bug#41242: Port feature/native-comp to Windows - Reduce the number of files probed when finding a lisp file.

[Nicolas Bértolo]

> In which folders are we going to search if we do (load "...a/path/foo.eln")?

> I believe in this case we should search the file only in "...a/path/"
> because the user really want to load this specific file.  Am I correct?

I'm not sure we want the load function to be that smart. This is from
the manual:

-----
The load function is not clever about looking at filename. In the perverse case
of a file named foo.el.el, evaluation of (load "foo.el") will indeed find it.
-----

I think we should respect that principle when dealing with .eln files, even if
it leads to trying to open absurd filenames.

I did some tests, and these are the files probed in each case:

(load "dir/foo.eln")

"{elt}/dir/foo.eln.eln"
"{elt}/dir/eln-hash/foo.eln.eln"
"{elt}/dir/foo.eln.dll"
"{elt}/dir/foo.eln.elc"
"{elt}/dir/foo.eln.elc.gz"
"{elt}/dir/foo.eln.el"
"{elt}/dir/foo.eln.el.gz"
"{elt}/dir/foo.eln"
"{elt}/dir/foo.eln.gz"

where {elt} is an element from `load-path`.

(load "C:/dir/foo.eln")

"c:/dir/foo.eln.eln"
"c:/dir/eln-hash/foo.eln.eln"
"c:/dir/foo.eln.dll"
"c:/dir/foo.eln.elc"
"c:/dir/foo.eln.elc.gz"
"c:/dir/foo.eln.el"
"c:/dir/foo.eln.el.gz"
"c:/dir/foo.eln"
"c:/dir/foo.eln.gz"

(load "dir/foo.eln" nil nil t) <- nosuffix: t

"{elt}/dir/foo.eln"

(load "C:/dir/foo.eln" nil nil t) <- nosuffix: t

"C:/dir/foo.eln"

> That said IMO this logic is sufficiently complex to deserve a minimum of
> testing to make sure we have it under control.  Not sure if the best
> place is files-tests.el or comp-tests.el.

I agree about this. I am not sure what is the best way to do it. The list of
files probed is inaccessible from Lisp.

Thanks,

Nico.