[NFC][CLANG] Fix Static Code Analyzer Concerns with dereference null return value in applyObjCTypeArgs()

[Manna]

Summary

This patch uses castAs instead of getAs to resolve dereference issue with nullptr boundObjC when calling canAssignObjCInterfaces() or isObjCIdType() in applyObjCTypeArgs() since getAs returns nullptr.

[erichkeane]

clang/lib/Sema/SemaType.cpp

956

Note for future reviewers: This 'if' on both branches dereferences the boundObjC pointer. The true path is just below here, on 959. Second is in the condition inside of the else if on 961, canAssignObjCInterfaces immediately dereferences the parameters.

[Manna]

clang/lib/Sema/SemaType.cpp

956

This 'if' on both branches dereferences the boundObjC pointer. The true path is just below here, on 959. Second is in the condition inside of the else if on 961, canAssignObjCInterfaces immediately dereferences the parameters.

Yes.

Thank you @erichkeane for reviews!

clang/lib/Sema/SemaType.cpp

if (const auto *typeArgObjC = typeArg->getAs<ObjCObjectPointerType>()) {
       // means we won't be able to match anything.
       if (!typeParam) {
         assert(anyPackExpansions && "Too many arguments?");
         continue;
       }
 
       // Retrieve the bound.
       QualType bound = typeParam->getUnderlyingType();
-      const auto *boundObjC = bound->getAs<ObjCObjectPointerType>();
+      const auto *boundObjC = bound->castAs<ObjCObjectPointerType>();
 
       // Determine whether the type argument is substitutable for the bound.
       if (typeArgObjC->isObjCIdType()) {
         // When the type argument is 'id', the only acceptable type
         // parameter bound is 'id'.
         if (boundObjC->isObjCIdType())
           continue;
       } else if (S.Context.canAssignObjCInterfaces(boundObjC, typeArgObjC)) {
         // Otherwise, we follow the assignability rules.
         continue;
       }