cmd/doc: add a -src flag to show original source

It's long-desired but was blocked by #26835. That is now fixed, so
it's easy. When -src is off, we behave as before. But with -src
set, initialize the go/doc package to preserve the original AST and
things flow very easily.

With -src, since you're seeing inside the package source anyway it
shows unexported fields and constants: you see the original source.
But you still need -u to ask about them.

Fixes #18807

Change-Id: I473e90323b4eff0735360274dc0d2d9dba16ff8b
Reviewed-on: https://go-review.googlesource.com/c/140959
Reviewed-by: Andrew Gerrand <adg@golang.org>
Run-TryBot: Andrew Gerrand <adg@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

6 files changed, 141 insertions, 56 deletions

diff --git a/src/cmd/doc/doc_test.go b/src/cmd/doc/doc_test.go
index 6010f04b56..64b1fb596b 100644
--- a/src/cmd/doc/doc_test.go
+++ b/src/cmd/doc/doc_test.go
@@ -127,24 +127,24 @@ var tests = []test{
 			`type T1 = T2`,                                                 // Type alias
 		},
 		[]string{
-			`const internalConstant = 2`,        // No internal constants.
-			`var internalVariable = 2`,          // No internal variables.
-			`func internalFunc(a int) bool`,     // No internal functions.
-			`Comment about exported constant`,   // No comment for single constant.
-			`Comment about exported variable`,   // No comment for single variable.
-			`Comment about block of constants.`, // No comment for constant block.
-			`Comment about block of variables.`, // No comment for variable block.
-			`Comment before ConstOne`,           // No comment for first entry in constant block.
-			`Comment before VarOne`,             // No comment for first entry in variable block.
-			`ConstTwo = 2`,                      // No second entry in constant block.
-			`VarTwo = 2`,                        // No second entry in variable block.
-			`VarFive = 5`,                       // From block starting with unexported variable.
-			`type unexportedType`,               // No unexported type.
-			`unexportedTypedConstant`,           // No unexported typed constant.
-			`\bField`,                           // No fields.
-			`Method`,                            // No methods.
-			`someArgument[5-8]`,                 // No truncated arguments.
-			`type T1 T2`,                        // Type alias does not display as type declaration.
+			`const internalConstant = 2`,       // No internal constants.
+			`var internalVariable = 2`,         // No internal variables.
+			`func internalFunc(a int) bool`,    // No internal functions.
+			`Comment about exported constant`,  // No comment for single constant.
+			`Comment about exported variable`,  // No comment for single variable.
+			`Comment about block of constants`, // No comment for constant block.
+			`Comment about block of variables`, // No comment for variable block.
+			`Comment before ConstOne`,          // No comment for first entry in constant block.
+			`Comment before VarOne`,            // No comment for first entry in variable block.
+			`ConstTwo = 2`,                     // No second entry in constant block.
+			`VarTwo = 2`,                       // No second entry in variable block.
+			`VarFive = 5`,                      // From block starting with unexported variable.
+			`type unexportedType`,              // No unexported type.
+			`unexportedTypedConstant`,          // No unexported typed constant.
+			`\bField`,                          // No fields.
+			`Method`,                           // No methods.
+			`someArgument[5-8]`,                // No truncated arguments.
+			`type T1 T2`,                       // Type alias does not display as type declaration.
 		},
 	},
 	// Package dump -u
@@ -207,6 +207,18 @@ var tests = []test{
 		},
 		nil,
 	},
+	// Block of constants -src.
+	{
+		"block of constants with -src",
+		[]string{"-src", p, `ConstTwo`},
+		[]string{
+			`Comment about block of constants`, // Top comment.
+			`ConstOne.*=.*1`,                   // Each constant seen.
+			`ConstTwo.*=.*2.*Comment on line with ConstTwo`,
+			`constThree`, // Even unexported constants.
+		},
+		nil,
+	},
 	// Block of constants with carryover type from unexported field.
 	{
 		"block of constants with carryover type",
@@ -295,6 +307,17 @@ var tests = []test{
 		},
 		nil,
 	},
+	// Function with -src.
+	{
+		"function with -src",
+		[]string{"-src", p, `ExportedFunc`},
+		[]string{
+			`Comment about exported function`, // Include comment.
+			`func ExportedFunc\(a int\) bool`,
+			`return true != false`, // Include body.
+		},
+		nil,
+	},
 
