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Re: [SG16] P2348: Feedback on r1 draft

From: Jens Maurer <Jens.Maurer_at_[hidden]>
Date: Fri, 10 Sep 2021 09:36:37 +0200
On 09/09/2021 22.54, Hubert Tong wrote:

> (2)
> In the new [lex.whitespaces] subclause, the following is added:
> whitespaces are ignored except as they serve to separate tokens
> This seems to have come from the text being removed out of [lex.token] (where it was excusable). Whitespace separation is significant in [cpp.replace.general], etc. This sentence should at best be a note in relation to phase 7 of translation.
> I am happy to remove it entirely.
> It's certainly not needed for phase 7. And I think phase 3 wording says something similar.
> In [cpp.pre], Jens objected to my removal of
> > The only whitespace characters that shall appear between preprocessing tokens within a preprocessing directive (from just after the directive-introducing token through just before the terminating new-line character) are space and horizontal-tab (including spaces that have replaced comments or possibly other whitespace characters in translation phase 3).
> I am not able to convince myself than the grammar described at the start at [cpp.pre] allows line-breaks to appear between preprocessing tokens within a preprocessing directive,
> but I'm happy to replaced the striked paragraph by
> Only /horizontal-whitespace/s shall appear between preprocessing tokens within a preprocessing directive.
> This is neither necessary nor harmless. The term "preprocessing directive" is defined right after the grammar in [cpp.pre]. Its definition precludes the presence of line-breaks outside of /**/ between preprocessing tokens within the directive. We do want to allow comments in preprocessing directives.

Good point; I was missing [cpp.pre] p1, which seems to say everything we want to say.
So, I'm good with the removal now.

> This seems to point to another problem with the wording:
> (3)
> The removal of the comment replacement in phase 3 means that the definition of preprocessing directives requires an update to qualify that it wants to talk about line-breaks (but not those that are inside /**/ comments).

Indeed, the status quo seems to allow new-lines within /* comments */ inside a preprocessing-directive.

Maybe it would be clearer/easier to retain the replacement of comments with a single space
character in phase 3? While we do need to differentiate different kinds of whitespace
(horizontal whitespace vs. new-lines) in phase 4, there's no point in talking about comments
separately beyond phase 3.


Received on 2021-09-10 02:36:47