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+// Copyright 2011 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.
+
+// Extract example functions from file ASTs.
+
+package doc
+
+import (
+ "go/ast"
+ "go/token"
+ "path"
+ "regexp"
+ "sort"
+ "strconv"
+ "strings"
+ "unicode"
+ "unicode/utf8"
+)
+
+// An Example represents an example function found in a source files.
+type Example struct {
+ Name string // name of the item being exemplified
+ Doc string // example function doc string
+ Code ast.Node
+ Play *ast.File // a whole program version of the example
+ Comments []*ast.CommentGroup
+ Output string // expected output
+ EmptyOutput bool // expect empty output
+ Order int // original source code order
+}
+
+// Examples returns the examples found in the files, sorted by Name field.
+// The Order fields record the order in which the examples were encountered.
+//
+// Playable Examples must be in a package whose name ends in "_test".
+// An Example is "playable" (the Play field is non-nil) in either of these
+// circumstances:
+// - The example function is self-contained: the function references only
+// identifiers from other packages (or predeclared identifiers, such as
+// "int") and the test file does not include a dot import.
+// - The entire test file is the example: the file contains exactly one
+// example function, zero test or benchmark functions, and at least one
+// top-level function, type, variable, or constant declaration other
+// than the example function.
+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.(*ast.GenDecl); ok && g.Tok != token.IMPORT {
+ numDecl++
+ continue
+ }
+ f, ok := decl.(*ast.FuncDecl)
+ if !ok {
+ continue
+ }
+ numDecl++
+ name := f.Name.Name
+ if isTest(name, "Test") || isTest(name, "Benchmark") {
+ hasTests = true
+ continue
+ }
+ if !isTest(name, "Example") {
+ continue
+ }
+ var doc string
+ if f.Doc != nil {
+ doc = f.Doc.Text()
+ }
+ output, hasOutput := exampleOutput(f.Body, file.Comments)
+ flist = append(flist, &Example{
+ Name: name[len("Example"):],
+ Doc: doc,
+ Code: f.Body,
+ Play: playExample(file, f.Body),
+ Comments: file.Comments,
+ Output: output,
+ EmptyOutput: output == "" && hasOutput,
+ Order: len(flist),
+ })
+ }
+ if !hasTests && numDecl > 1 && len(flist) == 1 {
+ // If this file only has one example function, some
+ // other top-level declarations, and no tests or
+ // benchmarks, use the whole file as the example.
+ flist[0].Code = file
+ flist[0].Play = playExampleFile(file)
+ }
+ list = append(list, flist...)
+ }
+ sort.Sort(exampleByName(list))
+ return list
+}
+
+var outputPrefix = regexp.MustCompile(`(?i)^[[:space:]]*output:`)
+
+// Extracts the expected output and whether there was a valid output comment
+func exampleOutput(b *ast.BlockStmt, comments []*ast.CommentGroup) (output string, ok bool) {
+ if _, last := lastComment(b, comments); last != nil {
+ // test that it begins with the correct prefix
+ text := last.Text()
+ if loc := outputPrefix.FindStringIndex(text); loc != nil {
+ text = text[loc[1]:]
+ // Strip zero or more spaces followed by \n or a single space.
+ text = strings.TrimLeft(text, " ")
+ if len(text) > 0 && text[0] == '\n' {
+ text = text[1:]
+ }
+ return text, true
+ }
+ }
+ return "", false // no suitable comment found
+}
+
+// isTest tells whether name looks like a test, example, or benchmark.
+// It is a Test (say) if there is a character after Test that is not a
+// lower-case letter. (We don't want Testiness.)
