[Ada] Fix generic formal parameter incorrectly visible from outside of instance

[Eric Botcazou]

The problem had been partially fixed two decades ago and the original testcase 
correctly rejected, but almost 4 years later the submitter made a small tweak 
to it which exposed the issue again...

The original fix was a change to Find_Expanded_Name, this additional fix is to 
make the same change to the processing of Collect_Interps for expanded names.

Tested on x86-64/Linux, applied on the mainline.


2025-10-30  Eric Botcazou  <ebotca...@adacore.com>

        PR ada/15610
        * sem_type.adb (Collect_Interps): Apply the same visibility
        criterion to expanded names as Find_Expanded_Name.


2025-10-30  Eric Botcazou  <ebotca...@adacore.com>

        * gnat.dg/specs/generic_inst7.ads: New test.
        * gnat.dg/specs/generic_inst8.ads: New test.

-- 
Eric Botcazou
diff --git a/gcc/ada/sem_type.adb b/gcc/ada/sem_type.adb
index 32d0833f3a8..0d13765c31c 100644
--- a/gcc/ada/sem_type.adb
+++ b/gcc/ada/sem_type.adb
@@ -610,14 +610,17 @@ package body Sem_Type is
       First_Interp := All_Interp.Last;
       Add_One_Interp (N, Ent, Etype (N));
 
-      --  For expanded name, pick up all additional entities from the
-      --  same scope, since these are obviously also visible. Note that
-      --  these are not necessarily contiguous on the homonym chain.
+      --  For an expanded name, pick up additional visible entities from
+      --  the same scope. Note that these are not necessarily contiguous
+      --  on the homonym chain.
 
       if Nkind (N) = N_Expanded_Name then
          H := Homonym (Ent);
          while Present (H) loop
-            if Scope (H) = Scope (Entity (N)) then
+            if Scope (H) = Scope (Entity (N))
+              and then (not Is_Hidden (H)
+                         or else Is_Immediately_Visible (H))
+            then
                Add_One_Interp (N, H, Etype (H));
             end if;
 

-- { dg-do compile }

package Generic_Inst7 is

   function F return Integer is (0);

   generic
     with function Foo return Integer;
   package P is
     type Color is (Foo);
   end P;

   package My_P is new P (F);

   I : Integer := My_P.Foo; -- { dg-error "expected type|found type" }

end Generic_Inst7;

-- { dg-do compile }

package Generic_Inst8 is

   function F return Integer is (0);

   generic
     with function Foo return Integer;
   package P is
     type Color1 is (Foo);
     type Color2 is (Foo);
   end P;

   package My_P is new P (F);

   I : Integer := My_P.Foo; -- { dg-error "no visible interpretation|use" }

end Generic_Inst8;