On 02/04/2025 23.57, Herb Sutter wrote:
> Shafik’s fork below adds tags such as \ifndriref{tag} and \ubiref{tag}, for example:
>
> - no diagnostic required.
> + no diagnostic required\ifndriref{basic.def.odr.exact.one.def}.
>
> - program has undefined behavior if
> + program has undefined behavior\ubiref{lifetime.outside.pointer} if
>
> These are considered editorial and can be added while still working on C++26.
>
> The Appendix notes that after the EWG telecon I got strong feedback/suggestions (but that was NOT yet presented and approved by EWG) that the tag should include the specific phrase that introduces the UB/IF-NDR (if explicit), and a short description of how it arises?

"if explicit" can go. All UB/IF-NDR should be explicit; if some particular instance isn't,
it needs to be a core issue to add the explicitness.

> *Jens and Thomas (and everyone)*, what do you suggest that the LaTeX spelling and format for that UB/IF-NDR tag to be? And should it include a description of the UB/IF-NDR?

There are different meanings of "tag" that we're considering here, and it
helps to clearly differentiate those.

The LaTeX markup that Shafik's patch adds creates a cross-reference to the Annex
section in the main body of the text, plus creates verbose-ish Annex entries.
That's clearly editorial; if (for some transition period) we don't want the
Annex (yet), we could add the main-body LaTeX tags without any change to the textual
contents of the rendered PDF.

The Annex itself is clearly descriptive (quotes and examples) and thus is not
normative, either. At the time Shafik's approach was discussed in CWG,
CWG was tentatively-happy with it. Now, this appears to be considered an
EWG matter (why?), so are they ok with that style, or do they want something else?

An alternative approach would be the one employed for the
"Index of implementation-defined behavior"
where we add a short phrase into the main body LaTeX source proper and the index
is generated automatically.
However, this approach does not work well on the LaTeX source maintenance level
if we want to add examples and more elaborate explanation: those additional
large-ish chunks of text should be maintained in the LaTeX source for the Annex,
not inline with the main body.

> Example: Please show how you would like to tag [basic.life]/7, which says in part:
>
>
>
> […] The program has undefined behavior if
>
> (7.1) <https://eel.is/c++draft/basic.life#7.1> — the pointer is used as the operand of a /delete-expression/ <https://eel.is/c++draft/expr.delete#nt:delete-expression>,
>
> […]
>
> Shafik has added this edit:
>
> - program has undefined behavior if
> + program has undefined behavior\ubiref{lifetime.outside.pointer} if
>
>
>
> What should this example look like in LaTeX?
>
>
> Goal: To get enough unofficial direction here to write a paper proposing the diff for a initial small set of cases (perhaps a subset of Shafik’s, thanks Shafik!) for EWG to review, and if approved send to CWG for review, just to set out a precedent that we can then follow as we ramp up doing this systematically.

There is nothing for EWG to review here, because there is no language change being proposed
here. (Unlike when we get to the point how to address particular instances of undefined behavior.)

Thanks,
Jens