Type Ahead isn't "on" for cursor movement when using PowerShell on non-Windows

[TylerLeonhardt]

Version: 1.53.0-insider
Commit: 4a875e2
Date: 2020-12-21T12:32:43.927Z
Electron: 11.1.0
Chrome: 87.0.4280.88
Node.js: 12.18.3
V8: 8.7.220.29-electron.0
OS: Darwin x64 20.2.0

This seems to be because right arrow in PowerShell on non-Windows emits \x1bOC instead of what the ANSI spec says which is \x1b[C.

Does this issue occur when all extensions are disabled?: Yes

[JacksonKearl]

Steps to verify?

[TylerLeonhardt]

It'll be easiest to see this in Codespaces or Remote probably (or throttle the CPU via dev tools maybe):

• Install PowerShell on non-Windows: https://github.com/PowerShell/PowerShell#get-powershell
• Set it as the default shell: "terminal.integrated.shell.linux": "pwsh",
• Open a terminal and type really fast

You should see characters start grey and then become colorized. This is the work of typeahead.

[JacksonKearl]

I should have said what does "on" for cursor movement mean in the context of TypeAhead?

[TylerLeonhardt]

This would be transparent to the end user, unfortunately. The true test is verifying that when you use the left or right arrow key that this code block gets hit:

vscode/src/vs/workbench/contrib/terminal/browser/terminalTypeAheadAddon.ts

Lines 1451 to 1458 in 3f3e35b

	const direction = cursorMv[3] as CursorMoveDirection;
	const p = new CursorMovePrediction(direction, !!cursorMv[2], Number(cursorMv[1]) || 1);
	if (direction === CursorMoveDirection.Back) {
	addLeftNavigating(p);
	} else {
	addRightNavigating(p);
	}
	continue;

before my 1 character change, it did not hit that block.

[TylerLeonhardt]

ok I think ive got a valid test...

1. Open the vscode repo in Codespaces
2. launch pwsh
3. type asdf asd fasdf asd fasd fas dfsd afsdf a sadfsadf a sdfaf sdsaf dsadf to fill the prompt a bit
4. Hit left arrow a few times to be in the middle of that ^
5. do: Ctrl+LeftArrow a few times

TypeAhead assumes that Ctrl+LeftArrow moves the cursor by a word (tbh this is a bad assumption... but since 95% of the time Codespaces will use bash or zsh... it's slightly less bad of an assumption I guess)
PowerShell doesn't use Ctrl+LeftArrow to move back a word so what you see is:

TypeAhead guesses by moving the cursor back a word
PowerShell responds saying "the cursor didn't go anywhere"
TypeAhead's prediction is reverted and the cursor goes back to where it was

[TylerLeonhardt]

If TypeAhead was off, by doing:

"terminal.integrated.localEchoLatencyThreshold": -1

The word jump wouldn't happen at all