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[Motion cwg 7] P2915R0 (Proposed resolution for CWG1223) #6329

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merged 2 commits into from Jul 16, 2023
Merged

[Motion cwg 7] P2915R0 (Proposed resolution for CWG1223) #6329

merged 2 commits into from Jul 16, 2023

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burblebee
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@burblebee burblebee commented Jun 21, 2023 •
edited by jensmaurer

Fixes #6282.
Fixes cplusplus/papers#1596

Notes:

  • The wording for this paper is problematic, both for type-id and for declaration (e.g. trying to redefine grammar production rules). I did my best to improve it editorially with the changes you see, and inserted FIXMEs to point out the remaining badness.

@burblebee burblebee marked this pull request as ready for review June 21, 2023 21:32
JohelEGP
JohelEGP suggested changes Jun 26, 2023
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source/statements.tex Outdated
@@ -1081,7 +1081,8 @@
conversion\iref{expr.type.conv} as its leftmost subexpression can be
indistinguishable from a \grammarterm{declaration} where the first
\grammarterm{declarator} starts with a \tcode{(}. In those cases the
\grammarterm{statement} is a \grammarterm{declaration}.
\grammarterm{statement} is a declaration,
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Suggested change
\grammarterm{statement} is a declaration,
\grammarterm{statement} is a \grammarterm{declaration},

Restore the change by commit 8b1bd98.
That's bogus because \grammarterm is for uses,
not definitions (which happen in a special LaTeX environment).

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One cannot say that a grammar production rule is another grammar production rule. Hence, this was an attempt to improve the wording, taking advantage of the fact that "declaration" is loosely used as a term, so it's possible to alter/embellish/clarify it's definition. This change also follows existing precedence.

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We have ambiguous grammar, and this sentence says whether you take one or the other choice. Since grammar is presented as non-terminals expanding to other non-terminals, it seems plausible to say "is a declaration" (i.e. is this branch, not the other one).

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@burblebee burblebee Jun 29, 2023 •
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Ok to say "is to be considered a declaration"? That way we're claiming it's a rule rather than saying it is a rule, and we've used that wording elsewhere so it has precedence.

I reverted the change and added "to be considered" in a separate commit. Note that it's in a separate commit so the editor can choose to apply it (or not) at his discretion.

source/statements.tex Outdated
A syntactically ambiguous statement that can syntactically be
a \grammarterm{declaration} with an outermost \grammarterm{declarator}
with a \grammarterm{trailing-return-type}
is a declaration only if it starts with \keyword{auto}.
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Suggested change
is a declaration only if it starts with \keyword{auto}.
is a \grammarterm{declaration} only if it starts with \keyword{auto}.

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... likewise ...

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Fixed original commit to follow paper (as suggested) and added "to be considered" in a separate commit.

source/declarations.tex Outdated
whose outermost \grammarterm{abstract-declarator}
would match the grammar of an \grammarterm{abstract-declarator}
with a \grammarterm{trailing-return-type}
is to be considered a \grammarterm{type-id} only if it starts with \keyword{auto}.
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I'm using https://isocpp.org/files/papers/P2915R0.pdf to review.
It actually says

Suggested change
is to be considered a \grammarterm{type-id} only if it starts with \keyword{auto}.
is a \grammarterm{type-id} only if it starts with \keyword{auto}.

which is more consistent with the other additions.

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I disagree - it makes no sense for something to be a grammarterm. A grammarterm names a production rule, a purely lexical construct - it is its rule. "is to be considered" isn't right either, but at least we're not trying to redefine a rule.

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Fixed original commit to follow paper (as suggested) and added "to be considered" in a separate commit.

source/declarations.tex Outdated Show resolved Hide resolved
@jensmaurer jensmaurer added this to the post-2023-06 milestone Jun 28, 2023
@burblebee @tkoeppe
P2915R0 Proposed resolution for CWG1223
1cf424e 
Editorial notes:
- [dcl.ambig.res] Use "is to be considered a" instead of "is"
  to avoid redefining the grammar production /type-id/.
- [stmt.ambig] Likewise, don't use \grammarterm "declaration"
  in "is a declaration" to avoid redefining /declaration/.
- [stmt.ambig] Reword comment in example for consistency.
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tkoeppe commented Jul 16, 2023

The additional editorial change seems useful, but would it be enough to say "is considered a type-id" instead of "is to be considered a type-id"?

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The additional editorial change seems useful, but would it be enough to say "is considered a type-id" instead of "is to be considered a type-id"?

Works for me.

@burblebee @tkoeppe
[dcl.ambig.res][stmt.ambig] Change "is" to "is considered".
9b9ebcc 
This avoids suggesting that any \grammarterms are being (re)defined.
@tkoeppe tkoeppe merged commit baea8ec into main Jul 16, 2023
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@cor3ntin cor3ntin mentioned this pull request Jul 21, 2023
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@jensmaurer jensmaurer deleted the motions-2023-06-cwg-7 branch November 12, 2023 21:28
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@JohelEGP JohelEGP JohelEGP approved these changes

@jensmaurer jensmaurer Awaiting requested review from jensmaurer

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P2915 R0 Proposed resolution to CWG1223 [2023-06 CWG Motion 7] P2915R0 Proposed resolution for CWG1223
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