Dynamically resize line number gutter width

[dgkf]

Addressing #2583, this PR implements the second proposed option.

Behavior

• The line number gutter will resize based on the number of digits in the line count for the Document
• The line number gutter will have a minimum width of 2 characters. This is so that configurations using line-number: "relative" aren't adversely affected by this change. In the future, the min/max width could perhaps be configurable and this hard-coded minimum could be removed.
• Enabled the GutterType::Spacer option. (I think the default gutter config should probably become ["diagnostics", "spacer", "line-number"] now numbers will butt right up against diagnostics past line 100)

behaviors that have been modified after review comments

• If the number of digits on screen exceeds 5 digits, only the last 4 digits are displayed (preceded by …) no longer truncates (as suggested in Dynamically resize line number gutter width #3469 (comment))
• Line number gutter width based on view bottom, not document bottom. Fixed

Screenshots

A very short window to highlight shrinking width (gutters: ["diagnostics", "spacer", "line-number"])

With default config, diagnostic symbols look a bit cramped

[dgkf]

width is no longer passed to gutter_type.row_styler (formerly constructor), though I could see the argument for calculating width first and providing it to the row_styler.

[archseer]

• The line number gutter will resize based on the number of digits for the line at the bottom of the view*

Bottom of the document is what we want though, otherwise the document will jitter sideways as you scroll.

[dgkf]

This is the only place where the Document isn't easily available to calculate the inner area (now that the gutter width is based on the Document contents). A simple solution is to use the entire view area instead.

I think this would affect things like moving to a split when the screen location that you would move to would be in the gutter of a neighboring split. Previously, if you were to try to find a neighboring split at a gutter, you would get the window to the left, now you would get the window that contains the gutter.

[the-mikedavis]

I've been testing this for a bit and I think you're right about the diagnostics being too cramped when there aren't many lines in a file. I think changing the default gutters to include a spacer between the diagnostics and line-numbers elements looks much better 👍

[dgkf]

Thanks @the-mikedavis - I forgot that was even non-standard. I've been using this with the spacer for so long now. I'll update with the change to the default.

[dgkf]

@the-mikedavis, the gutter spacer has been added as default (separating the diagnostics from the line numbers). Let me know if you want anything else to change before it's in an acceptable place.

[dgkf]

@archseer - Any chance I could grab your attention on this one?

Along those lines, I can't tell if I'm being annoying or helpful when I ping you all or re-request review. I know you all have an absolutely enormous PR backlog (IMO a reflection on the community's enthusiasm and not the pace of the maintainers 🎉), and I can't tell what is the best way to grab your attention.

After this PR, would it be helpful to submit a "PR Etiquette" section to the CONTRIBUTING guide to make this relationship less ambiguous? I can draft something up, but you all would probably need to weigh in on how you want things to flow.

[archseer]

I think in this case a ping is fine because I was going to merge this once the last change was addressed :)

[archseer]

Thanks for working on this!