[libcxx-commits] [libcxx] [libc++] Fix constexpr initialization of std::array<T, 0> (PR #74667)

[via libcxx-commits]

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@@ -18,26 +18,33 @@ struct NoDefault {
     TEST_CONSTEXPR NoDefault(int) { }
 };
 
-// Test default initialization
-// This one isn't constexpr because omitting to initialize fundamental types
-// isn't valid in a constexpr context.
-struct test_default_initialization {
+struct test_initialization {
     template <typename T>
-    void operator()() const
+    TEST_CONSTEXPR_CXX14 void operator()() const
     {
-        std::array<T, 0> a0; (void)a0;
-        std::array<T, 1> a1; (void)a1;
-        std::array<T, 2> a2; (void)a2;
-        std::array<T, 3> a3; (void)a3;
+        // Check default initalization
+        {
+            std::array<T, 0> a0; (void)a0;
+            // 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) {
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EricWF wrote:

I really hate logic in tests. The point where we have this many conditionals is the point where we should probably make the tests less generic and just spam the test out multiple times.

https://github.com/llvm/llvm-project/pull/74667