Add register statusline element

[spectre256]

Resolves issue #1585 by adding a status message when a register is selected with the select_register command, similar to the message produced when starting to record a macro. Additionally, an indicator appears on the right with the selected register.

[the-mikedavis]

I would prefer to see a new statusline element StatusLineElement::Register which could be rendered like so:

// ... helix-term/src/ui/statusline.rs ...
fn render_register<F>(context: &mut RenderContext, write: F)
where
    F: Fn(&mut RenderContext, String, Option<Style>) + Copy,
{
    if let Some(reg) = context.editor.selected_register {
        write(context, format!(" reg={} ", reg), None)
    }
}

and included in the default statusline config:

helix/helix-view/src/editor.rs

Lines 394 to 411 in 2f9b639

	impl Default for StatusLineConfig {
	fn default() -> Self {
	use StatusLineElement as E;
	Self {
	left: vec![
	E::Mode,
	E::Spinner,
	E::FileName,
	E::FileModificationIndicator,
	],
	center: vec![],
	right: vec![E::Diagnostics, E::Selections, E::Position, E::FileEncoding],
	separator: String::from("│"),
	mode: ModeConfig::default(),
	}
	}
	}

probably between Selections and Position. I think that's a better fit for this kind of display. (The macro recording symbol is sort of special like the tracker of typed keys.)

[spectre256]

Done! Would it be helpful to add a similar component for when a macro is being recorded? Seems like it would be more consistent that way.

[the-mikedavis]

I would like the consitency of it being a statusline element too but I think it's ok where it is now. It only shows up rarely (depending on how often you use macros) and it's somewhat related to the pseudo-pending text indicator next to it

[spectre256]

Alright, well let me know if you change your mind; I'd be happy to help with that :)

[the-mikedavis]

Could you add this to the docs?

helix/book/src/configuration.md

Lines 98 to 119 in e2a1678

	The following statusline elements can be configured:
	| Key | Description |
	| ------ | ----------- |
	| `mode` | The current editor mode (`mode.normal`/`mode.insert`/`mode.select`) |
	| `spinner` | A progress spinner indicating LSP activity |
	| `file-name` | The path/name of the opened file |
	| `file-base-name` | The basename of the opened file |
	| `file-modification-indicator` | The indicator to show whether the file is modified (a `[+]` appears when there are unsaved changes) |
	| `file-encoding` | The encoding of the opened file if it differs from UTF-8 |
	| `file-line-ending` | The file line endings (CRLF or LF) |
	| `total-line-numbers` | The total line numbers of the opened file |
	| `file-type` | The type of the opened file |
	| `diagnostics` | The number of warnings and/or errors |
	| `workspace-diagnostics` | The number of warnings and/or errors on workspace |
	| `selections` | The number of active selections |
	| `primary-selection-length` | The number of characters currently in primary selection |
	| `position` | The cursor position |
	| `position-percentage` | The cursor position as a percentage of the total number of lines |
	| `separator` | The string defined in `editor.statusline.separator` (defaults to `"│"`) |
	| `spacer` | Inserts a space between elements (multiple/contiguous spacers may be specified) |
	| `version-control` | The current branch name or detached commit hash of the opened workspace |

[spectre256]

Done! Anything else I need to do for the documentation? I tried running cargo xtask docgen but nothing seemed to change.

[the-mikedavis]

Nope, just that part of the book needed updating. cargo xtask docgen generates the files under book/src/generated/ which is currently just the list of typable commands and the language support table

[the-mikedavis]

Looks great, thanks!