[flang] Non-generic interface must shadow outer generic (llvm#164469)

A procedure defined in non-generic INTERFACE block must completely
shadow any generic interface of the same name in an outer scope.

Fixes llvm#164303.

Author: klausler

flang/lib/Semantics/resolve-names.cpp

@@ -5451,7 +5451,8 @@ void SubprogramVisitor::PushBlockDataScope(const parser::Name &name) {
   }
 }
 
-// If name is a generic, return specific subprogram with the same name.
+// If name is a generic in the same scope, return its specific subprogram with
+// the same name, if any.
 Symbol *SubprogramVisitor::GetSpecificFromGeneric(const parser::Name &name) {
   // Search for the name but don't resolve it
   if (auto *symbol{currScope().FindSymbol(name.source)}) {
@@ -5461,6 +5462,9 @@ Symbol *SubprogramVisitor::GetSpecificFromGeneric(const parser::Name &name) {
         // symbol doesn't inherit it and ruin the ability to check it.
         symbol->attrs().reset(Attr::MODULE);
       }
+    } else if (&symbol->owner() != &currScope() && inInterfaceBlock() &&
+        !isGeneric()) {
+      // non-generic interface shadows outer definition
     } else if (auto *details{symbol->detailsIf<GenericDetails>()}) {
       // found generic, want specific procedure
       auto *specific{details->specific()};

flang/test/Semantics/bug164303.f90

@@ -0,0 +1,31 @@
+!RUN: %flang -fc1 -fsyntax-only %s 2>&1 | FileCheck --allow-empty %s
+module foo_mod
+  use, intrinsic :: iso_fortran_env
+  use, intrinsic :: iso_c_binding
+  implicit none
+
+  interface new_foo
+    procedure :: foo_ctor
+  end interface
+
+contains
+
+function foo_ctor(options) result(retval)
+  implicit none
+  integer, intent(in) :: options
+  integer :: retval
+
+  interface
+!CHECK-NOT: error:
+    subroutine new_foo(f, opt) bind(c, name='new_foo')
+      import
+      implicit none
+      integer, intent(inout) :: f
+      integer(c_int), intent(in) :: opt
+    end subroutine
+  end interface
+
+  call new_foo(retval, options)
+end function
+
+end module