go/types: use []*TypeParam rather than []*TypeName type param lists

Making this change improves type safety slightly, and avoids many
internal type assertions.

Change-Id: I26519b0e57068e944e8243983ae90553d79e59c2
Reviewed-on: https://go-review.googlesource.com/c/go/+/343932
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

11 files changed, 57 insertions, 59 deletions

diff --git a/src/go/types/decl.go b/src/go/types/decl.go
index c6505b63a1..8ebaf289f1 100644
--- a/src/go/types/decl.go
+++ b/src/go/types/decl.go
@@ -632,7 +632,7 @@ func (check *Checker) typeDecl(obj *TypeName, tdecl *ast.TypeSpec, def *Named) {
 }
 
 func (check *Checker) collectTypeParams(list *ast.FieldList) *TParamList {
-	var tparams []*TypeName
+	var tparams []*TypeParam
 	// Declare type parameters up-front, with empty interface as type bound.
 	// The scope of type parameters starts at the beginning of the type parameter
 	// list (so we can have mutually recursive parameterized interfaces).
@@ -648,7 +648,7 @@ func (check *Checker) collectTypeParams(list *ast.FieldList) *TParamList {
 		}
 		bound = check.boundType(f.Type)
 		for i := range f.Names {
-			tparams[index+i].typ.(*TypeParam).bound = bound
+			tparams[index+i].bound = bound
 		}
 
 	next:
@@ -658,11 +658,11 @@ func (check *Checker) collectTypeParams(list *ast.FieldList) *TParamList {
 	return bindTParams(tparams)
 }
 
-func (check *Checker) declareTypeParams(tparams []*TypeName, names []*ast.Ident) []*TypeName {
+func (check *Checker) declareTypeParams(tparams []*TypeParam, names []*ast.Ident) []*TypeParam {
 	for _, name := range names {
-		tpar := NewTypeName(name.Pos(), check.pkg, name.Name, nil)
-		check.NewTypeParam(tpar, &emptyInterface)               // assigns type to tpar as a side-effect
-		check.declare(check.scope, name, tpar, check.scope.pos) // TODO(gri) check scope position
+		tname := NewTypeName(name.Pos(), check.pkg, name.Name, nil)
+		tpar := check.NewTypeParam(tname, &emptyInterface)       // assigns type to tpar as a side-effect
+		check.declare(check.scope, name, tname, check.scope.pos) // TODO(gri) check scope position
 		tparams = append(tparams, tpar)
 	}
 
diff --git a/src/go/types/infer.go b/src/go/types/infer.go
index 57ec327d12..58456444ed 100644
--- a/src/go/types/infer.go
+++ b/src/go/types/infer.go
@@ -27,7 +27,7 @@ import (
 //
 // Constraint type inference is used after each step to expand the set of type arguments.
 //
-func (check *Checker) infer(posn positioner, tparams []*TypeName, targs []Type, params *Tuple, args []*operand, report bool) (result []Type) {
+func (check *Checker) infer(posn positioner, tparams []*TypeParam, targs []Type, params *Tuple, args []*operand, report bool) (result []Type) {
 	if debug {
 		defer func() {
 			assert(result == nil || len(result) == len(tparams))
@@ -121,7 +121,7 @@ func (check *Checker) infer(posn positioner, tparams []*TypeName, targs []Type,
 				}
 			}
 			if allFailed {
-				check.errorf(arg, _Todo, "%s %s of %s does not match %s (cannot infer %s)", kind, targ, arg.expr, tpar, typeNamesString(tparams))
+				check.errorf(arg, _Todo, "%s %s of %s does not match %s (cannot infer %s)", kind, targ, arg.expr, tpar, typeParamsString(tparams))
 				return
 			}
 		}
@@ -218,23 +218,23 @@ func (check *Checker) infer(posn positioner, tparams []*TypeName, targs []Type,
 	assert(index >= 0 && targs[index] == nil)
 	tpar := tparams[index]
 	if report {
-		check.errorf(posn, _Todo, "cannot infer %s (%v) (%v)", tpar.name, tpar.pos, targs)
+		check.errorf(posn, _Todo, "cannot infer %s (%v) (%v)", tpar.obj.name, tpar.obj.pos, targs)
 	}
 	return nil
 }
 