 	// Type.
 	{
@@ -304,21 +327,44 @@ var tests = []test{
 			`Comment about exported type`, // Include comment.
 			`type ExportedType struct`,    // Type definition.
 			`Comment before exported field.*\n.*ExportedField +int` +
-				`.*Comment on line with exported field.`,
-			`ExportedEmbeddedType.*Comment on line with exported embedded field.`,
+				`.*Comment on line with exported field`,
+			`ExportedEmbeddedType.*Comment on line with exported embedded field`,
 			`Has unexported fields`,
 			`func \(ExportedType\) ExportedMethod\(a int\) bool`,
 			`const ExportedTypedConstant ExportedType = iota`, // Must include associated constant.
 			`func ExportedTypeConstructor\(\) \*ExportedType`, // Must include constructor.
-			`io.Reader.*Comment on line with embedded Reader.`,
+			`io.Reader.*Comment on line with embedded Reader`,
 		},
 		[]string{
-			`unexportedField`,                // No unexported field.
-			`int.*embedded`,                  // No unexported embedded field.
-			`Comment about exported method.`, // No comment about exported method.
-			`unexportedMethod`,               // No unexported method.
-			`unexportedTypedConstant`,        // No unexported constant.
-			`error`,                          // No embedded error.
+			`unexportedField`,               // No unexported field.
+			`int.*embedded`,                 // No unexported embedded field.
+			`Comment about exported method`, // No comment about exported method.
+			`unexportedMethod`,              // No unexported method.
+			`unexportedTypedConstant`,       // No unexported constant.
+			`error`,                         // No embedded error.
+		},
+	},
+	// Type with -src. Will see unexported fields.
+	{
+		"type",
+		[]string{"-src", p, `ExportedType`},
+		[]string{
+			`Comment about exported type`, // Include comment.
+			`type ExportedType struct`,    // Type definition.
+			`Comment before exported field.*\n.*ExportedField +int` +
+				`.*Comment on line with exported field`,
+			`ExportedEmbeddedType.*Comment on line with exported embedded field`,
+			`unexportedType.*Comment on line with unexported embedded field`,
+			`func \(ExportedType\) ExportedMethod\(a int\) bool`,
+			`const ExportedTypedConstant ExportedType = iota`, // Must include associated constant.
+			`func ExportedTypeConstructor\(\) \*ExportedType`, // Must include constructor.
+			`io.Reader.*Comment on line with embedded Reader`,
+		},
+		[]string{
+			`int.*embedded`,                 // No unexported embedded field.
+			`Comment about exported method`, // No comment about exported method.
+			`unexportedMethod`,              // No unexported method.
+			`unexportedTypedConstant`,       // No unexported constant.
 		},
 	},
 	// Type T1 dump (alias).
@@ -341,14 +387,14 @@ var tests = []test{
 			`Comment about exported type`, // Include comment.
 			`type ExportedType struct`,    // Type definition.
 			`Comment before exported field.*\n.*ExportedField +int`,
-			`unexportedField.*int.*Comment on line with unexported field.`,
-			`ExportedEmbeddedType.*Comment on line with exported embedded field.`,
-			`\*ExportedEmbeddedType.*Comment on line with exported embedded \*field.`,
-			`\*qualified.ExportedEmbeddedType.*Comment on line with exported embedded \*selector.field.`,
-			`unexportedType.*Comment on line with unexported embedded field.`,
-			`\*unexportedType.*Comment on line with unexported embedded \*field.`,
-			`io.Reader.*Comment on line with embedded Reader.`,
-			`error.*Comment on line with embedded error.`,
+			`unexportedField.*int.*Comment on line with unexported field`,
+			`ExportedEmbeddedType.*Comment on line with exported embedded field`,
+			`\*ExportedEmbeddedType.*Comment on line with exported embedded \*field`,
+			`\*qualified.ExportedEmbeddedType.*Comment on line with exported embedded \*selector.field`,
+			`unexportedType.*Comment on line with unexported embedded field`,
+			`\*unexportedType.*Comment on line with unexported embedded \*field`,
+			`io.Reader.*Comment on line with embedded Reader`,
+			`error.*Comment on line with embedded error`,
 			`func \(ExportedType\) unexportedMethod\(a int\) bool`,
 			`unexportedTypedConstant`,
 		},
@@ -380,8 +426,8 @@ var tests = []test{
 			`type ExportedInterface interface`, // Interface definition.
 			`Comment before exported method.*\n.*ExportedMethod\(\)` +
 				`.*Comment on line with exported method`,
-			`io.Reader.*Comment on line with embedded Reader.`,
-			`error.*Comment on line with embedded error.`,
+			`io.Reader.*Comment on line with embedded Reader`,
+			`error.*Comment on line with embedded error`,
 			`Has unexported methods`,
 		},
 		[]string{
@@ -400,9 +446,9 @@ var tests = []test{
 			`type ExportedInterface interface`, // Interface definition.
 			`Comment before exported method.*\n.*ExportedMethod\(\)` +
 				`.*Comment on line with exported method`,
-			`unexportedMethod\(\).*Comment on line with unexported method.`,
-			`io.Reader.*Comment on line with embedded Reader.`,
-			`error.*Comment on line with embedded error.`,
+			`unexportedMethod\(\).*Comment on line with unexported method`,
+			`io.Reader.*Comment on line with embedded Reader`,
+			`error.*Comment on line with embedded error`,
 		},
 		[]string{
 			`Has unexported methods`,
@@ -418,7 +464,7 @@ var tests = []test{
 				`.*Comment on line with exported method`,
 		},
 		[]string{
-			`Comment about exported interface.`,
+			`Comment about exported interface`,
 		},
 	},
 
