Support line number offsets for inline stylesheets

[jdm]

The DOM-side work will be very similar to the work in #14963.

[jdm]

The CSS parser work will require:

• adding a way to create a Parser with a given starting line number
• using that to create a Tokenizer with the starting line (and resetting it later)

[jdm]

On the other hand, we could avoid touching the CSS parser at all and store the offset in ParserContext, and pass it as an argument to the report_error API instead. That's an easier plan.

[nox]

Claiming this one for a contributor.

[PratikDhanave]

I am working on it.

[jdm]

@PratikDhanave Have you made any progress? Any questions?

[PratikDhanave]

No not yet

…

On Thu, Mar 16, 2017 at 1:29 PM, Josh Matthews ***@***.***> wrote: @PratikDhanave <https://github.com/PratikDhanave> Have you made any progress? Any questions? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#15693 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ACFKH_FHhVl2FyazMguasUjr0ng1nJrbks5rmOvdgaJpZM4MI9KP> .

[jdm]

Unassigning due to lack of activity.

[jdm]

Necessary work:

• store the offset in ParserContext, add a new offset argument to report_error
• add a new offset argument to ParserContext::new_with_extra_data, as well as Stylesheet::parse_rules and Stylesheet::from_str
• store the line number in HTMLStyleElement, obtained via the ElementCreator value that is present in the new_inherited method
• pass this line number as the offset when calling Stylesheet::from_str in HTMLStyleElement::parse_own_stylesheet

Code: components/script/htmlstyleelement.rs, components/style/parser.rs, components/style/stylesheets.rs, components/style/error_reporting.rs

[jdm]

The idea here is that we get incorrect line numbers in HTML like this:

<style>
:matches(thead)[align=absmiddle i] {
  color: red
}
</style>

If we run RUST_LOG=script_layout_interface::reporter ./mach run file.html, we see:

INFO:script_layout_interface::reporter: Url:    file:///tmp/style.html
2:1 Invalid rule: ':matches(thead)[align=absmiddle i] {'

when the invalid CSS is clearly not line 2 of the actual file.

[SimonSapin]

Maybe also a column offset, for the first line? Especially for style attributes.

[jdm]

I think that will require additional changes to html5ever. Let's keep this focused on line offsets for now.

[SimonSapin]

Also counting "columns" is more tricky than it seems. UTF-8 bytes v.s. code points v.s. grapheme clusters v.s. east-asian width… Deferring for now avoids this question.

[mckaymatt]

@highfive: assign me

[highfive]

Hey @mckaymatt! Thanks for your interest in working on this issue. It's now assigned to you!

[mckaymatt]

@jdm when you say

pass this line number as the offset when calling Stylesheet::from_str in HTMLStyleElement::parse_own_stylesheet

Do you mean HTMLStyleElement::parse_own_css?

[jdm]

Yes.