x/tools/gopls: panic using experimentalWorkspaceModule: expected 1 module, got 2

[findleyr]

Just got this panic a couple times at master, while using experimentalWorkspaceModule and working on x/tools. Haven't looked into it yet.

panic: unsupported use of -modfile, expected 1 module, got 2                                                                                      
                                                                                                                                                  
goroutine 582872 [running]:                                              
golang.org/x/tools/internal/lsp/cache.(*snapshot).load(0xc029a0d8c0, 0x1048660, 0xc013ed23f0, 0xc00d5d68c0, 0x3, 0x4, 0x0, 0x0)
        /usr/local/google/home/rfindley/src/tools/internal/lsp/cache/load.go:117 +0x2d0d                  
golang.org/x/tools/internal/lsp/cache.(*snapshot).initialize.func2()                                                                              
        /usr/local/google/home/rfindley/src/tools/internal/lsp/cache/view.go:770 +0x470                   
sync.(*Once).doSlow(0xc01b647260, 0xc0239256f8)                                                                                                   
        /usr/lib/google-golang/src/sync/once.go:66 +0xec                                                                                          
sync.(*Once).Do(...)                                                     
        /usr/lib/google-golang/src/sync/once.go:57                                                                                                
golang.org/x/tools/internal/lsp/cache.(*snapshot).initialize(0xc029a0d8c0, 0x10485a0, 0xc00c5010c0, 0xc00ef64e01)
        /usr/local/google/home/rfindley/src/tools/internal/lsp/cache/view.go:729 +0x1d5
golang.org/x/tools/internal/lsp/cache.(*Session).createView.func3(0xc029a0d8c0, 0x10485a0, 0xc00c5010c0, 0xc00ef65190)
        /usr/local/google/home/rfindley/src/tools/internal/lsp/cache/session.go:237 +0x45
created by golang.org/x/tools/internal/lsp/cache.(*Session).createView                                                                            
        /usr/local/google/home/rfindley/src/tools/internal/lsp/cache/session.go:236 +0x9d0                
exit status 2

CC @stamblerre @heschik

[stamblerre]

Hm, we must have somehow found two modules but not set workspaceMode to useWorkspaceModule--https://github.com/golang/tools/blob/e57f6d466a487e9c19a486ad98e20048ea425bc8/internal/lsp/cache/load.go#L91.

This does make me realize that we add to the modules map unconditionally when things change rather than checking ExperimentalWorkspaceModule, but not relevant here.

[stamblerre]

@pjweinb has been able to reproduce this by opening the src directory of the golang/go repository.

[findleyr]

🤦 it's likely that I was doing the same thing. Thanks Peter for doing a better job of investigating!

[stamblerre]

The issue is that go/src and go/src/cmd have vendor directories, so we don't use the workspace module, but we still have 2 modules in the snapshot's modules. We should probably disqualify modules with vendor directories earlier.

[gopherbot]

Change https://golang.org/cl/259623 mentions this issue: internal/lsp: revert back to one module per view with vendoring