x/tools/gopls: race to ModuleResolver.moduleCacheCache

[davecheney]

gopls version: v0.7.3
gopls flags:
update flags: proxy
extension version: 0.29.0
go version: devel go1.18-d032b2b2c8
environment: Visual Studio Code darwin
initialization error: undefined
issue timestamp: Sun, 31 Oct 2021 22:55:38 GMT
restart history:
Fri, 29 Oct 2021 12:19:24 GMT: activation (enabled: false)
Sun, 31 Oct 2021 22:31:02 GMT: installation (enabled: true)
Sun, 31 Oct 2021 22:33:56 GMT: installation (enabled: true)

ATTENTION: PLEASE PROVIDE THE DETAILS REQUESTED BELOW.

Describe what you observed.

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x12e6fe2]

goroutine 7181 [running]:
golang.org/x/tools/internal/imports.(*dirInfoCache).Load(0xa8cba40%3F, {0xc0046de000%3F, 0xc004889f10%3F})
	  mod_cache.go:184  0x62
golang.org/x/tools/internal/imports.(*ModuleResolver).cacheLoad(0xc0002b2780, {0xc0046de000, 0x3e})
	  mod.go:273  0xa6
golang.org/x/tools/internal/imports.(*ModuleResolver).findPackage(0xc0002b2780, {0xc00030eea0, 0x10})
	  mod.go:235  0x1f1
golang.org/x/tools/internal/imports.(*ModuleResolver).scoreImportPath(0x0%3F, {0x0%3F, 0x0%3F}, {0xc00030eea0, 0x10})
	  mod.go:512  0x6a
golang.org/x/tools/internal/imports.ScoreImportPaths({0x1b8e288, 0xc006f74000}, 0xc00488a360%3F, {0xc00785a000, 0xa, 0x18f6560%3F})
	  fix.go:670  0xef
golang.org/x/tools/internal/lsp/source/completion.(*completer).unimportedPackages.func1(0x180d9a0%3F)
	  completion.go:1441  0x3f
golang.org/x/tools/internal/lsp/cache.(*importsState).runProcessEnvFunc(0xc0005ed320, {0x1b8e288, 0xc006f74000}, 0xc002cc0900, 0xc00469c210)
	  imports.go:109  0x5a3
golang.org/x/tools/internal/lsp/cache.(*snapshot).RunProcessEnvFunc(0xc00488a728%3F, {0x1b8e288%3F, 0xc006f74000%3F}, 0x400%3F)
	  view.go:332  0x34
golang.org/x/tools/internal/lsp/source/completion.(*completer).unimportedPackages(0xc000160a00, {0x1b8e288, 0xc006f74000}, 0xc00469c0f0)
	  completion.go:1439  0x47c
golang.org/x/tools/internal/lsp/source/completion.(*completer).lexical(0xc000160a00, {0x1b8e288, 0xc006f74000})
	  completion.go:1371  0x749
golang.org/x/tools/internal/lsp/source/completion.(*completer).collectCompletions(0xc000160a00, {0x1b8e288%3F, 0xc006f74000%3F})
	  completion.go:626  0x3d4
golang.org/x/tools/internal/lsp/source/completion.Completion({0x1b8e218%3F, 0xc00242c680%3F}, {0x1b95990%3F, 0xc002cc0900%3F}, {0x1b8ec50%3F, 0xc004442180%3F}, {0x2b8f328%3F, 0xc0%3F}, {0x3ff0000000000000, {0x0, ...}})
	  completion.go:551  0xfe9
golang.org/x/tools/internal/lsp.(*Server).completion(0xc006a7e9b8%3F, {0x1b8e218, 0xc00242c680}, 0xc005384cd0)
	  completion.go:32  0x24c
golang.org/x/tools/internal/lsp.(*Server).Completion(0xc002c6c9a0%3F, {0x1b8e218%3F, 0xc00242c680%3F}, 0x17f9d60%3F)
	  server_gen.go:32  0x25
golang.org/x/tools/internal/lsp/protocol.serverDispatch({0x1b8e218, 0xc00242c680}, {0x1b98be0, 0xc000288240}, 0xc0039e20f0, {0x1b8e480, 0xc00242c600})
	  tsserver.go:382  0x18dd
golang.org/x/tools/internal/lsp/protocol.ServerHandler.func1({0x1b8e218, 0xc00242c680}, 0xc0039e20f0, {0x1b8e480, 0xc00242c600})
	  protocol.go:154  0x90
golang.org/x/tools/internal/lsp/lsprpc.handshaker.func1({0x1b8e218, 0xc00242c680}, 0xc0039e20f0, {0x1b8e480%3F, 0xc00242c600%3F})
	  lsprpc.go:506  0xa43
golang.org/x/tools/internal/jsonrpc2.MustReplyHandler.func1({0x1b8e218, 0xc00242c680}, 0xc003178978, {0x1b8e480%3F, 0xc00242c600%3F})
	  handler.go:35  0xf6
golang.org/x/tools/internal/jsonrpc2.AsyncHandler.func1.2()
	  handler.go:103  0xa3
created by golang.org/x/tools/internal/jsonrpc2.AsyncHandler.func1
	  handler.go:100  0x20a
[Error - 9:40:47 AM] 

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[findleyr]

This is a bug (a race) in x/tools.

Notes:

• looks like it's possible to reach the ModuleResolver.moduleCacheCache before initialization.
• from discussion with @heschi, it might be OK to eagerly initialize in ProcessEnv.GetResolver: presumably by the time we get the resolver we actually need it. There may be edge cases, however.

[findleyr]

I just realized that https://go.dev/cl/492679 should fix this.