false
+}
+
+// IsMethodSet returns true, as no interfaces are type-restricted at this Go
+// version.
+func IsMethodSet(*types.Interface) bool {
+	return true
+}
+
+// IsImplicit returns false, as no interfaces are implicit at this Go version.
+func IsImplicit(*types.Interface) bool {
+	return false
+}
+
+// MarkImplicit does nothing, because this Go version does not have implicit
+// interfaces.
+func MarkImplicit(*types.Interface) {}
+
+// ForNamed returns an empty type parameter list, as type parameters are not
+// supported at this Go version.
+func ForNamed(*types.Named) *TypeParamList {
+	return nil
+}
+
+// SetForNamed panics if tparams is non-empty.
+func SetForNamed(_ *types.Named, tparams []*TypeParam) {
+	if len(tparams) > 0 {
+		unsupported()
+	}
+}
+
+// NamedTypeArgs returns nil.
+func NamedTypeArgs(*types.Named) *TypeList {
+	return nil
+}
+
+// NamedTypeOrigin is the identity method at this Go version.
+func NamedTypeOrigin(named *types.Named) types.Type {
+	return named
+}
+
+// Term holds information about a structural type restriction.
+type Term struct {
+	tilde bool
+	typ   types.Type
+}
+
+func (m *Term) Tilde() bool      { return m.tilde }
+func (m *Term) Type() types.Type { return m.typ }
+func (m *Term) String() string {
+	pre := ""
+	if m.tilde {
+		pre = "~"
+	}
+	return pre + m.typ.String()
+}
+
+// NewTerm is unsupported at this Go version, and panics.
+func NewTerm(tilde bool, typ types.Type) *Term {
+	return &Term{tilde, typ}
+}
+
+// Union is a placeholder type, as type parameters are not supported at this Go
+// version. Its methods panic on use.
+type Union struct{ types.Type }
+
+func (*Union) Len() int         { return 0 }
+func (*Union) Term(i int) *Term { unsupported(); return nil }
+
+// NewUnion is unsupported at this Go version, and panics.
+func NewUnion(terms []*Term) *Union {
+	unsupported()
+	return nil
+}
+
+// InitInstanceInfo is a noop at this Go version.
+func InitInstanceInfo(*types.Info) {}
+
+// Instance is a placeholder type, as type parameters are not supported at this
+// Go version.
+type Instance struct {
+	TypeArgs *TypeList
+	Type     types.Type
+}
+
+// GetInstances returns a nil map, as type parameters are not supported at this
+// Go version.
+func GetInstances(info *types.Info) map[*ast.Ident]Instance { return nil }
+
+// Context is a placeholder type, as type parameters are not supported at
+// this Go version.
+type Context struct{}
+
+// Instantiate is unsupported on this Go version, and panics.
+func Instantiate(ctxt *Context, typ types.Type, targs []types.Type, validate bool) (types.Type, error) {
+	unsupported()
+	return nil, nil
+}
diff --git a/libgo/go/golang.org/x/tools/internal/typeparams/typeparams_go118.go b/libgo/go/golang.org/x/tools/internal/typeparams/typeparams_go118.go
new file mode 100644
index 00000000000..7470aed8c99
--- /dev/null
+++ b/libgo/go/golang.org/x/tools/internal/typeparams/typeparams_go118.go
@@ -0,0 +1,146 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build go1.18
+// +build go1.18
+
+package typeparams
+
+import (
+	"go/ast"
+	"go/types"
+)
+
+// IndexListExpr is an alias for ast.IndexListExpr.
+type IndexListExpr = ast.IndexListExpr
+
+// ForTypeSpec returns n.TypeParams.
+func ForTypeSpec(n *ast.TypeSpec) *ast.FieldList {
+	if n == nil {
+		return nil
+	}
+	return n.TypeParams
+}
+
+// ForFuncType returns n.TypeParams.
+func ForFuncType(n *ast.FuncType) *ast.FieldList {
+	if n == nil {
+		return nil
+	}
+	return n.TypeParams
+}
+
+// TypeParam is an alias for types.TypeParam
+type TypeParam = types.TypeParam
+
+// TypeParamList is an alias for types.TypeParamList
+type TypeParamList = types.TypeParamList
+
+// TypeList is an alias for types.TypeList
+type TypeList = types.TypeList
+
+// NewTypeParam calls types.NewTypeParam.
+func NewTypeParam(name *types.TypeName, constraint types.Type) *TypeParam {
+	return types.NewTypeParam(name, constraint)
+}
+
+// SetTypeParamConstraint calls tparam.SetConstraint(constraint).
