Impressively difficult to compile code for GNAT

Impressively difficult to compile code for GNAT

[gcc]

Hello.

I'm working on a small project to create an abstraction over directories
and archives. I've managed to write some code that seems simple enough
(using tagged limited types) and even though the code appears to be valid,
it seems to either trigger bugs in the runtime (causing crashes on execution)
or fails to compile:

Both Debian GCC 4.3, GNAT GPL 2009 and FreeBSD GCC 4.4 fail with the following:

  pfseudo-archiver-directory.adb:24:41: wrong type for return_subtype_indication
  pfseudo-archiver-directory.adb:46:35: wrong type for return_subtype_indication

GCC SVN (r154285) fails to build with a strange error:

  arc_dir_003.adb:25:32: "_master" conflicts with declaration at line 21

The output of -gnatG shows this error to be apparently incorrect:

   error := false;
   B_1 : declare
      _master : constant integer := system__soft_links__current_master.all;
      A6bM : integer renames _master;
      type A6b is access all pfseudo__archiver__Tarchive_tC;
      R7b : A6b := pfseudo__archiver__directory.

The code is available here:

  http://git.coreland.ath.cx/gitweb.cgi?p=pfseudo/.git;a=summary
  $ git clone http://git.coreland.ath.cx/pfseudo/.git

Configure and build with:

  $ echo 'gcc'      > conf-adacomp
  $ echo 'gnatbind' > conf-adabind
  $ echo 'gnatlink' > conf-adalink
  $ make
  $ make tests

Regards,
M

Re: Impressively difficult to compile code for GNAT

[gcc]

Here's another case from a prototype that causes a crash on GCC 4.4
but, ironically, gives every impression of compiling and running
on earlier versions (4.3, GPL 2009):

with Ada.Streams.Stream_IO;
with Ada.Finalization;

package Archiver is

  type Archiver_t is tagged limited private;
  type Archive_t  is tagged limited private;

  function Open_Archive
    (Archiver : in Archiver_t;
     Path     : in String) return Archive_t'Class;

  function Stream
    (Archive : in Archive_t)
      return Ada.Streams.Stream_IO.Stream_Access;

private
  package Stream_IO renames Ada.Streams.Stream_IO;

  type Archiver_t is tagged limited null record;

  type Archive_t is new Ada.Finalization.Limited_Controlled with record
    Name : access String;
    File : Stream_IO.File_Type;
  end record;

end Archiver;

package body Archiver is

  function Open_Archive
    (Archiver : in Archiver_t;
     Path     : in String) return Archive_t'Class
  is
    pragma Unreferenced (Archiver);
  begin
    -- This line causes a segmentation fault.
    return A : Archive_t'Class := Archive_t'(Ada.Finalization.Limited_Controlled with others => <>) do
      A.Name := new String'(Path);
      Stream_IO.Open
        (Name => A.Name.all,
         File => A.File,
         Mode => Stream_IO.In_File);
    end return;
  end Open_Archive;

  function Stream
    (Archive : in Archive_t)
      return Ada.Streams.Stream_IO.Stream_Access is
  begin
    return Stream_IO.Stream (Archive.File);
  end Stream;

end Archiver;

with Ada.Text_IO;
with Ada.Streams.Stream_IO;
with Archiver;

procedure Main is

  A : Archiver.Archiver_t;
  S : constant Ada.Streams.Stream_IO.Stream_Access := Archiver.Stream (Archiver.Open_Archive (A, "file.zip"));
  X : Integer;

begin
  X := Integer'Input (S);

  Ada.Text_IO.Put_Line (Integer'Image (X));
end Main;

Re: Impressively difficult to compile code for GNAT

[Robert Dewar]

By the way, a general note is that it is usually a good
idea to stay away from anonymous access types, since
for one thing, there are real issues in freeing them.

Re: Impressively difficult to compile code for GNAT

[gcc]

On 2009-11-21 12:09:11, Robert Dewar wrote:
> By the way, a general note is that it is usually a good
> idea to stay away from anonymous access types, since
> for one thing, there are real issues in freeing them.

Agreed, yes.

In the real project, the String_Access types from the unbounded
strings package was used.

Regards,
Mark

Re: Impressively difficult to compile code for GNAT

[gcc]

Bug filed here:

  http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42140

Re: Impressively difficult to compile code for GNAT

[Eric Botcazou]

> The code is available here:
>
>   http://git.coreland.ath.cx/gitweb.cgi?p=pfseudo/.git;a=summary
>   $ git clone http://git.coreland.ath.cx/pfseudo/.git

See http://gcc.gnu.org/bugs for instructions on how to report bugs.

-- 
Eric Botcazou