+func isTest(name, prefix string) bool {
+ if !strings.HasPrefix(name, prefix) {
+ return false
+ }
+ if len(name) == len(prefix) { // "Test" is ok
+ return true
+ }
+ rune, _ := utf8.DecodeRuneInString(name[len(prefix):])
+ return !unicode.IsLower(rune)
+}
+
+type exampleByName []*Example
+
+func (s exampleByName) Len() int { return len(s) }
+func (s exampleByName) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
+func (s exampleByName) Less(i, j int) bool { return s[i].Name < s[j].Name }
+
+// playExample synthesizes a new *ast.File based on the provided
+// file with the provided function body as the body of main.
+func playExample(file *ast.File, body *ast.BlockStmt) *ast.File {
+ if !strings.HasSuffix(file.Name.Name, "_test") {
+ // We don't support examples that are part of the
+ // greater package (yet).
+ return nil
+ }
+
+ // Find top-level declarations in the file.
+ topDecls := make(map[*ast.Object]bool)
+ for _, decl := range file.Decls {
+ switch d := decl.(type) {
+ case *ast.FuncDecl:
+ topDecls[d.Name.Obj] = true
+ case *ast.GenDecl:
+ for _, spec := range d.Specs {
+ switch s := spec.(type) {
+ case *ast.TypeSpec:
+ topDecls[s.Name.Obj] = true
+ case *ast.ValueSpec:
+ for _, id := range s.Names {
+ topDecls[id.Obj] = true
+ }
+ }
+ }
+ }
+ }
+
+ // Find unresolved identifiers and uses of top-level declarations.
+ unresolved := make(map[string]bool)
+ usesTopDecl := false
+ var inspectFunc func(ast.Node) bool
+ inspectFunc = func(n ast.Node) bool {
+ // For selector expressions, only inspect the left hand side.
+ // (For an expression like fmt.Println, only add "fmt" to the
+ // set of unresolved names, not "Println".)
+ if e, ok := n.(*ast.SelectorExpr); ok {
+ ast.Inspect(e.X, inspectFunc)
+ return false
+ }
+ // For key value expressions, only inspect the value
+ // as the key should be resolved by the type of the
+ // composite literal.
+ if e, ok := n.(*ast.KeyValueExpr); ok {
+ ast.Inspect(e.Value, inspectFunc)
+ return false
+ }
+ if id, ok := n.(*ast.Ident); ok {
+ if id.Obj == nil {
+ unresolved[id.Name] = true
+ } else if topDecls[id.Obj] {
+ usesTopDecl = true
+ }
+ }
+ return true
+ }
+ ast.Inspect(body, inspectFunc)
+ if usesTopDecl {
+ // We don't support examples that are not self-contained (yet).
+ return nil
+ }
+
+ // Remove predeclared identifiers from unresolved list.
+ for n := range unresolved {
+ if predeclaredTypes[n] || predeclaredConstants[n] || predeclaredFuncs[n] {
+ delete(unresolved, n)
+ }
+ }
+
+ // Use unresolved identifiers to determine the imports used by this
+ // example. The heuristic assumes package names match base import
+ // paths for imports w/o renames (should be good enough most of the time).
+ namedImports := make(map[string]string) // [name]path
+ var blankImports []ast.Spec // _ imports
+ for _, s := range file.Imports {
+ p, err := strconv.Unquote(s.Path.Value)
+ if err != nil {
+ continue
+ }
+ n := path.Base(p)
+ if s.Name != nil {
+ n = s.Name.Name
+ switch n {
+ case "_":
+ blankImports = append(blankImports, s)
+ continue
+ case ".":
+ // We can't resolve dot imports (yet).
+ return nil
+ }
+ }
+ if unresolved[n] {
+ namedImports[n] = p
+ delete(unresolved, n)
+ }
+ }
+
+ // If there are other unresolved identifiers, give up because this
+ // synthesized file is not going to build.
+ if len(unresolved) > 0 {
+ return nil
+ }
+
+ // Include documentation belonging to blank imports.
+ var comments []*ast.CommentGroup
+ for _, s := range blankImports {
+ if c := s.(*ast.ImportSpec).Doc; c != nil {
+ comments = append(comments, c)
+ }
+ }
+
+ // Include comments that are inside the function body.