+func SetTypeParamConstraint(tparam *TypeParam, constraint types.Type) {
+	tparam.SetConstraint(constraint)
+}
+
+// NewSignatureType calls types.NewSignatureType.
+func NewSignatureType(recv *types.Var, recvTypeParams, typeParams []*TypeParam, params, results *types.Tuple, variadic bool) *types.Signature {
+	return types.NewSignatureType(recv, recvTypeParams, typeParams, params, results, variadic)
+}
+
+// ForSignature returns sig.TypeParams()
+func ForSignature(sig *types.Signature) *TypeParamList {
+	return sig.TypeParams()
+}
+
+// RecvTypeParams returns sig.RecvTypeParams().
+func RecvTypeParams(sig *types.Signature) *TypeParamList {
+	return sig.RecvTypeParams()
+}
+
+// IsComparable calls iface.IsComparable().
+func IsComparable(iface *types.Interface) bool {
+	return iface.IsComparable()
+}
+
+// IsMethodSet calls iface.IsMethodSet().
+func IsMethodSet(iface *types.Interface) bool {
+	return iface.IsMethodSet()
+}
+
+// IsImplicit calls iface.IsImplicit().
+func IsImplicit(iface *types.Interface) bool {
+	return iface.IsImplicit()
+}
+
+// MarkImplicit calls iface.MarkImplicit().
+func MarkImplicit(iface *types.Interface) {
+	iface.MarkImplicit()
+}
+
+// ForNamed extracts the (possibly empty) type parameter object list from
+// named.
+func ForNamed(named *types.Named) *TypeParamList {
+	return named.TypeParams()
+}
+
+// SetForNamed sets the type params tparams on n. Each tparam must be of
+// dynamic type *types.TypeParam.
+func SetForNamed(n *types.Named, tparams []*TypeParam) {
+	n.SetTypeParams(tparams)
+}
+
+// NamedTypeArgs returns named.TypeArgs().
+func NamedTypeArgs(named *types.Named) *TypeList {
+	return named.TypeArgs()
+}
+
+// NamedTypeOrigin returns named.Orig().
+func NamedTypeOrigin(named *types.Named) types.Type {
+	return named.Origin()
+}
+
+// Term is an alias for types.Term.
+type Term = types.Term
+
+// NewTerm calls types.NewTerm.
+func NewTerm(tilde bool, typ types.Type) *Term {
+	return types.NewTerm(tilde, typ)
+}
+
+// Union is an alias for types.Union
+type Union = types.Union
+
+// NewUnion calls types.NewUnion.
+func NewUnion(terms []*Term) *Union {
+	return types.NewUnion(terms)
+}
+
+// InitInstanceInfo initializes info to record information about type and
+// function instances.
+func InitInstanceInfo(info *types.Info) {
+	info.Instances = make(map[*ast.Ident]types.Instance)
+}
+
+// Instance is an alias for types.Instance.
+type Instance = types.Instance
+
+// GetInstances returns info.Instances.
+func GetInstances(info *types.Info) map[*ast.Ident]Instance {
+	return info.Instances
+}
+
+// Context is an alias for types.Context.
+type Context = types.Context
+
+// Instantiate calls types.Instantiate.
+func Instantiate(ctxt *Context, typ types.Type, targs []types.Type, validate bool) (types.Type, error) {
+	return types.Instantiate(ctxt, typ, targs, validate)
+}
diff --git a/libgo/go/golang.org/x/tools/internal/typeparams/typeterm.go b/libgo/go/golang.org/x/tools/internal/typeparams/typeterm.go
new file mode 100644
index 00000000000..7ddee28d987
--- /dev/null
+++ b/libgo/go/golang.org/x/tools/internal/typeparams/typeterm.go
@@ -0,0 +1,170 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Code generated by copytermlist.go DO NOT EDIT.
+
+package typeparams
+
+import "go/types"
+
+// A term describes elementary type sets:
+//
+//   ∅:  (*term)(nil)     == ∅                      // set of no types (empty set)
+//   𝓤:  &term{}          == 𝓤                      // set of all types (𝓤niverse)
+//   T:  &term{false, T}  == {T}                    // set of type T
+//  ~t:  &term{true, t}   == {t' | under(t') == t}  // set of types with underlying type t
+//
+type term struct {
+	tilde bool // valid if typ != nil
+	typ   types.Type
+}
+
+func (x *term) String() string {
+	switch {
+	case x == nil:
+		return "∅"
+	case x.typ == nil:
+		return "𝓤"
+	case x.tilde:
+		return "~" + x.typ.String()
+	default:
+		return x.typ.String()
+	}
+}
+
+// equal reports whether x and y represent the same type set.
