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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
Unordered bool
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, unordered, 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,
Unordered: unordered,
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:]]*(unordered )?output:`)
// Extracts the expected output and whether there was a valid output comment
func exampleOutput(b *ast.BlockStmt, comments []*ast.CommentGroup) (output string, unordered, ok bool) {
if _, last := lastComment(b, comments); last != nil {
// test that it begins with the correct prefix
text := last.Text()
if loc := outputPrefix.FindStringSubmatchIndex(text); loc != nil {
if loc[2] != -1 {
unordered = true
}
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, unordered, true
}
}
return "", false, 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 the "Output:" or "Unordered 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 the "Output:" or "Unordered 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 there is no "Output:" or "Unordered output:" comment.
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
}