llvm/llvm-project

guarded_by attributes not supported using c++11 style

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#158,116 opened on Sep 11, 2025

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clang:frontendgood first issue

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Description

#include <mutex>

class Foo {
    std::mutex m;
    int y __attribute__((guarded_by(m)));
    int z [[clang::guarded_by(m)]];
};

<source>:6:13: warning: unknown attribute 'clang::guarded_by' ignored [-Wunknown-attributes]
    6 |     int z [[clang::guarded_by(m)]];
      |             ^~~~~~~~~~~~~~~~~

Contributor guide

Research direction
Examine the clang attribute system, specifically how `[[clang::guarded by]]` is supposed to be handled. Look for where `guarded by` is defined as an attribute and verify that C++11 style syntax is supported. Identify the missing configuration or code path.
Tech stack
cpp
Domain
tooling
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
C++GitLLVM
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
45