go example 源码
golang example 代码
文件路径：/src/go/doc/example.go
// 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"
"internal/lazyregexp"
"path"
"sort"
"strconv"
"strings"
"unicode"
"unicode/utf8"
)
// An Example represents an example function found in a test source file.
type Example struct {
Name string // name of the item being exemplified (including optional suffix)
Suffix string // example suffix, without leading '_' (only populated by NewFromFiles)
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 testFiles, sorted by Name field.
// The Order fields record the order in which the examples were encountered.
// The Suffix field is not populated when Examples is called directly, it is
// only populated by NewFromFiles for examples it finds in _test.go files.
//
// 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, fuzz test, or benchmark function, and at
// least one top-level function, type, variable, or constant declaration
// other than the example function.
func Examples(testFiles ...*ast.File) []*Example {
var list []*Example
for _, file := range testFiles {
hasTests := false // file contains tests, fuzz test, 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 || f.Recv != nil {
continue
}
numDecl++
name := f.Name.Name
if isTest(name, "Test") || isTest(name, "Benchmark") || isTest(name, "Fuzz") {
hasTests = true
continue
}
if !isTest(name, "Example") {
continue
}
if params := f.Type.Params; len(params.List) != 0 {
continue // function has params; not a valid example
}
if f.Body == nil { // ast.File.Body nil dereference (see issue 28044)
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),
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 by name
sort.Slice(list, func(i, j int) bool {
return list[i].Name < list[j].Name
})
return list
}
var outputPrefix = lazyregexp.New(`(?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, fuzz test, 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)
}
// 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, f *ast.FuncDecl) *ast.File {
body := f.Body
if !strings.HasSuffix(file.Name.Name, "_test") {
// We don't support examples that are part of the
// greater package (yet).
return nil
}
// Collect top-level declarations in the file.
topDecls := make(map[*ast.Object]ast.Decl)
typMethods := make(map[string][]ast.Decl)
for _, decl := range file.Decls {
switch d := decl.(type) {
case *ast.FuncDecl:
if d.Recv == nil {
topDecls[d.Name.Obj] = d
} else {
if len(d.Recv.List) == 1 {
t := d.Recv.List[0].Type
tname, _ := baseTypeName(t)
typMethods[tname] = append(typMethods[tname], d)
}
}
case *ast.GenDecl:
for _, spec := range d.Specs {
switch s := spec.(type) {
case *ast.TypeSpec:
topDecls[s.Name.Obj] = d
case *ast.ValueSpec:
for _, name := range s.Names {
topDecls[name.Obj] = d
}
}
}
}
}
// Find unresolved identifiers and uses of top-level declarations.
depDecls, unresolved := findDeclsAndUnresolved(body, topDecls, typMethods)
// 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).
var namedImports []ast.Spec
var blankImports []ast.Spec // _ imports
// To preserve the blank lines between groups of imports, find the
// start position of each group, and assign that position to all
// imports from that group.
groupStarts := findImportGroupStarts(file.Imports)
groupStart := func(s *ast.ImportSpec) token.Pos {
for i, start := range groupStarts {
if s.Path.ValuePos < start {
return groupStarts[i-1]
}
}
return groupStarts[len(groupStarts)-1]
}
for _, s := range file.Imports {
p, err := strconv.Unquote(s.Path.Value)
if err != nil {
continue
}
if p == "syscall/js" {
// We don't support examples that import syscall/js,
// because the package syscall/js is not available in the playground.
return nil
}
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] {
// Copy the spec and its path to avoid modifying the original.
spec := *s
path := *s.Path
spec.Path = &path
spec.Path.ValuePos = groupStart(&spec)
namedImports = append(namedImports, &spec)
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)
// Include documentation belonging to dependent declarations.
for _, d := range depDecls {
switch d := d.(type) {
case *ast.GenDecl:
if d.Doc != nil {
comments = append(comments, d.Doc)
}
case *ast.FuncDecl:
if d.Doc != nil {
comments = append(comments, d.Doc)
}
}
}
// 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.
}
importDecl.Specs = append(namedImports, blankImports...)
// Synthesize main function.
funcDecl := &ast.FuncDecl{
Name: ast.NewIdent("main"),
Type: f.Type,
Body: body,
}
decls := make([]ast.Decl, 0, 2+len(depDecls))
decls = append(decls, importDecl)
decls = append(decls, depDecls...)
decls = append(decls, funcDecl)
sort.Slice(decls, func(i, j int) bool {
return decls[i].Pos() < decls[j].Pos()
})
sort.Slice(comments, func(i, j int) bool {
return comments[i].Pos() < comments[j].Pos()
})
// Synthesize file.
return &ast.File{
Name: ast.NewIdent("main"),
Decls: decls,
Comments: comments,
}
}
// findDeclsAndUnresolved returns all the top-level declarations mentioned in
// the body, and a set of unresolved symbols (those that appear in the body but
// have no declaration in the program).