-// typeNamesString produces a string containing all the
-// type names in list suitable for human consumption.
-func typeNamesString(list []*TypeName) string {
+// typeParamsString produces a string containing all the type parameter names
+// in list suitable for human consumption.
+func typeParamsString(list []*TypeParam) string {
 	// common cases
 	n := len(list)
 	switch n {
 	case 0:
 		return ""
 	case 1:
-		return list[0].name
+		return list[0].obj.name
 	case 2:
-		return list[0].name + " and " + list[1].name
+		return list[0].obj.name + " and " + list[1].obj.name
 	}
 
 	// general case (n > 2)
@@ -243,15 +243,15 @@ func typeNamesString(list []*TypeName) string {
 		if i > 0 {
 			b.WriteString(", ")
 		}
-		b.WriteString(tname.name)
+		b.WriteString(tname.obj.name)
 	}
 	b.WriteString(", and ")
-	b.WriteString(list[n-1].name)
+	b.WriteString(list[n-1].obj.name)
 	return b.String()
 }
 
 // IsParameterized reports whether typ contains any of the type parameters of tparams.
-func isParameterized(tparams []*TypeName, typ Type) bool {
+func isParameterized(tparams []*TypeParam, typ Type) bool {
 	w := tpWalker{
 		seen:    make(map[Type]bool),
 		tparams: tparams,
@@ -261,7 +261,7 @@ func isParameterized(tparams []*TypeName, typ Type) bool {
 
 type tpWalker struct {
 	seen    map[Type]bool
-	tparams []*TypeName
+	tparams []*TypeParam
 }
 
 func (w *tpWalker) isParameterized(typ Type) (res bool) {
@@ -334,7 +334,7 @@ func (w *tpWalker) isParameterized(typ Type) (res bool) {
 
 	case *TypeParam:
 		// t must be one of w.tparams
-		return t.index < len(w.tparams) && w.tparams[t.index].typ == t
+		return t.index < len(w.tparams) && w.tparams[t.index] == t
 
 	default:
 		unreachable()
@@ -360,7 +360,7 @@ func (w *tpWalker) isParameterizedTypeList(list []Type) bool {
 // first type argument in that list that couldn't be inferred (and thus is nil). If all
 // type arguments were inferred successfully, index is < 0. The number of type arguments
 // provided may be less than the number of type parameters, but there must be at least one.
-func (check *Checker) inferB(tparams []*TypeName, targs []Type, report bool) (types []Type, index int) {
+func (check *Checker) inferB(tparams []*TypeParam, targs []Type, report bool) (types []Type, index int) {
 	assert(len(tparams) >= len(targs) && len(targs) > 0)
 
 	// Setup bidirectional unification between those structural bounds
@@ -378,12 +378,12 @@ func (check *Checker) inferB(tparams []*TypeName, targs []Type, report bool) (ty
 
 	// Unify type parameters with their structural constraints, if any.
 	for _, tpar := range tparams {
-		typ := tpar.typ.(*TypeParam)
+		typ := tpar
 		sbound := typ.structuralType()
 		if sbound != nil {
 			if !u.unify(typ, sbound) {
 				if report {
-					check.errorf(tpar, _Todo, "%s does not match %s", tpar, sbound)
+					check.errorf(tpar.obj, _Todo, "%s does not match %s", tpar.obj, sbound)
 				}
 				return nil, 0
 			}
diff --git a/src/go/types/instantiate.go b/src/go/types/instantiate.go
index 8d7a9ecfb2..fb2fddfc0f 100644
--- a/src/go/types/instantiate.go
+++ b/src/go/types/instantiate.go
@@ -48,7 +48,7 @@ func Instantiate(env *Environment, typ Type, targs []Type, validate bool) (Type,
 
 	var err error
 	if validate {
-		var tparams []*TypeName
+		var tparams []*TypeParam
 		switch t := typ.(type) {
 		case *Named:
 			tparams = t.TParams().list()
@@ -90,7 +90,7 @@ func (check *Checker) instantiate(pos token.Pos, typ Type, targs []Type, posList
 	check.later(func() {
 		// Collect tparams again because lazily loaded *Named types may not have
 		// had tparams set up above.
-		var tparams []*TypeName
+		var tparams []*TypeParam
 		switch t := typ.(type) {
 		case *Named:
 			tparams = t.TParams().list()
@@ -186,11 +186,11 @@ func (check *Checker) validateTArgLen(pos token.Pos, tparams *TParamList, targs
 	return true
 }
 
