[Sema] Don't crash when recovering from a misspelled pseudo destructor call to an incomplete type.

When attempting to correct a misspelled pseudo destructor call as in:

struct Foo;
void foo(Foo *p) {
  p.~Foo();
}

a call is made in canRecoverDotPseudoDestructorCallsOnPointerObjects
to LookupDestructor without checking that the record has a definition.

This causes an assertion later in LookupSpecialMember which assumes that
the record has a definition.

Patch By Roman Zhikharevich!

Differential Revision: https://reviews.llvm.org/D57111

Reviewed By: riccibruno

llvm-svn: 352047

clang/lib/Sema/SemaExprCXX.cpp

@@ -6854,8 +6854,9 @@ canRecoverDotPseudoDestructorCallsOnPointerObjects(Sema &SemaRef,
                                                    QualType DestructedType) {
   // If this is a record type, check if its destructor is callable.
   if (auto *RD = DestructedType->getAsCXXRecordDecl()) {
-    if (CXXDestructorDecl *D = SemaRef.LookupDestructor(RD))
-      return SemaRef.CanUseDecl(D, /*TreatUnavailableAsInvalid=*/false);
+    if (RD->hasDefinition())
+      if (CXXDestructorDecl *D = SemaRef.LookupDestructor(RD))
+        return SemaRef.CanUseDecl(D, /*TreatUnavailableAsInvalid=*/false);
     return false;
   }
 

clang/test/SemaCXX/incomplete-call.cpp

@@ -48,6 +48,10 @@ void test_incomplete_object_call(C& c) {
   c(); // expected-error{{incomplete type in call to object of type}}
 }
 
+void test_incomplete_object_dtor(C *p) {
+  p.~C(); // expected-error{{member reference type 'C *' is a pointer; did you mean to use '->'?}}
+}
+
 namespace pr18542 {
   struct X {
     int count;