[LyX/master] Implement properly \limits and \nolimits

[Enrico Forestieri]

On Wed, Sep 09, 2020 at 12:01:32PM +0200, Jean-Marc Lasgouttes wrote:
> Le 09/09/2020 à 11:00, Enrico Forestieri a écrit :
> > > Do you have a concrete case in mind where deriving requirements from the
> > > contents of the macro goes wrong? Note that in this case, we could decide
> > > that the requirements given to the macro override whatever is decided from
> > > its contents.
> > 
> > The point is that the macros defined in the symbols file are only used
> > for on-screen representation. Their definition will never appear in the
> > output. So, if \int is defined in the symbols file as
> > 
> > \def\int{\intop\nolimits}	esint|amsmath
> > 
> > meaning that it requires either esint or masmath, the requirements for
> > \intop should not be taken into account because \intop will never
> > appear in the latex file.
> 
> But \intop can appear in a LaTeX file, and it should work. So we have to set
> the requirements of \intop anyway.

Sure, and, indeed, when \intop appears its requirements are accounted for.

> > Here, the definition of \int is only used
> > for representing it on the screen. For example, if you define
> > 
> > \def\int{\vcentcolon}		esint|amsmath
> > 
> > because you like to see \vcentcolon instead of \int on screen, then
> > you would get the package mathtools as a requirement. But \vcentcolon
> > does not really appear in the output and that requirement is bogus.
> 
> I understand that but:
> 
> 1/ we do not want to do such bogus things in symbols file, unless you
>    have a better use case in mind.

That was only an example. However, the actual definition of \int is using
\intop and this was bringing in also its requirements. This was the cause
of the problem reported by Scott.

> 2/ this is why I proposed that in the case where requirements are given
>    for the macro, the requirements induced by the definition are
>    skipped.

This is exactly what the patch I applied is doing.

> The proposal 2/ is of course not 100% precise, since it is difficult to make
> a difference between "no requirement needed" and "no requirement given".

I don't understand. If the macro has a requirement (as far as latex is
concerned), it has to be listed and will be taken into account. If no
requirement is given, it means that pristine latex can deal with it.

> But in practice it seems easier in terms of maintenance to let LyX infer the
> requirements.

I fear there is a misunderstanding here. LyX does infer the requirements
for a user defined macro, but should not do it for the macros in the
symbols file. See the attached, where \int is redefined so that it now
requires the wasysym package.

-- 
Enrico
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