Announce characters when navigating on a line using arrow keys or deleting characters

[pattch]

Details

• Browser and browser version: All
• OS version: All

Steps to reproduce

1. Initialize a Terminal with screenReaderMode set to true
2. Using a screen reader, enter some text into the Terminal
3. Navigate to previously entered text using the left / right arrow keys
4. Observe that although the cursor position changes, the hovered characters are not announced
5. Compare to native Terminals, where the hovered characters are announced

[Tyriar]

This is a lot more complicated that you might expect since we can't access native a11y apis. The way the announcing works in the web is by synchronizing the textarea with the prompt, but we can't reliably know what the prompt is without additional smarts. Right now the fix here will likely involve shell integration (most of which probably won't live in xterm.js) and I've been tracking it in microsoft/vscode#133084

[pattch]

That's a good point I hadn't considered, but I do think that these a11y features are important for screen reader users.

Integrators with xterm could more easily implement these a11y features without requiring xterm to implement them directly if xterm had hooks for these events. In Google Cloud Shell, we listen to backspace inputs from the user and manually calculate the difference between the previous terminal content and the new terminal content; this is hampered a bit by having to access terminal content using the buffer.

If xterm were to expose hooks for things like this, integrators could simply announce those characters if they so choose. What I'm proposing is two interfaces added to the Terminal:

• onCharacterDeleted: IEvent
  • just after the user enters the backspace character, if just one character is removed / overwritten, this would send off an Event with the character that was deleted
• onCursorMove: IEvent
  • Using the existing onCursorMove, which fires an Event with type void, we simply fire an Event with the character at the position the cursor has moved to

Let me know if this sounds at all reasonable

[Tyriar]

@pattch I think you can handle that today by recording the latest keystroke via attachCustomKeyEventHandler and then handling it when the existing onCursorMove event fires, checking the buffer as needed?

FYI the plan is to look into microsoft/vscode#133084 in December I believe.

[meganrogge]

This now works in VS Code microsoft/vscode#186904