Package ast

import "go/ast"
Overview
Index
Examples
Documentation

Overview

Package ast declares the types used to represent syntax trees for Go packages.

Index

func FileExports(src *File) bool
func FilterDecl(decl Decl, f Filter) bool
func FilterFile(src *File, f Filter) bool
func FilterPackage(pkg *Package, f Filter) bool
func Fprint(w io.Writer, fset *token.FileSet, x interface{}, f FieldFilter) error
func Inspect(node Node, f func(Node) bool)
func IsExported(name string) bool
func NotNilFilter(_ string, v reflect.Value) bool
func PackageExports(pkg *Package) bool
func Print(fset *token.FileSet, x interface{}) error
func SortImports(fset *token.FileSet, f *File)
func Walk(v Visitor, node Node)
type ArrayType
func (x *ArrayType) End() token.Pos
func (x *ArrayType) Pos() token.Pos
type AssignStmt
func (s *AssignStmt) End() token.Pos
func (s *AssignStmt) Pos() token.Pos
type BadDecl
func (d *BadDecl) End() token.Pos
func (d *BadDecl) Pos() token.Pos
type BadExpr
func (x *BadExpr) End() token.Pos
func (x *BadExpr) Pos() token.Pos
type BadStmt
func (s *BadStmt) End() token.Pos
func (s *BadStmt) Pos() token.Pos
type BasicLit
func (x *BasicLit) End() token.Pos
func (x *BasicLit) Pos() token.Pos
type BinaryExpr
func (x *BinaryExpr) End() token.Pos
func (x *BinaryExpr) Pos() token.Pos
type BlockStmt
func (s *BlockStmt) End() token.Pos
func (s *BlockStmt) Pos() token.Pos
type BranchStmt
func (s *BranchStmt) End() token.Pos
func (s *BranchStmt) Pos() token.Pos
type CallExpr
func (x *CallExpr) End() token.Pos
func (x *CallExpr) Pos() token.Pos
type CaseClause
func (s *CaseClause) End() token.Pos
func (s *CaseClause) Pos() token.Pos
type ChanDir
type ChanType
func (x *ChanType) End() token.Pos
func (x *ChanType) Pos() token.Pos
type CommClause
func (s *CommClause) End() token.Pos
func (s *CommClause) Pos() token.Pos
type Comment
func (c *Comment) End() token.Pos
func (c *Comment) Pos() token.Pos
type CommentGroup
func (g *CommentGroup) End() token.Pos
func (g *CommentGroup) Pos() token.Pos
func (g *CommentGroup) Text() string
type CommentMap
func NewCommentMap(fset *token.FileSet, node Node, comments []*CommentGroup) CommentMap
func (cmap CommentMap) Comments() []*CommentGroup
func (cmap CommentMap) Filter(node Node) CommentMap
func (cmap CommentMap) String() string
func (cmap CommentMap) Update(old, new Node) Node
type CompositeLit
func (x *CompositeLit) End() token.Pos
func (x *CompositeLit) Pos() token.Pos
type Decl
type DeclStmt
func (s *DeclStmt) End() token.Pos
func (s *DeclStmt) Pos() token.Pos
type DeferStmt
func (s *DeferStmt) End() token.Pos
func (s *DeferStmt) Pos() token.Pos
type Ellipsis
func (x *Ellipsis) End() token.Pos
func (x *Ellipsis) Pos() token.Pos
type EmptyStmt
func (s *EmptyStmt) End() token.Pos
func (s *EmptyStmt) Pos() token.Pos
type Expr
type ExprStmt
func (s *ExprStmt) End() token.Pos
func (s *ExprStmt) Pos() token.Pos
type Field
func (f *Field) End() token.Pos
func (f *Field) Pos() token.Pos
type FieldFilter
type FieldList
func (f *FieldList) End() token.Pos
func (f *FieldList) NumFields() int
func (f *FieldList) Pos() token.Pos
type File
func MergePackageFiles(pkg *Package, mode MergeMode) *File
func (f *File) End() token.Pos
func (f *File) Pos() token.Pos
type Filter
type ForStmt
func (s *ForStmt) End() token.Pos
func (s *ForStmt) Pos() token.Pos
type FuncDecl
func (d *FuncDecl) End() token.Pos
func (d *FuncDecl) Pos() token.Pos
type FuncLit
func (x *FuncLit) End() token.Pos
func (x *FuncLit) Pos() token.Pos
type FuncType
func (x *FuncType) End() token.Pos
func (x *FuncType) Pos() token.Pos
type GenDecl
func (d *GenDecl) End() token.Pos
func (d *GenDecl) Pos() token.Pos
type GoStmt
func (s *GoStmt) End() token.Pos
func (s *GoStmt) Pos() token.Pos
type Ident
func NewIdent(name string) *Ident
func (x *Ident) End() token.Pos
func (id *Ident) IsExported() bool
func (x *Ident) Pos() token.Pos
func (id *Ident) String() string
type IfStmt
func (s *IfStmt) End() token.Pos
func (s *IfStmt) Pos() token.Pos
type ImportSpec
func (s *ImportSpec) End() token.Pos
func (s *ImportSpec) Pos() token.Pos
type Importer
type IncDecStmt
func (s *IncDecStmt) End() token.Pos
func (s *IncDecStmt) Pos() token.Pos
type IndexExpr
func (x *IndexExpr) End() token.Pos
func (x *IndexExpr) Pos() token.Pos
type InterfaceType
func (x *InterfaceType) End() token.Pos
func (x *InterfaceType) Pos() token.Pos
type KeyValueExpr
func (x *KeyValueExpr) End() token.Pos
func (x *KeyValueExpr) Pos() token.Pos
type LabeledStmt
func (s *LabeledStmt) End() token.Pos
func (s *LabeledStmt) Pos() token.Pos
type MapType
func (x *MapType) End() token.Pos
func (x *MapType) Pos() token.Pos
type MergeMode
type Node
type ObjKind
func (kind ObjKind) String() string
type Object
func NewObj(kind ObjKind, name string) *Object
func (obj *Object) Pos() token.Pos
type Package
func NewPackage(fset *token.FileSet, files map[string]*File, importer Importer, ...) (*Package, error)
func (p *Package) End() token.Pos
func (p *Package) Pos() token.Pos
type ParenExpr
func (x *ParenExpr) End() token.Pos
func (x *ParenExpr) Pos() token.Pos
type RangeStmt
func (s *RangeStmt) End() token.Pos
func (s *RangeStmt) Pos() token.Pos
type ReturnStmt
func (s *ReturnStmt) End() token.Pos
func (s *ReturnStmt) Pos() token.Pos
type Scope
func NewScope(outer *Scope) *Scope
func (s *Scope) Insert(obj *Object) (alt *Object)
func (s *Scope) Lookup(name string) *Object
func (s *Scope) String() string
type SelectStmt
func (s *SelectStmt) End() token.Pos
func (s *SelectStmt) Pos() token.Pos
type SelectorExpr
func (x *SelectorExpr) End() token.Pos
func (x *SelectorExpr) Pos() token.Pos
type SendStmt
func (s *SendStmt) End() token.Pos
func (s *SendStmt) Pos() token.Pos
type SliceExpr
func (x *SliceExpr) End() token.Pos
func (x *SliceExpr) Pos() token.Pos
type Spec
type StarExpr
func (x *StarExpr) End() token.Pos
func (x *StarExpr) Pos() token.Pos
type Stmt
type StructType
func (x *StructType) End() token.Pos
func (x *StructType) Pos() token.Pos
type SwitchStmt
func (s *SwitchStmt) End() token.Pos
func (s *SwitchStmt) Pos() token.Pos
type TypeAssertExpr
func (x *TypeAssertExpr) End() token.Pos
func (x *TypeAssertExpr) Pos() token.Pos
type TypeSpec
func (s *TypeSpec) End() token.Pos
func (s *TypeSpec) Pos() token.Pos
type TypeSwitchStmt
func (s *TypeSwitchStmt) End() token.Pos
func (s *TypeSwitchStmt) Pos() token.Pos
type UnaryExpr
func (x *UnaryExpr) End() token.Pos
func (x *UnaryExpr) Pos() token.Pos
type ValueSpec
func (s *ValueSpec) End() token.Pos
func (s *ValueSpec) Pos() token.Pos
type Visitor

