Re: How to autoload Tramp methods

[Michael Albinus]

Eshel Yaron <me@eshelyaron.com> writes:

Hi Eshel,

>> The idea is good. However, tramp-dissect-file-name is the most often
>> calles function in Tramp (a workhorse), I wouldn't like to make it
>> heavier.
>
> Makes sense, although I'd be surprised if this makes any noticeable
> performance difference: in the common case of a method that is already
> in tramp-methods, there's no runtime cost; for methods that are not yet
> in tramp-methods, there's a one-time cost.  For bogus methods, there's a
> tiny added cost of one intern-soft, and these calls are just about to
> error out anyway.  Still, maybe there's a better way to do this.
>
> Perhaps a slightly nicer interface would be:
>
> Here the contract of tramp-foo-method-params would be that it is called
> with no arguments (or maybe with the method name as a sole argument?)
> and returns a list of parameters that is used as the cdr of a
> tramp-methods entry.  This way extensions just need to provide an
> autoloaded function that returns some parameters, no need to worry about
> how and when exactly to modify tramp-methods.

Even more complicate and error-prone.

As said above, tramp-dissect-file-name is such an essential function in
Tramp, that I won't add unrelated functionality. I fear collateral
damages, and yes, this happened in the past already.

The Tramp package should not try to check for external extensions. Such
external extensions must plug into Tramp on their own. This was one of
the motivations to create tramp-container.el, which has integrated
existing ELPA packages like docker-tramp, kubernetes-tramp, and
tramp-nspawn.

>> How about defining and autoloading tramp-enable-foo-method, and *also*
>> adding in foo-tramp.el
>>
>> ;;;###autoload
>> (tramp-enable-method "foo")
>>
>> In order to avoid loading foo-tramp due to this call, you must autoload
>> the *implementation* of tramp-enable-foo-method, like
>>
>> ;;;###autoload
>> (progn (defun tramp-enable-foo-method ()
>>   "Enable connection to foo."
>>   (add-to-list 'tramp-methods
>>             `("foo"
>>               ...))))
>
> Interesting, wouldn't autoloading the call to tramp-enable-method end up
> loading Tramp to define tramp-enable-method during Emacs start up?

Yes, it would load tramp.el. But this is needed anyway, if you want
Emacs to detect "/foo:host:/path/to/file" as remote file name.

Another, minor, advantage of this approach is that Tramp would
reconsider foo as possible candidate of method completion of "C-x C-f
/fo TAB" even if tramp-dissect-file-name hasn't been called ever.

> Thanks,
>
> Eshel

Best regards, Michael.