1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
|
// 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.
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]
break
}
}
// 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
// }
}
|
