1704179 - Warn for attempts to combine `:host` pseudoclass in ways that never select anything

Status: RESOLVED FIXED

(Core :: CSS Parsing and Computation, defect)

Description

[:Gijs (he/him)]

Things like div:host or :host:hover can never work, you want :host(div) and :host(:hover). This is somewhat unintuitive as div:before or window:root or :root:-moz-lwtheme and so on all work - it'd be useful if the non-working :host ones tripped a CSS parsing warning so web/Firefox devs know what they're doing.

Emilio says:

I don't think it should be hard. Somewhere around here we could do something like if reporting_css_errors && has_useless_selector { context.error_reporter.log_css_error(...) } or something
it's a pretty hot code-path I guess, that might be an issue, but since we disable error reporting by default hopefully the extra branch doesn't matter

Comment 1

[Emilio Cobos Álvarez (:emilio)]

Attachment: Bug 1704179 - Add a CSS error to the console when using non-featureless :host selectors. r=#style,#layout-reviewers

(which would never match by definition).

Comment 2

[Emilio Cobos Álvarez (:emilio)]

Attachment: Bug 1704179 - Fix a bogus selector in info-group.css. r=Gijs

Maybe I should just remove the rule? It's effect is very subtle :-)

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/7f01fb5e6cfa
Add a CSS error to the console when using non-featureless :host selectors. r=boris

Comment 4

[Natalia Csoregi [:nataliaCs]]

https://hg.mozilla.org/mozilla-central/rev/7f01fb5e6cfa