+func (x *term) equal(y *term) bool {
+	// easy cases
+	switch {
+	case x == nil || y == nil:
+		return x == y
+	case x.typ == nil || y.typ == nil:
+		return x.typ == y.typ
+	}
+	// ∅ ⊂ x, y ⊂ 𝓤
+
+	return x.tilde == y.tilde && types.Identical(x.typ, y.typ)
+}
+
+// union returns the union x ∪ y: zero, one, or two non-nil terms.
+func (x *term) union(y *term) (_, _ *term) {
+	// easy cases
+	switch {
+	case x == nil && y == nil:
+		return nil, nil // ∅ ∪ ∅ == ∅
+	case x == nil:
+		return y, nil // ∅ ∪ y == y
+	case y == nil:
+		return x, nil // x ∪ ∅ == x
+	case x.typ == nil:
+		return x, nil // 𝓤 ∪ y == 𝓤
+	case y.typ == nil:
+		return y, nil // x ∪ 𝓤 == 𝓤
+	}
+	// ∅ ⊂ x, y ⊂ 𝓤
+
+	if x.disjoint(y) {
+		return x, y // x ∪ y == (x, y) if x ∩ y == ∅
+	}
+	// x.typ == y.typ
+
+	// ~t ∪ ~t == ~t
+	// ~t ∪  T == ~t
+	//  T ∪ ~t == ~t
+	//  T ∪  T ==  T
+	if x.tilde || !y.tilde {
+		return x, nil
+	}
+	return y, nil
+}
+
+// intersect returns the intersection x ∩ y.
+func (x *term) intersect(y *term) *term {
+	// easy cases
+	switch {
+	case x == nil || y == nil:
+		return nil // ∅ ∩ y == ∅ and ∩ ∅ == ∅
+	case x.typ == nil:
+		return y // 𝓤 ∩ y == y
+	case y.typ == nil:
+		return x // x ∩ 𝓤 == x
+	}
+	// ∅ ⊂ x, y ⊂ 𝓤
+
+	if x.disjoint(y) {
+		return nil // x ∩ y == ∅ if x ∩ y == ∅
+	}
+	// x.typ == y.typ
+
+	// ~t ∩ ~t == ~t
+	// ~t ∩  T ==  T
+	//  T ∩ ~t ==  T
+	//  T ∩  T ==  T
+	if !x.tilde || y.tilde {
+		return x
+	}
+	return y
+}
+
+// includes reports whether t ∈ x.
+func (x *term) includes(t types.Type) bool {
+	// easy cases
+	switch {
+	case x == nil:
+		return false // t ∈ ∅ == false
+	case x.typ == nil:
+		return true // t ∈ 𝓤 == true
+	}
+	// ∅ ⊂ x ⊂ 𝓤
+
+	u := t
+	if x.tilde {
+		u = under(u)
+	}
+	return types.Identical(x.typ, u)
+}
+
+// subsetOf reports whether x ⊆ y.
+func (x *term) subsetOf(y *term) bool {
+	// easy cases
+	switch {
+	case x == nil:
+		return true // ∅ ⊆ y == true
+	case y == nil:
+		return false // x ⊆ ∅ == false since x != ∅
+	case y.typ == nil:
+		return true // x ⊆ 𝓤 == true
+	case x.typ == nil:
+		return false // 𝓤 ⊆ y == false since y != 𝓤
+	}
+	// ∅ ⊂ x, y ⊂ 𝓤
+
+	if x.disjoint(y) {
+		return false // x ⊆ y == false if x ∩ y == ∅
+	}
+	// x.typ == y.typ
+
+	// ~t ⊆ ~t == true
+	// ~t ⊆ T == false
+	//  T ⊆ ~t == true
+	//  T ⊆  T == true
+	return !x.tilde || y.tilde
+}
+
+// disjoint reports whether x ∩ y == ∅.
+// x.typ and y.typ must not be nil.
+func (x *term) disjoint(y *term) bool {
+	if debug && (x.typ == nil || y.typ == nil) {
+		panic("invalid argument(s)")
+	}
+	ux := x.typ
+	if y.tilde {
+		ux = under(ux)
+	}
+	uy := y.typ
+	if x.tilde {
+		uy = under(uy)
+	}
+	return !types.Identical(ux, uy)
+}
diff --git a/libgo/go/golang.org/x/tools/txtar/archive.go b/libgo/go/golang.org/x/tools/txtar/archive.go
new file mode 100644
index 00000000000..214256617b5
--- /dev/null
+++ b/libgo/go/golang.org/x/tools/txtar/archive.go
@@ -0,0 +1,140 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package txtar implements a trivial text-based file archive format.
