os: RemoveAll hangs on a path longer than 260 characters on Windows versions before Windows 10 1607

[bsamek]

On Go 1.13.5 on Windows 2008 R2, running os.RemoveAll on a directory that contains a path longer than 260 characters hangs.

In the following repro, the directory is created, and then the program hangs on os.RemoveAll.

package main

import (
	"log"
	"os"
	"path/filepath"
)

func main() {
	// make a long path
	a := ""
	b := ""
	for i := 0; i < 150; i++ {
		a += "a"
		b += "b"
	}
	wd, err := os.Getwd()
	if err != nil {
		log.Fatal(err)
	}
	err = os.MkdirAll(filepath.Join(wd, "foo", "bar", a, b), 0755)
	if err != nil {
		log.Fatal(err)
	}

	// remove the root of the long path
	err = os.RemoveAll("foo")
	if err != nil {
		log.Fatal(err)
	}
}

[ALTree]

Previously: #3358

[networkimprov]

cc @zx2c4 @alexbrainman @mattn

[alexbrainman]

@bsamek I can reproduce it here, thank you very much.

The problem is that

os.RemoveAll("foo")

calls

os.Remove(`foo\bar\aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb`)

which calls

syscall.RemoveDirectory(`foo\bar\aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb`)

which fails, because syscalls don't allow for relative path to be longer than 256 chars. But syscall.RemoveDirectory should succeeds, because directory exists and can be deleted.

Path is converted with os.fixLongPath in os.Remove, but os.fixLongPath does not handle relative path, and returns them as is.

Alex

[networkimprov]

Could os.RemoveAll() construct an absolute path and pass that to os.Remove() ?

[gopherbot]

Change https://golang.org/cl/214437 mentions this issue: os: handle long path in RemoveAll for windows

[networkimprov]

I don't think that fix is correct...

[gopherbot]

Change https://golang.org/cl/214598 mentions this issue: os: actually remove long path in TestRemoveAll

[gopherbot]

Change https://golang.org/cl/214601 mentions this issue: Revert "os: handle long path in RemoveAll for windows"

[ianlancetaylor]

Patch was reverted, so reopening issue.