Examples

CommentMap
Inspect
Print

Documentation

func FileExports

func FileExports(src *File) bool

FileExports trims the AST for a Go source file in place such that only exported nodes remain: all top-level identifiers which are not exported and their associated information (such as type, initial value, or function body) are removed. Non-exported fields and methods of exported types are stripped. The File.Comments list is not changed.

FileExports reports whether there are exported declarations.

func FilterDecl

func FilterDecl(decl Decl, f Filter) bool

FilterDecl trims the AST for a Go declaration in place by removing all names (including struct field and interface method names, but not from parameter lists) that don't pass through the filter f.

FilterDecl reports whether there are any declared names left after filtering.

func FilterFile

func FilterFile(src *File, f Filter) bool

FilterFile trims the AST for a Go file in place by removing all names from top-level declarations (including struct field and interface method names, but not from parameter lists) that don't pass through the filter f. If the declaration is empty afterwards, the declaration is removed from the AST. Import declarations are always removed. The File.Comments list is not changed.

FilterFile reports whether there are any top-level declarations left after filtering.

func FilterPackage

func FilterPackage(pkg *Package, f Filter) bool

FilterPackage trims the AST for a Go package in place by removing all names from top-level declarations (including struct field and interface method names, but not from parameter lists) that don't pass through the filter f. If the declaration is empty afterwards, the declaration is removed from the AST. The pkg.Files list is not changed, so that file names and top-level package comments don't get lost.

FilterPackage reports whether there are any top-level declarations left after filtering.

func Fprint

func Fprint(w io.Writer, fset *token.FileSet, x interface{}, f FieldFilter) error

Fprint prints the (sub-)tree starting at AST node x to w. If fset != nil, position information is interpreted relative to that file set. Otherwise positions are printed as integer values (file set specific offsets).

A non-nil FieldFilter f may be provided to control the output: struct fields for which f(fieldname, fieldvalue) is true are printed; all others are filtered from the output. Unexported struct fields are never printed.

func Inspect

func Inspect(node Node, f func(Node) bool)

Inspect traverses an AST in depth-first order: It starts by calling f(node); node must not be nil. If f returns true, Inspect invokes f recursively for each of the non-nil children of node, followed by a call of f(nil).

This example demonstrates how to inspect the AST of a Go program.

Code:

// src is the input for which we want to inspect the AST.
src := `
package p
const c = 1.0
var X = f(3.14)*2 + c
`

// Create the AST by parsing src.
fset := token.NewFileSet() // positions are relative to fset
f, err := parser.ParseFile(fset, "src.go", src, 0)
if err != nil {
    panic(err)
}

// Inspect the AST and print all identifiers and literals.
ast.Inspect(f, func(n ast.Node) bool {
    var s string
    switch x := n.(type) {
    case *ast.BasicLit:
        s = x.Value
    case *ast.Ident:
        s = x.Name
    }
    if s != "" {
        fmt.Printf("%s:\t%s\n", fset.Position(n.Pos()), s)
    }
    return true
})

Output:

src.go:2:9:	p
src.go:3:7:	c
src.go:3:11:	1.0
src.go:4:5:	X
src.go:4:9:	f
src.go:4:11:	3.14
src.go:4:17:	2
src.go:4:21:	c

func IsExported

func IsExported(name string) bool

IsExported reports whether name is an exported Go symbol (that is, whether it begins with an upper-case letter).

func NotNilFilter

func NotNilFilter(_ string, v reflect.Value) bool

NotNilFilter returns true for field values that are not nil; it returns false otherwise.

func PackageExports

func PackageExports(pkg *Package) bool

PackageExports trims the AST for a Go package in place such that only exported nodes remain. The pkg.Files list is not changed, so that file names and top-level package comments don't get lost.

PackageExports reports whether there are exported declarations; it returns false otherwise.

func Print

func Print(fset *token.FileSet, x interface{}) error

Print prints x to standard output, skipping nil fields. Print(fset, x) is the same as Fprint(os.Stdout, fset, x, NotNilFilter).

