From 59a3142200269bec7d65b48f3f3fb2ed2e9e24e1 Mon Sep 17 00:00:00 2001
From: Brian Birtles <birtles@gmail.com>
Date: Thu, 6 Jul 2017 06:38:17 +0900
Subject: [PATCH] Handle zero-length lists in add_weighted

---
 .../style/properties/helpers/animated_properties.mako.rs  | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/components/style/properties/helpers/animated_properties.mako.rs b/components/style/properties/helpers/animated_properties.mako.rs
index 3f5d91ba467..e68faeb8924 100644
--- a/components/style/properties/helpers/animated_properties.mako.rs
+++ b/components/style/properties/helpers/animated_properties.mako.rs
@@ -828,6 +828,10 @@ macro_rules! repeated_vec_impl {
         $(impl<T: RepeatableListAnimatable> Animatable for $ty {
             fn add_weighted(&self, other: &Self, self_portion: f64, other_portion: f64)
                 -> Result<Self, ()> {
+                // If the length of either list is zero, the least common multiple is undefined.
+                if cmp::min(self.len(), other.len()) < 1 {
+                    return Err(());
+                }
                 use num_integer::lcm;
                 let len = lcm(self.len(), other.len());
                 self.iter().cycle().zip(other.iter().cycle()).take(len).map(|(me, you)| {
@@ -842,6 +846,10 @@ macro_rules! repeated_vec_impl {
 
             #[inline]
             fn compute_squared_distance(&self, other: &Self) -> Result<f64, ()> {
+                // If the length of either list is zero, the least common multiple is undefined.
+                if cmp::min(self.len(), other.len()) < 1 {
+                    return Err(());
+                }
                 use num_integer::lcm;
                 let len = lcm(self.len(), other.len());
                 self.iter().cycle().zip(other.iter().cycle()).take(len).map(|(me, you)| {