!standard 13.12.1 (0)                                  04-06-08  AI95-00381/01
!class amendment 04-06-08
!status work item 04-06-08
!status received 04-06-08
!priority Medium
!difficulty Low
!subject New Restrictions identifier No_Dependence

!summary

A new Restrictions identifier is proposed to specify that there are no
dependences on a given language-defined or implementation-defined package.

!problem

There are a number of Restrictions identifiers provided for disallowing
dependence on one language-defined package or another.  Rather than
adding more of these identifiers piece-meal, it would seem to make sense to
have a general No_Dependence restriction, identifying the restricted
package by the expression associated with the restriction.

!proposal

(See wording.)

!wording

New section 13.12.1:

    13.12.1 Restriction No_Dependence

        Static Semantics

    The following restriction_parameter_identifier is language defined:

    No_Dependence
            Specifies a language-defined or implementation-defined
            library unit on which there are no semantic dependences.

        Name Resolution Rules

    The expression of a No_Dependence restriction is expected to be of
    type Standard.String.

        Legality Rules

    The expression of a No_Dependence restriction shall be a static
    string expression. The value of the string shall correspond (in
    upper, lower, or mixed case) to the full expanded name of a
    language-defined or implementation-defined library unit.

        Post-Compilation Rule

    No compilation unit included in the partition shall depend semantically
    on the library unit identified by the static string expression.

!discussion

This restriction should reduce the need for having a separate restriction
identifier for each potentially interesting language-defined library unit.

We considered using a name rather than a static string to identify the
library unit, but the name could not be construed as an expression
of any actual type, and the basic syntax of pragma Restrictions specifies
the use of an expression after a restriction_parameter_identifier.
Furthermore, using a name in some sense implies a dependence on the named
unit, whereas the whole point is to avoid any dependence. A static string
seems to have the right semantics for this purpose.

We could also consider supporting some kind of "wildcard" notation,
such as "Ada.Wide_*". This would clearly depend on using a string
rather than a name for the argument.

!example

    pragma Restrictions(No_Dependence => "Ada.Command_Line");
        -- Example of restriction on language-defined package

    pragma Restrictions(No_Dependence => "System.RTS.Tasking");
        -- Example of restriction on implemenation-defined package

!ACATS test

An ACATS test should be created for this pragma.

!appendix

****************************************************************