Make pygments mandatory and fix string highlighting

[The-Compiler]

• Closes Add "color" install extra #7683
• Fixes (🎁) color the diff of strings #13175

[nicoddemus]

Awesome, thanks!

[The-Compiler]

Didn't quite work out as planned, as I didn't see that the not in assertion output also uses _diff_text, but then post-processes the diff to show a nicer output:

pytest/src/_pytest/assertion/util.py

Lines 590 to 599 in afdf03b

	newdiff = [f"{saferepr(term, maxsize=42)} is contained here:"]
	for line in diff:
	if line.startswith("Skipping"):
	continue
	if line.startswith("- "):
	continue
	if line.startswith("+ "):
	newdiff.append(" " + line[2:])
	else:
	newdiff.append(line)

Opted to add a dummy_highlighter function to avoid having to special-case this in _diff_text, WDYT?

[nicoddemus]

Opted to add a dummy_highlighter function to avoid having to special-case this in _diff_text, WDYT?

Sounds good to me. 👍

[BenjaminSchubert]

Looks great, thanks!

[KotlinIsland]

awesome PR, this is a very welcome change

I think it would make sense to document the extra somewhere. explain why it exists/what it does

[The-Compiler]

I think it would make sense to document the extra somewhere. explain why it exists/what it does

I don't think there's a good place for this in the docs, especially because we don't do this kind of thing for any of the other dependencies either. And if you see it in action (and/or know what Pygments does), I think it's kind of obvious.

[KotlinIsland]

think it's kind of obvious

I have no idea what pygments is/does, and I have no idea how to discover if a package has any extras or not. I think not stating that this extra functionality is available would be a disservice to your users 🙂

[The-Compiler]

This PR makes it a dependency, not an extra. You don't need to know it exists, you will just get syntax highlighting after installing pytest.

[KotlinIsland]

oh, my mistake! sorry, okay that's great!

[The-Compiler]

@Pierre-Sassoulas @Zac-HD @RonnyPfannschmidt Do you have any objections/concerns with adding Pygments as a default dependency (at least until PEP 771 – Default Extras for Python Software Packages | peps.python.org is a thing), or should I merge this?

(Sorry for the explicit ping - not asking for a full review as I think we have this covered, just for an opinion on the dependency because I'd like to give everyone a chance to speak up if there is some implication I didn't consider)

[Zac-HD]

In general I prefer minimal dependencies, but I think the case for Pygments is strong enough to add it in this case.

If we do get a default-extras PEP I'd be keen to move it to that and make sure we test without it too though.

[hugovk]

(at least until PEP 771 – Default Extras for Python Software Packages | peps.python.org is a thing)

The PEP is now up for discussion, please leave a comment if you'd like to add your support or give other feedback:

https://discuss.python.org/t/pep-771-default-extras-for-python-software-packages/79706