-func (check *Checker) verify(pos token.Pos, tparams []*TypeName, targs []Type) (int, error) {
+func (check *Checker) verify(pos token.Pos, tparams []*TypeParam, targs []Type) (int, error) {
 	smap := makeSubstMap(tparams, targs)
-	for i, tname := range tparams {
+	for i, tpar := range tparams {
 		// stop checking bounds after the first failure
-		if err := check.satisfies(pos, targs[i], tname.typ.(*TypeParam), smap); err != nil {
+		if err := check.satisfies(pos, targs[i], tpar, smap); err != nil {
 			return i, err
 		}
 	}
diff --git a/src/go/types/named.go b/src/go/types/named.go
index d547c47f8e..105f34e1fb 100644
--- a/src/go/types/named.go
+++ b/src/go/types/named.go
@@ -24,7 +24,7 @@ type Named struct {
 	targs      []Type      // type arguments (after instantiation), or nil
 	methods    []*Func     // methods declared for this type (not the method set of this type); signatures are type-checked lazily
 
-	resolve func(*Named) ([]*TypeName, Type, []*Func)
+	resolve func(*Named) ([]*TypeParam, Type, []*Func)
 	once    sync.Once
 }
 
@@ -126,7 +126,7 @@ func (t *Named) _Orig() *Named { return t.orig }
 func (t *Named) TParams() *TParamList { return t.load().tparams }
 
 // SetTParams sets the type parameters of the named type t.
-func (t *Named) SetTParams(tparams []*TypeName) { t.load().tparams = bindTParams(tparams) }
+func (t *Named) SetTParams(tparams []*TypeParam) { t.load().tparams = bindTParams(tparams) }
 
 // NumTArgs returns the number of type arguments used to instantiate the named
 // type t, or 0 if t is not an instantiated type.
diff --git a/src/go/types/object.go b/src/go/types/object.go
index 7266623fbe..eb5df56d14 100644
--- a/src/go/types/object.go
+++ b/src/go/types/object.go
@@ -232,7 +232,7 @@ func NewTypeName(pos token.Pos, pkg *Package, name string, typ Type) *TypeName {
 
 // _NewTypeNameLazy returns a new defined type like NewTypeName, but it
 // lazily calls resolve to finish constructing the Named object.
-func _NewTypeNameLazy(pos token.Pos, pkg *Package, name string, resolve func(named *Named) (tparams []*TypeName, underlying Type, methods []*Func)) *TypeName {
+func _NewTypeNameLazy(pos token.Pos, pkg *Package, name string, resolve func(named *Named) (tparams []*TypeParam, underlying Type, methods []*Func)) *TypeName {
 	obj := NewTypeName(pos, pkg, name, nil)
 	NewNamed(obj, nil, nil).resolve = resolve
 	return obj
diff --git a/src/go/types/predicates.go b/src/go/types/predicates.go
index 0945dac722..027e30c1a1 100644
--- a/src/go/types/predicates.go
+++ b/src/go/types/predicates.go
@@ -351,13 +351,13 @@ func identical(x, y Type, cmpTags bool, p *ifacePair) bool {
 	return false
 }
 
-func identicalTParams(x, y []*TypeName, cmpTags bool, p *ifacePair) bool {
+func identicalTParams(x, y []*TypeParam, cmpTags bool, p *ifacePair) bool {
 	if len(x) != len(y) {
 		return false
 	}
 	for i, x := range x {
 		y := y[i]
-		if !identical(x.typ.(*TypeParam).bound, y.typ.(*TypeParam).bound, cmpTags, p) {
+		if !identical(x.bound, y.bound, cmpTags, p) {
 			return false
 		}
 	}
diff --git a/src/go/types/signature.go b/src/go/types/signature.go
index 9bfb1683a7..d6c12cf3d9 100644
--- a/src/go/types/signature.go
+++ b/src/go/types/signature.go
@@ -59,13 +59,13 @@ func (s *Signature) Recv() *Var { return s.recv }
 func (s *Signature) TParams() *TParamList { return s.tparams }
 
