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// Copyright 2012 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 ast_test
import (
"bytes"
"fmt"
"go/ast"
"go/format"
"go/parser"
"go/token"
)
// This example demonstrates how to inspect the AST of a Go program.
func ExampleInspect() {
// 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
}
// This example shows what an AST looks like when printed for debugging.
func ExamplePrint() {
// 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 }
}
// This example illustrates how to remove a variable declaration
// in a Go program while maintaining correct comment association
// using an ast.CommentMap.
func ExampleCommentMap() {
// 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.
f.Decls = removeFirstVarDecl(f.Decls)
// 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 removeFirstVarDecl(list []ast.Decl) []ast.Decl {
for i, decl := range list {
if gen, ok := decl.(*ast.GenDecl); ok && gen.Tok == token.VAR {
copy(list[i:], list[i+1:])
return list[:len(list)-1]
}
}
panic("variable declaration not found")
}
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