Clang thread-safety analysis not producing a warning for accessing a guarded field in different object

[Qwinci]

Given the following code (full code in godbolt link below) Clang doesn't report any warnings for accessing b.some_field even though b.lock is not locked at any point (removing a.lock.acquire() + a.lock.release() calls makes the warning appear but that's obviously not something that you should have to do as they are two distinct objects):

struct CAPABILITY("spinlock") Spinlock {
    void acquire() ACQUIRE();
    void release() RELEASE();
};

struct Foo {
    Spinlock lock;
    bool some_field GUARDED_BY(lock);
};

void foobar() {
    Foo a {};
    Foo b {};
    a.lock.acquire();
    b.some_field = true;
    a.lock.release();
}

godbolt

[gle8098]

That's because by default the analysis checks capabilities in a relaxed way to reduce false positives. In your case a.lock partially matches b.lock since they share the same declaration, so it is considered to be probably the same lock, although it is clearly a false negative here.

To disable partial matching add the -Wthread-safety-precise flag. That would work for you.

Upd. Alternatively, you may enable -Wthread-safety instead of the basic -Wthread-safety-analysis to get the precise behavior.