AI22-0013-2

!standard 5.1(12.1/3)          22-02-03 AI22-0013-2/02

!standard 2.8(12)

!class binding interpretation 22-01-22

!status Amendment 1-2022 22-02-03

!status WG9 Approved 22-10-18

!status ARG Approved 16-0-0 22-02-03

!status work item 22-01-22

!status received 21-06-23

!submitter Tucker Taft

!priority Low

!difficulty Easy

!qualifier Clarification

!subject Pragma after a final label

!summary

A pragma is permitted after a label, even if there are no statements following the label. More generally, a pragma in the place of a statement is treated as a statement by other rules of the language.

!issue

Is the following legal:

begin
  if Some_Test then
      goto label;
  end if;
  Do_This;
  Do_That;
  <<label>>
  pragma Assert (X = Y);
end;

(Yes.)

!recommendation

A pragma is allowed immediately after a label, even if there are no statements after the label. This is a ramification of 2.8(7.1/3) which says that a pragma is allowed:

• In place of a statement in a sequence_of_statements.

Clearly if the pragma in the example above were replaced with a statement it would be syntactically legal, so that implies the pragma is legal even if there are no statements following it.

However, there is other wording that depends on a statement following a label. In particular, a goto statement jumps to a target statement rather than a target label, and for that reason, the change to allow a label at the end of a sequence of statements introduced the notion of an implicit null statement in 5.1(12.1/3):

If one or more labels end a sequence_of_statements, an implicit null_statement follows the labels before any following constructs.

One way to solve this is to say that a pragma that is used in the place of a statement is treated as a statement.

!wording

Modify 2.8(12):

Any pragma that appears at the place of an executable construct is executed{, and is treated for the purposes of other rules of the language as being of the same sort of executable construct}. Unless otherwise specified for a particular pragma, this execution consists of the evaluation of each evaluable pragma argument in an arbitrary order.

!discussion

It seems clear that a pragma immediately after a label makes sense, no matter where the label might be. The current wording for placement of pragmas already allows that, so this requires no change.

However, the existing wording for goto statements talks about a target statement, and that becomes more confusing if that target statement is actually a pragma. Hence, we propose to say that a pragma is treated as a statement when used in the place of a statement, and similarly for any other construct that it effectively replaces.

!corrigendum 2.8(12)

@drepl
Any @fa{pragma} that appears at the place of an executable construct is executed.
Unless otherwise specified for a
particular pragma, this execution consists of the evaluation of each
evaluable pragma argument in an arbitrary order.
@dby
Any @fa{pragma} that appears at the place of an executable construct is executed,
and is treated for the purposes of other rules of the language as being of
the same sort of executable construct. Unless otherwise specified for a
particular pragma, this execution consists of the evaluation of each
evaluable pragma argument in an arbitrary order.

!ACATS test

An ACATS C-Test should try an example similar to that in the !question.

!appendix

See the !appendix of AI22-0013-1 for the mail thread that led to this

solution.

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