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
}