+ for _, c := range file.Comments {
+ if body.Pos() <= c.Pos() && c.End() <= body.End() {
+ comments = append(comments, c)
+ }
+ }
+
+ // Strip "Output:" comment and adjust body end position.
+ body, comments = stripOutputComment(body, comments)
+
+ // Synthesize import declaration.
+ importDecl := &ast.GenDecl{
+ Tok: token.IMPORT,
+ Lparen: 1, // Need non-zero Lparen and Rparen so that printer
+ Rparen: 1, // treats this as a factored import.
+ }
+ for n, p := range namedImports {
+ s := &ast.ImportSpec{Path: &ast.BasicLit{Value: strconv.Quote(p)}}
+ if path.Base(p) != n {
+ s.Name = ast.NewIdent(n)
+ }
+ importDecl.Specs = append(importDecl.Specs, s)
+ }
+ importDecl.Specs = append(importDecl.Specs, blankImports...)
+
+ // Synthesize main function.
+ funcDecl := &ast.FuncDecl{
+ Name: ast.NewIdent("main"),
+ Type: &ast.FuncType{Params: &ast.FieldList{}}, // FuncType.Params must be non-nil
+ Body: body,
+ }
+
+ // Synthesize file.
+ return &ast.File{
+ Name: ast.NewIdent("main"),
+ Decls: []ast.Decl{importDecl, funcDecl},
+ Comments: comments,
+ }
+}
+
+// playExampleFile takes a whole file example and synthesizes a new *ast.File
+// such that the example is function main in package main.
+func playExampleFile(file *ast.File) *ast.File {
+ // Strip copyright comment if present.
+ comments := file.Comments
+ if len(comments) > 0 && strings.HasPrefix(comments[0].Text(), "Copyright") {
+ comments = comments[1:]
+ }
+
+ // Copy declaration slice, rewriting the ExampleX function to main.
+ var decls []ast.Decl
+ for _, d := range file.Decls {
+ if f, ok := d.(*ast.FuncDecl); ok && isTest(f.Name.Name, "Example") {
+ // Copy the FuncDecl, as it may be used elsewhere.
+ newF := *f
+ newF.Name = ast.NewIdent("main")
+ newF.Body, comments = stripOutputComment(f.Body, comments)
+ d = &newF
+ }
+ decls = append(decls, d)
+ }
+
+ // Copy the File, as it may be used elsewhere.
+ f := *file
+ f.Name = ast.NewIdent("main")
+ f.Decls = decls
+ f.Comments = comments
+ return &f
+}
+
+// stripOutputComment finds and removes an "Output:" comment from body
+// and comments, and adjusts the body block's end position.
+func stripOutputComment(body *ast.BlockStmt, comments []*ast.CommentGroup) (*ast.BlockStmt, []*ast.CommentGroup) {
+ // Do nothing if no "Output:" comment found.
+ i, last := lastComment(body, comments)
+ if last == nil || !outputPrefix.MatchString(last.Text()) {
+ return body, comments
+ }
+
+ // Copy body and comments, as the originals may be used elsewhere.
+ newBody := &ast.BlockStmt{
+ Lbrace: body.Lbrace,
+ List: body.List,
+ Rbrace: last.Pos(),
+ }
+ newComments := make([]*ast.CommentGroup, len(comments)-1)
+ copy(newComments, comments[:i])
+ copy(newComments[i:], comments[i+1:])
+ return newBody, newComments
+}
+
+// lastComment returns the last comment inside the provided block.
+func lastComment(b *ast.BlockStmt, c []*ast.CommentGroup) (i int, last *ast.CommentGroup) {
+ pos, end := b.Pos(), b.End()
+ for j, cg := range c {
+ if cg.Pos() < pos {
+ continue
+ }
+ if cg.End() > end {
+ break
+ }
+ i, last = j, cg
+ }
+ return
+}
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