[libcxx-commits] [PATCH] D68879: P1152R4: Fix deprecation warnings in libc++ testsuite and in uses of is_invocable that would internally conjure up a deprecated function type.

[Richard Smith - zygoloid via Phabricator via libcxx-commits]

rsmith marked an inline comment as done.
rsmith added inline comments.


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Comment at: libcxx/include/type_traits:1123
+// Suppress deprecation notice for volatile-qualified return type.
+_LIBCPP_SUPPRESS_DEPRECATED_PUSH
 template <class _Tp> _Tp&& __declval(int);
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ldionne wrote:
> rsmith wrote:
> > ldionne wrote:
> > > Wait, I don't see any `volatile` qualification here?
> > The volatile comes from `_Tp`, specified indirectly through various callers that internally use `declval`. In particular, the `is_invocable<volatile T>` tests end up here.
> That's what I thought, but isn't that warning broken then? Isn't any template going to produce a warning when instantiated with a `volatile T`? I must be misunderstanding something.
We warn when instantiating the second overload of `__declval` with `_Tp` = `volatile T`, because that causes it to have a volatile-qualified return type, which is deprecated. We don't warn on the first overload, because it doesn't have a volatile-qualified return type regardless of `_Tp`. Does that make more sense?


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