Hi Thierry,

> On 30 Jul 2023, at 01:55, LARONDE Thierry <[log in to unmask]> wrote:
> 
> So, as far as I'm concerned, I will make the file primitives behave like
> \input, state it in the documentation (so if someone wants to write
> another engine LaTeX compliant, it can at least start with that if he
> doesn't want my change file), with the TeX behavior (ignoring kpathsea),
> that is: one can not input or size etc. a file without an extension
> ---and this should not cause any problem for LaTeX per se because, if it
> was the case with the present state of core LaTeX, the problem would
> have been seen before in kerTeX.

Apologies if I’m misinterpreting there -- TeX *does* \input a file without an extension on TeX Live if there is one to be found:

echo "\write0{this is a file without an extension}" > TMP && tex "\input TMP\relax\bye"
This is TeX, Version 3.141592653 (TeX Live 2021) (preloaded format=tex)
(./TMP) [1
this is a file without an extension
]
Output written on TMP.dvi (1 page, 196 bytes).
Transcript written on TMP.log.

Similarly in LaTeX (albeit I’m not up-to-date here...) with

echo "\typeout{this is a file without an extension}" > TMP && latex "\input{TMP}\csname @@end\endcsname"
This is pdfTeX, Version 3.141592653-2.6-1.40.23 (TeX Live 2022/dev) (preloaded format=latex)
 restricted \write18 enabled.
entering extended mode
LaTeX2e <2021-11-15> patch level 1
L3 programming layer <2021-11-22> (./TMP
this is a file without an extension
)
No pages of output.
Transcript written on TMP.log.

It is only LaTeX commands such as \include which cannot include a file without an extension. 

Regards,
Will
(From phone)