os: TestUserConfigDir and TestUserCacheDir expect writable $HOME on linux

[zhsj]

Go version

go version go1.22rc1 linux/amd64

Output of go env in your module/workspace:

GO111MODULE='on'
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/zsj/.cache/go-build'
GOENV='/home/zsj/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/zsj/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/zsj/go'
GOPRIVATE=''
GOPROXY='https://goproxy.cn'
GOROOT='/home/zsj/Workspaces/debian/package/pkg-go/build-area/x/usr/lib/go-1.22'
GOSUMDB='sum.golang.google.cn'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/home/zsj/Workspaces/debian/package/pkg-go/build-area/x/usr/lib/go-1.22/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.22rc1'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build3035930955=/tmp/go-build -gno-record-gcc-switches'

What did you do?

Building Go 1.22 on Debian build system.

What did you see happen?

https://buildd.debian.org/status/fetch.php?pkg=golang-1.22&arch=arm64&ver=1.22%7Erc1-1&stamp=1704505334&raw=0

--- FAIL: TestUserConfigDir (0.00s)
    os_test.go:2874: could not create UserConfigDir: mkdir /sbuild-nonexistent: permission denied
--- FAIL: TestUserCacheDir (0.00s)
    os_test.go:2851: could not create UserCacheDir: mkdir /sbuild-nonexistent: permission denied

What did you expect to see?

Build successfully without distro patch.

While reading #57630 and #57638, @bcmills said

Perhaps it should return an error if the chosen directory is not writable

However UserConfigDir and UserCacheDir don't report such error, and only the tests expect the returned paths are writable.

The Debian build system is intentionally configured to have a non-writable $HOME dir. Previously the Debian package carries a patch to skip TestUserHomeDir which failed if $HOME is not writable. However this is fixed in bb4ea80. But for the new added TestUserConfigDir and TestUserCacheDir, they fail again.

[bcmills]

Hmm, the XDG spec does seem to explicitly allow non-writable directories:

If, when attempting to write a file, the destination directory is non-existent an attempt should be made to create it with permission 0700. If the destination directory exists already the permissions should not be changed. The application should be prepared to handle the case where the file could not be written, either because the directory was non-existent and could not be created, or for any other reason. In such case it may choose to present an error message to the user.

So perhaps the tests should be converted to examples instead.

[gopherbot]

Change https://go.dev/cl/554815 mentions this issue: os: relax tests and add examples for UserCacheDir and UserConfigDir