!standard 13.12 (4)                                   04-06-17  AI95-00381/02
!standard 13.12.1 (1)
!class amendment 04-06-08
!status Amendment 200Y 04-06-29
!status ARG Approved 11-0-1  04-06-17
!status work item 04-06-08
!status received 04-06-08
!priority Medium
!difficulty Easy
!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 make sense to
have a general No_Dependence restriction, identifying the restricted
package by the expression associated with the restriction.

!proposal

(See wording.)

!wording

  Change 13.12(4) to:

  restriction ::= restriction_identifier
    | restriction_parameter_identifier => restriction_parameter_argument

  restriction_parameter_argument ::= name | expression

  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 library unit on which there
            are no semantic dependences.

        Name Resolution Rules

    The restriction_parameter_argument of a No_Dependence restriction shall be
    a name that corresponds to the full expanded name of a language-defined library unit.

        Post-Compilation Rule

    No compilation unit included in the partition shall depend semantically
    on the library unit identified by the name.

!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 static string identify the library unit, as this
would allow a "wildcard" notation (like "Ada.Wide_*"), and would require less
changes to the existing language. But it was just too unnatural.

!example

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

!ACATS test

An ACATS test should be created for this pragma.

!corrigendum 13.12(4)

@drepl
@xcode<@fa<restriction ::= >@ft<@i<restriction>>@fa<_identifier
    | >@ft<@i<restriction_parameter>>@fa<_identifier =@> expression>>
@dby
@xcode<@fa<restriction ::= >@ft<@i<restriction>>@fa<_identifier
    | >@ft<@i<restriction_parameter>>@fa<_identifier =@> restriction_parameter_argument>

restriction_parameter_argument ::= name | expression>

!corrigendum 13.12.1(1)

@dinsc
@i<@s8<Static Semantics>>

The following @i<restriction_parameter>@fa<_identifier> is language defined:

@xhang<@xterm<No_Dependence>
Specifies a language-defined library unit on which there are no semantic dependences.>

@i<@s8<Name Resolution Rules>>

The @fa<restriction_parameter_argument> of a No_Dependence restriction shall be
a name that corresponds to the full expanded name of a language-defined
library unit.

@i<@s8<Post-Compilation Rules>>

No compilation unit included in the partition shall depend semantically
on the library unit identified by the @fa<name>.

!appendix

From: Tucker Taft
Sent: Monday, June 7, 2004 11:48 PM

Here is my last homework assignment (I hope, and probably
so do you ;-).  It is a proposal to add a restriction-parameter
identifier "No_Dependence" whose expression is a static string
identifying a language-defined or implementation-defined
library unit.  No compilation unit in the partition may
have a semantic dependence on this library unit.

I chose to use a static string rather than an unquoted
name to conform to the basic syntax of
    restriction_parameter_identifier => expression
This decision is debatable.  See the !discussion for
a bit more rationale.

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

From: Robert A Duff
Sent: Wednesday, June 9, 2004 10:30 AM

I don't care much one way or the other, but I suspect most users would
find the quotes to be superfluous.

Also, I wonder whether the string can contain blanks and other
whitespace:

    pragma Restrictions
        (No_Dependence => "Ada.     " & ascii.nl & " Command_Line");

I don't want to clutter the RM with rules forbidding such.
But when it comes to ascii.nl, whether that's whitespace might
be considered implementation dependent.

Does "Ada.Command_Line -- comment" correspond to a full expanded name?

Syntactically using a 'name' avoids worrying about such silliness.
I realize it might complicate the wording.

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