x/tools/gopls: crash during internal/imports.scanDirForPackage (crash)

[Sangwaniya]

gopls version: v0.15.3/go1.21.6
gopls flags:
update flags: proxy
extension version: 0.41.4
environment: Visual Studio Code win32
initialization error: undefined
issue timestamp: Thu, 02 May 2024 17:33:19 GMT
restart history:
Thu, 02 May 2024 17:30:10 GMT: activation (enabled: true)

ATTENTION: PLEASE PROVIDE THE DETAILS REQUESTED BELOW.

Describe what you observed.

panic: runtime error: slice bounds out of range [45:44]

goroutine 7611 [running]:
golang.org/x/tools/internal/imports.(*ModuleResolver).scanDirForPackage(0xc001898420, {{0xc004182665%3F, 0x81c8a92bb60e9ba5%3F}, 0x8%3F}, {0xc008108db0, 0x2c})
	  mod.go:727  0x705
golang.org/x/tools/internal/imports.(*ModuleResolver).scan.func3({{0xc004182665%3F, 0xdc5e20%3F}, 0xc0067f8f90%3F}, {0xc008108db0%3F, 0x17d12a8%3F})
	  mod.go:601  0x50
golang.org/x/tools/internal/gopathwalk.(*walker).walk(0xc0067b7830, {0xc0071f8100, 0x37}, 0x0, {0x1200af8, 0xc0071f0380})
	  walk.go:268  0x3d7
golang.org/x/tools/internal/gopathwalk.(*walker).walk(0xc0067b7830, {0xc004182665, 0x2c}, 0x0, {0x1200b30, 0xc0067f8f70})
	  walk.go:334  0x87b
golang.org/x/tools/internal/gopathwalk.walkDir({{0xc004182665%3F, 0xc0045a5f18%3F}, 0xc0045a5f18%3F}, 0xc0067f8f40, 0xc0067f8f30, {0x0%3F, 0x40%3F, 0x4%3F})
	  walk.go:120  0x366
golang.org/x/tools/internal/gopathwalk.WalkSkip(...)
	  walk.go:77
golang.org/x/tools/internal/imports.(*ModuleResolver).scan.func4()
	  mod.go:626  0x2db
created by golang.org/x/tools/internal/imports.(*ModuleResolver).scan in goroutine 4670
	  mod.go:610  0x465

gopls stats -anon

{ "DirStats": { "Files": 2035, "TestdataFiles": 0, "GoFiles": 1626, "ModFiles": 2, "Dirs": 528 }, "GOARCH": "amd64", "GOOS": "windows", "GOPACKAGESDRIVER": "", "GOPLSCACHE": "", "GoVersion": "go1.21.6", "GoplsVersion": "v0.15.3", "InitialWorkspaceLoadDuration": "7.6558984s", "MemStats": { "HeapAlloc": 31132976, "HeapInUse": 41328640, "TotalAlloc": 79278536 }, "WorkspaceStats": { "Files": { "Total": 2207, "Largest": 1654271, "Errs": 0 }, "Views": [ { "GoCommandVersion": "go1.21.6", "AllPackages": { "Packages": 417, "LargestPackage": 134, "CompiledGoFiles": 2217, "Modules": 49 }, "WorkspacePackages": { "Packages": 0, "LargestPackage": 0, "CompiledGoFiles": 0, "Modules": 0 }, "Diagnostics": 0 } ] } }

OPTIONAL: If you would like to share more information, you can attach your complete gopls logs.

NOTE: THESE MAY CONTAIN SENSITIVE INFORMATION ABOUT YOUR CODEBASE.
DO NOT SHARE LOGS IF YOU ARE WORKING IN A PRIVATE REPOSITORY.

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[hyangah]

Thanks for the report @Sangwaniya
Transferring to the gopls issue tracker.

[adonovan]

Looks like root.Path has the same length as dir, but is not a prefix of it.

func (r *ModuleResolver) scanDirForPackage(root gopathwalk.Root, dir string) directoryPackageInfo {
	subdir := ""
	if dir != root.Path {
		subdir = dir[len(root.Path)+len("/"):] // slice bounds out of range [45:44]
	}

[findleyr]

Moving to the v0.17.0 milestone, since this seems to be affecting only one user (and in golang/vscode-go#3401 (comment), it appears that the cause may be related to a modified GOROOT).

