Add transient arg for pytest-xdist parallelization

[cvdub]

This PR adds rudimentary support for the pytest-xdist -n flag.

[wbolster]

thanks, but i think this won't work out of the box because it depends on pytest plugins?

not sure how to handle that gracefully. thoughts?

similar things apply for for coverage flags (pytest-cov)

[pkryger]

One option could be to query for installed plugins and display their respective options. Having said that, I found that pip is borderline unacceptable slow on my machine to do it on each popup (cache it in buffer local, but how to refresh?). Anyway, did that dirty bit of code (requires json) that may be of help

(defun pytest--plugins (packages)
  "Find information about installed PACKAGES.

Return an alist that elements are cons of package from PACKAGES
and the installed version (or nil if not installed)."
  (let ((installed-packages
         (with-temp-buffer
           (shell-command  "pip list --format=json" (current-buffer))
           (goto-char (point-min))
           (json-read))))
    (seq-map
     (lambda (plugin)
       (cons plugin
             (seq-some
              (lambda (pkg-info)
                (let-alist pkg-info
                  (when (string= .name plugin)
                    .version)))
              installed-packages)))
     packages)))

(pytest--plugins '("pytest-xdist" "pytest-cov" "pytest-foo"))
-> (("pytest-xdist" . "2.4.0") ("pytest-cov" . "2.12.1") ("pytest-foo"))

Edit: now when I think of it, it doesn't account that pytest may be called from "somewhere". I.e., /my/special/path/to/pytest-wrapper.sh that will call pytest installed somewhere with some plugins... a simple pip called shell-command won't cut it

[cvdub]

Good call on only adding this if the plugins are installed.

pytest actually returns plugin information if you pass -V/--version twice.

This function returns t if a plugin is installed:

(defun python-pytest--plugin-installed-p (plugin-name)
  "Returns t if PLUGIN-NAME is installed."
  (let* ((default-directory (python-pytest--project-root))
         (pytest-version-string (shell-command-to-string (concat python-pytest-executable " -V -V"))))
    (and (string-match-p plugin-name pytest-version-string) t)))

But I'm not sure the best way to conditionally include the plugin flags to the transient. Any ideas there?

[wbolster]

tbh i'm not a fan of dynamic plugin inspection

• potentially slows down
• caching may help, but they can go stale
• requires venv activation (direnv ftw, btw) for correct behaviour

both pytest-cov and pytest-xdist are widely used; are there any downsides to just including some flags (maybe with a hint in the section title) in the popup?

[pkryger]

tbh i'm not a fan of dynamic plugin inspection [...]

To add to that list, I'm not sure neither how to deal with it (redefine python-pytest-dispatch each time it's invoked?) nor how it would interfere with other transient's features, i.e., restoring a saved state when option is not available.

both pytest-cov and pytest-xdist are widely used; are there any downside to just including some flags (maybe with a hint in the section title) in the popup?

While I can see the former is being used in a few projects I'm working with these days, I cannot see the latter. Calling pytest -n 2 yields:

ERROR: usage: pytest [options] [file_or_dir] [file_or_dir] [...]
pytest: error: unrecognized arguments: -n
  inifile: /project/dir/setup.cfg
  rootdir: /project/dir

While I don't know yet how to achieve that and I acknowledge that would require some work, perhaps it's worth investigating filtering out unknown options right before calling pytest? It would add some time (pytest -V -V is a few hundred ms in one of my projects), but could result in more desirable UX. The filter out could be after a question or a warning, that is suppressible with a customization option. @cvdub @wbolster what do you think?

[wbolster]

i've added a variation of this pr (i kept @cvdub as main author) in e491a98.

it adds these dispatch options:

• -n which expands to --numprocesses=... with a shorter list of options
• -f which expands to --looponfail (toggle)

@cvdub and @pkryger sounds good?

[wbolster]

re pytest-cov: it's widely used but thinking of it, it requires proper config in pyproject.toml (or pytest.ini) anyway to be useful, which basically leaves a --no-cov option for toggling it off. i don't think that's worth it

[pkryger]

With all that has been said, I'm loosing my appreciation for dynamic plugin discovery. At least for now. Perhaps in a future we may want to revisit.

What's been done in e491a98 - LGTM

[cvdub]

Thanks for your work on this @wbolster!