style: Document the keyframes module.

components/style/keyframes.rs

@@ -2,6 +2,10 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+//! Keyframes: https://drafts.csswg.org/css-animations/#keyframes
+
+#![deny(missing_docs)]
+
 use cssparser::{AtRuleParser, Parser, QualifiedRuleParser, RuleListParser};
 use cssparser::{DeclarationListParser, DeclarationParser, parse_one_rule};
 use parking_lot::RwLock;
@@ -14,8 +18,8 @@ use std::sync::Arc;
 use style_traits::ToCss;
 use stylesheets::{MemoryHoleReporter, Stylesheet};
 
-/// A number from 0 to 1, indicating the percentage of the animation where
-/// this keyframe should run.
+/// A number from 0 to 1, indicating the percentage of the animation when this
+/// keyframe should run.
 #[derive(Debug, Copy, Clone, PartialEq, PartialOrd)]
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
 pub struct KeyframePercentage(pub f32);
@@ -37,6 +41,7 @@ impl ToCss for KeyframePercentage {
 }
 
 impl KeyframePercentage {
+    /// Trivially constructs a new `KeyframePercentage`.
     #[inline]
     pub fn new(value: f32) -> KeyframePercentage {
         debug_assert!(value >= 0. && value <= 1.);
@@ -67,6 +72,7 @@ impl KeyframePercentage {
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
 pub struct KeyframeSelector(Vec<KeyframePercentage>);
 impl KeyframeSelector {
+    /// Return the list of percentages this selector contains.
     #[inline]
     pub fn percentages(&self) -> &[KeyframePercentage] {
         &self.0
@@ -77,6 +83,7 @@ impl KeyframeSelector {
         KeyframeSelector(percentages)
     }
 
+    /// Parse a keyframe selector from CSS input.
     pub fn parse(input: &mut Parser) -> Result<Self, ()> {
         input.parse_comma_separated(KeyframePercentage::parse)
              .map(KeyframeSelector)
@@ -87,12 +94,13 @@ impl KeyframeSelector {
 #[derive(Debug, Clone)]
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
 pub struct Keyframe {
+    /// The selector this keyframe was specified from.
     pub selector: KeyframeSelector,
 
-    /// `!important` is not allowed in keyframe declarations,
-    /// so the second value of these tuples is always `Importance::Normal`.
-    /// But including them enables `compute_style_for_animation_step` to create a `ApplicableDeclarationBlock`
-    /// by cloning an `Arc<_>` (incrementing a reference count) rather than re-creating a `Vec<_>`.
+    /// The declaration block that was declared inside this keyframe.
+    ///
+    /// Note that `!important` rules in keyframes don't apply, but we keep this
+    /// `Arc` just for convenience.
     #[cfg_attr(feature = "servo", ignore_heap_size_of = "Arc")]
     pub block: Arc<RwLock<PropertyDeclarationBlock>>,
 }
@@ -114,7 +122,10 @@ impl ToCss for Keyframe {
 
 
 impl Keyframe {
-    pub fn parse(css: &str, parent_stylesheet: &Stylesheet, extra_data: ParserContextExtraData)
+    /// Parse a CSS keyframe.
+    pub fn parse(css: &str,
+                 parent_stylesheet: &Stylesheet,
+                 extra_data: ParserContextExtraData)
                  -> Result<Arc<RwLock<Self>>, ()> {
         let error_reporter = Box::new(MemoryHoleReporter);
         let context = ParserContext::new_with_extra_data(parent_stylesheet.origin,
@@ -133,15 +144,19 @@ impl Keyframe {
 /// A keyframes step value. This can be a synthetised keyframes animation, that
 /// is, one autogenerated from the current computed values, or a list of
 /// declarations to apply.
-// TODO: Find a better name for this?
+///
+/// TODO: Find a better name for this?
 #[derive(Debug, Clone)]
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
 pub enum KeyframesStepValue {
-    /// See `Keyframe::declarations`’s docs about the presence of `Importance`.
+    /// A step formed by a declaration block specified by the CSS.
     Declarations {
+        /// The declaration block per se.
         #[cfg_attr(feature = "servo", ignore_heap_size_of = "Arc")]
         block: Arc<RwLock<PropertyDeclarationBlock>>
     },
+    /// A synthetic step computed from the current computed values at the time
+    /// of the animation.
     ComputedValues,
 }
 
@@ -162,7 +177,6 @@ pub struct KeyframesStep {
 }
 
 impl KeyframesStep {
-    #[allow(unsafe_code)]
     #[inline]
     fn new(percentage: KeyframePercentage,
            value: KeyframesStepValue) -> Self {
@@ -193,6 +207,7 @@ impl KeyframesStep {
 #[derive(Debug, Clone)]
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
 pub struct KeyframesAnimation {
+    /// The difference steps of the animation.
     pub steps: Vec<KeyframesStep>,
     /// The properties that change in this animation.
     pub properties_changed: Vec<TransitionProperty>,
@@ -204,7 +219,6 @@ pub struct KeyframesAnimation {
 ///
 /// In practice, browsers seem to try to do their best job at it, so we might
 /// want to go through all the actual keyframes and deduplicate properties.
-#[allow(unsafe_code)]
 fn get_animated_properties(keyframe: &Keyframe) -> Vec<TransitionProperty> {
     let mut ret = vec![];
     // NB: declarations are already deduplicated, so we don't have to check for
@@ -219,6 +233,13 @@ fn get_animated_properties(keyframe: &Keyframe) -> Vec<TransitionProperty> {
 }
 
 impl KeyframesAnimation {
+    /// Create a keyframes animation from a given list of keyframes.
+    ///
+    /// This will return `None` if the list of keyframes is empty, or there are
+    /// no animated properties obtained from the keyframes.
+    ///
+    /// Otherwise, this will compute and sort the steps used for the animation,
+    /// and return the animation object.
     pub fn from_keyframes(keyframes: &[Arc<RwLock<Keyframe>>]) -> Option<Self> {
         if keyframes.is_empty() {
             return None;
@@ -273,6 +294,7 @@ struct KeyframeListParser<'a> {
     context: &'a ParserContext<'a>,
 }
 
+/// Parses a keyframe list from CSS input.
 pub fn parse_keyframe_list(context: &ParserContext, input: &mut Parser) -> Vec<Arc<RwLock<Keyframe>>> {
     RuleListParser::new_for_nested_rule(input, KeyframeListParser { context: context })
         .filter_map(Result::ok)