@@ -428,7 +474,7 @@ var tests = []test{
 		[]string{p, `ExportedType.ExportedMethod`},
 		[]string{
 			`func \(ExportedType\) ExportedMethod\(a int\) bool`,
-			`Comment about exported method.`,
+			`Comment about exported method`,
 		},
 		nil,
 	},
@@ -438,7 +484,18 @@ var tests = []test{
 		[]string{"-u", p, `ExportedType.unexportedMethod`},
 		[]string{
 			`func \(ExportedType\) unexportedMethod\(a int\) bool`,
-			`Comment about unexported method.`,
+			`Comment about unexported method`,
+		},
+		nil,
+	},
+	// Method with -src.
+	{
+		"method with -src",
+		[]string{"-src", p, `ExportedType.ExportedMethod`},
+		[]string{
+			`func \(ExportedType\) ExportedMethod\(a int\) bool`,
+			`Comment about exported method`,
+			`return true != true`,
 		},
 		nil,
 	},
@@ -450,8 +507,8 @@ var tests = []test{
 		[]string{
 			`type ExportedType struct`,
 			`ExportedField int`,
-			`Comment before exported field.`,
-			`Comment on line with exported field.`,
+			`Comment before exported field`,
+			`Comment on line with exported field`,
 			`other fields elided`,
 		},
 		nil,
@@ -463,7 +520,7 @@ var tests = []test{
 		[]string{"-u", p, `ExportedType.unexportedField`},
 		[]string{
 			`unexportedField int`,
-			`Comment on line with unexported field.`,
+			`Comment on line with unexported field`,
 		},
 		nil,
 	},
diff --git a/src/cmd/doc/main.go b/src/cmd/doc/main.go
index 982c8e054a..a3e09d3f87 100644
--- a/src/cmd/doc/main.go
+++ b/src/cmd/doc/main.go
@@ -28,6 +28,9 @@
 // For commands, unless the -cmd flag is present "go doc command"
 // shows only the package-level docs for the package.
 //
+// The -src flag causes doc to print the full source code for the symbol, such
+// as the body of a struct, function or method.
+//
 // For complete documentation, run "go help doc".
 package main
 
@@ -50,6 +53,7 @@ var (
 	unexported bool // -u flag
 	matchCase  bool // -c flag
 	showCmd    bool // -cmd flag
+	showSrc    bool // -src flag
 )
 
 // usage is a replacement usage function for the flags package.
@@ -85,6 +89,7 @@ func do(writer io.Writer, flagSet *flag.FlagSet, args []string) (err error) {
 	flagSet.BoolVar(&unexported, "u", false, "show unexported symbols as well as exported")
 	flagSet.BoolVar(&matchCase, "c", false, "symbol matching honors case (paths not affected)")
 	flagSet.BoolVar(&showCmd, "cmd", false, "show symbols with package docs even if package is a command")
+	flagSet.BoolVar(&showSrc, "src", false, "show source code for symbol")
 	flagSet.Parse(args)
 	var paths []string
 	var symbol, method string
diff --git a/src/cmd/doc/pkg.go b/src/cmd/doc/pkg.go
index 14e41b9106..154fb7b45f 100644
--- a/src/cmd/doc/pkg.go
+++ b/src/cmd/doc/pkg.go
@@ -137,7 +137,11 @@ func parsePackage(writer io.Writer, pkg *build.Package, userPath string) *Packag
 	// from finding the symbol. Work around this for now, but we
 	// should fix it in go/doc.
 	// A similar story applies to factory functions.
-	docPkg := doc.New(astPkg, pkg.ImportPath, doc.AllDecls)
+	mode := doc.AllDecls
+	if showSrc {
+		mode |= doc.PreserveAST // See comment for Package.emit.
+	}
+	docPkg := doc.New(astPkg, pkg.ImportPath, mode)
 	for _, typ := range docPkg.Types {
 		docPkg.Consts = append(docPkg.Consts, typ.Consts...)
 		docPkg.Vars = append(docPkg.Vars, typ.Vars...)
@@ -177,14 +181,16 @@ func (pkg *Package) newlines(n int) {
 	}
 }
 
