extension: fix env.app deprecation warning

[jnikula]

Switch from env.app.emit() to env.events.emit() to fix the Sphinx deprecation warning introduced in version v9.0.0:

RemovedInSphinx11Warning: 'sphinx.environment.BuildEnvironment.app' is deprecated

The env.events.emit() interface has been there since Sphinx v3.0.0, so there shouldn't be any need to bump dependencies for this.

See also sphinx-doc/sphinx#14119

[BrunoMSantos]

Nice to see these recent clean ups in sphinx, even if they break a couple of things along the way.

Just to confirm, this is still valid on older Sphinx versions, right?

[jnikula]

Just to confirm, this is still valid on older Sphinx versions, right?

It should work with Sphinx v3.0.0 and later, based on looking at Sphinx git history, but I was only able to test v6.2.1. Earlier Sphinx would have required an earlier Python version, and I didn't want to go through that rabbit hole.

[BrunoMSantos]

It should work with Sphinx v3.0.0 and later, based on looking at Sphinx git history, but I was only able to test v6.2.1. Earlier Sphinx would have required an earlier Python version, and I didn't want to go through that rabbit hole.

Ah, sure. I only meant to check that self.env.events was not a new API that was missing in earlier versions. I think that's far enough ;)