[Bug ada/123302] New: Deeply nested generics cause visibility issues for container aggregate expressions

[liam at liampwll dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123302

            Bug ID: 123302
           Summary: Deeply nested generics cause visibility issues for
                    container aggregate expressions
           Product: gcc
           Version: 15.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ada
          Assignee: unassigned at gcc dot gnu.org
          Reporter: liam at liampwll dot com
                CC: dkm at gcc dot gnu.org
  Target Milestone: ---

Take the set of files at the end of this message which contain a vector behind
4 levels of generics (also included as an attachment). Compile with:

gnatmake -gnat2022 ./controller.adb

and you should observe the following error:

controller.ads:7:04: error: instantiation error at basic_config.adb:4
controller.ads:7:04: error: "Vector" is not visible
controller.ads:7:04: error: instantiation error at basic_config.adb:4
controller.ads:7:04: error: non-visible declaration from "Config_Data_Paths" at
a-coinve.ads:60, instance at config.ads:5

Obviously Vector should be visible here. This appears to be specific to
container aggregates and high levels of nested generics, as the following cases
compile successfully:

1. The same call to My_Config.Set inside of Controller instead of Basic_Config.
2. Replacing the Set procedure with `procedure Set (Path :
Config_Data_Paths.Extended_Index) is null;`.
3. Replacing `Config_Data_Paths.Vector` with a type defined within config.ads.
4. Compiling with `gnatmake -gnat2022 ./basic_config.adb`

This has been tested on 15.2.1 and the current trunk.

The file contents to reproduce this error follows (also attached):

==> basic_config.adb <==
package body Basic_Config is
   procedure Disable_Prunt is
   begin
      My_Config.Set (["a", "b"]);
   end Disable_Prunt;
end Basic_Config;

==> basic_config.ads <==
with Config;

generic
   with package My_Config is new Config;
package Basic_Config is
   procedure Disable_Prunt;
end Basic_Config;

==> config.ads <==
with Ada.Containers.Indefinite_Vectors;

generic
package Config is
   package Config_Data_Paths is new Ada.Containers.Indefinite_Vectors
(Positive, String);
   procedure Set (Path : Config_Data_Paths.Vector) is null;
end Config;

==> controller.adb <==
package body Controller is
   procedure Foo is
   begin
      My_Config.Set (["a", "b"]);
   end Foo;
end Controller;

==> controller.ads <==
with Config;
with Basic_Config;

generic
   with package My_Config is new Config (<>);
package Controller is
   package My_Module_Basic_Config is new Basic_Config (My_Config);
   procedure Foo;
end Controller;