[Wdocumentation] fixes an assertion failure with typedefed function and block pointer

Summary:
The assertion happens when compiling with -Wdocumentation with variable declaration to a typedefed function pointer. I not too familiar with the ObjC syntax but first two tests assert without this patch.

Fixes https://bugs.llvm.org/show_bug.cgi?id=42844

Reviewers: gribozavr

Reviewed By: gribozavr

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D66706

llvm-svn: 370677
diff --git a/clang/lib/AST/CommentSema.cpp b/clang/lib/AST/CommentSema.cpp
index 067b3ae..69d61dc 100644
--- a/clang/lib/AST/CommentSema.cpp
+++ b/clang/lib/AST/CommentSema.cpp
@@ -588,6 +588,8 @@
   if (isObjCPropertyDecl())
     return;
   if (isFunctionDecl() || isFunctionOrBlockPointerVarLikeDecl()) {
+    assert(!ThisDeclInfo->ReturnType.isNull() &&
+           "should have a valid return type");
     if (ThisDeclInfo->ReturnType->isVoidType()) {
       unsigned DiagKind;
       switch (ThisDeclInfo->CommentDecl->getKind()) {
@@ -873,6 +875,12 @@
   // can be ignored.
   if (QT->getAs<TypedefType>())
     return false;
+  if (const auto *P = QT->getAs<PointerType>())
+    if (P->getPointeeType()->getAs<TypedefType>())
+      return false;
+  if (const auto *P = QT->getAs<BlockPointerType>())
+    if (P->getPointeeType()->getAs<TypedefType>())
+      return false;
   return QT->isFunctionPointerType() || QT->isBlockPointerType();
 }