[terminal] Always open terminal links on touch events

[jankeromnes]

What it does

Fixes #6320.

This PR attempts to detect whether a click event on an XtermJS link was from a touch screen (should always open) or not (should only open if Cmd was also pressed).

This is achieved by keeping track of the last touchend event, and comparing times / coordinates.

How to test

1. yarn
2. cd examples/browser && yarn start --hostname=0.0.0.0
3. Open port 3000 in desktop browser: run echo http://perdu.com
   • Simple click on link (should not open)
   • Cmd + click on link (should open)
4. Open port 3000 on touch device, e.g. iPad: run echo http://perdu.com
   • Tap on link (should open)

Review checklist

• as an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• as a reviewer, I agree to behave in accordance with the review guidelines

[jankeromnes]

I still need to sign-off & add to changelog, but I'd love an initial review because I feel like my approach is a bit awkward.

[akosyakov]

@vince-fugnitto Could you try it out? i don't have ipad unfortunately

[lmcbout]

I cannot test this one, I don't have an IPAD and/or a touch screen to test

[vince-fugnitto]

@vince-fugnitto Could you try it out? i don't have ipad unfortunately

I forgot to mention, I unfortunately do not have an iPad or any tablet for that matter to properly test out the pull request 😞

[jankeromnes]

I guess there are two main risks here:

1. Terminal links stop working properly on non-touch devices (e.g. link can't be opened anymore, or link opens without Cmd being pressed)
2. Terminal links continue not working properly on touch devices (i.e. they still don't work, or they open inadvertently when not wanted)

I believe that 1. can be tested on non-touch devices, and that 2. is not critical (because Terminal links already don't work on touch today), but I can upload a video of me testing 2. on my iPad.

[akosyakov]

One can emulate with Chrome. I'm going to test like that:

[akosyakov]

It works as described, although I wonder how a user can figure out on iPad that a link is tappable? Can we highlight it with underscore and hover as on the desktop? Or you think it would be too much.

[jankeromnes]

Here is a video where I test this PR on my iPad: https://youtu.be/TL5EaIOfUZI

However, please note that the main motivation for this fix was that on iPad (iOS 1.12), even with an external keyboard, you could not open Terminal links at all. But now that iOS 1.13 is out, if you have an external keyboard, Cmd + click works properly now. Thus, this fix is now only relevant for touch devices that don't have an external keyboard (for example smartphones).

It works as described, although I wonder how a user can figure out on iPad that a link is tappable? Can we highlight it with underscore and hover as on the desktop? Or you think it would be too much.

On iPad, the normal XtermJS styling of underlining links will happen when you focus on a link (I don't think there is an actual "hover" state on touch screens, except maybe modern/high-end screens that detect a nearby finger that's not yet in touch contact?):

• Currently, when you tap on a Terminal link on a touch device to focus it, it will get underlined, and the Cmd + click to follow link pop-up will appear. But the link won't get visited (unless you press Cmd on an external keyboard first).

• What changes with this PR is that when you tap on a Terminal link, it will now open directly (without the need for pressing Cmd). So I don't think there will be a way to focus the link without visiting (unless you drag your finger elsewhere to discard/cancel the touchend event maybe?)

But if you were talking about passive link styling to reveal what's clickable, I don't think XtermJS allows it, because they render everything via a <canvas> (so no custom CSS rules for links). See also: xtermjs/xterm.js#1540

[jankeromnes]

Thank you for merging this!

This change is a UX improvement for touch devices without external keyboard (e.g. tablet, smartphone).

However, if it turns out that force-opening Terminal links when touched is not a desirable feature (e.g. if Theia users report issues about it), please feel free to revert my commit.