This example shows what an AST looks like when printed for debugging.

Code:

// src is the input for which we want to print the AST.
src := `
package main
func main() {
	println("Hello, World!")
}
`

// Create the AST by parsing src.
fset := token.NewFileSet() // positions are relative to fset
f, err := parser.ParseFile(fset, "", src, 0)
if err != nil {
    panic(err)
}

// Print the AST.
ast.Print(fset, f)

Output:

     0  *ast.File {
     1  .  Package: 2:1
     2  .  Name: *ast.Ident {
     3  .  .  NamePos: 2:9
     4  .  .  Name: "main"
     5  .  }
     6  .  Decls: []ast.Decl (len = 1) {
     7  .  .  0: *ast.FuncDecl {
     8  .  .  .  Name: *ast.Ident {
     9  .  .  .  .  NamePos: 3:6
    10  .  .  .  .  Name: "main"
    11  .  .  .  .  Obj: *ast.Object {
    12  .  .  .  .  .  Kind: func
    13  .  .  .  .  .  Name: "main"
    14  .  .  .  .  .  Decl: *(obj @ 7)
    15  .  .  .  .  }
    16  .  .  .  }
    17  .  .  .  Type: *ast.FuncType {
    18  .  .  .  .  Func: 3:1
    19  .  .  .  .  Params: *ast.FieldList {
    20  .  .  .  .  .  Opening: 3:10
    21  .  .  .  .  .  Closing: 3:11
    22  .  .  .  .  }
    23  .  .  .  }
    24  .  .  .  Body: *ast.BlockStmt {
    25  .  .  .  .  Lbrace: 3:13
    26  .  .  .  .  List: []ast.Stmt (len = 1) {
    27  .  .  .  .  .  0: *ast.ExprStmt {
    28  .  .  .  .  .  .  X: *ast.CallExpr {
    29  .  .  .  .  .  .  .  Fun: *ast.Ident {
    30  .  .  .  .  .  .  .  .  NamePos: 4:2
    31  .  .  .  .  .  .  .  .  Name: "println"
    32  .  .  .  .  .  .  .  }
    33  .  .  .  .  .  .  .  Lparen: 4:9
    34  .  .  .  .  .  .  .  Args: []ast.Expr (len = 1) {
    35  .  .  .  .  .  .  .  .  0: *ast.BasicLit {
    36  .  .  .  .  .  .  .  .  .  ValuePos: 4:10
    37  .  .  .  .  .  .  .  .  .  Kind: STRING
    38  .  .  .  .  .  .  .  .  .  Value: "\"Hello, World!\""
    39  .  .  .  .  .  .  .  .  }
    40  .  .  .  .  .  .  .  }
    41  .  .  .  .  .  .  .  Ellipsis: -
    42  .  .  .  .  .  .  .  Rparen: 4:25
    43  .  .  .  .  .  .  }
    44  .  .  .  .  .  }
    45  .  .  .  .  }
    46  .  .  .  .  Rbrace: 5:1
    47  .  .  .  }
    48  .  .  }
    49  .  }
    50  .  Scope: *ast.Scope {
    51  .  .  Objects: map[string]*ast.Object (len = 1) {
    52  .  .  .  "main": *(obj @ 11)
    53  .  .  }
    54  .  }
    55  .  Unresolved: []*ast.Ident (len = 1) {
    56  .  .  0: *(obj @ 29)
    57  .  }
    58  }

func SortImports

func SortImports(fset *token.FileSet, f *File)

SortImports sorts runs of consecutive import lines in import blocks in f. It also removes duplicate imports when it is possible to do so without data loss.

func Walk

func Walk(v Visitor, node Node)

Walk traverses an AST in depth-first order: It starts by calling v.Visit(node); node must not be nil. If the visitor w returned by v.Visit(node) is not nil, Walk is invoked recursively with visitor w for each of the non-nil children of node, followed by a call of w.Visit(nil).

type ArrayType

type ArrayType struct {
    Lbrack token.Pos // position of "["
    Len    Expr      // Ellipsis node for [...]T array types, nil for slice types
    Elt    Expr      // element type
}

An ArrayType node represents an array or slice type.

func ArrayType.End

func (x *ArrayType) End() token.Pos

func ArrayType.Pos

func (x *ArrayType) Pos() token.Pos

type AssignStmt

type AssignStmt struct {
    Lhs    []Expr
    TokPos token.Pos   // position of Tok
    Tok    token.Token // assignment token, DEFINE
    Rhs    []Expr
}

An AssignStmt node represents an assignment or a short variable declaration.

func AssignStmt.End

func (s *AssignStmt) End() token.Pos

func AssignStmt.Pos

func (s *AssignStmt) Pos() token.Pos

type BadDecl

type BadDecl struct {
    From, To token.Pos // position range of bad declaration
}

A BadDecl node is a placeholder for declarations containing syntax errors for which no correct declaration nodes can be created.

func BadDecl.End

func (d *BadDecl) End() token.Pos

func BadDecl.Pos

func (d *BadDecl) Pos() token.Pos

type BadExpr

type BadExpr struct {
    From, To token.Pos // position range of bad expression
}

A BadExpr node is a placeholder for expressions containing syntax errors for which no correct expression nodes can be created.

func BadExpr.End

func (x *BadExpr) End() token.Pos

func BadExpr.Pos

func (x *BadExpr) Pos() token.Pos

type BadStmt

type BadStmt struct {
    From, To token.Pos // position range of bad statement
}

A BadStmt node is a placeholder for statements containing syntax errors for which no correct statement nodes can be created.

func BadStmt.End

func (s *BadStmt) End() token.Pos

func BadStmt.Pos

func (s *BadStmt) Pos() token.Pos

type BasicLit

type BasicLit struct {
    ValuePos token.Pos   // literal position
    Kind     token.Token // token.INT, token.FLOAT, token.IMAG, token.CHAR, or token.STRING
    Value    string      // literal string; e.g. 42, 0x7f, 3.14, 1e-9, 2.4i, 'a', '\x7f', "foo" or `\m\n\o`
}