-// emit prints the node.
+// emit prints the node. If showSrc is true, it ignores the provided comment,
+// assuming the comment is in the node itself. Otherwise, the go/doc package
+// clears the stuff we don't want to print anyway. It's a bit of a magic trick.
 func (pkg *Package) emit(comment string, node ast.Node) {
 	if node != nil {
 		err := format.Node(&pkg.buf, pkg.fs, node)
 		if err != nil {
 			log.Fatal(err)
 		}
-		if comment != "" {
+		if comment != "" && !showSrc {
 			pkg.newlines(1)
 			doc.ToText(&pkg.buf, comment, "    ", indent, indentedWidth)
 			pkg.newlines(2) // Blank line after comment to separate from next item.
@@ -611,7 +617,6 @@ func (pkg *Package) symbolDoc(symbol string) bool {
 		}
 		// Symbol is a function.
 		decl := fun.Decl
-		decl.Body = nil
 		pkg.emit(fun.Doc, decl)
 		found = true
 	}
@@ -641,7 +646,7 @@ func (pkg *Package) symbolDoc(symbol string) bool {
 			}
 
 			for _, ident := range vspec.Names {
-				if isExported(ident.Name) {
+				if showSrc || isExported(ident.Name) {
 					if vspec.Type == nil && vspec.Values == nil && typ != nil {
 						// This a standalone identifier, as in the case of iota usage.
 						// Thus, assume the type comes from the previous type.
@@ -701,9 +706,10 @@ func (pkg *Package) symbolDoc(symbol string) bool {
 }
 
 // trimUnexportedElems modifies spec in place to elide unexported fields from
-// structs and methods from interfaces (unless the unexported flag is set).
+// structs and methods from interfaces (unless the unexported flag is set or we
+// are asked to show the original source).
 func trimUnexportedElems(spec *ast.TypeSpec) {
-	if unexported {
+	if unexported || showSrc {
 		return
 	}
 	switch typ := spec.Type.(type) {
@@ -808,7 +814,6 @@ func (pkg *Package) printMethodDoc(symbol, method string) bool {
 			for _, meth := range typ.Methods {
 				if match(method, meth.Name) {
 					decl := meth.Decl
-					decl.Body = nil
 					pkg.emit(meth.Doc, decl)
 					found = true
 				}
diff --git a/src/cmd/doc/testdata/pkg.go b/src/cmd/doc/testdata/pkg.go
index bc069939f8..50105b5fcc 100644
--- a/src/cmd/doc/testdata/pkg.go
+++ b/src/cmd/doc/testdata/pkg.go
@@ -5,6 +5,8 @@
 // Package comment.
 package pkg
 
+import "io"
+
 // Constants
 
 // Comment about exported constant.
@@ -52,7 +54,9 @@ var (
 )
 
 // Comment about exported function.
-func ExportedFunc(a int) bool
+func ExportedFunc(a int) bool {
+	return true != false
+}
 
 // Comment about internal function.
 func internalFunc(a int) bool
@@ -73,7 +77,7 @@ type ExportedType struct {
 
 // Comment about exported method.
 func (ExportedType) ExportedMethod(a int) bool {
-	return true
+	return true != true
 }
 
 // Comment about unexported method.
diff --git a/src/cmd/go/alldocs.go b/src/cmd/go/alldocs.go
index 9528ca2984..f54f000b07 100644
--- a/src/cmd/go/alldocs.go
+++ b/src/cmd/go/alldocs.go
@@ -348,6 +348,13 @@
 // 		Treat a command (package main) like a regular package.
 // 		Otherwise package main's exported symbols are hidden
 // 		when showing the package's top-level documentation.
+// 	-src
+// 		Show the full source code for the symbol. This will
+// 		display the full Go source of its declaration and
+// 		definition, such as a function definition (including
+// 		the body), type declaration or enclosing const
+// 		block. The output may therefore include unexported
+// 		details.
 // 	-u
 // 		Show documentation for unexported as well as exported
 // 		symbols, methods, and fields.
diff --git a/src/cmd/go/internal/doc/doc.go b/src/cmd/go/internal/doc/doc.go
index 4e7dca082d..262bbb3ecb 100644
--- a/src/cmd/go/internal/doc/doc.go
+++ b/src/cmd/go/internal/doc/doc.go
@@ -112,6 +112,13 @@ Flags:
 		Treat a command (package main) like a regular package.
 		Otherwise package main's exported symbols are hidden
 		when showing the package's top-level documentation.
+	-src
+		Show the full source code for the symbol. This will
+		display the full Go source of its declaration and
+		definition, such as a function definition (including
+		the body), type declaration or enclosing const
+		block. The output may therefore include unexported
+		details.
 	-u
 		Show documentation for unexported as well as exported
 		symbols, methods, and fields.