1854658 - Exportparts and ::part() selector leak internal component details

Status: VERIFIED FIXED

(Core :: CSS Parsing and Computation, defect, P3)

Description

[vrugtehagel]

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:109.0) Gecko/20100101 Firefox/117.0

Steps to reproduce:

Let's say we have the following markup structure:

<style>my-bar::part(text) { color: red; }</style>
<my-foo>
    #shadow-root
        <my-bar exportparts="text">
            #shadow-root
                <span part="text">Hello!</span>
        </my-bar>
</my-foo>

Here's a fiddle: https://jsfiddle.net/cj5z2kd9/

Actual results:

The text goes red.

Expected results:

The CSS rule should not apply; my-bar is not in the document (only my-foo is), so my-bar::part(text) should not apply even though my-bar is the tag name of the element that would be matched by ::part(text).

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug should belong to the 'Core::CSS Parsing and Computation' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Comment 2

[Emilio Cobos Álvarez (:emilio)]

Attachment: Test-case from reporter

Comment 3

[Emilio Cobos Álvarez (:emilio)]

Attachment: Bug 1854658 - Fix the part combinator to deal with exportparts correctly. r=#style,#layout

We need to jump to an element in the correct scope just like ::slotted()
does.

Factor that code to its own function both so that it's easier to reason
about and so that the code for that function remains small. At the end
of the day other combinators like descendant or sibling get executed a
ton of times (while pseudo-elements only jump once).

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/d4e50ba4e3bb
Fix the part combinator to deal with exportparts correctly. r=zrhoffman

Comment 5

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Created web-platform-tests PR https://github.com/web-platform-tests/wpt/pull/42281 for changes under testing/web-platform/tests

Comment 6

[Natalia Csoregi [:nataliaCs]]

https://hg.mozilla.org/mozilla-central/rev/d4e50ba4e3bb

Comment 7

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Upstream PR merged by moz-wptsync-bot

Comment 8

[Ardelean Oana, Desktop QA [:oardelean]]

Reproducible on a 2023-10-01 Nightly build on macOS 12.
Verified as fixed on Firefox 120.0b5 and Nightly 121.0a1 on macOS 12, Windows 10, Ubuntu 22.