[Clang] Fix lambda CheckForDefaultedFunction(...) so that it checks the CXXMethodDecl is not deleted before attempting to call DefineDefaultedFunction(...)

[shafik]

Summary

I discovered this additional bug at the end of working on D132906

In Sema::CheckCompletedCXXClass(...) uses a lambda CheckForDefaultedFunction to verify each CXXMethodDecl holds to the expected invariants before passing them on to CheckForDefaultedFunction.

It is currently missing a check that it is not deleted, this adds that check and a test that crashed without this check.

This fixes: https://github.com/llvm/llvm-project/issues/57516

[shafik]

• Add Release note.

clang/lib/Sema/SemaDeclCXX.cpp

if (!M->isInvalidDecl() && M->isExplicitlyDefaulted() &&
         // Define after any fields with in-class initializers have been parsed.
         DelayedDllExportMemberFunctions.push_back(M);
       }
     }
 
     // Define defaulted constexpr virtual functions that override a base class
     // function right away.
     // FIXME: We can defer doing this until the vtable is marked as used.
-    if (CSM != CXXInvalid && M->isDefaulted() && M->isConstexpr() &&
-        M->size_overridden_methods())
+    if (CSM != CXXInvalid && !M->isDeleted() && M->isDefaulted() &&
+        M->isConstexpr() && M->size_overridden_methods())
       DefineDefaultedFunction(*this, M, M->getLocation());
 
     if (!Incomplete)
       CheckCompletedMemberFunction(M);
   };
 
   // Check the destructor before any other member function. We need to
   // determine whether it's trivial in order to determine whether the claas

clang/test/SemaCXX/constant-expression-cxx2a.cpp

 class B {
   virtual int constexpr f() = 0;
 };
 
 class D : B {
   virtual int constexpr f() = default; // expected-error {{only special member functions and comparison operators may be defaulted}}
 };
 }
+
+namespace GH57516 {
+class B{
+  virtual constexpr ~B() = 0; // expected-note {{overridden virtual function is here}}
+};
+
+class D : B{}; // expected-error {{deleted function '~D' cannot override a non-deleted function}}
+// expected-note@-1 {{destructor of 'D' is implicitly deleted because base class 'B' has an inaccessible destructor}}
+}