[libc++] [test] Fix MSVC warnings (llvm#93257)

Found while running libc++'s tests with MSVC's STL.

* Avoid MSVC warning C5101: use of preprocessor directive in
function-like macro argument list is undefined behavior.
+ We can easily make this portable by extracting `const bool is_newlib`.
  + Followup to llvm#73440.
  + See llvm#73598.
  + See llvm#73836.
* Avoid MSVC warning C4267: 'return': conversion from 'size_t' to 'int',
possible loss of data.
+ This warning is valid, but harmless for the test, so
`static_cast<int>` will avoid it.
* Avoid MSVC warning C4146: unary minus operator applied to unsigned
type, result still unsigned.
+ This warning is also valid (the scenario is sometimes intentional, but
surprising enough that it's worth warning about). This is a C++17 test,
so we can easily avoid it by testing `is_signed_v` at compile-time
before testing `m < 0` and `n < 0` at run-time.
* Silence MSVC warning C4310: cast truncates constant value.
+ These warnings are being emitted by `T(255)`. Disabling the warning is
simpler than attempting to restructure the code.
  + Followup to llvm#79791.
* MSVC no longer emits warning C4521: multiple copy constructors
specified.
+ This warning was removed from the compiler, since at least 2021-12-09.

libcxx/test/std/atomics/atomics.ref/compare_exchange_strong.pass.cpp

@@ -9,6 +9,9 @@
 // XFAIL: !has-64-bit-atomics
 // XFAIL: !has-1024-bit-atomics
 
+// MSVC warning C4310: cast truncates constant value
+// ADDITIONAL_COMPILE_FLAGS(cl-style-warnings): /wd4310
+
 // bool compare_exchange_strong(T&, T, memory_order, memory_order) const noexcept;
 // bool compare_exchange_strong(T&, T, memory_order = memory_order::seq_cst) const noexcept;
 

libcxx/test/std/atomics/atomics.ref/compare_exchange_weak.pass.cpp

@@ -9,6 +9,9 @@
 // XFAIL: !has-64-bit-atomics
 // XFAIL: !has-1024-bit-atomics
 
+// MSVC warning C4310: cast truncates constant value
+// ADDITIONAL_COMPILE_FLAGS(cl-style-warnings): /wd4310
+
 // bool compare_exchange_weak(T&, T, memory_order, memory_order) const noexcept;
 // bool compare_exchange_weak(T&, T, memory_order = memory_order::seq_cst) const noexcept;
 

libcxx/test/std/atomics/atomics.ref/wait.pass.cpp

@@ -11,6 +11,9 @@
 // XFAIL: !has-64-bit-atomics
 // XFAIL: !has-1024-bit-atomics
 
+// MSVC warning C4310: cast truncates constant value
+// ADDITIONAL_COMPILE_FLAGS(cl-style-warnings): /wd4310
+
 // void wait(T, memory_order = memory_order::seq_cst) const noexcept;
 
 #include <atomic>

libcxx/test/std/containers/views/views.span/span.cons/initializer_list.pass.cpp

@@ -93,9 +93,9 @@ constexpr bool test() {
 
 // Test P2447R4 "Annex C examples"
 
-constexpr int three(std::span<void* const> sp) { return sp.size(); }
+constexpr int three(std::span<void* const> sp) { return static_cast<int>(sp.size()); }
 
-constexpr int four(std::span<const std::any> sp) { return sp.size(); }
+constexpr int four(std::span<const std::any> sp) { return static_cast<int>(sp.size()); }
 
 bool test_P2447R4_annex_c_examples() {
   // 1. Overload resolution is affected

libcxx/test/std/diagnostics/syserr/syserr.errcat/syserr.errcat.objects/generic_category.pass.cpp

@@ -50,13 +50,16 @@ int main(int, char**)
         // responds with an empty message, which we probably want to
         // treat as a failure code otherwise, but we can detect that
         // with the preprocessor.
+#if defined(_NEWLIB_VERSION)
+        const bool is_newlib = true;
+#else
+        const bool is_newlib = false;
+#endif
+        (void)is_newlib;
         LIBCPP_ASSERT(msg.rfind("Error -1 occurred", 0) == 0       // AIX
                       || msg.rfind("No error information", 0) == 0 // Musl
                       || msg.rfind("Unknown error", 0) == 0        // Glibc
-#if defined(_NEWLIB_VERSION)
-                      || msg.empty()
-#endif
-        );
+                      || (is_newlib && msg.empty()));
         assert(errno == E2BIG);
     }
 

libcxx/test/std/diagnostics/syserr/syserr.errcat/syserr.errcat.objects/system_category.pass.cpp

@@ -56,13 +56,16 @@ int main(int, char**) {
     // responds with an empty message, which we probably want to
     // treat as a failure code otherwise, but we can detect that
     // with the preprocessor.
+#if defined(_NEWLIB_VERSION)
+    const bool is_newlib = true;
+#else
+    const bool is_newlib = false;
+#endif
+    (void)is_newlib;
     LIBCPP_ASSERT(msg.rfind("Error -1 occurred", 0) == 0       // AIX
                   || msg.rfind("No error information", 0) == 0 // Musl
                   || msg.rfind("Unknown error", 0) == 0        // Glibc
-#if defined(_NEWLIB_VERSION)
-                  || msg.empty()
-#endif
-    );
+                  || (is_newlib && msg.empty()));
     assert(errno == E2BIG);
   }
 

libcxx/test/std/numerics/numeric.ops/numeric.ops.gcd/gcd.pass.cpp

@@ -57,10 +57,12 @@ T basic_gcd_(T m, T n) {
 template <typename T>
 T basic_gcd(T m, T n) {
   using Tp = std::make_unsigned_t<T>;
-  if (m < 0 && m != std::numeric_limits<T>::min())
-    m = -m;
-  if (n < 0 && n != std::numeric_limits<T>::min())
-    n = -n;
+  if constexpr (std::is_signed_v<T>) {
+    if (m < 0 && m != std::numeric_limits<T>::min())
+      m = -m;
+    if (n < 0 && n != std::numeric_limits<T>::min())
+      n = -n;
+  }
   return basic_gcd_(static_cast<Tp>(m), static_cast<Tp>(n));
 }
 

libcxx/test/support/msvc_stdlib_force_include.h

@@ -67,7 +67,6 @@ const AssertionDialogAvoider assertion_dialog_avoider{};
 // Silence compiler warnings.
 #  pragma warning(disable : 4180)  // qualifier applied to function type has no meaning; ignored
 #  pragma warning(disable : 4324)  // structure was padded due to alignment specifier
-#  pragma warning(disable : 4521)  // multiple copy constructors specified
 #  pragma warning(disable : 4702)  // unreachable code
 #  pragma warning(disable : 28251) // Inconsistent annotation for 'new': this instance has no annotations.
 #endif                             // !defined(__clang__)