[libcxx-commits] [libcxx] [libc++][test] Fix MSVC warning C4127 in `array.cons/initialization.pass.cpp` (PR #79793)

[Stephan T. Lavavej via libcxx-commits]

https://github.com/StephanTLavavej created https://github.com/llvm/llvm-project/pull/79793

This fixes MSVC warning C4127: conditional expression is constant.

Testing `TEST_STD_AT_LEAST_20_OR_RUNTIME_EVALUATED` by itself doesn't emit this warning, but the condition here is more complicated. I'm expanding the macro and mechanically simplifying the resulting code.

(Yeah, this warning is often annoying, and I introduced `TEST_STD_AT_LEAST_20_OR_RUNTIME_EVALUATED` to avoid this warning elsewhere, so it's disappointing that it doesn't make the compiler happy here. If this change is undesirable, I can replace it with `ADDITIONAL_COMPILE_FLAGS(cl-style-warnings)`, but ideally I'd like to avoid having to suppress it.)

>From 9e81886878ea9759a61e1f4154af24cec3150d81 Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl at nuwen.net>
Date: Sun, 28 Jan 2024 21:52:10 -0800
Subject: [PATCH] Fix MSVC warning C4127: conditional expression is constant

Testing TEST_STD_AT_LEAST_20_OR_RUNTIME_EVALUATED by itself doesn't
emit this warning, but the condition here is more complicated. I'm
expanding the macro and mechanically simplifying the resulting code.
---
 .../sequences/array/array.cons/initialization.pass.cpp       | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/libcxx/test/std/containers/sequences/array/array.cons/initialization.pass.cpp b/libcxx/test/std/containers/sequences/array/array.cons/initialization.pass.cpp
index 7991d4738d9699..acd176cce91d9e 100644
--- a/libcxx/test/std/containers/sequences/array/array.cons/initialization.pass.cpp
+++ b/libcxx/test/std/containers/sequences/array/array.cons/initialization.pass.cpp
@@ -28,7 +28,10 @@ struct test_initialization {
             // Before C++20, default initialization doesn't work inside constexpr for
             // trivially default constructible types. This only apply to non-empty arrays,
             // since empty arrays don't hold an element of type T.
-            if (TEST_STD_AT_LEAST_20_OR_RUNTIME_EVALUATED || !std::is_trivially_default_constructible<T>::value) {
+#if TEST_STD_VER < 20
+            if (!TEST_IS_CONSTANT_EVALUATED || !std::is_trivially_default_constructible<T>::value)
+#endif
+            {
                 std::array<T, 1> a1; (void)a1;
                 std::array<T, 2> a2; (void)a2;
                 std::array<T, 3> a3; (void)a3;