+//
+// The goals for the format are:
+//
+//	- be trivial enough to create and edit by hand.
+//	- be able to store trees of text files describing go command test cases.
+//	- diff nicely in git history and code reviews.
+//
+// Non-goals include being a completely general archive format,
+// storing binary data, storing file modes, storing special files like
+// symbolic links, and so on.
+//
+// Txtar format
+//
+// A txtar archive is zero or more comment lines and then a sequence of file entries.
+// Each file entry begins with a file marker line of the form "-- FILENAME --"
+// and is followed by zero or more file content lines making up the file data.
+// The comment or file content ends at the next file marker line.
+// The file marker line must begin with the three-byte sequence "-- "
+// and end with the three-byte sequence " --", but the enclosed
+// file name can be surrounding by additional white space,
+// all of which is stripped.
+//
+// If the txtar file is missing a trailing newline on the final line,
+// parsers should consider a final newline to be present anyway.
+//
+// There are no possible syntax errors in a txtar archive.
+package txtar
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"strings"
+)
+
+// An Archive is a collection of files.
+type Archive struct {
+	Comment []byte
+	Files   []File
+}
+
+// A File is a single file in an archive.
+type File struct {
+	Name string // name of file ("foo/bar.txt")
+	Data []byte // text content of file
+}
+
+// Format returns the serialized form of an Archive.
+// It is assumed that the Archive data structure is well-formed:
+// a.Comment and all a.File[i].Data contain no file marker lines,
+// and all a.File[i].Name is non-empty.
+func Format(a *Archive) []byte {
+	var buf bytes.Buffer
+	buf.Write(fixNL(a.Comment))
+	for _, f := range a.Files {
+		fmt.Fprintf(&buf, "-- %s --\n", f.Name)
+		buf.Write(fixNL(f.Data))
+	}
+	return buf.Bytes()
+}
+
+// ParseFile parses the named file as an archive.
+func ParseFile(file string) (*Archive, error) {
+	data, err := ioutil.ReadFile(file)
+	if err != nil {
+		return nil, err
+	}
+	return Parse(data), nil
+}
+
+// Parse parses the serialized form of an Archive.
+// The returned Archive holds slices of data.
+func Parse(data []byte) *Archive {
+	a := new(Archive)
+	var name string
+	a.Comment, name, data = findFileMarker(data)
+	for name != "" {
+		f := File{name, nil}
+		f.Data, name, data = findFileMarker(data)
+		a.Files = append(a.Files, f)
+	}
+	return a
+}
+
+var (
+	newlineMarker = []byte("\n-- ")
+	marker        = []byte("-- ")
+	markerEnd     = []byte(" --")
+)
+
+// findFileMarker finds the next file marker in data,
+// extracts the file name, and returns the data before the marker,
+// the file name, and the data after the marker.
+// If there is no next marker, findFileMarker returns before = fixNL(data), name = "", after = nil.
+func findFileMarker(data []byte) (before []byte, name string, after []byte) {
+	var i int
+	for {
+		if name, after = isMarker(data[i:]); name != "" {
+			return data[:i], name, after
+		}
+		j := bytes.Index(data[i:], newlineMarker)
+		if j < 0 {
+			return fixNL(data), "", nil
+		}
+		i += j + 1 // positioned at start of new possible marker
+	}
+}
+
+// isMarker checks whether data begins with a file marker line.
+// If so, it returns the name from the line and the data after the line.
+// Otherwise it returns name == "" with an unspecified after.
+func isMarker(data []byte) (name string, after []byte) {
+	if !bytes.HasPrefix(data, marker) {
+		return "", nil
+	}
+	if i := bytes.IndexByte(data, '\n'); i >= 0 {
+		data, after = data[:i], data[i+1:]
+	}
+	if !(bytes.HasSuffix(data, markerEnd) && len(data) >= len(marker)+len(markerEnd)) {
+		return "", nil
+	}
+	return strings.TrimSpace(string(data[len(marker) : len(data)-len(markerEnd)])), after
+}
+
+// If data is empty or ends in \n, fixNL returns data.
+// Otherwise fixNL returns a new slice consisting of data with a final \n added.
+func fixNL(data []byte) []byte {
+	if len(data) == 0 || data[len(data)-1] == '\n' {
+		return data
+	}
+	d := make([]byte, len(data)+1)
+	copy(d, data)
+	d[len(data)] = '\n'
+	return d
+}