A BasicLit node represents a literal of basic type.

func BasicLit.End

func (x *BasicLit) End() token.Pos

func BasicLit.Pos

func (x *BasicLit) Pos() token.Pos

type BinaryExpr

type BinaryExpr struct {
    X     Expr        // left operand
    OpPos token.Pos   // position of Op
    Op    token.Token // operator
    Y     Expr        // right operand
}

A BinaryExpr node represents a binary expression.

func BinaryExpr.End

func (x *BinaryExpr) End() token.Pos

func BinaryExpr.Pos

func (x *BinaryExpr) Pos() token.Pos

type BlockStmt

type BlockStmt struct {
    Lbrace token.Pos // position of "{"
    List   []Stmt
    Rbrace token.Pos // position of "}"
}

A BlockStmt node represents a braced statement list.

func BlockStmt.End

func (s *BlockStmt) End() token.Pos

func BlockStmt.Pos

func (s *BlockStmt) Pos() token.Pos

type BranchStmt

type BranchStmt struct {
    TokPos token.Pos   // position of Tok
    Tok    token.Token // keyword token (BREAK, CONTINUE, GOTO, FALLTHROUGH)
    Label  *Ident      // label name; or nil
}

A BranchStmt node represents a break, continue, goto, or fallthrough statement.

func BranchStmt.End

func (s *BranchStmt) End() token.Pos

func BranchStmt.Pos

func (s *BranchStmt) Pos() token.Pos

type CallExpr

type CallExpr struct {
    Fun      Expr      // function expression
    Lparen   token.Pos // position of "("
    Args     []Expr    // function arguments; or nil
    Ellipsis token.Pos // position of "..." (token.NoPos if there is no "...")
    Rparen   token.Pos // position of ")"
}

A CallExpr node represents an expression followed by an argument list.

func CallExpr.End

func (x *CallExpr) End() token.Pos

func CallExpr.Pos

func (x *CallExpr) Pos() token.Pos

type CaseClause

type CaseClause struct {
    Case  token.Pos // position of "case" or "default" keyword
    List  []Expr    // list of expressions or types; nil means default case
    Colon token.Pos // position of ":"
    Body  []Stmt    // statement list; or nil
}

A CaseClause represents a case of an expression or type switch statement.

func CaseClause.End

func (s *CaseClause) End() token.Pos

func CaseClause.Pos

func (s *CaseClause) Pos() token.Pos

type ChanDir

type ChanDir int

The direction of a channel type is indicated by one of the following constants.

const (
    SEND ChanDir = 1 << iota
    RECV
)

type ChanType

type ChanType struct {
    Begin token.Pos // position of "chan" keyword or "<-" (whichever comes first)
    Arrow token.Pos // position of "<-" (token.NoPos if there is no "<-")
    Dir   ChanDir   // channel direction
    Value Expr      // value type
}

A ChanType node represents a channel type.

func ChanType.End

func (x *ChanType) End() token.Pos

func ChanType.Pos

func (x *ChanType) Pos() token.Pos

type CommClause

type CommClause struct {
    Case  token.Pos // position of "case" or "default" keyword
    Comm  Stmt      // send or receive statement; nil means default case
    Colon token.Pos // position of ":"
    Body  []Stmt    // statement list; or nil
}

A CommClause node represents a case of a select statement.

func CommClause.End

func (s *CommClause) End() token.Pos

func CommClause.Pos

func (s *CommClause) Pos() token.Pos

type Comment

type Comment struct {
    Slash token.Pos // position of "/" starting the comment
    Text  string    // comment text (excluding '\n' for //-style comments)
}

A Comment node represents a single //-style or /*-style comment.

func Comment.End

func (c *Comment) End() token.Pos

func Comment.Pos

func (c *Comment) Pos() token.Pos

type CommentGroup

type CommentGroup struct {
    List []*Comment // len(List) > 0
}

A CommentGroup represents a sequence of comments with no other tokens and no empty lines between.

func CommentGroup.End

func (g *CommentGroup) End() token.Pos

func CommentGroup.Pos

func (g *CommentGroup) Pos() token.Pos

func CommentGroup.Text

func (g *CommentGroup) Text() string

Text returns the text of the comment. Comment markers (//, /*, and */), the first space of a line comment, and leading and trailing empty lines are removed. Multiple empty lines are reduced to one, and trailing space on lines is trimmed. Unless the result is empty, it is newline-terminated.

type CommentMap

type CommentMap map[Node][]*CommentGroup

A CommentMap maps an AST node to a list of comment groups associated with it. See NewCommentMap for a description of the association.

This example illustrates how to remove a variable declaration in a Go program while maintaining correct comment association using an ast.CommentMap.

Code:

// src is the input for which we create the AST that we
// are going to manipulate.
src := `
// This is the package comment.
package main

// This comment is associated with the hello constant.
const hello = "Hello, World!" // line comment 1

// This comment is associated with the foo variable.
var foo = hello // line comment 2 

// This comment is associated with the main function.
func main() {
	fmt.Println(hello) // line comment 3
}
`

// Create the AST by parsing src.
fset := token.NewFileSet() // positions are relative to fset
f, err := parser.ParseFile(fset, "src.go", src, parser.ParseComments)
if err != nil {
    panic(err)
}

// Create an ast.CommentMap from the ast.File's comments.
// This helps keeping the association between comments
// and AST nodes.
cmap := ast.NewCommentMap(fset, f, f.Comments)

// Remove the first variable declaration from the list of declarations.
for i, decl := range f.Decls {
    if gen, ok := decl.(*ast.GenDecl); ok && gen.Tok == token.VAR {
        copy(f.Decls[i:], f.Decls[i+1:])
        f.Decls = f.Decls[:len(f.Decls)-1]
    }
}

// Use the comment map to filter comments that don't belong anymore
// (the comments associated with the variable declaration), and create
// the new comments list.
f.Comments = cmap.Filter(f).Comments()

// Print the modified AST.
var buf bytes.Buffer
if err := format.Node(&buf, fset, f); err != nil {
    panic(err)
}
fmt.Printf("%s", buf.Bytes())

Output:

// This is the package comment.
package main

// This comment is associated with the hello constant.
const hello = "Hello, World!" // line comment 1

// This comment is associated with the main function.
func main() {
	fmt.Println(hello) // line comment 3
}

func NewCommentMap

func NewCommentMap(fset *token.FileSet, node Node, comments []*CommentGroup) CommentMap

NewCommentMap creates a new comment map by associating comment groups of the comments list with the nodes of the AST specified by node.

