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// Copyright 2009 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.
// Package doc extracts source code documentation from a Go AST.
package doc
import (
// Package is the documentation for an entire package.
type Package struct {
Doc string
Name string
ImportPath string
Imports []string
Filenames []string
Notes map[string][]*Note
// Deprecated: For backward compatibility Bugs is still populated,
// but all new code should use Notes instead.
Bugs []string
// declarations
Consts []*Value
Types []*Type
Vars []*Value
Funcs []*Func
// Examples is a sorted list of examples associated with
// the package. Examples are extracted from _test.go files
// provided to NewFromFiles.
Examples []*Example
// Value is the documentation for a (possibly grouped) var or const declaration.
type Value struct {
Doc string
Names []string // var or const names in declaration order
Decl *ast.GenDecl
order int
// Type is the documentation for a type declaration.
type Type struct {
Doc string
Name string
Decl *ast.GenDecl
// associated declarations
Consts []*Value // sorted list of constants of (mostly) this type
Vars []*Value // sorted list of variables of (mostly) this type
Funcs []*Func // sorted list of functions returning this type
Methods []*Func // sorted list of methods (including embedded ones) of this type
// Examples is a sorted list of examples associated with
// this type. Examples are extracted from _test.go files
// provided to NewFromFiles.
Examples []*Example
// Func is the documentation for a func declaration.
type Func struct {
Doc string
Name string
Decl *ast.FuncDecl
// methods
// (for functions, these fields have the respective zero value)
Recv string // actual receiver "T" or "*T"
Orig string // original receiver "T" or "*T"
Level int // embedding level; 0 means not embedded
// Examples is a sorted list of examples associated with this
// function or method. Examples are extracted from _test.go files
// provided to NewFromFiles.
Examples []*Example
// A Note represents a marked comment starting with "MARKER(uid): note body".
// Any note with a marker of 2 or more upper case [A-Z] letters and a uid of
// at least one character is recognized. The ":" following the uid is optional.
// Notes are collected in the Package.Notes map indexed by the notes marker.
type Note struct {
Pos, End token.Pos // position range of the comment containing the marker
UID string // uid found with the marker
Body string // note body text
// Mode values control the operation of New and NewFromFiles.
type Mode int
const (
// AllDecls says to extract documentation for all package-level
// declarations, not just exported ones.
AllDecls Mode = 1 << iota
// AllMethods says to show all embedded methods, not just the ones of
// invisible (unexported) anonymous fields.
// PreserveAST says to leave the AST unmodified. Originally, pieces of
// the AST such as function bodies were nil-ed out to save memory in
// godoc, but not all programs want that behavior.
// New computes the package documentation for the given package AST.
// New takes ownership of the AST pkg and may edit or overwrite it.
// To have the Examples fields populated, use NewFromFiles and include
// the package's _test.go files.
func New(pkg *ast.Package, importPath string, mode Mode) *Package {
var r reader
r.readPackage(pkg, mode)
return &Package{
Doc: r.doc,
Name: pkg.Name,
ImportPath: importPath,
Imports: sortedKeys(r.imports),
Filenames: r.filenames,
Notes: r.notes,
Bugs: noteBodies(r.notes["BUG"]),
Consts: sortedValues(r.values, token.CONST),
Types: sortedTypes(r.types, mode&AllMethods != 0),
Vars: sortedValues(r.values, token.VAR),
Funcs: sortedFuncs(r.funcs, true),
// NewFromFiles computes documentation for a package.
// The package is specified by a list of *ast.Files and corresponding
// file set, which must not be nil.
// NewFromFiles uses all provided files when computing documentation,
// so it is the caller's responsibility to provide only the files that
// match the desired build context. "go/build".Context.MatchFile can
// be used for determining whether a file matches a build context with
// the desired GOOS and GOARCH values, and other build constraints.
// The import path of the package is specified by importPath.
// Examples found in _test.go files are associated with the corresponding
// type, function, method, or the package, based on their name.
// If the example has a suffix in its name, it is set in the
// Example.Suffix field. Examples with malformed names are skipped.
// Optionally, a single extra argument of type Mode can be provided to
// control low-level aspects of the documentation extraction behavior.
// NewFromFiles takes ownership of the AST files and may edit them,
// unless the PreserveAST Mode bit is on.
func NewFromFiles(fset *token.FileSet, files []*ast.File, importPath string, opts ...interface{}) (*Package, error) {
// Check for invalid API usage.
if fset == nil {
panic(fmt.Errorf("doc.NewFromFiles: no token.FileSet provided (fset == nil)"))
var mode Mode
switch len(opts) { // There can only be 0 or 1 options, so a simple switch works for now.
case 0:
// Nothing to do.
case 1:
m, ok := opts[0].(Mode)
if !ok {
panic(fmt.Errorf("doc.NewFromFiles: option argument type must be doc.Mode"))
mode = m
panic(fmt.Errorf("doc.NewFromFiles: there must not be more than 1 option argument"))
// Collect .go and _test.go files.
var (
goFiles = make(map[string]*ast.File)
testGoFiles []*ast.File
for i := range files {
f := fset.File(files[i].Pos())
if f == nil {
return nil, fmt.Errorf("file files[%d] is not found in the provided file set", i)
switch name := f.Name(); {
case strings.HasSuffix(name, ".go") && !strings.HasSuffix(name, "_test.go"):
goFiles[name] = files[i]
case strings.HasSuffix(name, "_test.go"):
testGoFiles = append(testGoFiles, files[i])
return nil, fmt.Errorf("file files[%d] filename %q does not have a .go extension", i, name)
// TODO(dmitshur,gri): A relatively high level call to ast.NewPackage with a simpleImporter
// ast.Importer implementation is made below. It might be possible to short-circuit and simplify.
// Compute package documentation.
pkg, _ := ast.NewPackage(fset, goFiles, simpleImporter, nil) // Ignore errors that can happen due to unresolved identifiers.
p := New(pkg, importPath, mode)
classifyExamples(p, Examples(testGoFiles...))
return p, nil
// simpleImporter returns a (dummy) package object named by the last path
// component of the provided package path (as is the convention for packages).
// This is sufficient to resolve package identifiers without doing an actual
// import. It never returns an error.
func simpleImporter(imports map[string]*ast.Object, path string) (*ast.Object, error) {
pkg := imports[path]
if pkg == nil {
// note that strings.LastIndex returns -1 if there is no "/"
pkg = ast.NewObj(ast.Pkg, path[strings.LastIndex(path, "/")+1:])
pkg.Data = ast.NewScope(nil) // required by ast.NewPackage for dot-import
imports[path] = pkg
return pkg, nil