1// Copyright 2018 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package token_test
6
7import (
8	"fmt"
9	"go/ast"
10	"go/parser"
11	"go/token"
12)
13
14func Example_retrievePositionInfo() {
15	fset := token.NewFileSet()
16
17	const src = `package main
18
19import "fmt"
20
21import "go/token"
22
23//line :1:5
24type p = token.Pos
25
26const bad = token.NoPos
27
28//line fake.go:42:11
29func ok(pos p) bool {
30	return pos != bad
31}
32
33/*line :7:9*/func main() {
34	fmt.Println(ok(bad) == bad.IsValid())
35}
36`
37
38	f, err := parser.ParseFile(fset, "main.go", src, 0)
39	if err != nil {
40		fmt.Println(err)
41		return
42	}
43
44	// Print the location and kind of each declaration in f.
45	for _, decl := range f.Decls {
46		// Get the filename, line, and column back via the file set.
47		// We get both the relative and absolute position.
48		// The relative position is relative to the last line directive.
49		// The absolute position is the exact position in the source.
50		pos := decl.Pos()
51		relPosition := fset.Position(pos)
52		absPosition := fset.PositionFor(pos, false)
53
54		// Either a FuncDecl or GenDecl, since we exit on error.
55		kind := "func"
56		if gen, ok := decl.(*ast.GenDecl); ok {
57			kind = gen.Tok.String()
58		}
59
60		// If the relative and absolute positions differ, show both.
61		fmtPosition := relPosition.String()
62		if relPosition != absPosition {
63			fmtPosition += "[" + absPosition.String() + "]"
64		}
65
66		fmt.Printf("%s: %s\n", fmtPosition, kind)
67	}
68
69	// Output:
70	//
71	// main.go:3:1: import
72	// main.go:5:1: import
73	// main.go:1:5[main.go:8:1]: type
74	// main.go:3:1[main.go:10:1]: const
75	// fake.go:42:11[main.go:13:1]: func
76	// fake.go:7:9[main.go:17:14]: func
77}
78