Auto merge of #18081 - hiikezoe:interpolation-with-auto, r=birtles,boris,mantaroh

Fix interpolation between auto and other values

<!-- Please describe your changes on the following line: -->
https://bugzilla.mozilla.org/show_bug.cgi?id=1387939

---
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors

<!-- 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/18081)
<!-- Reviewable:end -->

components/style/gecko/wrapper.rs

@@ -1396,6 +1396,8 @@ impl<'le> TElement for GeckoElement<'le> {
                                              existing_transitions: &HashMap<TransitionProperty,
                                                                             Arc<AnimationValue>>)
                                              -> bool {
+        use properties::animated_properties::Animatable;
+
         // |property| should be an animatable longhand
         let animatable_longhand = AnimatableLonghand::from_transition_property(property).unwrap();
 
@@ -1414,7 +1416,9 @@ impl<'le> TElement for GeckoElement<'le> {
         let to = AnimationValue::from_computed_values(&animatable_longhand,
                                                       after_change_style);
 
-        combined_duration > 0.0f32 && from != to
+        combined_duration > 0.0f32 &&
+        from != to &&
+        from.interpolate(&to, 0.5).is_ok()
     }
 
     #[inline]

components/style/properties/gecko.mako.rs

@@ -5434,10 +5434,10 @@ clip-path
     ${impl_simple_copy('column_count', 'mColumnCount')}
 
     pub fn clone_column_count(&self) -> longhands::column_count::computed_value::T {
-        use gecko_bindings::structs::NS_STYLE_COLUMN_COUNT_AUTO;
+        use gecko_bindings::structs::{NS_STYLE_COLUMN_COUNT_AUTO, nsStyleColumn_kMaxColumnCount};
         if self.gecko.mColumnCount != NS_STYLE_COLUMN_COUNT_AUTO {
-            debug_assert!((self.gecko.mColumnCount as i32) >= 0 &&
+            debug_assert!(self.gecko.mColumnCount >= 1 &&
-                          (self.gecko.mColumnCount as i32) < i32::max_value());
+                          self.gecko.mColumnCount <= nsStyleColumn_kMaxColumnCount);
             Either::First((self.gecko.mColumnCount as i32).into())
         } else {
             Either::Second(Auto)

components/style/properties/helpers/animated_properties.mako.rs

@@ -863,7 +863,7 @@ impl Animatable for f64 {
 impl Animatable for i32 {
     #[inline]
     fn add_weighted(&self, other: &i32, self_portion: f64, other_portion: f64) -> Result<Self, ()> {
-        Ok((*self as f64 * self_portion + *other as f64 * other_portion).round() as i32)
+        Ok((*self as f64 * self_portion + *other as f64 * other_portion + 0.5).floor() as i32)
     }
 }
 
@@ -2410,10 +2410,7 @@ impl<T, U> Animatable for Either<T, U>
             (Either::Second(ref this), Either::Second(ref other)) => {
                 this.add_weighted(&other, self_portion, other_portion).map(Either::Second)
             },
-            _ => {
+            _ => Err(()),
-                let result = if self_portion > other_portion {*self} else {*other};
-                Ok(result)
-            }
         }
     }
 }

components/style/values/animated/mod.rs

@@ -172,7 +172,7 @@ impl ToAnimatedValue for ComputedPositiveInteger {
 
     #[inline]
     fn from_animated_value(animated: Self::AnimatedValue) -> Self {
-        max(animated.0, 0).into()
+        max(animated.0, 1).into()
     }
 }