example_test.go

     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  
     5  package token_test
     6  
     7  import (
     8  	"fmt"
     9  	"go/ast"
    10  	"go/parser"
    11  	"go/token"
    12  )
    13  
    14  func Example_retrievePositionInfo() {
    15  	fset := token.NewFileSet()
    16  
    17  	const src = `package main
    18  
    19  import "fmt"
    20  
    21  import "go/token"
    22  
    23  //line :1:5
    24  type p = token.Pos
    25  
    26  const bad = token.NoPos
    27  
    28  //line fake.go:42:11
    29  func 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
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