test_driver actions don't work on targets in shadow DOM

[nt1m]

After merging #41251 (which works fine on webkit's test runner infrastructure), I realized test_driver does not actually support targets in shadow DOM, because it tries to create a selector, which doesn't really work in a shadow dom context.

cc @domenic @mfreed7 @josepharhar @rniwa @gsnedders @jgraham

[mfreed7]

Can you point to where it's trying to create a selector from element? I feel like I've used test_driver.Actions().pointerMove(x,y,{origin: element}) with element in a shadow root and things worked correctly. But I could be mistaken. I do notice none of the popover/shadow tests use it.

[nt1m]

wpt/tools/wptrunner/wptrunner/testdriver-extra.js

Line 220 in 109ee2d

action.origin = {selector: get_selector(action.origin)};

You can see the test failing here in Chrome for this exact reason: https://wpt.fyi/results/html/semantics/popovers/popover-light-dismiss-flat-tree.html?diff&filter=ADC&run_id=5102411146854400&run_id=5205993141567488

ValueError: Selector '#\69 \6e \6e \65 \72 \50 \6f \70 \6f \76 \65 \72 \54 \6f \67 \67 \6c \65 ' matches no elements

[mfreed7]

Ahh, you're right. I think maybe right here:

https://source.chromium.org/chromium/chromium/src/+/main:third_party/wpt_tools/wpt/tools/wptrunner/wptrunner/testdriver-extra.js;l=95;drc=9bf3c522b764982e35548f83f3253741f70454f7

That seems quite baked into the WPT runner platform, which is unfortunate. No quick fix that I can see.

[domenic]

I feel like in the past there was talk of adding shadow-piercing selectors specifically for use in automation tooling, not exposed to the web at large. I don't know where those discussions happened or where they ended up though...

I'll blindly tag @mathiasbynens as my general "person who knows these sorts of things".

[mathiasbynens]

We recently revisited this in the context of WebDriver BiDi: w3c/webdriver-bidi#342 The outcome was that at this point, this functionality should be implemented by clients rather than built into the spec.

[jgraham]

Right, I think the WebDriver group in particular don't want to try to specify custom selectors. If the CSSWG wanted to specify it they would probably be used.

In the meantime this is fixable with some effort; if you can get a reference to the element with script then at least in theory we can split the element selection into multiple parts, one for each shadow tree. Then the WebDriver side should be able to do the shadow tree traversal. Alternatively one could make it work for the same-origin case by not depending on postMessage for communication with the top-level test window and directly sending the element back rather than a selector that should match the element.

We're probably also pretty close to the point where we could implement a WebDriver-BiDi backend for wptrunner / testdriver, which would solve this problem by allowing us to avoid the pile of hacks required to handle the fact that WebDriver requires synchronous, blocking communication with a single Window at a time.

[josepharhar]

test_driver.click() doesn't work on elements in shadowdom, which I tried to fix here but it got complicated and I gave up for now: #37483
I don't think it was due to an issue with selectors, but it does fit under the title of this issue

[gsnedders]

test_driver.click() doesn't work on elements in shadowdom, which I tried to fix here but it got complicated and I gave up for now: #37483 I don't think it was due to an issue with selectors, but it does fit under the title of this issue

See also #37942

[emilio]

I have a workaround for this for the popover tests in https://phabricator.services.mozilla.com/D203152.