A comment group g is associated with a node n if:

- g starts on the same line as n ends
- g starts on the line immediately following n, and there is
  at least one empty line after g and before the next node
- g starts before n and is not associated to the node before n
  via the previous rules

NewCommentMap tries to associate a comment group to the "largest" node possible: For instance, if the comment is a line comment trailing an assignment, the comment is associated with the entire assignment rather than just the last operand in the assignment.

func CommentMap.Comments

func (cmap CommentMap) Comments() []*CommentGroup

Comments returns the list of comment groups in the comment map. The result is sorted in source order.

func CommentMap.Filter

func (cmap CommentMap) Filter(node Node) CommentMap

Filter returns a new comment map consisting of only those entries of cmap for which a corresponding node exists in the AST specified by node.

func CommentMap.String

func (cmap CommentMap) String() string

func CommentMap.Update

func (cmap CommentMap) Update(old, new Node) Node

Update replaces an old node in the comment map with the new node and returns the new node. Comments that were associated with the old node are associated with the new node.

type CompositeLit

type CompositeLit struct {
    Type   Expr      // literal type; or nil
    Lbrace token.Pos // position of "{"
    Elts   []Expr    // list of composite elements; or nil
    Rbrace token.Pos // position of "}"
}

A CompositeLit node represents a composite literal.

func CompositeLit.End

func (x *CompositeLit) End() token.Pos

func CompositeLit.Pos

func (x *CompositeLit) Pos() token.Pos

type Decl

type Decl interface {
    Node
    // contains filtered or unexported methods
}

All declaration nodes implement the Decl interface.

type DeclStmt

type DeclStmt struct {
    Decl Decl // *GenDecl with CONST, TYPE, or VAR token
}

A DeclStmt node represents a declaration in a statement list.

func DeclStmt.End

func (s *DeclStmt) End() token.Pos

func DeclStmt.Pos

func (s *DeclStmt) Pos() token.Pos

type DeferStmt

type DeferStmt struct {
    Defer token.Pos // position of "defer" keyword
    Call  *CallExpr
}

A DeferStmt node represents a defer statement.

func DeferStmt.End

func (s *DeferStmt) End() token.Pos

func DeferStmt.Pos

func (s *DeferStmt) Pos() token.Pos

type Ellipsis

type Ellipsis struct {
    Ellipsis token.Pos // position of "..."
    Elt      Expr      // ellipsis element type (parameter lists only); or nil
}

An Ellipsis node stands for the "..." type in a parameter list or the "..." length in an array type.

func Ellipsis.End

func (x *Ellipsis) End() token.Pos

func Ellipsis.Pos

func (x *Ellipsis) Pos() token.Pos

type EmptyStmt

type EmptyStmt struct {
    Semicolon token.Pos // position of following ";"
    Implicit  bool      // if set, ";" was omitted in the source
}

An EmptyStmt node represents an empty statement. The "position" of the empty statement is the position of the immediately following (explicit or implicit) semicolon.

func EmptyStmt.End

func (s *EmptyStmt) End() token.Pos

func EmptyStmt.Pos

func (s *EmptyStmt) Pos() token.Pos

type Expr

type Expr interface {
    Node
    // contains filtered or unexported methods
}

All expression nodes implement the Expr interface.

type ExprStmt

type ExprStmt struct {
    X Expr // expression
}

An ExprStmt node represents a (stand-alone) expression in a statement list.

func ExprStmt.End

func (s *ExprStmt) End() token.Pos

func ExprStmt.Pos

func (s *ExprStmt) Pos() token.Pos

type Field

type Field struct {
    Doc     *CommentGroup // associated documentation; or nil
    Names   []*Ident      // field/method/parameter names; or nil if anonymous field
    Type    Expr          // field/method/parameter type
    Tag     *BasicLit     // field tag; or nil
    Comment *CommentGroup // line comments; or nil
}

A Field represents a Field declaration list in a struct type, a method list in an interface type, or a parameter/result declaration in a signature.

func Field.End

func (f *Field) End() token.Pos

func Field.Pos

func (f *Field) Pos() token.Pos

type FieldFilter

type FieldFilter func(name string, value reflect.Value) bool

A FieldFilter may be provided to Fprint to control the output.

type FieldList

type FieldList struct {
    Opening token.Pos // position of opening parenthesis/brace, if any
    List    []*Field  // field list; or nil
    Closing token.Pos // position of closing parenthesis/brace, if any
}

A FieldList represents a list of Fields, enclosed by parentheses or braces.

func FieldList.End

func (f *FieldList) End() token.Pos

func FieldList.NumFields

func (f *FieldList) NumFields() int

NumFields returns the number of (named and anonymous fields) in a FieldList.

func FieldList.Pos

func (f *FieldList) Pos() token.Pos

type File

type File struct {
    Doc        *CommentGroup   // associated documentation; or nil
    Package    token.Pos       // position of "package" keyword
    Name       *Ident          // package name
    Decls      []Decl          // top-level declarations; or nil
    Scope      *Scope          // package scope (this file only)
    Imports    []*ImportSpec   // imports in this file
    Unresolved []*Ident        // unresolved identifiers in this file
    Comments   []*CommentGroup // list of all comments in the source file
}

A File node represents a Go source file.

The Comments list contains all comments in the source file in order of appearance, including the comments that are pointed to from other nodes via Doc and Comment fields.

For correct printing of source code containing comments (using packages go/format and go/printer), special care must be taken to update comments when a File's syntax tree is modified: For printing, comments are interspersed between tokens based on their position. If syntax tree nodes are removed or moved, relevant comments in their vicinity must also be removed (from the File.Comments list) or moved accordingly (by updating their positions). A CommentMap may be used to facilitate some of these operations.