 // SetTParams sets the type parameters of signature s.
-func (s *Signature) SetTParams(tparams []*TypeName) { s.tparams = bindTParams(tparams) }
+func (s *Signature) SetTParams(tparams []*TypeParam) { s.tparams = bindTParams(tparams) }
 
 // RParams returns the receiver type parameters of signature s, or nil.
 func (s *Signature) RParams() *TParamList { return s.rparams }
 
 // SetRParams sets the receiver type params of signature s.
-func (s *Signature) SetRParams(rparams []*TypeName) { s.rparams = bindTParams(rparams) }
+func (s *Signature) SetRParams(rparams []*TypeParam) { s.rparams = bindTParams(rparams) }
 
 // Params returns the parameters of signature s, or nil.
 func (s *Signature) Params() *Tuple { return s.params }
@@ -121,7 +121,7 @@ func (check *Checker) funcType(sig *Signature, recvPar *ast.FieldList, ftyp *ast
 			sig.rparams = bindTParams(check.declareTypeParams(nil, rparams))
 			// determine receiver type to get its type parameters
 			// and the respective type parameter bounds
-			var recvTParams []*TypeName
+			var recvTParams []*TypeParam
 			if rname != nil {
 				// recv should be a Named type (otherwise an error is reported elsewhere)
 				// Also: Don't report an error via genericType since it will be reported
@@ -137,19 +137,19 @@ func (check *Checker) funcType(sig *Signature, recvPar *ast.FieldList, ftyp *ast
 				// We have a list of *TypeNames but we need a list of Types.
 				list := make([]Type, sig.RParams().Len())
 				for i, t := range sig.RParams().list() {
-					list[i] = t.typ
+					list[i] = t
 				}
 				smap := makeSubstMap(recvTParams, list)
-				for i, tname := range sig.RParams().list() {
-					bound := recvTParams[i].typ.(*TypeParam).bound
+				for i, tpar := range sig.RParams().list() {
+					bound := recvTParams[i].bound
 					// bound is (possibly) parameterized in the context of the
 					// receiver type declaration. Substitute parameters for the
 					// current context.
 					// TODO(gri) should we assume now that bounds always exist?
 					//           (no bound == empty interface)
 					if bound != nil {
-						bound = check.subst(tname.pos, bound, smap, nil)
-						tname.typ.(*TypeParam).bound = bound
+						bound = check.subst(tpar.obj.pos, bound, smap, nil)
+						tpar.bound = bound
 					}
 				}
 			}
diff --git a/src/go/types/subst.go b/src/go/types/subst.go
index 72d5cac671..75f1ca5fab 100644
--- a/src/go/types/subst.go
+++ b/src/go/types/subst.go
@@ -18,11 +18,11 @@ type substMap map[*TypeParam]Type
 
 // makeSubstMap creates a new substitution map mapping tpars[i] to targs[i].
 // If targs[i] is nil, tpars[i] is not substituted.
-func makeSubstMap(tpars []*TypeName, targs []Type) substMap {
+func makeSubstMap(tpars []*TypeParam, targs []Type) substMap {
 	assert(len(tpars) == len(targs))
 	proj := make(substMap, len(tpars))
 	for i, tpar := range tpars {
-		proj[tpar.typ.(*TypeParam)] = targs[i]
+		proj[tpar] = targs[i]
 	}
 	return proj
 }
diff --git a/src/go/types/typeparam.go b/src/go/types/typeparam.go
index 8d19d5db76..49eda1b43a 100644
--- a/src/go/types/typeparam.go
+++ b/src/go/types/typeparam.go
@@ -89,7 +89,7 @@ func (t *TypeParam) Underlying() Type { return t }
 func (t *TypeParam) String() string   { return TypeString(t, nil) }
 
 // TParamList holds a list of type parameters bound to a type.
-type TParamList struct{ tparams []*TypeName }
+type TParamList struct{ tparams []*TypeParam }
 
 // Len returns the number of type parameters in the list.
 // It is safe to call on a nil receiver.
@@ -98,23 +98,22 @@ func (tps *TParamList) Len() int {
 }
 
 // At returns the i'th type parameter in the list.
-func (tps *TParamList) At(i int) *TypeName {
+func (tps *TParamList) At(i int) *TypeParam {
 	return tps.list()[i]
 }
 
-func (tps *TParamList) list() []*TypeName {
+func (tps *TParamList) list() []*TypeParam {
 	if tps == nil {
 		return nil
 	}
 	return tps.tparams
 }
 
