Re: catcode problems with `@include`

[Gavin Smith]

On Tue, Sep 12, 2023 at 08:32:10AM +0000, Werner LEMBERG wrote:
> 
> [texinfo.tex version 2023-08-13.14]
> 
> 
> Please consider the attached files.  If I say
> 
> ```
> luatex foo.texinfo
> ```
> 
> the `@tex` environment within this file works just fine, and file
> `foo.lua` is correctly loaded.  However, saying
> 
> ```
> luatex bar.texinfo
> ```
> 
> which includes file `bar.itexi`, I get an error:
> 
> ```
> (./bar.itexi[\directlua]:1: ')' expected near '@'.
> l.5     dofile(kpse.find_file("bar.lua")) }
> ```
> 
> AFAICS, there is a problem with the handling of underscores in
> included files that contain a `@tex` environment, having the wrong
> catcode.

The problem appears only to occur when the @tex directive follows the
"\input texinfo" line directly.  The @include directive is a red herring:
you get the same error if you remove the blank line after "\input texinfo" in
foo.texinfo:

\input texinfo
@tex
\ifx\luatexversion\thisisundefined
\else
  \directlua{
    dofile(kpse.find_file("foobar.lua")) }
\fi
@end tex

foobar

@bye

It appears to be related to code to support Texinfo as a "pre-dumped" TeX
format.  I'm not aware if this is ever used, but this support was always
present and previously relied on the presence of a "@setfilename" line
before we made that command optional in Texinfo files.  We try to run
this code as soon as possible.

I've made a change to support @tex (and other block commands) on the
second line of the input file (version 2023-09-12.17).  Please let me know
if it works.