x/tools/gopls: SignatureHelp crash (reported by telemetry)

[adonovan]

This stack GpSf_A was reported by telemetry:

crash/crash
runtime.gopanic:+69
runtime.panicmem:=261
runtime.sigpanic:+19
golang.org/x/tools/gopls/internal/server.(*server).SignatureHelp:+7
golang.org/x/tools/gopls/internal/protocol.serverDispatch:+544
golang.org/x/tools/gopls/internal/lsprpc.(*streamServer).ServeStream.ServerHandler.func3:+5
golang.org/x/tools/gopls/internal/lsprpc.(*streamServer).ServeStream.handshaker.func4:+52
golang.org/x/tools/gopls/internal/protocol.Handlers.MustReplyHandler.func1:+2
golang.org/x/tools/gopls/internal/protocol.Handlers.AsyncHandler.func2.2:+3
runtime.goexit:+0

golang.org/x/tools/gopls@v0.15.0-pre.3 devel linux/amd64 other (2)

Issue created by golang.org/x/tools/gopls/internal/telemetry/cmd/stacks.

[adonovan]

This is a strange one. The indicated line of SignatureHelp is infallible, as are its immediate neighbors. I wonder whether there is a bug in the processing of stack frames. (The neighboring frames +/-2 all look sound though.)

[findleyr]

Here's another example of this:
https://storage.googleapis.com/prod-telemetry-merged/2024-03-09.json

[findleyr]

Aha, the panic is because release is deferred before the error is checked. Let's fix for gopls@v0.15.2.

[gopherbot]

Change https://go.dev/cl/570675 mentions this issue: gopls/internal/server: fix crash in SignatureHelp

[gopherbot]

Change https://go.dev/cl/570596 mentions this issue: [gopls-release-branch.0.15] gopls/internal/server: fix crash in SignatureHelp

[adonovan]

The line number mystery has a simple explanation: a panic caused by executing a deferred function that is nil is reported at the return statement: https://go.dev/play/p/TRTwguxqivI?v=gotip