From 5c5a72c1d81eef9889a5355cd9c87207313d1316 Mon Sep 17 00:00:00 2001
From: Boris Chiou <boris.chiou@gmail.com>
Date: Wed, 30 Aug 2017 12:03:25 +0800
Subject: [PATCH] Return Err(()) if determinant is not 1 or -1 while
 decomposing the 2d matrix.

This may happen in some cases, and we shouldn't panic in debug mode,
so let's return Err(()) for it to fall back to discrete animation.
---
 .../style/properties/helpers/animated_properties.mako.rs  | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/components/style/properties/helpers/animated_properties.mako.rs b/components/style/properties/helpers/animated_properties.mako.rs
index 4c2057f61d9..5cdcb52851c 100644
--- a/components/style/properties/helpers/animated_properties.mako.rs
+++ b/components/style/properties/helpers/animated_properties.mako.rs
@@ -1692,8 +1692,8 @@ fn decompose_2d_matrix(matrix: &ComputedMatrix) -> Result<MatrixDecomposed3D, ()
     // |   0   0  0   1 |
     let (mut m11, mut m12) = (matrix.m11, matrix.m12);
     let (mut m21, mut m22) = (matrix.m21, matrix.m22);
+    // Check if this is a singular matrix.
     if m11 * m22 == m12 * m21 {
-        // singular matrix
         return Err(());
     }
 
@@ -1711,8 +1711,10 @@ fn decompose_2d_matrix(matrix: &ComputedMatrix) -> Result<MatrixDecomposed3D, ()
     shear_xy /= scale_y;
 
     let determinant = m11 * m22 - m12 * m21;
-    debug_assert!(0.99 < determinant.abs() && determinant.abs() < 1.01,
-                  "determinant should now be 1 or -1");
+    // Determinant should now be 1 or -1.
+    if 0.99 > determinant.abs() || determinant.abs() > 1.01 {
+        return Err(());
+    }
 
     if determinant < 0. {
         m11 = -m11;