Whether and how a comment is associated with a node depends on the interpretation of the syntax tree by the manipulating program: Except for Doc and Comment comments directly associated with nodes, the remaining comments are "free-floating" (see also issues #18593, #20744).

func MergePackageFiles

func MergePackageFiles(pkg *Package, mode MergeMode) *File

MergePackageFiles creates a file AST by merging the ASTs of the files belonging to a package. The mode flags control merging behavior.

func File.End

func (f *File) End() token.Pos

func File.Pos

func (f *File) Pos() token.Pos

type Filter

type Filter func(string) bool

type ForStmt

type ForStmt struct {
    For  token.Pos // position of "for" keyword
    Init Stmt      // initialization statement; or nil
    Cond Expr      // condition; or nil
    Post Stmt      // post iteration statement; or nil
    Body *BlockStmt
}

A ForStmt represents a for statement.

func ForStmt.End

func (s *ForStmt) End() token.Pos

func ForStmt.Pos

func (s *ForStmt) Pos() token.Pos

type FuncDecl

type FuncDecl struct {
    Doc  *CommentGroup // associated documentation; or nil
    Recv *FieldList    // receiver (methods); or nil (functions)
    Name *Ident        // function/method name
    Type *FuncType     // function signature: parameters, results, and position of "func" keyword
    Body *BlockStmt    // function body; or nil for external (non-Go) function
}

A FuncDecl node represents a function declaration.

func FuncDecl.End

func (d *FuncDecl) End() token.Pos

func FuncDecl.Pos

func (d *FuncDecl) Pos() token.Pos

type FuncLit

type FuncLit struct {
    Type *FuncType  // function type
    Body *BlockStmt // function body
}

A FuncLit node represents a function literal.

func FuncLit.End

func (x *FuncLit) End() token.Pos

func FuncLit.Pos

func (x *FuncLit) Pos() token.Pos

type FuncType

type FuncType struct {
    Func    token.Pos  // position of "func" keyword (token.NoPos if there is no "func")
    Params  *FieldList // (incoming) parameters; non-nil
    Results *FieldList // (outgoing) results; or nil
}

A FuncType node represents a function type.

func FuncType.End

func (x *FuncType) End() token.Pos

func FuncType.Pos

func (x *FuncType) Pos() token.Pos

type GenDecl

type GenDecl struct {
    Doc    *CommentGroup // associated documentation; or nil
    TokPos token.Pos     // position of Tok
    Tok    token.Token   // IMPORT, CONST, TYPE, VAR
    Lparen token.Pos     // position of '(', if any
    Specs  []Spec
    Rparen token.Pos // position of ')', if any
}

A GenDecl node (generic declaration node) represents an import, constant, type or variable declaration. A valid Lparen position (Lparen.IsValid()) indicates a parenthesized declaration.

Relationship between Tok value and Specs element type:

token.IMPORT  *ImportSpec
token.CONST   *ValueSpec
token.TYPE    *TypeSpec
token.VAR     *ValueSpec

func GenDecl.End

func (d *GenDecl) End() token.Pos

func GenDecl.Pos

func (d *GenDecl) Pos() token.Pos

type GoStmt

type GoStmt struct {
    Go   token.Pos // position of "go" keyword
    Call *CallExpr
}

A GoStmt node represents a go statement.

func GoStmt.End

func (s *GoStmt) End() token.Pos

func GoStmt.Pos

func (s *GoStmt) Pos() token.Pos

type Ident

type Ident struct {
    NamePos token.Pos // identifier position
    Name    string    // identifier name
    Obj     *Object   // denoted object; or nil
}

An Ident node represents an identifier.

func NewIdent

func NewIdent(name string) *Ident

NewIdent creates a new Ident without position. Useful for ASTs generated by code other than the Go parser.

func Ident.End

func (x *Ident) End() token.Pos

func Ident.IsExported

func (id *Ident) IsExported() bool

IsExported reports whether id is an exported Go symbol (that is, whether it begins with an uppercase letter).

func Ident.Pos

func (x *Ident) Pos() token.Pos

func Ident.String

func (id *Ident) String() string

type IfStmt

type IfStmt struct {
    If   token.Pos // position of "if" keyword
    Init Stmt      // initialization statement; or nil
    Cond Expr      // condition
    Body *BlockStmt
    Else Stmt // else branch; or nil
}

An IfStmt node represents an if statement.

func IfStmt.End

func (s *IfStmt) End() token.Pos

func IfStmt.Pos

func (s *IfStmt) Pos() token.Pos

type ImportSpec

type ImportSpec struct {
    Doc     *CommentGroup // associated documentation; or nil
    Name    *Ident        // local package name (including "."); or nil
    Path    *BasicLit     // import path
    Comment *CommentGroup // line comments; or nil
    EndPos  token.Pos     // end of spec (overrides Path.Pos if nonzero)
}

An ImportSpec node represents a single package import.

func ImportSpec.End

func (s *ImportSpec) End() token.Pos

func ImportSpec.Pos

func (s *ImportSpec) Pos() token.Pos

type Importer

type Importer func(imports map[string]*Object, path string) (pkg *Object, err error)

An Importer resolves import paths to package Objects. The imports map records the packages already imported, indexed by package id (canonical import path). An Importer must determine the canonical import path and check the map to see if it is already present in the imports map. If so, the Importer can return the map entry. Otherwise, the Importer should load the package data for the given path into a new *Object (pkg), record pkg in the imports map, and then return pkg.

type IncDecStmt

type IncDecStmt struct {
    X      Expr
    TokPos token.Pos   // position of Tok
    Tok    token.Token // INC or DEC
}

An IncDecStmt node represents an increment or decrement statement.

func IncDecStmt.End

func (s *IncDecStmt) End() token.Pos

func IncDecStmt.Pos

func (s *IncDecStmt) Pos() token.Pos

type IndexExpr

type IndexExpr struct {
    X      Expr      // expression
    Lbrack token.Pos // position of "["
    Index  Expr      // index expression
    Rbrack token.Pos // position of "]"
}

An IndexExpr node represents an expression followed by an index.

