x/tools/gopls: OOB index in stubmethods.fromValueSpec (reported by telemetry)

[adonovan]

This stack 5wndWg was reported by telemetry:

func fromValueSpec(fset *token.FileSet, ti *types.Info, vs *ast.ValueSpec, pos token.Pos) *StubInfo {
	var idx int
	for i, vs := range vs.Values {
		if pos >= vs.Pos() && pos <= vs.End() {
			idx = i
			break
		}
	}

	valueNode := vs.Values[idx] // <-- the crash implies that idx == len(vs.Values) == 0

gopls/bug
golang.org/x/tools/gopls/internal/bug.report:35
golang.org/x/tools/gopls/internal/bug.Errorf:2
golang.org/x/tools/gopls/internal/lsp.(*Server).codeAction.func1.1:2
runtime.gopanic:88
runtime.goPanicIndex:2
golang.org/x/tools/gopls/internal/lsp/analysis/stubmethods.fromValueSpec:9
golang.org/x/tools/gopls/internal/lsp/analysis/stubmethods.GetStubInfo:4
golang.org/x/tools/gopls/internal/lsp/analysis/stubmethods.DiagnosticForError:6
golang.org/x/tools/gopls/internal/lsp.(*Server).codeAction.func1:11
golang.org/x/tools/gopls/internal/lsp.(*Server).codeAction:210
golang.org/x/tools/gopls/internal/lsp.(*Server).CodeAction:1
golang.org/x/tools/gopls/internal/lsp/protocol.serverDispatch:142
golang.org/x/tools/gopls/internal/lsp/lsprpc.(*StreamServer).ServeStream.ServerHandler.func3:5
golang.org/x/tools/gopls/internal/lsp/lsprpc.(*StreamServer).ServeStream.handshaker.func4:52
golang.org/x/tools/gopls/internal/lsp/protocol.Handlers.MustReplyHandler.func1:2
golang.org/x/tools/gopls/internal/lsp/protocol.Handlers.AsyncHandler.func2.2:3

golang.org/x/tools/gopls@v0.14.2 go1.21.2 darwin/arm64 (1)

This OOB index looks very similar (but not the same) as a recent bug in StubMethods: #64087.

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

Dups:

This stack KFS4Ow was reported by telemetry:

gopls/bug
golang.org/x/tools/gopls/internal/bug.report:35
golang.org/x/tools/gopls/internal/bug.Errorf:2
golang.org/x/tools/gopls/internal/lsp.(*Server).codeAction.func1.1:2
runtime.gopanic:50
runtime.goPanicIndex:2
golang.org/x/tools/gopls/internal/lsp/analysis/stubmethods.fromValueSpec:9
golang.org/x/tools/gopls/internal/lsp/analysis/stubmethods.GetStubInfo:4
golang.org/x/tools/gopls/internal/lsp/analysis/stubmethods.DiagnosticForError:6
golang.org/x/tools/gopls/internal/lsp.(*Server).codeAction.func1:11
golang.org/x/tools/gopls/internal/lsp.(*Server).codeAction:210
golang.org/x/tools/gopls/internal/lsp.(*Server).CodeAction:1
golang.org/x/tools/gopls/internal/lsp/protocol.serverDispatch:142
golang.org/x/tools/gopls/internal/lsp/lsprpc.(*StreamServer).ServeStream.ServerHandler.func3:5
golang.org/x/tools/gopls/internal/lsp/lsprpc.(*StreamServer).ServeStream.handshaker.func4:52
golang.org/x/tools/gopls/internal/lsp/protocol.Handlers.MustReplyHandler.func1:2
golang.org/x/tools/gopls/internal/lsp/protocol.Handlers.AsyncHandler.func2.2:3

golang.org/x/tools/gopls@v0.14.2 go1.22.0 darwin/arm64 vscode (1)

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

[gopherbot]

Change https://go.dev/cl/548737 mentions this issue: gopls/internal/analysis/stubmethods: fix OOB panic in fromValueSpec