x/tools/cmd/gorename: renaming clobbers files that import "C"

[alandonovan]

If a renaming edits a file that imports "C", that file gets completely overwritten by the result of cgo preprocessing (and renaming) applied to that file, potentially destroying source code:

$ cat test.go 
package test

/* #include <stdio.h> */
import "C"

func f() { C.puts(nil) }
$ cat test2.go 
package test

func _() { f() }
$ gorename -from test::f -to g
Renamed 2 occurrences in 2 files in 1 package.
$ cat test.go 
// Created by cgo - DO NOT EDIT

//line /usr/local/google/home/adonovan/go/src/test/test.go:1
package test

//line /usr/local/google/home/adonovan/go/src/test/test.go:7

//line /usr/local/google/home/adonovan/go/src/test/test.go:6
func g() { _Cfunc_puts(nil) }
$ cat test2.go 
package test

func _() { g() }

[mdempsky]

FYI, my test case was to rename p to q here:

package main

/*
#include <stdio.h>
void put(int* x) {
  printf("%p\n", x);
}
*/
import "C"

var p *C.int

func main() {
    C.put(p)
}

[gopherbot]

CL https://golang.org/cl/45930 mentions this issue.