func IndexExpr.End

func (x *IndexExpr) End() token.Pos

func IndexExpr.Pos

func (x *IndexExpr) Pos() token.Pos

type InterfaceType

type InterfaceType struct {
    Interface  token.Pos  // position of "interface" keyword
    Methods    *FieldList // list of methods
    Incomplete bool       // true if (source) methods are missing in the Methods list
}

An InterfaceType node represents an interface type.

func InterfaceType.End

func (x *InterfaceType) End() token.Pos

func InterfaceType.Pos

func (x *InterfaceType) Pos() token.Pos

type KeyValueExpr

type KeyValueExpr struct {
    Key   Expr
    Colon token.Pos // position of ":"
    Value Expr
}

A KeyValueExpr node represents (key : value) pairs in composite literals.

func KeyValueExpr.End

func (x *KeyValueExpr) End() token.Pos

func KeyValueExpr.Pos

func (x *KeyValueExpr) Pos() token.Pos

type LabeledStmt

type LabeledStmt struct {
    Label *Ident
    Colon token.Pos // position of ":"
    Stmt  Stmt
}

A LabeledStmt node represents a labeled statement.

func LabeledStmt.End

func (s *LabeledStmt) End() token.Pos

func LabeledStmt.Pos

func (s *LabeledStmt) Pos() token.Pos

type MapType

type MapType struct {
    Map   token.Pos // position of "map" keyword
    Key   Expr
    Value Expr
}

A MapType node represents a map type.

func MapType.End

func (x *MapType) End() token.Pos

func MapType.Pos

func (x *MapType) Pos() token.Pos

type MergeMode

type MergeMode uint

The MergeMode flags control the behavior of MergePackageFiles.

const (
    // If set, duplicate function declarations are excluded.
    FilterFuncDuplicates MergeMode = 1 << iota
    // If set, comments that are not associated with a specific
    // AST node (as Doc or Comment) are excluded.
    FilterUnassociatedComments
    // If set, duplicate import declarations are excluded.
    FilterImportDuplicates
)

type Node

type Node interface {
    Pos() token.Pos // position of first character belonging to the node
    End() token.Pos // position of first character immediately after the node
}

All node types implement the Node interface.

type ObjKind

type ObjKind int

ObjKind describes what an object represents.

const (
    Bad ObjKind = iota // for error handling
    Pkg                // package
    Con                // constant
    Typ                // type
    Var                // variable
    Fun                // function or method
    Lbl                // label
)

The list of possible Object kinds.

func ObjKind.String

func (kind ObjKind) String() string

type Object

type Object struct {
    Kind ObjKind
    Name string      // declared name
    Decl interface{} // corresponding Field, XxxSpec, FuncDecl, LabeledStmt, AssignStmt, Scope; or nil
    Data interface{} // object-specific data; or nil
    Type interface{} // placeholder for type information; may be nil
}

An Object describes a named language entity such as a package, constant, type, variable, function (incl. methods), or label.

The Data fields contains object-specific data:

Kind    Data type         Data value
Pkg     *Scope            package scope
Con     int               iota for the respective declaration

func NewObj

func NewObj(kind ObjKind, name string) *Object

NewObj creates a new object of a given kind and name.

func Object.Pos

func (obj *Object) Pos() token.Pos

Pos computes the source position of the declaration of an object name. The result may be an invalid position if it cannot be computed (obj.Decl may be nil or not correct).

type Package

type Package struct {
    Name    string             // package name
    Scope   *Scope             // package scope across all files
    Imports map[string]*Object // map of package id -> package object
    Files   map[string]*File   // Go source files by filename
}

A Package node represents a set of source files collectively building a Go package.

func NewPackage

func NewPackage(fset *token.FileSet, files map[string]*File, importer Importer, universe *Scope) (*Package, error)

NewPackage creates a new Package node from a set of File nodes. It resolves unresolved identifiers across files and updates each file's Unresolved list accordingly. If a non-nil importer and universe scope are provided, they are used to resolve identifiers not declared in any of the package files. Any remaining unresolved identifiers are reported as undeclared. If the files belong to different packages, one package name is selected and files with different package names are reported and then ignored. The result is a package node and a scanner.ErrorList if there were errors.

func Package.End

func (p *Package) End() token.Pos

func Package.Pos

func (p *Package) Pos() token.Pos

type ParenExpr

type ParenExpr struct {
    Lparen token.Pos // position of "("
    X      Expr      // parenthesized expression
    Rparen token.Pos // position of ")"
}

A ParenExpr node represents a parenthesized expression.

func ParenExpr.End

func (x *ParenExpr) End() token.Pos

func ParenExpr.Pos

func (x *ParenExpr) Pos() token.Pos

type RangeStmt

type RangeStmt struct {
    For        token.Pos   // position of "for" keyword
    Key, Value Expr        // Key, Value may be nil
    TokPos     token.Pos   // position of Tok; invalid if Key == nil
    Tok        token.Token // ILLEGAL if Key == nil, ASSIGN, DEFINE
    X          Expr        // value to range over
    Body       *BlockStmt
}

A RangeStmt represents a for statement with a range clause.

func RangeStmt.End

func (s *RangeStmt) End() token.Pos

func RangeStmt.Pos

func (s *RangeStmt) Pos() token.Pos

type ReturnStmt

type ReturnStmt struct {
    Return  token.Pos // position of "return" keyword
    Results []Expr    // result expressions; or nil
}

A ReturnStmt node represents a return statement.

func ReturnStmt.End

func (s *ReturnStmt) End() token.Pos

func ReturnStmt.Pos

func (s *ReturnStmt) Pos() token.Pos

type Scope

type Scope struct {
    Outer   *Scope
    Objects map[string]*Object
}

A Scope maintains the set of named language entities declared in the scope and a link to the immediately surrounding (outer) scope.

func NewScope

func NewScope(outer *Scope) *Scope

NewScope creates a new scope nested in the outer scope.

func Scope.Insert

func (s *Scope) Insert(obj *Object) (alt *Object)

Insert attempts to insert a named object obj into the scope s. If the scope already contains an object alt with the same name, Insert leaves the scope unchanged and returns alt. Otherwise it inserts obj and returns nil.

