No longer hang on typeof of a function type

We were calling `isFunctionProtoType()` on a `ParsedType` rather than
creating a valid semantic type first and calling the function on that.
The call to `isFunctionProtoType()` would eventually call
`getUnqualifiedDesugaredType()`, which loops indefinitely until we get
a desugared type and a `ParsedType` will never finish desugaring.

Fixes llvm#64713

Author: AaronBallman

clang/docs/ReleaseNotes.rst

@@ -477,6 +477,7 @@ Bug Fixes in This Version
   instantiated in one module and whose definition is instantiated in another
   module may end up with members associated with the wrong declaration of the
   class, which can result in miscompiles in some cases.
+<<<<<<< HEAD
 
 - Added a new diagnostic warning group
   ``-Wdeprecated-redundant-constexpr-static-def``, under the existing
@@ -700,6 +701,11 @@ Bug Fixes in This Version
   (`#64005 <https://github.com/llvm/llvm-project/issues/64005>_`)
 - Fix crash on nested templated class with template function call.
   (`#61159 <https://github.com/llvm/llvm-project/issues/61159>_`)
+- Fix crash on use of a variadic overloaded operator.
+  (`#42535 <https://github.com/llvm/llvm-project/issues/42535>_`)
+- Fix a hang on valid C code passing a function type as an argument to
+  ``typeof`` to form a function declaration.
+  (`#64713 <https://github.com/llvm/llvm-project/issues/64713>_`)
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaDecl.cpp

@@ -9154,7 +9154,8 @@ static FunctionDecl *CreateNewFunctionDecl(Sema &SemaRef, Declarator &D,
     bool HasPrototype =
         (D.isFunctionDeclarator() && D.getFunctionTypeInfo().hasPrototype) ||
         (D.getDeclSpec().isTypeRep() &&
-         D.getDeclSpec().getRepAsType().get()->isFunctionProtoType()) ||
+         SemaRef.GetTypeFromParser(D.getDeclSpec().getRepAsType(), nullptr)
+             ->isFunctionProtoType()) ||
         (!R->getAsAdjusted<FunctionType>() && R->isFunctionProtoType());
     assert(
         (HasPrototype || !SemaRef.getLangOpts().requiresStrictPrototypes()) &&

clang/test/C/C2x/n2927.c

@@ -90,3 +90,7 @@ extern typeof(D) C;                // C has type "double[2]"
 typeof(D) D = { 5, 8.9, 0.1, 99 }; // D is now completed to "double[4]"
 extern double E[4];
 extern typeof(D) E;                // E has type "double[4]" from D’s completed type
+
+// GH64713 -- this used to trigger an infinite loop when creating the function
+// declaration for F from the function designator specified by typeof.
+typeof(int(int)) F;                // F has type "int(int)"