[flang] Specific procedures named the same as the generic and a derived type

[PeteSteinfeld]

Summary

If you specify a specific procedure of a generic interface that has the same
name as both the generic interface and a preceding derived type, the compiler
would fail an internal call to CHECK(). I fixed this by testing for this
situation when processing specific procedures. I also added a test that will
cause the call to CHECK() to fail without this new code.

flang/lib/Semantics/resolve-names.cpp

 Symbol *SubprogramVisitor::GetSpecificFromGeneric(const parser::Name &name) {
   if (auto *symbol{FindSymbol(name)}) {
     if (auto *details{symbol->detailsIf<GenericDetails>()}) {
       // found generic, want subprogram
       auto *specific{details->specific()};
       if (!specific) {
         specific =
             &currScope().MakeSymbol(name.source, Attrs{}, SubprogramDetails{});
+        if (details->derivedType()) {
+          // A specific procedure with the same name as a derived type
+          SayAlreadyDeclared(name, *details->derivedType());
+        } else {
           details->set_specific(Resolve(name, *specific));
+        }
       } else if (isGeneric()) {
         SayAlreadyDeclared(name, *specific);
       }
       if (!specific->has<SubprogramDetails>()) {
         specific->set_details(SubprogramDetails{});
       }
       return specific;
     }

flang/test/Semantics/resolve18.f90

module m4b
   !ERROR: 'foo' is already declared in this scoping unit
   interface foo
     procedure :: foo
   end interface foo
 contains
   function foo(x)
   end
 end
+module m4c
+  type :: foo
+  end type
+  interface foo
+    !ERROR: 'foo' is already declared in this scoping unit
+    real function foo()
+    end function foo
+  end interface foo
+end
 
 ! Use associating a name that is a generic and a derived type
 module m5a
   interface g
   end interface
   type g
   end type
 end module