Implement CSS Properties & Values API in Servo. #18167

Part 1 of a series of patches to implement the CSS Properties & Values API.

The pref is layout.css.properties-and-values.enabled, and it currently defaults to false. Future patches in this series will add code that uses this pref. Part 2 of a series of patches to implement the CSS Properties & Values API.

Part 3 of a series of patches to implement the CSS Properties & Values API.

A later patch in this series will use this when to inspect transform values for typed custom properties. Part 4 of a series of patches to implement the CSS Properties & Values API.

Add a new ExtraData enum. We carry it along with a custom property's specified value in order to compute it, if it ends up being registered as being able to contain URLs through Properties & Values. When the specified value comes from a declaration, we keep track of the associated UrlExtraData in the Specified variant. However, specified values will also (implemented by a later patch in this series) be able to come from animations: in that case we are able to carry along a copy of the computed value in the Precomputed variant, to save us from recomputation and also to save us from having to re-resolve the URL. Add a new BorrowedExtraData enum, which is used for BorrowedSpecifiedValues. We use BorrowedSpecifiedValues when resolving custom properties; in the case that we inherit an untyped custom property, we create one from its computed value, which is a token stream. In this case we don't have a UrlExtraData or (Properties & Values) ComputedValue to compute with, and in fact we don't want to perform any computation. The BorrowedExtraData enum thus has an additional InheritedUntyped variant for that case. Pull out the css, first_token_type, and last_token_type fields of SpecifiedValue, BorrowedSpecifiedValue, and ComputedValue into a TokenStream struct (ComptuedValue then becomes a type alias of TokenStream). We'll use the TokenStream to store computed token stream values for typed custom properties: it wouldn't make sense to use SpecifiedValue because we have no need of the additional information (and that would also lead to properties_and_values::ComputedValue containing a SpecifiedValue which contains an ExtraData which may contain a properties_and_values::ComputedValue, which the compiler does not like). The properties_and_values module is addded by a later patch in this series, so we omit the Precomputed variant for now. Part 5 of a series of patches to implement the CSS Properties & Values API.

Typed custom properties are exactly the same as regular custom properties except when it comes to inheritance, computed values, and animation, so this module is intended to be as independent from custom_properties as possible (they do use types from each other, though, where it would be clumsy to do otherwise). This commit doesn't hook up the module to anything: that's handled by later patches in this series. Part 6 of a series of patches to implement the CSS Properties & Values API.

CSS Properties & Values API says the set of registered properties should be associated with the document. Part 7 of a series of patches to implement the CSS Properties & Values API.

Add a guard to StylesheetGuards for the RegisteredPropertySet. Part 8 of a series of patches to implement the CSS Properties & Values API.

We store a pointer to the registered property set on the Stylist because that seems to be the cleanest way to give access to it to all the functions that might need to cascade or compute typed custom properties. This also lets us use the Stylist's existing mechanism for determining we need to rebuild styles: if it last saw the registered property set with an older generation than the current generation, we should do things again. This is handled by the same path in layout_thread::lib as the device being dirtied or the stylesheets changing. Also update the comment on Stylist::rebuild, which appears not to have been updated when stylesheets_changed was replaced with origins_to_rebuild. Part 9 of a series of patches to implement the CSS Properties & Values API.

"An CSS-wide keyword" should be "A CSS-wide keyword." Also, the PropertyDeclaration::Custom variant must not contain a DeclaredValueOwned::WithVariables variant: this is in fact already asserted in style::custom_properties::cascade. Part 10 of a series of patches to implement the CSS Properties & Values API.

We have to do some additional work to compute typed custom properties and to handle cyclical declarations involving font-size. (Unfortunately there doesn't seem to be a really good way to split this patch up without spending a ton of effort, and I don't think it'd make the patch more clear. Sorry!) Make custom_properties::OrderedMap::remove public, so that we can remove cyclical custom property declarations from properties. We also need to insert the initial value (possibly typed) if necessary and detect if font size is cyclical and remove it in that case, so it makes sense to handle them in the same place instead of custom_properties mutating things behind the scenes and making it worry about typed custom properties. custom_properties::cascade takes two function arguments, inherited_computed and handle_keyword. This allows us to maintain separation of concerns wrt typed custom property registrations (also makes it clearer who is getting data from where). custom_properties::substitute_all and custom_properties::substitute_one gains function arguments compute handle_invalid with the same justification. custom_properties::finish_cascade is replaced by custom_properties::compute_ordering, which computes whether or not font-size's declaration is cycles, the custom properties to compute before early properties (including those upon which early properties depend), and the set of properties that are cyclical. Fix the comment on substitute, which does not type. Have Gecko's ComputedValuesInner::get_custom_properties return a properties_and_values::CustomPropertiesMap instead of a custom_properties::CustomPropertiesMap. This stores typed computed values as well. Replace Servo's Stylist::custom_properties with get_custom_properties, which returns a reference instead of an Arc, because it doesn't make sense to clone the Arc when we never need it as one. Also add get_parent_custom_properties, so a later patch in the series can inherit typed custom property values. Note that this also requires a change to ServoBindings.toml to account for replacing custom_properties::CustomPropertiesMap with properties_and_values::CustomPropertiesMap. Part 11 of a series of patches to implement the CSS Properties & Values API.

Part 12 of a series of patches to implement the CSS Properties & Values API.

Some disabled tests: - We don't implement <transform-list> serialization. - We don't serialize colors according to spec & as Gecko does. - We don't round floats correctly (see rust-cssparser/#173). - We don't implement <resolution>. It's not clear whether or not we actually need initialValue (see css-houdini-drafts/#286). Part 13 of a series of patches to implement the CSS Properties & Values API.

servo / servo

Implement CSS Properties & Values API in Servo. #18167

Implement CSS Properties & Values API in Servo. #18167

Commits on Aug 23, 2017