[PATCH] D45179: [libc++] Add _LIBCPP_FORCE_NODISCARD define to force-enable nodiscard in pre-C++17

[Marshall Clow via Phabricator via cfe-commits]

mclow.lists added inline comments.


================
Comment at: include/__config:1016
+// because GCC does not silence them via (void) cast.
+#if __has_cpp_attribute(nodiscard) && _LIBCPP_STD_VER > 17
+#  define _LIBCPP_NODISCARD [[nodiscard]]
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lebedev.ri wrote:
> mclow.lists wrote:
> > `[[nodiscard]]` is a C++17 feature. This test should be `>=`, not `>`.
> Indeed, though the left hand side of the diff already specified `_LIBCPP_STD_VER > 17`.
> Interesting, isn't it.
That was because the flag `_LIBCPP_NODISCARD_AFTER_CXX17` was only active post-c++17.

Now we're talking about doing stuff in earlier standards, we should use `[[nodiscard]]` for C++17


================
Comment at: include/__config:1026
+    (_LIBCPP_STD_VER > 17 || defined(_LIBCPP_FORCE_NODISCARD))
+#  define _LIBCPP_NODISCARD_AFTER_CXX17 _LIBCPP_NODISCARD
 #else
----------------
lebedev.ri wrote:
> mclow.lists wrote:
> > I wouldn't change this; just leave it as `[[nodiscard]]`
> But that would defy the purpose?
That's a fair point - but I don't want this to be anything but `[[nodiscard]]` if we're compiling for C++2a or later.



Repository:
  rCXX libc++

https://reviews.llvm.org/D45179