1363778 - stylo: Implement the class/id case-insensitive matching quirk

Status: RESOLVED FIXED

(Core :: CSS Parsing and Computation, enhancement, P2)

Description

[Boris Zbarsky [:bzbarsky]]

Spec: https://drafts.csswg.org/selectors/#id-selectors and https://drafts.csswg.org/selectors/#class-html both say that matching is ASCII-case-insensitive in quirks mode.

Testcase:

  <style>#foo { color: green; }</style>                                                
  <div id="FOO">Should be green</div>

Comment 1

[Boris Zbarsky [:bzbarsky]]

Just to scope out the work, there are two main parts here:

1)  Fixing selector matching to do case-insensitive matching for ids and classes in quirks mode.
2)  Fixing the rulehashes in stylist to do case-insensitive lookups.

Comment 2

[Bobby Holley (:bholley)]

Simon, you seem to be working on parts of this. How much overlap is there?

Comment 3

[Bobby Holley (:bholley)]

Oh nevermind, looks like Simon was working on regular case-insensitive matching.

Comment 4

[Simon Sapin (:SimonSapin)]

In current code there’s an asymmetry between handling of IDs and classes. In the selectors::Element trait, the impl return the optional ID of an element and the selectors crate does the string (or atom) comparison. For classes, selectors provides the string/atom form the class selector and the impl returns a boolean. I think these should be "unified", picking one of:

* The impl does the string comparisons, replacing Element::get_id with Element::has_id. However Servo + Stylo has a number of these impls (I think 5 in total?), so it’s as many places that need to not forget to check for quirks mode.

* The selectors crate does the string comparisons, deciding which kind based on a new Element::in_quirks_mode_document method. The selectors crate needs some way to iterate on an element’s classes. An external iterator with the std::iter::Iterator trait is verbose to implement, especially in a generic context. So we could have an internal iterator: an FnMut(&ClassName) callback called for each class. But we need to stop iteration when a match is found so the callback needs to return at least a boolean, but I’d prefer a new `enum Next { Continue, Stop }`. [1] has a trait for internal iterators, but it seems to be unmaintained [2].

[1] https://docs.rs/traverse/
[2] https://github.com/reem/rust-traverse/pull/26 is months old and didn’t get a response.

Comment 5

[Boris Zbarsky [:bzbarsky]]

One note on the above: We want to minimize the number of FFI calls as we go, and we do NOT want to be doing UTF16-to-UTF8-and-back conversions and allocating string copies.

That means we'll probably want a Rust-side no-copy no-conversion ASCII-case-insensitive comparison on atoms.

Comment 6

[Simon Sapin (:SimonSapin)]

We already have Atom::eq_ignore_ascii_case: https://github.com/servo/servo/blob/7f80d9cb45/components/style/gecko_string_cache/mod.rs#L241

We probably want to add a fast path that tries `self == other` first.

Comment 7

[Bobby Holley (:bholley)]

(In reply to Simon Sapin (:SimonSapin) from comment #6)
> We already have Atom::eq_ignore_ascii_case:
> https://github.com/servo/servo/blob/7f80d9cb45/components/style/
> gecko_string_cache/mod.rs#L241

Nice!

> We probably want to add a fast path that tries `self == other` first.

Pushed https://github.com/servo/servo/pull/17022 for this.

Comment 8

[Simon Sapin (:SimonSapin)]

https://github.com/servo/servo/pull/17213 is up for review, but it doesn’t seem to fix any test: https://treeherder.mozilla.org/#/jobs?repo=try&revision=2bd8e7f69cf56046c8fd685a57d0f8db8f43c4e8 . I don’t know if we don’t have relevant tests, or if I did something wrong.

Comment 9

[Boris Zbarsky [:bzbarsky]]

We have relevant tests.  See layout/reftests/bugs/571347-2c.html for example.

I don't see changes to stylist or SelectorMap in the PR.  See comment 1 item 2.  I suspect that's why that test still fails with the chagnes in the PR.

Comment 10

[Simon Sapin (:SimonSapin)]

Ah that makes sense. Thanks.

Comment 11

[Simon Sapin (:SimonSapin)]

https://hg.mozilla.org/integration/autoland/rev/5eca9cc75c3f
https://hg.mozilla.org/integration/autoland/rev/ad90f0a5b56c