//
// topDecls maps objects to the top-level declaration declaring them (not
// necessarily obj.Decl, as obj.Decl will be a Spec for GenDecls, but
// topDecls[obj] will be the GenDecl itself).
func findDeclsAndUnresolved(body ast.Node, topDecls map[*ast.Object]ast.Decl, typMethods map[string][]ast.Decl) ([]ast.Decl, map[string]bool) {
// This function recursively finds every top-level declaration used
// transitively by the body, populating usedDecls and usedObjs. Then it
// trims down the declarations to include only the symbols actually
// referenced by the body.
unresolved := make(map[string]bool)
var depDecls []ast.Decl
usedDecls := make(map[ast.Decl]bool) // set of top-level decls reachable from the body
usedObjs := make(map[*ast.Object]bool) // set of objects reachable from the body (each declared by a usedDecl)
var inspectFunc func(ast.Node) bool
inspectFunc = func(n ast.Node) bool {
switch e := n.(type) {
case *ast.Ident:
if e.Obj == nil && e.Name != "_" {
unresolved[e.Name] = true
} else if d := topDecls[e.Obj]; d != nil {
usedObjs[e.Obj] = true
if !usedDecls[d] {
usedDecls[d] = true
depDecls = append(depDecls, d)
}
}
return true
case *ast.SelectorExpr:
// 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".)
ast.Inspect(e.X, inspectFunc)
return false
case *ast.KeyValueExpr:
// For key value expressions, only inspect the value
// as the key should be resolved by the type of the
// composite literal.
ast.Inspect(e.Value, inspectFunc)
return false
}
return true
}
inspectFieldList := func(fl *ast.FieldList) {
if fl != nil {
for _, f := range fl.List {
ast.Inspect(f.Type, inspectFunc)
}
}
}
// Find the decls immediately referenced by body.
ast.Inspect(body, inspectFunc)
// Now loop over them, adding to the list when we find a new decl that the
// body depends on. Keep going until we don't find anything new.
for i := 0; i < len(depDecls); i++ {
switch d := depDecls[i].(type) {
case *ast.FuncDecl:
// Inpect type parameters.
inspectFieldList(d.Type.TypeParams)
// Inspect types of parameters and results. See #28492.
inspectFieldList(d.Type.Params)
inspectFieldList(d.Type.Results)
// Functions might not have a body. See #42706.
if d.Body != nil {
ast.Inspect(d.Body, inspectFunc)
}
case *ast.GenDecl:
for _, spec := range d.Specs {
switch s := spec.(type) {
case *ast.TypeSpec:
inspectFieldList(s.TypeParams)
ast.Inspect(s.Type, inspectFunc)
depDecls = append(depDecls, typMethods[s.Name.Name]...)
case *ast.ValueSpec:
if s.Type != nil {
ast.Inspect(s.Type, inspectFunc)
}
for _, val := range s.Values {
ast.Inspect(val, inspectFunc)
}
}
}
}
}
// Some decls include multiple specs, such as a variable declaration with
// multiple variables on the same line, or a parenthesized declaration. Trim
// the declarations to include only the specs that are actually mentioned.
// However, if there is a constant group with iota, leave it all: later
// constant declarations in the group may have no value and so cannot stand
// on their own, and removing any constant from the group could change the
// values of subsequent ones.
// See testdata/examples/iota.go for a minimal example.
var ds []ast.Decl
for _, d := range depDecls {
switch d := d.(type) {
case *ast.FuncDecl:
ds = append(ds, d)
case *ast.GenDecl:
containsIota := false // does any spec have iota?
// Collect all Specs that were mentioned in the example.
var specs []ast.Spec
for _, s := range d.Specs {
switch s := s.(type) {
case *ast.TypeSpec:
if usedObjs[s.Name.Obj] {
specs = append(specs, s)
}
case *ast.ValueSpec:
if !containsIota {
containsIota = hasIota(s)
}
// A ValueSpec may have multiple names (e.g. "var a, b int").
// Keep only the names that were mentioned in the example.
// Exception: the multiple names have a single initializer (which
// would be a function call with multiple return values). In that
// case, keep everything.
if len(s.Names) > 1 && len(s.Values) == 1 {
specs = append(specs, s)
continue
}
ns := *s
ns.Names = nil
ns.Values = nil
for i, n := range s.Names {
if usedObjs[n.Obj] {
ns.Names = append(ns.Names, n)
if s.Values != nil {
ns.Values = append(ns.Values, s.Values[i])
}
}
}
if len(ns.Names) > 0 {
specs = append(specs, &ns)
}
}
}
if len(specs) > 0 {
// Constant with iota? Keep it all.
if d.Tok == token.CONST && containsIota {
ds = append(ds, d)
} else {
// Synthesize a GenDecl with just the Specs we need.
nd := *d // copy the GenDecl
nd.Specs = specs
if len(specs) == 1 {
// Remove grouping parens if there is only one spec.
nd.Lparen = 0
}
ds = append(ds, &nd)
}
}
}
}
return ds, unresolved
}
func hasIota(s ast.Spec) bool {
has := false
ast.Inspect(s, func(n ast.Node) bool {
// Check that this is the special built-in "iota" identifier, not
// a user-defined shadow.
