[libcxx] [test] Fix valarray UB and MSVC warnings.

[libcxx] [test] Calling min and max on an empty valarray is UB.

libcxx/test/std/numerics/numarray/template.valarray/valarray.members/min.pass.cpp
libcxx/test/std/numerics/numarray/template.valarray/valarray.members/max.pass.cpp

The calls `v1.min();` and `v1.max();` were emitting nodiscard warnings
with MSVC's STL. Upon closer inspection, these calls were triggering
undefined behavior. N4842 [valarray.members] says:

"T min() const;
8 Preconditions: size() > 0 is true.
T max() const;
10 Preconditions: size() > 0 is true."

As these tests already provide coverage for non-empty valarrays
(immediately above), I've simply deleted the code for empty valarrays.

[libcxx] [test] Add macros to msvc_stdlib_force_include.h (NFC).

libcxx/test/support/msvc_stdlib_force_include.h

These macros are being used by:
libcxx/test/std/utilities/meta/meta.trans/meta.trans.other/result_of11.pass.cpp
Defining them to nothing allows that test to pass.

[libcxx] [test] Silence MSVC warning C5063 for is_constant_evaluated (NFC).

libcxx/test/std/utilities/meta/meta.const.eval/is_constant_evaluated.pass.cpp

This test is intentionally writing code that MSVC intentionally warns
about, so the warning should be silenced.

Additionally, comment an endif for clarity.

[libcxx] [test] Silence MSVC warning C4127 (NFC).

libcxx/test/support/charconv_test_helpers.h

MSVC avoids emitting this warning when it sees a single constexpr value
being tested, but this condition is a mix of compile-time and run-time.
Using push-disable-pop is the least intrusive way to silence this.

[libcxx] [test] Silence MSVC truncation warning (NFC).

libcxx/test/std/containers/sequences/vector/vector.cons/construct_iter_iter.pass.cpp

This test is intentionally truncating float to int, which MSVC
intentionally warns about, so push-disable-pop is necessary.

[libcxx] [test] Avoid truncation warnings in erase_if tests (NFC).

libcxx/test/std/containers/associative/map/map.erasure/erase_if.pass.cpp
libcxx/test/std/containers/associative/multimap/multimap.erasure/erase_if.pass.cpp
libcxx/test/std/containers/unord/unord.map/erase_if.pass.cpp
libcxx/test/std/containers/unord/unord.multimap/erase_if.pass.cpp

These tests use maps with `short` keys and values, emitting MSVC
truncation warnings from `int`. Adding `static_cast` to `key_type`
and `mapped_type` avoids these warnings.

As these tests require C++20 mode (or newer), for brevity I've changed
the multimap tests to use emplace to initialize the test data.
This has no effect on the erase_if testing.

1 files changed, 8 insertions, 1 deletions

diff --git a/libcxx/test/std/utilities/meta/meta.const.eval/is_constant_evaluated.pass.cpp b/libcxx/test/std/utilities/meta/meta.const.eval/is_constant_evaluated.pass.cpp
index e4b8a7575b0..a1fdd288240 100644
--- a/libcxx/test/std/utilities/meta/meta.const.eval/is_constant_evaluated.pass.cpp
+++ b/libcxx/test/std/utilities/meta/meta.const.eval/is_constant_evaluated.pass.cpp
@@ -34,6 +34,10 @@ template <bool> struct InTemplate {};
 int main(int, char**)
 {
 #ifdef __cpp_lib_is_constant_evaluated
+#ifdef TEST_COMPILER_C1XX
+    #pragma warning(push)
+    #pragma warning(disable: 5063) // 'std::is_constant_evaluated' always evaluates to true in manifestly constant-evaluated expressions
+#endif // TEST_COMPILER_C1XX
   // Test the signature
   {
     ASSERT_SAME_TYPE(decltype(std::is_constant_evaluated()), bool);
@@ -51,6 +55,9 @@ int main(int, char**)
     static int local_static = std::is_constant_evaluated() ? 42 : -1;
     assert(local_static == 42);
   }
-#endif
+#ifdef TEST_COMPILER_C1XX
+    #pragma warning(pop)
+#endif // TEST_COMPILER_C1XX
+#endif // __cpp_lib_is_constant_evaluated
   return 0;
 }