[clang] [clang] Reject VLAs in `__is_layout_compatible()` (PR #87737)

[Vlad Serebrennikov via cfe-commits]

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@@ -1741,8 +1741,10 @@ void is_layout_compatible(int n)
   static_assert(!__is_layout_compatible(unsigned char, signed char));
   static_assert(__is_layout_compatible(int[], int[]));
   static_assert(__is_layout_compatible(int[2], int[2]));
-  static_assert(!__is_layout_compatible(int[n], int[2])); // FIXME: VLAs should be rejected
-  static_assert(!__is_layout_compatible(int[n], int[n])); // FIXME: VLAs should be rejected
+  static_assert(!__is_layout_compatible(int[n], int[2]));
+  // expected-error at -1 {{variable length arrays are not supported for '__is_layout_compatible'}}
+  static_assert(!__is_layout_compatible(int[n], int[n]));
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Endilll wrote:

I recognize that discussion has spiraled out of VLAs into incomplete types and flexible array members, but can I keep the original scope of this PR, focusing on just VLAs?

https://github.com/llvm/llvm-project/pull/87737