[Bug ada/114708] New: Creating access to an incomplete formal in a generic package sometimes causes GNAT to crash

[Bug ada/114708] New: Creating access to an incomplete formal in a generic package sometimes causes GNAT to crash

[jhb.chat at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114708

            Bug ID: 114708
           Summary: Creating access to an incomplete formal in a generic
                    package sometimes causes GNAT to crash
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ada
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jhb.chat at gmail dot com
                CC: dkm at gcc dot gnu.org
  Target Milestone: ---

Created attachment 57939
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57939&action=edit
incomplete formal example

When making a generic package that takes an incomplete formal as a parameter
and then creating an access type to that formal type inside the generic, GNAT
will crash if an actual incomplete type is supplied in the generic
instantiation.

This happens on gnat 13.0, on mwys2, Windows 10 Home, fully patched
    GNATMAKE 13.2.0
    Copyright (C) 1995-2023, Free Software Foundation, Inc.
    This is free software; see the source for copying conditions.
    There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A 
    PARTICULAR PURPOSE.

Checked Godbolt and this happens on trunk there and the ICE appeared to start
with GNAT 12.1 as GNAT 11.4 did not trigger the crash (on Godbolt).

Example:
procedure Main is

   generic
      type Element_Type(<>);
   package Test_Incomplete_Formal is
      type Element_Access is access Element_Type;
   end Test_Incomplete_Formal;

   type Node;

   package P is new Test_Incomplete_Formal(Node);

   type Node is limited null record;

begin
   null;
end Main;


Output:
$ gnatmake.exe main.adb 
gcc -c main.adb
+===========================GNAT BUG DETECTED==============================+
| 13.2.0 (x86_64-w64-mingw32) Program_Error EXCEPTION_ACCESS_VIOLATION     |
| Error detected at main.adb:6:7 [main.adb:11:4]                           |
| Compiling main.adb                                                       |
| Please submit a bug report; see https://gcc.gnu.org/bugs/ .              |
| Use a subject line meaningful to you and us to track the bug.            |
| Include the entire contents of this bug box in the report.               |
| Include the exact command that you entered.                              |
| Also include sources listed below.                                       |
+==========================================================================+

Please include these source files with error report
Note that list may not be accurate in some cases,
so please double check that the problem can still
be reproduced with the set of files listed.
Consider also -gnatd.n switch (see debug.adb).

main.adb

compilation abandoned
gnatmake: "main.adb" compilation error

[Bug ada/114708] [12/13/14 regression] internal error on access to an incomplete formal in generic package

[ebotcazou at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114708

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ebotcazou at gcc dot gnu.org
             Status|UNCONFIRMED                 |NEW
            Summary|Creating access to an       |[12/13/14 regression]
                   |incomplete formal in a      |internal error on access to
                   |generic package sometimes   |an incomplete formal in
                   |causes GNAT to crash        |generic package
   Last reconfirmed|                            |2024-04-20
     Ever confirmed|0                           |1

--- Comment #1 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
Confirmed as a regression in GCC 12 and later.

[Bug ada/114708] [12/13/14 regression] internal error on access to an incomplete formal in generic package

[ebotcazou at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114708

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |ebotcazou at gcc dot gnu.org

--- Comment #2 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
I'll have a look.

[Bug ada/114708] [12/13/14 regression] internal error on access to an incomplete formal in generic package

[ebotcazou at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114708

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED

[Bug ada/114708] [12/13/14 regression] internal error on access to an incomplete formal in generic package

[ebotcazou at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114708

--- Comment #3 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
This appears to be sufficient:

diff --git a/gcc/ada/exp_util.adb b/gcc/ada/exp_util.adb
index 04d114694ab..f81380846e0 100644
--- a/gcc/ada/exp_util.adb
+++ b/gcc/ada/exp_util.adb
@@ -6076,6 +6076,12 @@ package body Exp_Util is

       Utyp := Underlying_Type (Base_Type (Utyp));

+      --  Handle incomplete types
+
+      if No (Utyp) then
+         return Empty;
+      end if;
+
       --  Deal with untagged derivation of private views. If the parent is
       --  now known to be protected, the finalization routine is the one
       --  defined on the corresponding record of the ancestor (corresponding