1479240 - Consider disallowing returning a null CSSValue from media expressions.

Status: RESOLVED FIXED

(Core :: CSS Parsing and Computation, enhancement)

Description

[Emilio Cobos Álvarez (:emilio)]

It's a bit footgunny, see bug 1479239.

There are only a few that use this with a reason to do so.

Comment 1

[Emilio Cobos Álvarez (:emilio)]

Attachment: Bug 1479240: Make system metric queries always return false instead of not matching for fingerprinting-resistance. r=heycam

Looks like these used this mechanism for no great reason, and actually doing
this exposes trivially whether fingerprinting-resistance is enabled, which looks
like an anti-goal (if a media query parses correctly, and doesn't match either 1
or 0, then fingerprinting-resistance is enabled).

Comment 2

[Emilio Cobos Álvarez (:emilio)]

Attachment: Bug 1479240: Make scan: progressive always match. r=heycam

https://drafts.csswg.org/mediaqueries-4/#scan doesn't impose any requirement in
supporting the tv media type. Having this media feature without matching
anything is useless, we should either do this or remove it.

Comment 3

[Emilio Cobos Álvarez (:emilio)]

Attachment: Bug 1479240: Restrict this behavior to eIdent media features.

They have a good use-case for not returning a value and telling that's not a
match. That's fine since in eIdent media queries a value is required.

Actually this is just -moz-os-version, which is chrome-only, so we could
actually return a bogus 'other' value and make this a keyword media query, but
this looks a bit nicer.

Comment 4

[Cameron McCormack (:heycam)]

(In reply to Emilio Cobos Álvarez (:emilio) from comment #3)
> Bug 1479240: Restrict this behavior to eIdent media features.

I think this commit message should be the opposite, i.e. we're restricting this behavior to all media features of types other than eIdent.

Comment 5

[Phabricator Automation]

Comment on attachment 8995771 [details]
Bug 1479240: Make system metric queries always return false instead of not matching for fingerprinting-resistance. r=heycam

Cameron McCormack (:heycam) has approved the revision.

https://phabricator.services.mozilla.com/D2493

Comment 6

[Phabricator Automation]

Comment on attachment 8995773 [details]
Bug 1479240: Restrict this behavior to eIdent media features.

Cameron McCormack (:heycam) has approved the revision.

https://phabricator.services.mozilla.com/D2495

Comment 7

[Emilio Cobos Álvarez (:emilio)]

I'll land only the first patch in this bug for now, since the third can't land without the second, and other browsers match our behavior in the second case.

I'll try to figure out a nicer interface to make this explicit rather than early-returning.

Comment 8

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/89bdc7c5f654
Make system metric queries always return false instead of not matching for fingerprinting-resistance. r=heycam

Comment 9

[Bogdan Tara[:bogdan_tara | bogdant]]

https://hg.mozilla.org/mozilla-central/rev/89bdc7c5f654