Drop explicit support for @-moz-document

[nex3]

See https://github.com/sass/sass/issues/2529.

• [x] Deprecate all syntax other than url-prefix() and url-prefix("").
• [x] ~~Deprecate all syntax (blocked on Firefox removing support for url-prefix()).~~
• [x] ~~Remove support entirely (waiting for breaking release).~~
• [ ] Drop explicit support for @-moz-document and treat it as an unknown at-rule.

[refi64]

Isn't @-moz-document is still used for userstyles? I could try migrating to url-prefix, but afaik userstyle support is still entirely present and not deprecated.

[nex3]

@refi64 Can you use @document there instead? One reason we want to drop support for @-moz-document is that it uses different syntax than @document, which requires special parser support.

[refi64]

Ah apologies, I didn't realize @document worked as well.

[stof]

@nex3 given that Firefox gave up on removing support for the empty prefix hack (see https://bugzilla.mozilla.org/show_bug.cgi?id=1449753#c17), what is the plan for Sass ?

[nex3]

Dang. In that case, I think what we should do is transition to treating @-moz-document like an unknown at-rule: parse its value as an interpolated declaration value and be done with it. That probably isn't even a breaking change, since only interpolated SassScript is allowed in the first place. I'll update the task list above.

[Rhys-T]

Firefox still allows @-moz-document rules with values other than url-prefix() in its user stylesheet files (userChrome.css and userContent.css), as well as the browser's own internal stylesheets. (Changing them to unprefixed @documents did not seem to work, and according to MDN, even Firefox only supports the prefixed version.) They're also used in the UserCSS format used by the Stylus user stylesheet manager[^1] and similar browser extensions. (In that case, they're being interpreted by the extension rather than the browser engine - which might not even be Firefox - ~but the spec still says to use the -moz--prefixed version~.)

[Edit: Just realized that user styles were mentioned above as supporting @document, and I somehow missed it. Still, userChrome.css and userContent.css do seem to need the prefixed version.]

Would it be feasible to limit the deprecation warning to forms of @-moz-document that are actually syntactically invalid according to the spec, and thus might fail when the explicit parser support is removed from Sass? If I understand correctly, that would be cases where url-prefix or domain has an unquoted argument - and they work just as well with quoted ones.

[^1]: Not to be confused with the CSS preprocessor also named Stylus.