x/tools/gopls: Completion: nil deref panic in addFieldItems

[adonovan]

#!stacks
"sigpanic" && "completion.(*completer).addFieldItems:+5"

Issue created by stacks.

// adds struct fields, interface methods, function declaration fields to completion
func (c *completer) addFieldItems(fields *ast.FieldList) {
	if fields == nil {
		return
	}

	cursor := c.surrounding.cursor <--- panic

From the calling context, it's clear that c is non-nil, so c.surrounding must be nil. This can happen if the various setSurrounding* functions are not called or return early. The fix is to make the panicking statement defensive.

This stack tANNhQ was reported by telemetry:

• crash/crash
• runtime.gopanic:+69
• runtime.panicmem:=262
• runtime.sigpanic:+19
• golang.org/x/tools/gopls/internal/golang/completion.(*completer).addFieldItems:+5
• golang.org/x/tools/gopls/internal/golang/completion.(*completer).populateCommentCompletions:+79
• golang.org/x/tools/gopls/internal/golang/completion.(*completer).collectCompletions:+12
• golang.org/x/tools/gopls/internal/golang/completion.Completion:+163
• golang.org/x/tools/gopls/internal/server.(*server).Completion:+19
• golang.org/x/tools/gopls/internal/protocol.serverDispatch:+193
• 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@v0.18.1 go1.23.5 darwin/arm64 neovim,vscode (1)

[gabyhelp]

Related Issues

• x/tools/gopls: Completion: nil deref in expectedCompositeLiteralType #72136
• x/tools/gopls: failed *types.Func type assertion in populateCommentCompletions #71273 (closed)
• x/tools/gopls: Completion: failed type assertion in completer.item #71044 (closed)
• x/tools/gopls: nil Signature (?) deref in Completion #70634 (closed)
• x/tools/gopls: completion: failed type assertion in inferExpectedTypeArg #70889 (closed)
• x/tools/gopls: Completion: "ZeroString for unexpected type" panic #70744 (closed)
• x/tools/gopls: OOB index crash in completion.expectedReturnStmtType #70636 (closed)
• x/tools/gopls: Hover: invalid nil entry in types.Defs map #69362 (closed)
• x/tools/gopls: stubmethods: nil deref of FuncType.Results in fromReturnStmt #70967 (closed)
• x/tools/gopls: panic in completion on variables of type *error #56505 (closed)

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