[NTG-context] No error when loading a non-existent module

[Max Chernoff]

On Fri, 2022-08-26 at 07:40 +0200, Hans Hagen wrote:
> On 8/26/2022 3:00 AM, Max Chernoff wrote:
> > Is there a way to make this produce a nice little "error" PDF as soon as
> > the error occurs just like using "\undefined" does?
> 
> Only If I add it as option (directive driven, must find some good name 
> for it).

You already have errors and warnings as an option, so a good name might
be "fatal"?

> Most modules add commands and that shows immediately. Modules that kick 
> in without some command that needs to enable something are sort of 
> not-done or rare and experimental only and comparable to when some 
> module patches or overloads core functionality withoutr mentioning it.

Here I'm mainly thinking about my lua-widow-control module, which
produces a visual effect, although it can be quite subtle if you're not
paying very close attention.

> > > and if needed can add that line to a local cont-loc.mkxl file so that it
> > > always kicks in.
> > 
> > Didn't know about that either.
> 
> Ah, that's one of the oldest features: cont-new (for patched before 
> updates), cont-loc (for local preferences) and cont-exp (for wolfgang 
> and me)

Not seeing anything on the Wiki about either of those. I guess that
means I'm volunteering myself :)

Similarly to "cont-loc.mkxl", is there some local file that is only read
during format generation? Some of my documents use pgf/TikZ and expl3,
and loading these during format generation can save quite a bit of time
when compiling. I know that I can just modify "cont-en.mkxl" or
"context.mkxl", but those can be overwritten by updates.

> > But wouldn't it make sense for this to be an error by default? Nothing
> > good can happen if a user loads a non-existent (or misspelled) module.
> > Loading a non-existent file is a fatal error even in Plain TeX
> > \nonstopmode. I think that making this an error by default would break
> > very few working documents. In exchange, most users would get much more
> > helpful error messages.
> It would never be default because it is quite possible to have cases 
> where a module became redundant or is optional. There arte very few 
> cases where we are not downward 'command and file' compatible (the most 
> noticeable exceptions are when font, language and encoding subsystems 
> fundamentally change).

Fair enough. 

Thanks,
-- Max