Support formatting specified lines.

[yilei]

Description

This adds a command-line option --line-ranges=, to tell Black to only format these specified lines.

Fixes #830

Checklist - did you ...

• Add an entry in CHANGES.md if necessary?
• Add / update tests if necessary?
• Add new / update outdated documentation?

[github-actions]

diff-shades reports zero changes comparing this PR (bd6d7ff) to main (ecbd9e8).

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What is this? | Workflow run | diff-shades documentation

[JelleZijlstra]

Thanks! This looks good, just a few pieces of minor feedback.

This has been a long-standing feature request, so it's great to finally see it in Black.

[yilei]

Thanks for the review! Updated.

[fearedbliss]

Thanks for implementing this @yilei. This will be extremely useful in many situations and circumstances.

[henriholopainen]

Funnily enough, I was working on the same feature and only now realised it had been finished when trying to open a draft PR. 😛 Oh well, what it's worth, my approach can be found here.

[henriholopainen]

Also this PR might be enough to close this issue

[yilei]

@henriholopainen Ah I'm sorry I didn't realize you were working on it. I should have sent the PR earlier as I've had it implemented for a while now.

[tartley]

This option doesn't appear to be working right for me. I'll post a minimal issue...

[tartley]

Minimal repro posted here: #4033