func Scope.Lookup

func (s *Scope) Lookup(name string) *Object

Lookup returns the object with the given name if it is found in scope s, otherwise it returns nil. Outer scopes are ignored.

func Scope.String

func (s *Scope) String() string

Debugging support

type SelectStmt

type SelectStmt struct {
    Select token.Pos  // position of "select" keyword
    Body   *BlockStmt // CommClauses only
}

An SelectStmt node represents a select statement.

func SelectStmt.End

func (s *SelectStmt) End() token.Pos

func SelectStmt.Pos

func (s *SelectStmt) Pos() token.Pos

type SelectorExpr

type SelectorExpr struct {
    X   Expr   // expression
    Sel *Ident // field selector
}

A SelectorExpr node represents an expression followed by a selector.

func SelectorExpr.End

func (x *SelectorExpr) End() token.Pos

func SelectorExpr.Pos

func (x *SelectorExpr) Pos() token.Pos

type SendStmt

type SendStmt struct {
    Chan  Expr
    Arrow token.Pos // position of "<-"
    Value Expr
}

A SendStmt node represents a send statement.

func SendStmt.End

func (s *SendStmt) End() token.Pos

func SendStmt.Pos

func (s *SendStmt) Pos() token.Pos

type SliceExpr

type SliceExpr struct {
    X      Expr      // expression
    Lbrack token.Pos // position of "["
    Low    Expr      // begin of slice range; or nil
    High   Expr      // end of slice range; or nil
    Max    Expr      // maximum capacity of slice; or nil
    Slice3 bool      // true if 3-index slice (2 colons present)
    Rbrack token.Pos // position of "]"
}

An SliceExpr node represents an expression followed by slice indices.

func SliceExpr.End

func (x *SliceExpr) End() token.Pos

func SliceExpr.Pos

func (x *SliceExpr) Pos() token.Pos

type Spec

type Spec interface {
    Node
    // contains filtered or unexported methods
}

The Spec type stands for any of *ImportSpec, *ValueSpec, and *TypeSpec.

type StarExpr

type StarExpr struct {
    Star token.Pos // position of "*"
    X    Expr      // operand
}

A StarExpr node represents an expression of the form "*" Expression. Semantically it could be a unary "*" expression, or a pointer type.

func StarExpr.End

func (x *StarExpr) End() token.Pos

func StarExpr.Pos

func (x *StarExpr) Pos() token.Pos

type Stmt

type Stmt interface {
    Node
    // contains filtered or unexported methods
}

All statement nodes implement the Stmt interface.

type StructType

type StructType struct {
    Struct     token.Pos  // position of "struct" keyword
    Fields     *FieldList // list of field declarations
    Incomplete bool       // true if (source) fields are missing in the Fields list
}

A StructType node represents a struct type.

func StructType.End

func (x *StructType) End() token.Pos

func StructType.Pos

func (x *StructType) Pos() token.Pos

type SwitchStmt

type SwitchStmt struct {
    Switch token.Pos  // position of "switch" keyword
    Init   Stmt       // initialization statement; or nil
    Tag    Expr       // tag expression; or nil
    Body   *BlockStmt // CaseClauses only
}

A SwitchStmt node represents an expression switch statement.

func SwitchStmt.End

func (s *SwitchStmt) End() token.Pos

func SwitchStmt.Pos

func (s *SwitchStmt) Pos() token.Pos

type TypeAssertExpr

type TypeAssertExpr struct {
    X      Expr      // expression
    Lparen token.Pos // position of "("
    Type   Expr      // asserted type; nil means type switch X.(type)
    Rparen token.Pos // position of ")"
}

A TypeAssertExpr node represents an expression followed by a type assertion.

func TypeAssertExpr.End

func (x *TypeAssertExpr) End() token.Pos

func TypeAssertExpr.Pos

func (x *TypeAssertExpr) Pos() token.Pos

type TypeSpec

type TypeSpec struct {
    Doc     *CommentGroup // associated documentation; or nil
    Name    *Ident        // type name
    Assign  token.Pos     // position of '=', if any
    Type    Expr          // *Ident, *ParenExpr, *SelectorExpr, *StarExpr, or any of the *XxxTypes
    Comment *CommentGroup // line comments; or nil
}

A TypeSpec node represents a type declaration (TypeSpec production).

func TypeSpec.End

func (s *TypeSpec) End() token.Pos

func TypeSpec.Pos

func (s *TypeSpec) Pos() token.Pos

type TypeSwitchStmt

type TypeSwitchStmt struct {
    Switch token.Pos  // position of "switch" keyword
    Init   Stmt       // initialization statement; or nil
    Assign Stmt       // x := y.(type) or y.(type)
    Body   *BlockStmt // CaseClauses only
}

An TypeSwitchStmt node represents a type switch statement.

func TypeSwitchStmt.End

func (s *TypeSwitchStmt) End() token.Pos

func TypeSwitchStmt.Pos

func (s *TypeSwitchStmt) Pos() token.Pos

type UnaryExpr

type UnaryExpr struct {
    OpPos token.Pos   // position of Op
    Op    token.Token // operator
    X     Expr        // operand
}

A UnaryExpr node represents a unary expression. Unary "*" expressions are represented via StarExpr nodes.

func UnaryExpr.End

func (x *UnaryExpr) End() token.Pos

func UnaryExpr.Pos

func (x *UnaryExpr) Pos() token.Pos

type ValueSpec

type ValueSpec struct {
    Doc     *CommentGroup // associated documentation; or nil
    Names   []*Ident      // value names (len(Names) > 0)
    Type    Expr          // value type; or nil
    Values  []Expr        // initial values; or nil
    Comment *CommentGroup // line comments; or nil
}

A ValueSpec node represents a constant or variable declaration (ConstSpec or VarSpec production).

func ValueSpec.End

func (s *ValueSpec) End() token.Pos

func ValueSpec.Pos

func (s *ValueSpec) Pos() token.Pos

type Visitor

type Visitor interface {
    Visit(node Node) (w Visitor)
}

A Visitor's Visit method is invoked for each node encountered by Walk. If the result visitor w is not nil, Walk visits each of the children of node with the visitor w, followed by a call of w.Visit(nil).