bug#54976: 29.0.50; Eshell breaks when unknown entries in eshell-modules-list

[Stefan Kangas]

close 54976 29.1
thanks

Sean Whitton <spwhitton@spwhitton.name> writes:

> Suppose you put this in your init.el:
>
>     (add-to-list 'eshell-modules-list 'eshell-elecslash)
>
> because you want to use the new em-elecslash.el module I'm working on.
>
> Then if you try to M-x eshell on an older version of Emacs which lacks
> em-elecslash, Eshell will fail to initialise at all.
>
> It is easy add a guard (when (locate-library ...)) or similar, but this
> is not possible if you have added eshell-elecslash using the customise
> interface.  In that case, by enabling the module, youq just make your
> init unusable with older Emacs.
>
> It would be better to print a warning, say, rather than error.

I agree that it makes more sense to warn here instead of refusing to
start.  So I have now done that in Emacs 29 (commit d6b4803850).