checker: fix downward view conversions false positive

Author: thvnx

lkql_checker/share/lkql/downward_view_conversions.lkql

@@ -3,11 +3,10 @@ fun is_downward_conv(expr_type, t) =
     |" of tagged types
     expr_type is AdaNode
     and t is AdaNode
-    and t.p_full_view() is target@BaseTypeDecl
       # Compare specific types in case one or the other is the classwide
       # version
-      when target.p_specific_type() != expr_type.p_specific_type()
-       and target.p_is_derived_type(expr_type)
+      when t.p_full_view().p_specific_type() != expr_type.p_full_view().p_specific_type()
+       and t.p_is_derived_type(expr_type)
 
 fun is_tagged(typ) =
     |" Whether typ is tagged or an access to a tagged type

testsuite/tests/checks/downward_view_conversions/test_downwardconv.adb

@@ -36,6 +36,33 @@ procedure Main is
       end Proc2;
 
    end Foo;
+
+   procedure No_Flag is
+      package P is
+         type T is tagged private;
+         subtype S is T;
+         type T_Access is access all T;
+         type T_Constant_Access is access constant T;
+
+         type U is new T with private;
+      private
+         type T is tagged null record;
+         type U is new T with null record;
+      end P;
+
+      package body P is
+         function F (X : T_Access) return T_Constant_Access
+         is (T_Constant_Access (X)); -- NOFLAG
+
+         function G (X : U) return T is (T (X)); -- NOFLAG
+
+         function I (X : T) return T is (T (X)); -- NOFLAG
+
+         function J (X : T) return S is (S (X)); -- NOFLAG
+      end P;
+   begin
+      null;
+   end No_Flag;
 begin
    null;
 end Main;