1959940 - Inherited properties from ::details-content pseudo element are not displayed in the computed panel

Status: RESOLVED FIXED

(DevTools :: Inspector, defect, P3)

Description

[Nicolas Chevobbe [:nchevobbe]]

0. Set layout.css.details-content.enabled to true
1. Navigate to data:text/html,<meta charset=utf8><style>details::details-content {color: tomato;}</style><details open><summary>Example summary</summary><p>First paragraph.</p><p>Second paragraph</p></details>
2. Open the inspector
3. Select one of the p element inside the <details> node
4. Open the computed panel
5. Expand the color property

Expected result: the ::details-content rule should be displayed
Actual result: it's not

---

I have a WIP patch for Bug 1953807 where I'm displaying inherited declarations from ::details-content rules, but it's not enough.
In https://searchfox.org/mozilla-central/rev/19764d620c02025bdcc8d1f3c4fcf5a580407a01/devtools/server/actors/inspector/css-logic.js#480,483

selectorMatchesElement(domRule, idx) {
...
    if (domRule.selectorMatchesElement(idx, element)) {

With domRule being the ::details-content, idx being 0, and element being the <slot> representing the ::details-content element, domRule.selectorMatchesElement returns false. It also returns false if element is <details>.
We probably need to make some tweaks to https://searchfox.org/mozilla-central/rev/19764d620c02025bdcc8d1f3c4fcf5a580407a01/layout/style/CSSStyleRule.cpp#254-297

Comment 1

[Nicolas Chevobbe [:nchevobbe]]

Attachment: Bug 1959940 - [devtools] Look for element-backed pseudo element match in CssLogic#selectorMatchesElement. r=#devtools.

This allows to actually show inherited element backed pseudo element rules
(e.g. ::details-content) in the computed panel selector matches.
A test is added to cover this scenario.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/1e4b7f0c279a
[devtools] Look for element-backed pseudo element match in CssLogic#selectorMatchesElement. r=devtools-reviewers,jdescottes.

Comment 3

[Sandor Molnar[:smolnar]]

https://hg.mozilla.org/mozilla-central/rev/1e4b7f0c279a