x/tools/gopls/internal/lsp/filecache: failures on android with read-only file system as of CL 443099

[bcmills]

https://build.golang.org/log/5b087fd350cb4eca1112dd3b79f8b74c1a2ef301:

2022/12/19 16:09:17 New session
	create_session=1
2022/12/19 16:09:17 go env for /data/local/tmp/go_android_exec/cmd.test-20630/fake3265390175
(root /data/local/tmp/go_android_exec/cmd.test-20630/fake3265390175)
(go version go version devel 0b2ad1d815ea8967c49b32d848b2992d0c588d88 android/386)
(valid build configuration = true)
(build flags: [])
GOSUMDB=sum.golang.org
GOINSECURE=
GOMOD=/data/local/tmp/go_android_exec/cmd.test-20630/fake3265390175/go.mod
GOPRIVATE=
GOWORK=
GOMODCACHE=/data/local/tmp/go_android_exec/cmd.test-20630/gopath/pkg/mod
GOPROXY=http://gk3-services-nap-jetxd907-8f582974-4wn4.c.symbolic-datum-552.internal:30157
GOPATH=/data/local/tmp/go_android_exec/cmd.test-20630/gopath
GOROOT=/data/local/tmp/go_android_exec/goroot
GOFLAGS=
GONOSUMDB=
GO111MODULE=
GONOPROXY=
GOCACHE=/data/local/tmp/go_android_exec/gocache

2022/12/19 16:09:17 go/packages.Load #1: err: exit status 2: stderr: go: no such tool "compile"

	snapshot=0
	directory=file:///data/local/tmp/go_android_exec/cmd.test-20630/fake3265390175
	query=[builtin fake/...]
	packages=0
2022/12/19 16:09:17 initial workspace load failed: packages.Load error: err: exit status 2: stderr: go: no such tool "compile"

2022/12/19 16:09:17 workspace packages: diagnosing file:///data/local/tmp/go_android_exec/cmd.test-20630/fake3265390175/go.mod: packages.Load error: err: exit status 2: stderr: go: no such tool "compile"

2022/12/19 16:09:17 errors loading workspace: packages.Load error: err: exit status 2: stderr: go: no such tool "compile"

	snapshot=0
	directory=file:///data/local/tmp/go_android_exec/cmd.test-20630/fake3265390175
2022/12/19 16:09:17 go/packages.Load #2
	snapshot=2
	directory=file:///data/local/tmp/go_android_exec/cmd.test-20630/fake3265390175
	query=[file=/data/local/tmp/go_android_exec/cmd.test-20630/fake3265390175/fake.go]
	packages=1
2022/12/19 16:09:17 go/packages.Load #2
	snapshot=2
	directory=file:///data/local/tmp/go_android_exec/cmd.test-20630/fake3265390175
	package="command-line-arguments"
	files=[/data/local/tmp/go_android_exec/cmd.test-20630/fake3265390175/fake.go]
2022/12/19 16:09:17 go/packages.Load #2: updating metadata for 1 packages
2022/12/19 16:09:17 go/packages.Load #4
	snapshot=2
	directory=file:///data/local/tmp/go_android_exec/cmd.test-20630/fake3265390175
	query=[file=/data/local/tmp/go_android_exec/cmd.test-20630/fake3265390175/fake.go]
	packages=1
2022/12/19 16:09:17 go/packages.Load #4
	snapshot=2
	directory=file:///data/local/tmp/go_android_exec/cmd.test-20630/fake3265390175
	package="command-line-arguments"
	files=[/data/local/tmp/go_android_exec/cmd.test-20630/fake3265390175/fake.go]
2022/12/19 16:09:17 go/packages.Load #4: updating metadata for 0 packages
2022/12/19 16:09:17 can't create cache: mkdir /.cache: read-only file system
exitcode=1
FAIL	golang.org/x/tools/gopls/internal/lsp/cmd	8.525s
…
2022/12/19 16:09:19 can't create cache: mkdir /.cache: read-only file system
exitcode=1
FAIL	golang.org/x/tools/gopls/internal/lsp/filecache	9.302s

[bcmills]

(CC @golang/android)

I'm not sure how it's ending up trying to create /.cache: it is using GOPLS_CACHE, then falling back to os.UserCacheDir(), and finally os.TempDir(). It seems plausible that neither $XDG_CACHE_HOME nor $HOME is defined on Android, but in that case os.userCacheDir() should be returning an error instead of /.cache.

(Maybe $HOME on the device is being explicitly set to /?)

[adonovan]

I agree with your analysis., and this testdata file is evidence that HOME is indeed (or once was) set to /. But I would argue that setting HOME to / without setting XDG_CACHE_HOME is a misconfiguration since it will cause os.UserCacheDir() to fail always.

Or are applications supposed to substitute /tmp/whatever when UserCacheDir fails? That would seem to violate the spirit of "[Applications] should create their own application-specific subdirectory within [UserCacheDir] and use that."

[bcmills]

I don't see any tests at all that exercise os.UserCacheDir. Is that really possible? 😵‍💫

(https://cs.opensource.google/search?q=UserCacheDir&ss=go%2Fgo)

[bcmills]

Indeed, it seems that UserCacheDir lacks tests entirely (filed as #57638). Perhaps it should return an error if the chosen directory is not writable, so that the caller can fall back to something more reasonable.

[adonovan]

In that case it should probably attempt to create the cache directory.

[findleyr]

@adonovan is there anything to do here, following https://go.dev/cl/460917? Can we close?