dotnet/roslyn

Nullability warning is missing on the lock statement

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#76,597 opened on Jan 2, 2025

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Area-CompilersFeature - Nullable Reference Typeshelp wanted

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Description

Version Used: 17.13.0 Preview 2.1

There is no nullability warning for lock (null) { } or lock (maybeNullExpr) { }, even though a null at runtime throws ArgumentNullException.

Expected

A nullability warning such as:

  • CS8604 - Possible null reference argument for parameter.

    • More literal, similar to how await or foreach simply reflect the warning you'd get if you had manually called GetAwaiter()/GetEnumerator().

  • CS8602 - Dereference of a possibly null reference.

    • A step back, if calling expr in lock (expr) a "parameter" is leaking too much information about how lock is being lowered.

Or, one in the same vein as "CS8597 Thrown value may be null."

Contributor guide

Research direction
Look up the lowering of lock statements in the Roslyn compiler source code. Specifically, examine the BoundLockStatement node and how it is transformed into lower level operations. Then, investigate the nullable flow analysis to see why null warnings are not emitted for the lock expression. Check for any existing nullable warning logic for similar constructs like 'await' or 'using'.
Tech stack
csharp
Domain
developer experience
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
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Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
GitC# compiler basics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50