Add DynamicPlugin object/context for ease of testing & dynamic plugin creation

[tlambert03]

was starting to work on some stuff over in napari/napari#4015 and realized we need a better way to inject temporary functionality into a test plugin manager. This adds a DynamicPlugin context manager that controls a manifest, and allows you to register commands with decorators:

from npe2 import DynamicPlugin

with DynamicPlugin() as plugin:
    @plugin.contribute.sample_data
    def make_image(x):
        ...

it will handle creation of a command, and the corresponding contribution type, and inject it into the plugin manifest and reindex. The decorator takes all the same parameters that the corresponding contribution would take:

    @plugin.contribute.writer(layer_types=["image"])
    def write_path(path, layer_data):
        ...

it cleans up after itself when leaving the context

edit: this also modifies a small amount of logic on the unregistering/deactivation of plugins in general, specifically around unregistering their commands

[codecov]

Codecov Report

Merging #128 (453cd9e) into main (41c557d) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              main      #128    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files           23        24     +1     
  Lines         1355      1483   +128     
==========================================
+ Hits          1355      1483   +128     

Impacted Files	Coverage Δ
npe2/__init__.py	100.00% <100.00%> (ø)
npe2/_command_registry.py	100.00% <100.00%> (ø)
npe2/_dynamic_plugin.py	100.00% <100.00%> (ø)
npe2/_plugin_manager.py	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 41c557d...453cd9e. Read the comment docs.

[nclack]

This is pretty interesting as a way of dynamically adding a plugin. I wonder if you think it'll be useful outside of testing?

[tlambert03]

I wonder if you think it'll be useful outside of testing?

I do! This PR started as a _testsupport module with a PluginFixture class... and as I realized the generality of it, I pulled it out into something different. It has a pattern that is not dissimilar to #75 in terms of associating a callable with a command and a contribution. As it currently stands, I think it's a relatively flexible base to use in many scenarios. (If you think a name other than TemporaryPlugin would help indicate that, I'm open :)

[tlambert03]

perhaps DynamicPlugin?

[tlambert03]

ok to merge if I change name to DynamicPlugin @nclack ?

[nclack]

ok to merge

Yes. Meant to approve before anyway.