Introduce term.* labels for [basic.types.general] terms

[jensmaurer]

For ease of review, these are all separate commits.
Feel free to squash on merge.

Fixes #4630

[JohelEGP]

https://github.com/cplusplus/draft/wiki/Specification-Style-Guidelines says "create a \label{term.this.name} at the start of the paragraph defining the term". Perhaps it should say "sentence" rather than "paragraph".

61245eb starts with [std} rather than [std].

[jensmaurer]

@JohelEGP , fixed both issues.

[tkoeppe]

@zygoloid, @opensdh: this looks very nice, but I'd welcome some more Core eyes on those new terms.

[JohelEGP]

No new terms were introduced.

[tkoeppe]

(I mean the internal labelling of terms. The labelling is new, I suppose, not the terms.)

[opensdh]

It seems like this is an opportunity to do something like \impldef, where instead of

shall be a foo type\iref{term.foo.type}.

we could write

shall be a \tref{foo.type}.

Of course, we sometimes use just the adjective alone (which is known by \defnadjx at least), so we might want \adjref as well.

[jensmaurer]

In order to make \tref workable, we need LaTeX foo to replace the periods with spaces (or the other way round).

[tkoeppe]

(Tangent: if we had a text replacement system for LaTeX, I would also have a nice improvement for the unicode-smallcaps formatting -- I would like to format numerals and letters differently, but I don't know how to do that as a macro.)

[tkoeppe]

Why can't \tref{foo.type} work like savebox where it stored the actual content somewhere else?

[jensmaurer]

I guess there are not sufficiently many \saveboxes; I thought that's a quite finite resource.
Anyway, the definition of the term would need to translate space to period, which is approximately the same problem.

[tkoeppe]

We could use a custom label to store terms. For example:

\documentclass[a4paper,11pt]{article}

\makeatletter
\newcommand{\termdef}[2]{%
\protected@write \@auxout {}{\string \newlabel {#1}{{#2}{}}}#2}
\makeatother

\begin{document}
The \ref{term.dcl.spec} shall not be empty.
A \termdef{term.dcl.spec}{decl-specifier} is a thing you can use.
\end{document}

This uses the aux file as storage and requires multiple passes etc etc.

[jensmaurer]

@tkoeppe, that's not substantially different from my \label{term...} approach, which requires less internal knowledge about the structure of the .aux files.

We'd reap real benefits if we could make \defn (etc) auto-generate a label that could then be used via \termref or similar, using human-readable space-separated terms in both cases, and internally mapping to a dotted form with a "term." prefix.

Ah, looks like the xstring package does exactly that: https://tex.stackexchange.com/questions/36266/replacing-characters-in-argument-strings

[tkoeppe]

@jensmaurer, sort of, but what I'm proposing is to just explicitly spell out both the label and the actual term, rather than deriving one from the other. Not only does that require less implementation magic, but it also makes it possible to change the term without changing the label, etc. And the auxfile labelling mechanism is pretty well-established and tractable.

We could make a new command to replace \ref, e.g. \termref, to make the use clearer at the callsite.

[jensmaurer]

@tkoeppe , thanks for your thoughts. See #5210 for an approach that introduces term.* labels automatically.

Note that for each \defn (i.e. each term definition), we produce three things:

• text to be shown in the document
• an index entry
• (new) a label

We need macros so that the common case is easy, but (if need be) all three items must be influenceable independently.
For now, #5210 auto-generates labels from (the indexing portion of) \defn, \defnx, \defnadj, \defnadjx, but for index entries using special characters such as ! or @ to fine-tune the indexing, the resulting term.* label is ugly.
That doesn't prevent us from introducing a nice-looking term.* label in the vicinity, though.

In my view, \termref should show both the term and the cross-reference to where it is defined, e.g. "odr-use (6.2)", while naming the term only once.

And just to point out: Memoir creates .aux entries like this for \label:

\newlabel{term.piecewise.construction}{{\M@TitleReference {20.4.2}{Class template \texttt {pair}}}{579}{Class template \tcode {pair}}{lstlisting.20.-1376}{}}

[jensmaurer]

Automating the term.* definitions does detect duplicate term definitions quite nicely; see #5210