Re: [PING][PATCH 1/2] Ada: Synchronized private extensions are always limited

[Arnaud Charlet <charlet@adacore.com>]

Richard,

For some reason, your email is endeing up in a strange format, I almost
missed the .patch file attached, making the review harder.

There's a typo in the comment added:

+      --  explicit limitedness implied by a synchronized private extension
+      --  the does not derive from a synchronized interface (see RM-7.3(6/2)).

the -> that does not derive...

OK with this change.

> From: Richard Wai <richard@annexi-strayline.com> 
> Sent: Thursday, August 10, 2023 12:55 AM
> To: 'gcc-patches@gcc.gnu.org' <gcc-patches@gcc.gnu.org>
> Cc: 'Eric Botcazou' <ebotcazou@adacore.com>; 'Arnaud Charlet'
> <charlet@adacore.com>; 'Stephen Baird' <baird@adacore.com>
> Subject: [PATCH 1/2] Ada: Synchronized private extensions are always limited
> 
>  
> 
> GNAT currently considers a synchronized private extension that derives from
> an interface to be limited only when said interface is a concurrent
> interface. However it is of course legal for a synchronized private
> extension to derive from a limited interface. In this case GNAT fails to
> correctly determine that the private extension is limited.
> 
>  
> 
> This causes two separate problems that makes discriminated types in such a
> case impossible:
> 
> 1.	GNAT inappropriately rejects compilation, claiming default
> discriminants on such a private extension are illegal.
> 2.	GNAT fails to generate the expected discriminals for the
> unconstrained discriminanted case, leading to the corresponding
> discriminants of the "corresponding record" of the underlying concurrent
> type to have no identifiers, and thus compilation fails.
> 
>  
> 
> Fairly simple fix. If "synchronized" appears in the private extension
> declaration, it is limited. This is explicit in the RM as well (7.3(6/2)).
> 
>  
> 
> Fixing this bug uncovered of a related bug wrt. TSS address finalizer
> generation for constrained subtypes of synchronized private extensions with
> no default discriminants. That patch is to follow separately.
> 
>  
> 
> Patch file is attached.
> 
>  
> 
> --  Begin change log entry --
> 
>  
> 
> ada: Private extensions with the keyword "synchronized" are always limited.
> 
>  
> 
> GNAT was relying on synchronized private type extensions deriving from a
> concurrent interface to determine its limitedness. This does not cover the
> case where such an extension derives a limited interface. RM-7.6(6/2) makes
> is clear that "synchronized" in a private extension implies the derived type
> is limited. GNAT should explicitly check for the presence of "synchronized"
> in a private extension declaration, and it should have the same effect as
> the presence of "limited".
> 
>  
> 
> gcc/ada/
> 
>                 * sem_ch3.adb (Build_Derived_Record_Type): Treat presence of
> keyword "synchronized" the same as "limited" when determining if a private
> extension is limited.
> 
> 
> -- End change log entry --
>  
> 
> This patch was bootstrapped on x86_64-*-freebsd13.2. Two new test cases were
> added. Note that 4 gnat test cases fail currently on master and are
> unrelated to this patch.