[clang] [Clang] Added explanation why a is constructible evaluated to false. (PR #143309)

[Corentin Jabot via cfe-commits]

================
@@ -2253,6 +2260,60 @@ static void DiagnoseNonTriviallyCopyableReason(Sema &SemaRef,
   }
 }
 
+static void DiagnoseNonConstructibleReason(
+    Sema &SemaRef, SourceLocation Loc,
+    const llvm::SmallVector<clang::QualType, 1> &Ts) {
+  bool CompleteTypes = true;
+  for (const auto &ArgTy : Ts) {
+    if (ArgTy->isVoidType() || ArgTy->isIncompleteArrayType())
+      continue;
+    if (ArgTy->isIncompleteType()) {
+      SemaRef.Diag(Loc, diag::err_incomplete_type_used_in_type_trait_expr)
+          << ArgTy;
+      CompleteTypes = false;
+    }
+  }
+  if (!CompleteTypes)
+    return;
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cor3ntin wrote:

Incomplete types should have been diagnosed already, so the check for incomplete type is not useful (we do need checks for void and incomplete array types)
https://godbolt.org/z/hc5jrjz51

https://github.com/llvm/llvm-project/pull/143309