x/tools/gopls: "negative WaitGroup counter" panic in diagnoseChangedViews

[adonovan]

#!stacks
"runtime.gopanic" && "sync.(*WaitGroup).Add:+19" && "diagnoseChangedViews.func1:+16`"

Issue created by stacks.

func (wg *WaitGroup) Add(delta int) {
...
	state := wg.state.Add(uint64(delta) << 32)
	v := int32(state >> 32)
	w := uint32(state)
...
	if v < 0 {
		panic("sync: negative WaitGroup counter") // <---------- here
	}

This stack OKWeGA was reported by telemetry:

• crash/crash
• runtime.gopanic:+69
• sync.(*WaitGroup).Add:+19
• sync.(*WaitGroup).Done:=89
• golang.org/x/tools/gopls/internal/server.(*server).diagnoseChangedViews.func1:+16
• golang.org/x/tools/gopls/internal/server.(*server).diagnoseChangedViews.gowrap1:+16
• runtime.goexit:+0

golang.org/x/tools/[email protected] go1.23.3 linux/amd64 vscode (1)

[adonovan]

I can't explain this. Calls to Add and Done are strictly paired and the Done always happens after the Add. There are no other salient uses of the WaitGroup.

Paging compiler and runtime folks. @prattmic

[gabyhelp]

Related Issues

• x/tools/gopls: CodeAction: nil panic in findMatchingDiagnostics #71028 (closed)
• x/tools/gopls: xrefs.Index panics after "can't fail" pgf.PosRange #70446 (closed)
• x/tools/gopls: crash when primary diagnostics have invalid positions #66731 (closed)
• x/tools/gopls: crash in Hover (telemetry) #69362
• x/tools/gopls: analysisinternal.ZeroValue crash on (presumably) unsafe.Pointer #70585 (closed)
• gopls: automated issue report (crash) #70247 (closed)
• x/tools/gopls: index out of range panic with v0.3.4 #37977 (closed)
• x/tools/gopls: automated issue report (crash) #66174 (closed)
• x/tools/gopls: panic in token.File.Name within PackageDocHTML (telemetry) #70149 (closed)
• x/tools/gopls: OOB index panic after parsing go list error from file with //line directives #67360 (closed)

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[prattmic]

I agree, this use of WaitGroup looks straightforward and bug free to me.