go/doc: move Example code from go/ast to go/doc.

Fixes #3048.

R=rsc
CC=golang-dev
https://golang.org/cl/5672081

src/cmd/dist/build.c

@@ -1126,6 +1126,7 @@ static char *buildorder[] = {
 	"pkg/net/url",
 	"pkg/text/template/parse",
 	"pkg/text/template",
+	"pkg/go/doc",
 	"cmd/go",
 };
 
@@ -1165,6 +1166,7 @@ static char *cleantab[] = {
 	"pkg/fmt",
 	"pkg/go/ast",
 	"pkg/go/build",
+	"pkg/go/doc",
 	"pkg/go/parser",
 	"pkg/go/scanner",
 	"pkg/go/token",

src/cmd/go/test.go

@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"go/ast"
 	"go/build"
+	"go/doc"
 	"go/parser"
 	"go/token"
 	"os"
@@ -719,7 +720,7 @@ func (t *testFuncs) load(filename, pkg string, seen *bool) error {
 			*seen = true
 		}
 	}
-	for _, e := range ast.Examples(f) {
+	for _, e := range doc.Examples(f) {
 		if e.Output == "" {
 			// Don't run examples with no output.
 			continue

src/cmd/godoc/godoc.go

@@ -501,7 +501,7 @@ func startsWithUppercase(s string) bool {
 
 var exampleOutputRx = regexp.MustCompile(`(?i)//[[:space:]]*output:`)
 
-func example_htmlFunc(funcName string, examples []*ast.Example, fset *token.FileSet) string {
+func example_htmlFunc(funcName string, examples []*doc.Example, fset *token.FileSet) string {
 	var buf bytes.Buffer
 	for _, eg := range examples {
 		name := eg.Name
@@ -979,7 +979,7 @@ type PageInfo struct {
 	FSet     *token.FileSet // corresponding file set
 	PAst     *ast.File      // nil if no single AST with package exports
 	PDoc     *doc.Package   // nil if no single package documentation
-	Examples []*ast.Example // nil if no example code
+	Examples []*doc.Example // nil if no example code
 	Dirs     *DirList       // nil if no directory information
 	DirTime  time.Time      // directory time stamp
 	DirFlat  bool           // if set, show directory in a flat (non-indented) manner
@@ -1128,7 +1128,7 @@ func (h *httpHandler) getPageInfo(abspath, relpath, pkgname string, mode PageInf
 	}
 
 	// get examples from *_test.go files
-	var examples []*ast.Example
+	var examples []*doc.Example
 	filter = func(d os.FileInfo) bool {
 		return isGoFile(d) && strings.HasSuffix(d.Name(), "_test.go")
 	}
@@ -1140,7 +1140,7 @@ func (h *httpHandler) getPageInfo(abspath, relpath, pkgname string, mode PageInf
 			for _, f := range testpkg.Files {
 				files = append(files, f)
 			}
-			examples = append(examples, ast.Examples(files...)...)
+			examples = append(examples, doc.Examples(files...)...)
 		}
 	}
 

src/pkg/go/ast/example.go → src/pkg/go/doc/example.go

@@ -4,9 +4,10 @@
 
 // Extract example functions from file ASTs.
 
-package ast
+package doc
 
 import (
+	"go/ast"
 	"go/token"
 	"regexp"
 	"sort"
@@ -18,23 +19,23 @@ import (
 type Example struct {
 	Name     string // name of the item being exemplified
 	Doc      string // example function doc string
-	Code     Node
-	Comments []*CommentGroup
+	Code     ast.Node
+	Comments []*ast.CommentGroup
 	Output   string // expected output
 }
 
-func Examples(files ...*File) []*Example {
+func Examples(files ...*ast.File) []*Example {
 	var list []*Example
 	for _, file := range files {
 		hasTests := false // file contains tests or benchmarks
 		numDecl := 0      // number of non-import declarations in the file
 		var flist []*Example
 		for _, decl := range file.Decls {
-			if g, ok := decl.(*GenDecl); ok && g.Tok != token.IMPORT {
+			if g, ok := decl.(*ast.GenDecl); ok && g.Tok != token.IMPORT {
 				numDecl++
 				continue
 			}
-			f, ok := decl.(*FuncDecl)
+			f, ok := decl.(*ast.FuncDecl)
 			if !ok {
 				continue
 			}
@@ -73,9 +74,9 @@ func Examples(files ...*File) []*Example {
 
 var outputPrefix = regexp.MustCompile(`(?i)^[[:space:]]*output:`)
 
-func exampleOutput(fun *FuncDecl, comments []*CommentGroup) string {
+func exampleOutput(fun *ast.FuncDecl, comments []*ast.CommentGroup) string {
 	// find the last comment in the function
-	var last *CommentGroup
+	var last *ast.CommentGroup
 	for _, cg := range comments {
 		if cg.Pos() < fun.Pos() {
 			continue