[flang] Silence bogus error on use after IMPORT

[klausler]

Summary

When a scope uses an explicit IMPORT statement to import a
symbol from the scope's host, it should not emit a bogus error
message later if that symbol is used in a specification construct.
The code that checks for imports being hidden by local declarations
was not allowing for the presence of host association (or USE)
indirection symbols in the local scope. Fix by using GetUltimate()
before checking for the hidden symbol.

[PeteSteinfeld]

Looks great! Thanks for doing this.

flang/lib/Semantics/resolve-names.cpp

 void ResolveNamesVisitor::CheckImport(
     const SourceName &location, const SourceName &name) {
   if (auto *symbol{FindInScope(name)}) {
-    Say(location, "'%s' from host is not accessible"_err_en_US, name)
-        .Attach(symbol->name(), "'%s' is hidden by this entity"_en_US,
-            symbol->name());
+    const Symbol &ultimate{symbol->GetUltimate()};
+    if (&ultimate.owner() == &currScope()) {
+      Say(location, "'%s' from host is not accessible"_err_en_US, name)
+          .Attach(symbol->name(), "'%s' is hidden by this entity"_en_US,
+              symbol->name());
+    }
   }
 }
 

flang/test/Semantics/resolve29.f90

 ! RUN: %python %S/test_errors.py %s %flang_fc1
-module m
+module m1
   type t1
   end type
   type t3

     call s5()
   end
 end module
+module m2
+  integer, parameter :: ck = kind('a')
+end module
+program main
+  use m2
+  interface
+    subroutine s0(x)
+      import :: ck
+      character(kind=ck) :: x ! no error
+    end subroutine
+  end interface
+end program