[clang] [clang] Implement P2582R1: CTAD from inherited constructors (PR #98788)

[Matheus Izvekov via cfe-commits]

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@@ -1186,17 +1281,34 @@ void DeclareImplicitDeductionGuidesForTypeAlias(
         NewParam->setScopeInfo(0, I);
         FPTL.setParam(I, NewParam);
       }
-      auto *Transformed = cast<FunctionDecl>(buildDeductionGuide(
-          SemaRef, AliasTemplate, /*TemplateParams=*/nullptr,
+
+      QualType ReturnType =
+          cast<FunctionProtoType>(FunctionType->getType())->getReturnType();
+      if (!FunctionType)
+        continue;
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mizvekov wrote:

Is this check really necessary? Since you already performed a cast above, this can't be null.
Can you add a test case for this?

https://github.com/llvm/llvm-project/pull/98788