[bug#50755] [PATCH v3] import: Generate list of importers based on available modules

[Maxime Devos <maximedevos@telenet.be>]

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pinoaffe schreef op do 30-09-2021 om 10:17 [+0200]:
> Maxime Devos writes:
> > These numbers turn out to be misleading, because 'scheme-modules'
> > (indirectly called from all-modules) calls 'resolve-interface' on every module
> > name.  For a module name, the first 'resolve-module' incurs disk I/O and some
> > CPU for loading the module, but the second 'resolve-module' on the same module
> > name would be free, as the module is already loaded.
> okay, the first incantation of 
> 
> (time (for-each (lambda (_)
>                    (delete-duplicates (filter-map (lambda (module)
>                      (match (module-name module)
>                             (`(guix scripts import ,importer)
>                              (symbol->string importer))
>                              (#t #f)))
>                      (all-modules (map (lambda (entry)
>                                     `(,entry . "guix/scripts/import"))
>                                     %load-path)))))
>                  (iota 1)))
> 
> on a "fresh" guix repl on my system results in 
> 
> clock utime stime cutime cstime gctime
>  1.28  0.76  0.13   0.00   0.00   0.16

On my fresh guix repl, it's a bit longer:

clock utime stime cutime cstime gctime
 9.54  1.79  0.31   0.00   0.00   0.53

(9 or 10 seconds)

If I restart the guix repl and run it again,
I get about half a second:

clock utime stime cutime cstime gctime
 0.47  0.57  0.02   0.00   0.00   0.19

> which is indeed a significant amount of time, though I don't think it'd
> be much of an issue considering that it's not likely that users will run
> lots of `guix import` shell commands in rapid succession.

The list of importers is only needed for two purposes, right?

   1. to print a list of importers when "guix import --help" is run
   2. to verify the string actually specifies an importer

Then 'guix import SOME-IMPORTER STUFF' could be optimised:

reolve-importer and guix-import could be modified to skip the validation
step and let resolve-importer print the error if the module couldn't be
found.  Possibly (resolve-module '(the possibly undefined module) #:ensure #f)
might be useful. Then 'importers' would only be required for purpose (1),
so it could be wrapped in a promise, such that if "guix import some-importer stuff"
is called, only the required importer module is loaded.

Greetings,
Maxime.

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