incorrect @math spacing for PDF output with an empty macro

[Vincent Lefevre]

On 2022-10-14 06:56:13 +0100, Gavin Smith wrote:
> On Thu, Oct 13, 2022 at 11:20:24PM +0200, Vincent Lefevre wrote:
> > is not true. More precisely, I would expect
> > 
> > @macro ttie
> > @end macro
> > 
> > to generate nothing, but inserting @ttie{} in a TeX expression
> > modifies the spacing in the generated PDF.
> 
> Please provide a minimal example showing the problem.

----------------------------------------
\input texinfo    @c -*-texinfo-*-

@macro ttie {}
@end macro

@deftypefun int f1 ()
@math{@var{n}=-2}.
@end deftypefun

@deftypefun int f2 ()
@math{@var{n}@ttie{}=@ttie{}-2}.
@end deftypefun

@bye
----------------------------------------

I've tested this with texinfo.tex 2022-10-01.15 (current version).
PDF generated with "texi2dvi --pdf test.texi".

pdftotext shows
  * for f1: n = −2.
  * for f2: n = − 2.

The incorrect spacing for f2 is also visible with a PDF viewer.

I suspect that for f2, TeX regards the minus sign as a subtraction
instead of the unary negation.

FYI, the goal is to have @ttie{} equivalent to @tie{} except for
PDF output (where @tie{} also gives incorrect spacing).

-- 
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)