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Message-ID:  <9bdba073-3e55-a6b6-f95e-9d4a2eb007ca@morningstar2.co.uk>
Date:         Fri, 28 Jul 2023 17:56:29 +0100
Reply-To:     Mailing list for the LaTeX3 project
              <LATEX-L@LISTSERV.UNI-HEIDELBERG.DE>
Sender:       Mailing list for the LaTeX3 project <LATEX-L@LISTSERV.UNI-HEIDELBERG.DE>
From:         Joseph Wright <joseph.wright@MORNINGSTAR2.CO.UK>
Subject: Re: "new" \input vs. primitive behavior
To:           LATEX-L@LISTSERV.UNI-HEIDELBERG.DE
In-Reply-To:  <f1b86bed-c65e-e919-b5d1-402f265b4d07@morningstar2.co.uk>
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Status: R

On 28/07/2023 17:29, Joseph Wright wrote:
> On 28/07/2023 16:44, LARONDE Thierry wrote:
>> On Fri, Jul 28, 2023 at 04:20:09PM +0100, Joseph Wright wrote:
>>> On 28/07/2023 16:18, David Carlisle wrote:
>>>> On 28/07/2023 16:14, LARONDE Thierry wrote:
>>>>> On Fri, Jul 28, 2023 at 03:58:49PM +0100, Joseph Wright wrote:
>>>>>> On 28/07/2023 15:28,  Thierry wrote:
>>>>>>> Yes. But the same engine does things differently between LaTeX
>>>>>>> 2022-11-01 and LaTeX 2023-06-01.
>>>>>>>
>>>>>>> So could someone give me the diff of the input related things in
>>>>>>> LaTeX between these two versions so that I can have a clue about
>>>>>>> what LaTeX is expecting and what it is eventually calling 
>>>>>>> (because it
>>>>>>> could be calling, low level, the open routine, and there is no
>>>>>>> acrobatics made in the open routine in kerTeX: the handling is made
>>>>>>> before calling the routine; so if LaTeX is calling low level like
>>>>>>> this, the result is not a surprise).
>>>>>> Older LaTeX used \openin + \ifeof to test for file existence; we 
>>>>>> now use
>>>>>> \(pdf)filesize, which is expandable and reports "0" for a
>>>>>> non-existent file.
>>>>>> Both methods should find "foo.tex" from "foo" in the same way.
>>>>>>
>>>>> Uh! You expect \filesize to do searching and file extension? Why?
>>>>> \filesize can be called with whatever file, not necessarily a .tex.
>>>>> Why would it assume it has to try an extension if it is not found?
>>>>>
>>>>> Where was this specified for the primitive?
>>>>
>>>> The primitive has always acted that way (since being added by pdftex)
>>>> it's not a latex feature.
>>>>
>>>> If \input{xxx} inputs a file, \(pdf)filesize{xxx} should refer to the
>>>> same file, so the primitive has always used the same file searching.
>>>
>>> Indeed, we (team) picked up the trick of using \(pdf)filesize from Heiko
>>> Oberdiek's code, where it has been used for I think 15+ years in some
>>> extensions to the graphics mechanisms for file searching.
>>>
>>
>> And it was specified nowhere.
> 
> True, but I think that's because it's implicit in TeX. The 'classical' 
> primitives \input, \openin and \openout all add .tex if no file 
> extension is given: this is why you cannot create extensionless files 
> from DocStrip, for example. So when Hans added other file-related 
> primitives to pdfTeX, the same underlying extension behaviour applied 
> automatically - the same low-level file access is used by everything.

Note that in order to do file testing by expansion (which we want for 
various expl3 functions), we *have* to avoid \openin and that 
realistically means \(pdf)filesize is the best option.

Joseph