if id, ok := n.(*ast.Ident); ok && id.Name == "iota" && id.Obj == nil {
has = true
return false
}
return true
})
return has
}
// findImportGroupStarts finds the start positions of each sequence of import
// specs that are not separated by a blank line.
func findImportGroupStarts(imps []*ast.ImportSpec) []token.Pos {
startImps := findImportGroupStarts1(imps)
groupStarts := make([]token.Pos, len(startImps))
for i, imp := range startImps {
groupStarts[i] = imp.Pos()
}
return groupStarts
}
// Helper for findImportGroupStarts to ease testing.
func findImportGroupStarts1(origImps []*ast.ImportSpec) []*ast.ImportSpec {
// Copy to avoid mutation.
imps := make([]*ast.ImportSpec, len(origImps))
copy(imps, origImps)
// Assume the imports are sorted by position.
sort.Slice(imps, func(i, j int) bool { return imps[i].Pos() < imps[j].Pos() })
// Assume gofmt has been applied, so there is a blank line between adjacent imps
// if and only if they are more than 2 positions apart (newline, tab).
var groupStarts []*ast.ImportSpec
prevEnd := token.Pos(-2)
for _, imp := range imps {
if imp.Pos()-prevEnd > 2 {
groupStarts = append(groupStarts, imp)
}
prevEnd = imp.End()
// Account for end-of-line comments.
if imp.Comment != nil {
prevEnd = imp.Comment.End()
}
}
return groupStarts
}
// 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) {
if b == nil {
return
}
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
}
// classifyExamples classifies examples and assigns them to the Examples field
// of the relevant Func, Type, or Package that the example is associated with.
//
// The classification process is ambiguous in some cases:
//
// - ExampleFoo_Bar matches a type named Foo_Bar
// or a method named Foo.Bar.
// - ExampleFoo_bar matches a type named Foo_bar
// or Foo (with a "bar" suffix).
//
// Examples with malformed names are not associated with anything.
func classifyExamples(p *Package, examples []*Example) {
if len(examples) == 0 {
return
}
// Mapping of names for funcs, types, and methods to the example listing.
ids := make(map[string]*[]*Example)
ids[""] = &p.Examples // package-level examples have an empty name
for _, f := range p.Funcs {
if !token.IsExported(f.Name) {
continue
}
ids[f.Name] = &f.Examples
}
for _, t := range p.Types {
if !token.IsExported(t.Name) {
continue
}
ids[t.Name] = &t.Examples
for _, f := range t.Funcs {
if !token.IsExported(f.Name) {
continue
}
ids[f.Name] = &f.Examples
}
for _, m := range t.Methods {
if !token.IsExported(m.Name) {
continue
}
ids[strings.TrimPrefix(nameWithoutInst(m.Recv), "*")+"_"+m.Name] = &m.Examples
}
}
// Group each example with the associated func, type, or method.
for _, ex := range examples {
// Consider all possible split points for the suffix
// by starting at the end of string (no suffix case),
// then trying all positions that contain a '_' character.
//
// An association is made on the first successful match.
// Examples with malformed names that match nothing are skipped.
for i := len(ex.Name); i >= 0; i = strings.LastIndexByte(ex.Name[:i], '_') {
prefix, suffix, ok := splitExampleName(ex.Name, i)
if !ok {
continue
}
exs, ok := ids[prefix]
if !ok {
continue
}
ex.Suffix = suffix
*exs = append(*exs, ex)
break
}
}
// Sort list of example according to the user-specified suffix name.
for _, exs := range ids {
sort.Slice((*exs), func(i, j int) bool {
return (*exs)[i].Suffix < (*exs)[j].Suffix
})
}
}
// nameWithoutInst returns name if name has no brackets. If name contains
// brackets, then it returns name with all the contents between (and including)
// the outermost left and right bracket removed.
//
// Adapted from debug/gosym/symtab.go:Sym.nameWithoutInst.
func nameWithoutInst(name string) string {
start := strings.Index(name, "[")
if start < 0 {
return name
}
end := strings.LastIndex(name, "]")
if end < 0 {
// Malformed name, should contain closing bracket too.
return name
}
return name[0:start] + name[end+1:]
}
// splitExampleName attempts to split example name s at index i,
// and reports if that produces a valid split. The suffix may be
// absent. Otherwise, it must start with a lower-case letter and
// be preceded by '_'.
//
// One of i == len(s) or s[i] == '_' must be true.
func splitExampleName(s string, i int) (prefix, suffix string, ok bool) {
if i == len(s) {
return s, "", true
}
if i == len(s)-1 {
return "", "", false
}
prefix, suffix = s[:i], s[i+1:]
return prefix, suffix, isExampleSuffix(suffix)
}
func isExampleSuffix(s string) bool {
r, size := utf8.DecodeRuneInString(s)
return size > 0 && unicode.IsLower(r)
}
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