-func bindTParams(list []*TypeName) *TParamList {
+func bindTParams(list []*TypeParam) *TParamList {
 	if len(list) == 0 {
 		return nil
 	}
-	for i, tp := range list {
-		typ := tp.Type().(*TypeParam)
+	for i, typ := range list {
 		if typ.index >= 0 {
 			panic("type parameter bound more than once")
 		}
diff --git a/src/go/types/typestring.go b/src/go/types/typestring.go
index 452c92f74d..41dde0e469 100644
--- a/src/go/types/typestring.go
+++ b/src/go/types/typestring.go
@@ -244,15 +244,14 @@ func writeTypeList(buf *bytes.Buffer, list []Type, qf Qualifier, visited []Type)
 	}
 }
 
-func writeTParamList(buf *bytes.Buffer, list []*TypeName, qf Qualifier, visited []Type) {
+func writeTParamList(buf *bytes.Buffer, list []*TypeParam, qf Qualifier, visited []Type) {
 	// TODO(rFindley) compare this with the corresponding implementation in types2
 	buf.WriteString("[")
 	var prev Type
-	for i, p := range list {
+	for i, tpar := range list {
 		// Determine the type parameter and its constraint.
 		// list is expected to hold type parameter names,
 		// but don't crash if that's not the case.
-		tpar, _ := p.typ.(*TypeParam)
 		var bound Type
 		if tpar != nil {
 			bound = tpar.bound // should not be nil but we want to see it if it is
@@ -271,7 +270,7 @@ func writeTParamList(buf *bytes.Buffer, list []*TypeName, qf Qualifier, visited
 		if tpar != nil {
 			writeType(buf, tpar, qf, visited)
 		} else {
-			buf.WriteString(p.name)
+			buf.WriteString(tpar.obj.name)
 		}
 	}
 	if prev != nil {
diff --git a/src/go/types/unify.go b/src/go/types/unify.go
index de87466fe8..8f5b23ce39 100644
--- a/src/go/types/unify.go
+++ b/src/go/types/unify.go
@@ -63,7 +63,7 @@ func (u *unifier) unify(x, y Type) bool {
 // A tparamsList describes a list of type parameters and the types inferred for them.
 type tparamsList struct {
 	unifier *unifier
-	tparams []*TypeName
+	tparams []*TypeParam
 	// For each tparams element, there is a corresponding type slot index in indices.
 	// index  < 0: unifier.types[-index-1] == nil
 	// index == 0: no type slot allocated yet
@@ -78,11 +78,11 @@ type tparamsList struct {
 func (d *tparamsList) String() string {
 	var buf bytes.Buffer
 	buf.WriteByte('[')
-	for i, tname := range d.tparams {
+	for i, tpar := range d.tparams {
 		if i > 0 {
 			buf.WriteString(", ")
 		}
-		writeType(&buf, tname.typ, nil, nil)
+		writeType(&buf, tpar, nil, nil)
 		buf.WriteString(": ")
 		writeType(&buf, d.at(i), nil, nil)
 	}
@@ -93,13 +93,13 @@ func (d *tparamsList) String() string {
 // init initializes d with the given type parameters.
 // The type parameters must be in the order in which they appear in their declaration
 // (this ensures that the tparams indices match the respective type parameter index).
-func (d *tparamsList) init(tparams []*TypeName) {
+func (d *tparamsList) init(tparams []*TypeParam) {
 	if len(tparams) == 0 {
 		return
 	}
 	if debug {
 		for i, tpar := range tparams {
-			assert(i == tpar.typ.(*TypeParam).index)
+			assert(i == tpar.index)
 		}
 	}
 	d.tparams = tparams
@@ -155,8 +155,8 @@ func (d *tparamsList) index(typ Type) int {
 
 // If tpar is a type parameter in list, tparamIndex returns the type parameter index.
 // Otherwise, the result is < 0. tpar must not be nil.
-func tparamIndex(list []*TypeName, tpar *TypeParam) int {
-	if i := tpar.index; i < len(list) && list[i].typ == tpar {
+func tparamIndex(list []*TypeParam, tpar *TypeParam) int {
+	if i := tpar.index; i < len(list) && list[i] == tpar {
 		return i
 	}
 	return -1