[Bug ada/38975] New: deferred constants of not null access types are not possible

[Bug ada/38975] New: deferred constants of not null access types are not possible

[Artem dot Andreev at oktetlabs dot ru]

The following does not compile:

package Test is
    type X is new Positive;
    type X_Access is not null access constant X;

    Y : constant X_Access;
private
    Y_Val : aliased constant X := 1;
    Y : constant X_Access := Y_Val'Access;
end Test;

with the following diagnostics:
test.ads:6:09: warning: (Ada 2005) null-excluding objects must be initialized
test.ads:6:09: warning: "Constraint_Error" will be raised at run time
test.ads:11:09: "Y" conflicts with declaration at line 6

If "not null" modifier is removed, everything is fine.

As I can see from the following code, the semantic analyzer sees a deferred
constant and (erroneously) assumes that it's an uninitialized object. It then
inserts an implicit null initialization. And when it comes to a full definition
of the constant, the compiler thinks it has been already defined:

(gcc/ada/checks.adb, procedure Null_Exclusion_Static_Checks, line 2728):
     if K = N_Object_Declaration
        and then No (Expression (N))
        and then not No_Initialization (N)
      then
         --  Add an expression that assigns null. This node is needed by
         --  Apply_Compile_Time_Constraint_Error, which will replace this with
         --  a Constraint_Error node.

         Set_Expression (N, Make_Null (Sloc (N)));
         Set_Etype (Expression (N), Etype (Defining_Identifier (N)));

         Apply_Compile_Time_Constraint_Error
           (N      => Expression (N),
            Msg    => "(Ada 2005) null-excluding objects must be initialized?",
            Reason => CE_Null_Not_Allowed);
      end if;

The code can be traced back to at least gcc 4.1.2


-- 
           Summary: deferred constants of not null access types are not
                    possible
           Product: gcc
           Version: 4.3.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ada
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: Artem dot Andreev at oktetlabs dot ru


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38975

[Bug ada/38975] deferred constants of not null access types are not possible

[sam at gcc dot gnu dot org]

------- Comment #1 from sam at gcc dot gnu dot org  2009-10-03 10:11 -------
It has been fixed on trunk by commit 134020. The fix will be in GCC 4.5.0.

    2008-04-08  Javier Miranda  <miranda@adacore.com>
            Robert Dewar  <dewar@adacore.com>
            Ed Schonberg  <schonberg@adacore.com>
[...]
        (Null_Exclusion_Static_Checks): If the non-null access type appears in
a
        deferred constant declaration. do not add a null expression, to prevent
        spurious errors when full declaration is analyzed.


-- 

sam at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sam at gcc dot gnu dot org
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.5.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38975

[Bug ada/38975] deferred constants of not null access types are not possible

[ebotcazou at gcc dot gnu dot org]

------- Comment #2 from ebotcazou at gcc dot gnu dot org  2009-10-03 10:31 -------
> It has been fixed on trunk by commit 134020. The fix will be in GCC 4.5.0.
> 
>     2008-04-08  Javier Miranda  <miranda@adacore.com>
>             Robert Dewar  <dewar@adacore.com>
>             Ed Schonberg  <schonberg@adacore.com>

The fix is already in GCC 4.4 then.


-- 

ebotcazou at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.5.0                       |4.4.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38975