Allow extensions control dimensions for existing terminals

[IlyaBiryukov]

Live Share has a feature where when a user starts a collaboration session as a host, all existing terminals are automatically shared. When other guests join, they'll see these shared terminals.

The problem is that guests' UI dimensions are different from the host, and such shared terminals may not render correctly there.

Live Share already solves this for Pseudoterminal that users can create via Live Share viewlet. Live Share uses onDidOverrideDimensions and setDimensions on Pseudoterminal. It needs VSCode support for regular Terminal objects.

Existing terminals has read-only dimensions property on Terminal objects which we can use to get current terminal dimensions (maximum ones I assume), but nothing that we can use to change the dimensions, and no event that would tell us when UI changes and max dimensions change.

So the feature request is to expose onDidOverrideDimensions and setDimensions equivalent on Terminal objects that would allow to:

1. Override current terminal dimensions
2. Get current max dimensions as allowed by UI
3. Know when max dimensions change (say when users resize UI).

cc @lostintangent, @Tyriar

[vscodebot]

(Experimental duplicate detection)
Thanks for submitting this issue. Please also check if it is already covered by an existing one, like:

• Improve terminal grid dimensions caching (#77298)

[Tyriar]

@IlyaBiryukov I remember chatting with you about this in the past, has this just never worked properly for Live Share?

[IlyaBiryukov]

@Tyriar it works for pseudoterminal-backed terminals that Live Share creates on its own. Pre-existing terminals, those that users create without Live Share, don't have means to change dimensions (the property is read-only) and there is no event to know when the max dimensions have changed due to UI changes. I don't think it ever worked for them.

[Tyriar]

there is no event to know when the max dimensions have changed due to UI changes

@IlyaBiryukov there is an event for this, the dimensions just can't be changed by extensions yet:

vscode/src/vs/vscode.proposed.d.ts

Lines 824 to 829 in 94c6893

	namespace window {
	/**
	* An event which fires when the [dimensions](#Terminal.dimensions) of the terminal change.
	*/
	export const onDidChangeTerminalDimensions: Event<TerminalDimensionsChangeEvent>;
	}

[Tyriar]

Proposal:

export interface Terminal {
	/**
	 * The current dimensions of the terminal. This will be `undefined` immediately after the
	 * terminal is created as the dimensions are not known until shortly after the terminal is
	 * created.
	 */
	readonly dimensions: ITerminalDimensions | undefined;

	// actualDimensions?
	// overrideDimensions?
	// setOverrideDimensions?
	overriddenDimensions: ITerminalDimensions | undefined;
}

export namespace window {
	/**
	 * An event which fires when the [dimensions](#Terminal.dimensions) of the terminal change.
	 */
	export const onDidChangeTerminalDimensions: Event<TerminalDimensionsChangeEvent>;
}

This uses similar language to the Pseudoterminal API where "dimensions" are the container dimensions and "override dimensions" are the actual terminal dimensions.

[vs-code-engineering]

We closed this issue because we don't plan to address it in the foreseeable future. If you disagree and feel that this issue is crucial: we are happy to listen and to reconsider.

If you wonder what we are up to, please see our roadmap and issue reporting guidelines.

Thanks for your understanding, and happy coding!