go rename

a.go

package main

import (
	"bytes"
	"go/format"
	"go/types"
	"io/ioutil"

	"golang.org/x/tools/go/packages"
)

func main() {

	// load std
	pkgs, err := packages.Load(
		&packages.Config{
			Mode: packages.NeedTypesInfo |
				packages.NeedTypes |
				packages.NeedSyntax |
				packages.NeedName,
		},
		"std",
	)
	if err != nil {
		panic(err)
	}
	if packages.PrintErrors(pkgs) > 0 {
		return
	}

	// find fmt.Sprintf object
	var obj types.Object
	for _, pkg := range pkgs {
		if pkg.Name != "fmt" {
			continue
		}
		obj = pkg.Types.Scope().Lookup("Sprintf")
		break
	}
	if obj == nil {
		panic("fmt.Sprintf not found")
	}

	for _, pkg := range pkgs {

		// find all fmt.Sprintf usages and rename identifiers
		affectedFiles := make(map[string]bool)
		for ident, o := range pkg.TypesInfo.Uses {
			if o == obj {
				ident.Name = "foobarbaz"
				affectedFiles[pkg.Fset.File(ident.Pos()).Name()] = true
			}
		}

		// write updated files
		for _, file := range pkg.Syntax {
			filePath := pkg.Fset.File(file.Pos()).Name()
			if _, ok := affectedFiles[filePath]; ok {
				buf := new(bytes.Buffer)
				if err := format.Node(buf, pkg.Fset, file); err != nil {
					panic(err)
				}
				if err := ioutil.WriteFile(filePath, buf.Bytes(), 0644); err != nil {
					panic(err)
				}
			}
		}

	}

}