[Sangwaniya]

hi @findleyr even after correcting the path and rebuilding gopls, still gopls is crashing
Here are the logs:
gopls version: v0.15.3/go1.21.6
gopls flags:
update flags: proxy
extension version: 0.41.4
environment: Visual Studio Code win32
initialization error: undefined
issue timestamp: Fri, 31 May 2024 05:05:47 GMT
restart history:
Fri, 31 May 2024 05:00:53 GMT: activation (enabled: true)

ATTENTION: PLEASE PROVIDE THE DETAILS REQUESTED BELOW.

Describe what you observed.

panic: runtime error: slice bounds out of range [45:44]

goroutine 1561 [running]:
golang.org/x/tools/internal/imports.(*ModuleResolver).scanDirForPackage(0xc00099c210, {{0xc000580de5%3F, 0x336f25b8b5a7258c%3F}, 0x8%3F}, {0xc0007dd1d0, 0x2c})
	  mod.go:727  0x705
golang.org/x/tools/internal/imports.(*ModuleResolver).scan.func3({{0xc000580de5%3F, 0x1215e20%3F}, 0xc000737ca0%3F}, {0xc0007dd1d0%3F, 0x1c212a8%3F})
	  mod.go:601  0x50
golang.org/x/tools/internal/gopathwalk.(*walker).walk(0xc000770cf0, {0xc000617a00, 0x37}, 0x0, {0x1650af8, 0xc0001bac40})
	  walk.go:268  0x3d7
golang.org/x/tools/internal/gopathwalk.(*walker).walk(0xc000770cf0, {0xc000580de5, 0x2c}, 0x0, {0x1650b30, 0xc000737c60})
	  walk.go:334  0x87b
golang.org/x/tools/internal/gopathwalk.walkDir({{0xc000580de5%3F, 0xc000bdff18%3F}, 0xc000bdff18%3F}, 0xc000737bf0, 0xc000737be0, {0x0%3F, 0x0%3F, 0x4%3F})
	  walk.go:120  0x366
golang.org/x/tools/internal/gopathwalk.WalkSkip(...)
	  walk.go:77
golang.org/x/tools/internal/imports.(*ModuleResolver).scan.func4()
	  mod.go:626  0x2db
created by golang.org/x/tools/internal/imports.(*ModuleResolver).scan in goroutine 226
	  mod.go:610  0x465

gopls stats -anon

{ "DirStats": { "Files": 2172, "TestdataFiles": 0, "GoFiles": 1626, "ModFiles": 2, "Dirs": 555 }, "GOARCH": "amd64", "GOOS": "windows", "GOPACKAGESDRIVER": "", "GOPLSCACHE": "", "GoVersion": "go1.21.6", "GoplsVersion": "v0.15.3", "InitialWorkspaceLoadDuration": "1.1454599s", "MemStats": { "HeapAlloc": 2580040, "HeapInUse": 5332992, "TotalAlloc": 36334560 }, "WorkspaceStats": { "Files": { "Total": 1, "Largest": 3429, "Errs": 0 }, "Views": [ { "GoCommandVersion": "go1.21.6", "AllPackages": { "Packages": 0, "LargestPackage": 0, "CompiledGoFiles": 0, "Modules": 0 }, "WorkspacePackages": { "Packages": 0, "LargestPackage": 0, "CompiledGoFiles": 0, "Modules": 0 }, "Diagnostics": 0 } ] } }

OPTIONAL: If you would like to share more information, you can attach your complete gopls logs.

NOTE: THESE MAY CONTAIN SENSITIVE INFORMATION ABOUT YOUR CODEBASE.
DO NOT SHARE LOGS IF YOU ARE WORKING IN A PRIVATE REPOSITORY.

<OPTIONAL: ATTACH LOGS HERE>

[hyangah]

golang/vscode-go#3456 is another crash report. The report came from Linux. (@feldgendler by any chance, are you using a modified go, or GOROOT source?)

[feldgendler]

My Go comes from an official tarball, GOROOT is not set.

[feldgendler]

I tried adding debug prints just before the crash.

Just before the crashing subdir = dir[len(root.Path)+len("/"):] line,

root.Path is /home/alexey/onboard/legio/bin/../tools/deps/../../_deps/go@1.22.5/pkg/mod
dir is /home/alexey/onboard/legio/_deps/go@1.22.5/pkg/mod/mvdan.cc/gofumpt@v0.6.0

They just accidentally happen to have the same length.

