Auto merge of #17469 - nox:empty-vs-initial, r=emilio

Distinguish the emptiness of a property from its initial value

<!-- Reviewable:start -->
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/17469)
<!-- Reviewable:end -->

4 files changed, 46 insertions, 36 deletions

diff --git a/components/style/properties/helpers.mako.rs b/components/style/properties/helpers.mako.rs
index 990e9e6646e..8c6701497e4 100644
--- a/components/style/properties/helpers.mako.rs
+++ b/components/style/properties/helpers.mako.rs
@@ -9,7 +9,7 @@
 
 <%def name="predefined_type(name, type, initial_value, parse_method='parse',
             needs_context=True, vector=False, computed_type=None, initial_specified_value=None,
-            allow_quirks=False, **kwargs)">
+            allow_quirks=False, allow_empty=False, **kwargs)">
     <%def name="predefined_type_inner(name, type, initial_value, parse_method)">
         #[allow(unused_imports)]
         use app_units::Au;
@@ -27,7 +27,9 @@
             pub use values::computed::${type} as T;
             % endif
         }
+        % if initial_value:
         #[inline] pub fn get_initial_value() -> computed_value::T { ${initial_value} }
+        % endif
         % if initial_specified_value:
         #[inline] pub fn get_initial_specified_value() -> SpecifiedValue { ${initial_specified_value} }
         % endif
@@ -46,7 +48,9 @@
         }
     </%def>
     % if vector:
-        <%call expr="vector_longhand(name, predefined_type=type, **kwargs)">
+        <%call
+            expr="vector_longhand(name, predefined_type=type, allow_empty=allow_empty or not initial_value, **kwargs)"
+        >
             ${predefined_type_inner(name, type, initial_value, parse_method)}
             % if caller:
             ${caller.body()}
@@ -202,7 +206,7 @@
             }
 
             pub fn get_initial_value() -> computed_value::T {
-                % if allow_empty:
+                % if allow_empty and allow_empty != "NotInitial":
                     computed_value::T(SmallVec::new())
                 % else:
                     let mut v = SmallVec::new();
diff --git a/components/style/properties/longhand/box.mako.rs b/components/style/properties/longhand/box.mako.rs
index 4f0449ad0bf..871eb37513d 100644
--- a/components/style/properties/longhand/box.mako.rs
+++ b/components/style/properties/longhand/box.mako.rs
@@ -429,17 +429,19 @@ ${helpers.predefined_type("transition-timing-function",
                           extra_prefixes="moz webkit",
                           spec="https://drafts.csswg.org/css-transitions/#propdef-transition-timing-function")}
 
-${helpers.predefined_type("transition-property",
-                          "TransitionProperty",
-                          "computed::TransitionProperty::All",
-                          initial_specified_value="specified::TransitionProperty::All",
-                          vector=True,
-                          allow_empty=True,
-                          need_index=True,
-                          needs_context=False,
-                          animation_value_type="none",
-                          extra_prefixes="moz webkit",
-                          spec="https://drafts.csswg.org/css-transitions/#propdef-transition-property")}
+${helpers.predefined_type(
+    "transition-property",
+    "TransitionProperty",
+    "computed::TransitionProperty::All",
+    initial_specified_value="specified::TransitionProperty::All",
+    vector=True,
+    allow_empty="NotInitial",
+    need_index=True,
+    needs_context=False,
+    animation_value_type="none",
+    extra_prefixes="moz webkit",
+    spec="https://drafts.csswg.org/css-transitions/#propdef-transition-property",
+)}
 
 ${helpers.predefined_type("transition-delay",
                           "Time",
@@ -668,16 +670,17 @@ ${helpers.predefined_type("scroll-snap-destination",
                           spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/scroll-snap-destination)",
                           animation_value_type="ComputedValue")}
 
-${helpers.predefined_type("scroll-snap-coordinate",
-                          "Position",
-                          "computed::Position::zero()",
-                          vector=True,
-                          products="gecko",
-                          spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/scroll-snap-destination)",
-                          animation_value_type="ComputedValue",
-                          allow_empty=True,
-                          delegate_animate=True)}
-
+${helpers.predefined_type(
+    "scroll-snap-coordinate",
+    "Position",
+    "computed::Position::zero()",
+    vector=True,
+    products="gecko",
+    spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/scroll-snap-destination)",
+    animation_value_type="ComputedValue",
+    allow_empty="NotInitial",
+    delegate_animate=True,
+)}
 
 <%helpers:longhand name="transform" extra_prefixes="webkit"
                    animation_value_type="ComputedValue"
diff --git a/components/style/properties/longhand/inherited_svg.mako.rs b/components/style/properties/longhand/inherited_svg.mako.rs
index 3799c89d3ad..1d7fd7a985a 100644
--- a/components/style/properties/longhand/inherited_svg.mako.rs
+++ b/components/style/properties/longhand/inherited_svg.mako.rs
@@ -88,17 +88,18 @@ ${helpers.predefined_type("stroke-opacity", "Opacity", "1.0",
                           products="gecko", animation_value_type="ComputedValue",
                           spec="https://www.w3.org/TR/SVG11/painting.html#StrokeOpacityProperty")}
 
-${helpers.predefined_type("stroke-dasharray",
-                          "LengthOrPercentageOrNumber",
-                          "Either::First(0.0)",
-                          "parse_non_negative",
-                          vector="True",
-                          delegate_animate="True",
-                          allow_empty="True",
-                          products="gecko",
-                          animation_value_type="ComputedValue",
-                          space_separated_allowed="True",
-                          spec="https://www.w3.org/TR/SVG2/painting.html#StrokeDashing")}
+${helpers.predefined_type(
+    "stroke-dasharray",
+    "LengthOrPercentageOrNumber",
+    None,
+    "parse_non_negative",
+    vector=True,
+    delegate_animate=True,
+    products="gecko",
+    animation_value_type="ComputedValue",
+    space_separated_allowed="True",
+    spec="https://www.w3.org/TR/SVG2/painting.html#StrokeDashing",
+)}
 
 ${helpers.predefined_type(
     "stroke-dashoffset", "LengthOrPercentageOrNumber",
diff --git a/components/style/properties/properties.mako.rs b/components/style/properties/properties.mako.rs
index f7deb43d492..4507ea5119a 100644
--- a/components/style/properties/properties.mako.rs
+++ b/components/style/properties/properties.mako.rs
@@ -1765,7 +1765,9 @@ pub mod style_structs {
             /// Returns whether there are any transitions specified.
             #[cfg(feature = "servo")]
             pub fn specifies_transitions(&self) -> bool {
-                self.transition_property_count() > 0
+                self.transition_duration_iter()
+                    .take(self.transition_property_count())
+                    .any(|t| t.seconds() > 0.)
             }
         % endif
     }