os: make MkdirAll support volume names

MkdirAll fails to create directories under root paths using volume
names (e.g. //?/Volume{GUID}/foo). This is because fixRootDirectory
only handle extended length paths using drive letters (e.g. //?/C:/foo).

This CL fixes that issue by also detecting volume names without path
separator.

Updates #22230
Fixes #39785

Change-Id: I813fdc0b968ce71a4297f69245b935558e6cd789
Reviewed-on: https://go-review.googlesource.com/c/go/+/517015
Run-TryBot: Quim Muntal <quimmuntal@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

1 files changed, 49 insertions, 0 deletions

diff --git a/src/os/path_windows_test.go b/src/os/path_windows_test.go
index 2506b4f0d8..4e5e501d1f 100644
--- a/src/os/path_windows_test.go
+++ b/src/os/path_windows_test.go
@@ -5,7 +5,11 @@
 package os_test
 
 import (
+	"fmt"
+	"internal/syscall/windows"
+	"internal/testenv"
 	"os"
+	"path/filepath"
 	"strings"
 	"syscall"
 	"testing"
@@ -106,3 +110,48 @@ func TestOpenRootSlash(t *testing.T) {
 		dir.Close()
 	}
 }
+
+func testMkdirAllAtRoot(t *testing.T, root string) {
+	// Create a unique-enough directory name in root.
+	base := fmt.Sprintf("%s-%d", t.Name(), os.Getpid())
+	path := filepath.Join(root, base)
+	if err := os.MkdirAll(path, 0777); err != nil {
+		t.Fatalf("MkdirAll(%q) failed: %v", path, err)
+	}
+	// Clean up
+	if err := os.RemoveAll(path); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestMkdirAllExtendedLengthAtRoot(t *testing.T) {
+	if testenv.Builder() == "" {
+		t.Skipf("skipping non-hermetic test outside of Go builders")
+	}
+
+	const prefix = `\\?\`
+	vol := filepath.VolumeName(t.TempDir()) + `\`
+	if len(vol) < 4 || vol[:4] != prefix {
+		vol = prefix + vol
+	}
+	testMkdirAllAtRoot(t, vol)
+}
+
+func TestMkdirAllVolumeNameAtRoot(t *testing.T) {
+	if testenv.Builder() == "" {
+		t.Skipf("skipping non-hermetic test outside of Go builders")
+	}
+
+	vol, err := syscall.UTF16PtrFromString(filepath.VolumeName(t.TempDir()) + `\`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	const maxVolNameLen = 50
+	var buf [maxVolNameLen]uint16
+	err = windows.GetVolumeNameForVolumeMountPoint(vol, &buf[0], maxVolNameLen)
+	if err != nil {
+		t.Fatal(err)
+	}
+	volName := syscall.UTF16ToString(buf[:])
+	testMkdirAllAtRoot(t, volName)
+}