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From: "mpolacek at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/107532] [13 Regression] -Werror=dangling-reference false
 positives in libcamera-0.0.1
Date: Tue, 24 Jan 2023 17:41:28 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107532

--- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #4)
> Yeah, without analyzing what the function call (constructor in this case)
> actually does
> hard to say whether the warning is ok or not.
> Maybe some heuristics based on the types?

Yes, I'm about to post another patch in response to
<https://gcc.gnu.org/pipermail/gcc-patches/2023-January/610353.html>.

> The reference in question is const Plane &, so see if the reference could
> bind to some member of the class that is destructed at the end of the
> statement (Ref<Plane>) or the class itself?
> Even with that there can be false positives and false negatives,
> e.g. the to be destructed temporary could contain a pointer to a heap
> allocated Plane and return a reference to that and then deallocate it in =
the
> destructor (it would then be a dangling reference that with the change
> wouldn't be warned about), or
> on the other side, e.g. if the possibly dangling reference is const Whate=
ver
> &
> and the temporary is Whatever, it might be likely that the reference is to
> the
> temporary, but it could be just a value of some member of it that would
> happen to have that type.

It's tricky.  I've seen unfixable problems with range-based for loops, for
instance.=