[libc++][math] Fix acceptance of convertible types in `std::isnan()` and `std::isinf()` (#98952)

Following up on https://github.com/llvm/llvm-project/pull/98841.

Changes:
- Properly test convert

[libc++][math] Fix acceptance of convertible types in `std::isnan()` and `std::isinf()` (#98952)

Following up on https://github.com/llvm/llvm-project/pull/98841.

Changes:
- Properly test convertible types for `std::isnan()` and `std::inf()`
- Tighten conditional in `cmath.pass.cpp` (Find insights on `_LIBCPP_PREFERRED_OVERLOAD` below)
- Tighten preprocessor guard in `traits.h`

Insights into why `_LIBCPP_PREFERRED_OVERLOAD` is needed:

(i) When libc++ is layered on top of glibc on Linux, glibc's `math.h` is
included. When compiling with `-std=c++03`, this header brings the
function declaration of `isinf(double)` [1] and `isnan(double)` [2]
into scope. This differs from the C99 Standard as only the macros
`#define isnan(arg)` and `#define isinf(arg)` are expected.

Therefore, libc++ needs to respect the presense of the `double` overload
and cannot redefine it as it will conflict with the declaration already
in scope. For `-std=c++11` and beyond this issue is fixed, as glibc
guards both the `isinf` and `isnan` by preprocessor macros.

(ii) When libc++ is layered on top of Bionic's libc, `math.h` exposes a
function prototype for `isinf(double)` with return type `int`. This
function prototype in Bionic's libc is not guarded by any preprocessor
macros [3].

`_LIBCPP_PREFERRED_OVERLOAD` specifies that a given overload is a better match
than an otherwise equally good function declaration. This is implemented in
modern versions of Clang via `__attribute__((__enable_if__))`, and not elsewhere.
See [4] for details. We use `_LIBCPP_PREFERRED_OVERLOAD` to define overloads in
the global namespace that displace the overloads provided by the C
libraries mentioned above.

[1]: https://github.com/bminor/glibc/blob/fe9408087583fd7a6f61bb0dbcf2fd4e83186afa/math/bits/mathcalls.h#L185-L194
[2]: https://github.com/bminor/glibc/blob/fe9408087583fd7a6f61bb0dbcf2fd4e83186afa/math/bits/mathcalls.h#L222-L231
[3]: https://cs.android.com/android/platform/superproject/+/master:bionic/libc/include/math.h;l=322-323;drc=master?hl=fr-BE%22https:%2F%2Fsupport.google.com%2Fmerchants%2Fanswer%2F188494%5C%22%22https:%2F%2Fsupport.google.com%2Fmerchants%2Fanswer%2F188494%5C%22
[4]: https://github.com/llvm/llvm-project/commit/5fd17ab1b093f6b59aabb27f6c2c2278e65c2707

show more ...

[libc++] Fix modules issues on OS X

First, fix a collision with the Point type from MacTypes.h, which was
reported on Slack, 2022-07-31: https://cpplang.slack.com/archives/C2X659D1B/p165928469127588

[libc++] Fix modules issues on OS X

First, fix a collision with the Point type from MacTypes.h, which was
reported on Slack, 2022-07-31: https://cpplang.slack.com/archives/C2X659D1B/p1659284691275889

Second, rename the meta:: namespace to types::. OSX's "/usr/include/ncurses.h"
defines a `meta` function, and is (for some reason) included in
"<SDK>/usr/include/module.modulemap", so that identifier is off-limits
for us to use in anything that compiles with -fmodules:

libcxx/test/support/type_algorithms.h:16:11: error: redefinition of 'meta' as different kind of symbol
namespace meta {
^
<SDK>/usr/include/ncurses.h:603:28: note: previous definition is here
extern NCURSES_EXPORT(int) meta (WINDOW *,bool); /* implemented */
^

Finally, add a CI configuration for modules on OS X to make sure it
does not regress.

Differential Revision: https://reviews.llvm.org/D144915

show more ...

[libc++] Implement constexpr {isfinite, isinf, isnan, isnormal}

This starts implementing P0533

Reviewed By: Mordante, #libc

Spies: libcxx-commits

Differential Revision: https://reviews.llvm.org/D

[libc++] Implement constexpr {isfinite, isinf, isnan, isnormal}

This starts implementing P0533

Reviewed By: Mordante, #libc

Spies: libcxx-commits

Differential Revision: https://reviews.llvm.org/D140277

show more ...