GO CommentMap用法及代码示例

package main

import (
	"bytes"
	"fmt"
	"go/ast"
	"go/format"
	"go/parser"
	"go/token"
)

func main() {
	// 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())

}

// 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
}