testing: `T.TempDir` does not clean illegal characters correctly on Go 1.16.13

[Juneezee]

What version of Go are you using (go version)?

$ go version
go version go1.16.13 windows/amd64

Does this issue reproduce with the latest release?

• Go 1.17.6: No
• Go 1.16.13: Yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
  set GO111MODULE=
  set GOARCH=amd64
  set GOBIN=
  set GOCACHE=C:\Users\runneradmin\AppData\Local\go-build
  set GOENV=C:\Users\runneradmin\AppData\Roaming\go\env
  set GOEXE=.exe
  set GOFLAGS=
  set GOHOSTARCH=amd64
  set GOHOSTOS=windows
  set GOINSECURE=
  set GOMODCACHE=C:\Users\runneradmin\go\pkg\mod
  set GONOPROXY=
  set GONOSUMDB=
  set GOOS=windows
  set GOPATH=C:\Users\runneradmin\go
  set GOPRIVATE=
  set GOPROXY=https://proxy.golang.org,direct
  set GOROOT=C:\hostedtoolcache\windows\go\1.16.13\x64
  set GOSUMDB=sum.golang.org
  set GOTMPDIR=
  set GOTOOLDIR=C:\hostedtoolcache\windows\go\1.16.13\x64\pkg\tool\windows_amd64
  set GOVCS=
  set GOVERSION=go1.16.13
  set GCCGO=gccgo
  set AR=ar
  set CC=gcc
  set CXX=g++
  set CGO_ENABLED=1
  set GOMOD=NUL
  set CGO_CFLAGS=-g -O2
  set CGO_CPPFLAGS=
  set CGO_CXXFLAGS=-g -O2
  set CGO_FFLAGS=-g -O2
  set CGO_LDFLAGS=-g -O2
  set PKG_CONFIG=pkg-config
  set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=C:\Users\RUNNER~1\AppData\Local\Temp\go-build10994681=/tmp/go-build -gno-record-gcc-switches

What did you do?

package main

import "testing"

func TestTempDir(t *testing.T) {
	tests := []struct {
		name string
	}{
		{
			name: "**aaa",
		},
		{
			name: "bbb**",
		},
		{
			name: "**aaa bbb**",
		},
		{
			name: "subdir/**",
		},
	}

	for _, test := range tests {
		t.Run(test.name, func(t *testing.T) {
			t.TempDir()
		})
	}
}

What did you expect to see?

=== RUN   TestTempDir
--- PASS: TestTempDir (0.00s)
=== RUN   TestTempDir/**aaa
    --- PASS: TestTempDir/**aaa (0.00s)
=== RUN   TestTempDir/bbb**
    --- PASS: TestTempDir/bbb** (0.00s)
=== RUN   TestTempDir/**aaa_bbb**
    --- PASS: TestTempDir/**aaa_bbb** (0.00s)
=== RUN   TestTempDir/subdir/**
    --- PASS: TestTempDir/subdir/** (0.00s)
PASS

What did you see instead?

--- FAIL: TestTempDir (0.00s)
    --- FAIL: TestTempDir/**aaa (0.00s)
        main_test.go:25: TempDir: mkdir C:\Users\RUNNER~1\AppData\Local\Temp\TestTempDir_*1134522990aaa: The filename, directory name, or volume label syntax is incorrect.
    --- FAIL: TestTempDir/bbb** (0.00s)
        main_test.go:25: TempDir: mkdir C:\Users\RUNNER~1\AppData\Local\Temp\TestTempDir_bbb*1840932692: The filename, directory name, or volume label syntax is incorrect.
    --- FAIL: TestTempDir/**aaa_bbb** (0.00s)
        main_test.go:25: TempDir: mkdir C:\Users\RUNNER~1\AppData\Local\Temp\TestTempDir_**aaa_bbb*2013955203: The filename, directory name, or volume label syntax is incorrect.
    --- FAIL: TestTempDir/subdir/** (0.00s)
        main_test.go:25: TempDir: mkdir C:\Users\RUNNER~1\AppData\Local\Temp\TestTempDir_subdir_*1630578384: The filename, directory name, or volume label syntax is incorrect.
FAIL
FAIL	tempdir	0.020s
FAIL

[Juneezee]

This commit 97cee43 fixes the problem. Should it be backported to Go 1.16?

[ianlancetaylor]

I opened #50645 to backport the fix. Thanks.