[PATCH] D84603: Thread safety analysis: More consistent warning message

[Aaron Puchert via Phabricator via cfe-commits]

aaronpuchert added inline comments.


================
Comment at: clang/lib/Analysis/ThreadSafety.cpp:1644
     if (!LDat) {
-      Analyzer->Handler.handleMutexNotHeld("", D, POK, Cp.toString(),
-                                           LK_Shared, Loc);
+      Analyzer->Handler.handleMutexNotHeld("negative capability", D, POK,
+                                           Cp.toString(), LK_Shared, Loc);
----------------
aaron.ballman wrote:
> aaronpuchert wrote:
> > aaron.ballman wrote:
> > > It's a bit odd that we aren't using `DiagKind` as below, I assume that's because this is a negative test and the others are positive tests, but doesn't this introduce a terminology difference where a positive failure may call it a mutex and a negative failure may call it a negative capability? Should this be hooked in to `ClassifyDiagnostic()` (perhaps we need a `ClassifyNegativeDiagnostic()`?
> > My thinking was that whatever the positive capability is called, we should only talk about a "negative capability" instead of a "negative mutex" or a "negative role". Also because not holding a capability is in some way its own kind of capability.
> I may still be confused or thinking of this differently, but I would assume that a negative mutex would be a mutex that's explicitly not held, which you may want to ensure on a function boundary to avoid deadlock. From that, I'd have guessed we would want the diagnostic to read `cannot call function 'bar' while mutex 'mu' is held` or `calling function 'bar' requires mutex 'mu' to not be held` because that's more clear than talking about negative capabilities (when the user is thinking in terms of mutexes which are or aren't held).
Now I get it. I don't see an issue with that, but we need to distinguish between `EXCLUDES(mu)` and `REQUIRES(!mu)`. The former will produce "cannot call function 'bar' while mutex 'mu' is held" and we probably want the latter to produce a different warning message.

Now one argument for the existing scheme remains that with `-Wthread-safety-negative`, if you see a warning like "acquiring mutex 'mu' requires negative capability '!mu'" on a lock operation, you know you can fix that by adding `REQUIRES(!mu)` to your function.

If we say "warning: acquiring mutex 'mu' requires mutex 'mu' not to be held" it might not be as clear what we want.


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https://reviews.llvm.org/D84603