[findleyr]

Thanks @feldgendler, that's useful information that the paths are completely unrelated. That suggests the bug is elsewhere (in the code that expects scanned directories to be a subdirectory of the root...).

My first guess is that there's something related to symlinks, but we'll need to investigate.

[feldgendler]

In /home/alexey/onboard/legio/bin, I have a few symlinks like this: dlv -> ../tools/deps/trampoline.sh. None of the symlinks point to a directory, but some of them point ot a file under ../tools/deps, which might explain the /home/alexey/onboard/legio/bin/../tools/deps prefix. However, that deps directory doesn't contain any symlinks, just plain files.

Now, I'd very much like to help debugging this because this bug is making my IDE almost completely useless. I don't understand the idea behind the code here — what should it really do with symlinks? Does it need to resolve them at all?

[findleyr]

Thanks, I will have more time to help investigate this later today.

In general, the philosophy around symlinks is:

1. Don't rewrite paths: treat symlink paths like any other path, but...
2. Keep track of symlinked directories to break cycles.

The code in question is very old, but has recently been modified to fix other bugs. It seems quite likely that some modification introduced a buggy handling of symlinks.

[feldgendler]

Thanks! Meanwhile, I tried replacing the crashing line with this:

	if s, ok := strings.CutPrefix(dir, root.Path+"/"); ok {
		subdir = s
	}

It seems to express the intent of the original line in a more robust way — assuming I understood it right.

This change seems to fix the issue for me — at least the scan now finishes without crashing.

[findleyr]

@feldgendler yes, at a minimum we'll do something like that. Now that we have a someone reproducing the issue, it would be great if we could track down the root cause.

If you don't mind, later today or tomorrow I'm going to come up with a list of things for you to check, which will help us narrow this down. In the meantime, please use your patch to unblock your work.

[feldgendler]

Sure! Thanks a lot.

[findleyr]

D'oh, I only just noticed that the scanned dir actually is a subdirectory of the root... if you clean the Root path.

Presumably you have a relative GOPATH, GOROOT, or replace directive, and that is being mishandled by goimports. I'm pretty confident that I can reproduce this -- peeking at the code indeed indicates that roots are not clean, and yet scanned directories are.

Thanks for taking the time to debug.

[feldgendler]

Is there anything else I can do to help you here?

[findleyr]

@feldgendler I've reproduced this crash in a test, and will send a fix shortly. If you could confirm that go env GOMODCACHE is unclean (includes /../), that would help me confirm that the context of my reproducer is accurate.

[gopherbot]

Change https://go.dev/cl/603635 mentions this issue: internal/imports: use clean GOMODCACHE for the scan root directory

[Sangwaniya]

@feldgendler yes correct

[feldgendler]

GOMODCACHE=/home/alexey/onboard/legio/bin/../tools/deps/../../_deps/go@1.22.5/pkg/mod

[feldgendler]

I just tested v0.16.2-pre.1, and the crash still happens.

[findleyr]

@feldgendler indeed we have not yet cherry-picked the fix to a prerelease (we were actually just testing our new release automation when we cut -pre.1). We will fix in a -pre.2, thanks.

[feldgendler]

I'm not good at this syntax — is there a Go version expression I could use with go install to test the fix?

[findleyr]

@feldgendler the best way to test the fix would be to install gopls@master, which you can do with the following command (we need to install from source as there is a replace directive in the gopls go.mod file during development).

git clone go.googlesource.com/tools
cd tools/gopls
go install

[feldgendler]

No crash when installed in this way, thank you!

[dottedmag]

(we need to install from source as there is a replace directive in the gopls go.mod file during development)

Is this a leftover from before workspaces were added, or is there a reason to keep this replacement instead of go.work?

[findleyr]

@dottedmag this is from before workspaces were added, but no we keep it because best practice is to not check in go.work files (see documentation here: https://go.dev/ref/mod#go-work-file).

In particular, while correctness requires that golang.org/x/tools/gopls imports the local golang.org/x/tools during development (because it uses the internals of x/tools), we want to support developers working on additional modules if they so choose. Checking in a go.work would circumvent that choice.