1 files changed, 32 insertions, 9 deletions

diff --git a/servo/components/style/properties/shorthands/ui.mako.rs b/servo/components/style/properties/shorthands/ui.mako.rs
index 1fdb5965fc..4a27d5e003 100644
--- a/servo/components/style/properties/shorthands/ui.mako.rs
+++ b/servo/components/style/properties/shorthands/ui.mako.rs
@@ -22,10 +22,10 @@ macro_rules! try_parse_one {
                     extra_prefixes="moz:layout.css.prefixes.transitions webkit"
                     sub_properties="transition-property transition-duration
                                     transition-timing-function
-                                    transition-delay"
+                                    transition-delay transition-behavior"
                     spec="https://drafts.csswg.org/css-transitions/#propdef-transition">
     use crate::parser::Parse;
-    % for prop in "delay duration property timing_function".split():
+    % for prop in "delay duration property timing_function behavior".split():
     use crate::properties::longhands::transition_${prop};
     % endfor
     use crate::values::specified::TransitionProperty;
@@ -35,7 +35,7 @@ macro_rules! try_parse_one {
         input: &mut Parser<'i, 't>,
     ) -> Result<Longhands, ParseError<'i>> {
         struct SingleTransition {
-            % for prop in "property duration timing_function delay".split():
+            % for prop in "property duration timing_function delay behavior".split():
             transition_${prop}: transition_${prop}::SingleSpecifiedValue,
             % endfor
         }
@@ -45,7 +45,7 @@ macro_rules! try_parse_one {
             input: &mut Parser<'i, 't>,
             first: bool,
         ) -> Result<SingleTransition,ParseError<'i>> {
-            % for prop in "property duration timing_function delay".split():
+            % for prop in "property duration timing_function delay behavior".split():
             let mut ${prop} = None;
             % endfor
 
@@ -56,6 +56,9 @@ macro_rules! try_parse_one {
                 try_parse_one!(context, input, duration, transition_duration);
                 try_parse_one!(context, input, timing_function, transition_timing_function);
                 try_parse_one!(context, input, delay, transition_delay);
+                if static_prefs::pref!("layout.css.transition-behavior.enabled") {
+                    try_parse_one!(context, input, behavior, transition_behavior);
+                }
                 // Must check 'transition-property' after 'transition-timing-function' since
                 // 'transition-property' accepts any keyword.
                 if property.is_none() {
@@ -78,7 +81,7 @@ macro_rules! try_parse_one {
 
             if parsed != 0 {
                 Ok(SingleTransition {
-                    % for prop in "property duration timing_function delay".split():
+                    % for prop in "property duration timing_function delay behavior".split():
                     transition_${prop}: ${prop}.unwrap_or_else(transition_${prop}::single_value
                                                                                  ::get_initial_specified_value),
                     % endfor
@@ -88,7 +91,7 @@ macro_rules! try_parse_one {
             }
         }
 
-        % for prop in "property duration timing_function delay".split():
+        % for prop in "property duration timing_function delay behavior".split():
         let mut ${prop}s = Vec::new();
         % endfor
 
@@ -105,13 +108,13 @@ macro_rules! try_parse_one {
             Ok(transition)
         })?;
         for result in results {
-            % for prop in "property duration timing_function delay".split():
+            % for prop in "property duration timing_function delay behavior".split():
             ${prop}s.push(result.transition_${prop});
             % endfor
         }
 
         Ok(expanded! {
-            % for prop in "property duration timing_function delay".split():
+            % for prop in "property duration timing_function delay behavior".split():
             transition_${prop}: transition_${prop}::SpecifiedValue(${prop}s.into()),
             % endfor
         })
@@ -133,12 +136,24 @@ macro_rules! try_parse_one {
                         return Ok(());
                     }
                 % endfor
+
+                if let Some(behavior) = self.transition_behavior {
+                    if behavior.0.len() != 1 {
+                        return Ok(());
+                    }
+                }
             } else {
                 % for name in "duration delay timing_function".split():
                     if self.transition_${name}.0.len() != property_len {
                         return Ok(());
                     }
                 % endfor
+
+                if let Some(behavior) = self.transition_behavior {
+                    if behavior.0.len() != property_len {
+                        return Ok(());
+                    }
+                }
             }
 
             // Representative length.
@@ -152,7 +167,11 @@ macro_rules! try_parse_one {
                 let has_duration = !self.transition_duration.0[i].is_zero();
                 let has_timing = !self.transition_timing_function.0[i].is_ease();
                 let has_delay = !self.transition_delay.0[i].is_zero();
-                let has_any = has_duration || has_timing || has_delay;
+                let has_behavior = match self.transition_behavior {
+                    Some(behavior) => !behavior.0[i].is_normal(),
+                    _ => false,
+                };
+                let has_any = has_duration || has_timing || has_delay || has_behavior;
 
                 let mut writer = SequenceWriter::new(dest, " ");
 
@@ -174,6 +193,10 @@ macro_rules! try_parse_one {
                 if has_delay {
                     writer.item(&self.transition_delay.0[i])?;
                 }
+
+                if has_behavior {
+                    writer.item(&self.transition_behavior.unwrap().0[i])?;
+                }
             }
             Ok(())
         }