correct for empty box shadow rects

webrender/src/frame_builder.rs

@@ -786,9 +786,13 @@ impl FrameBuilder {
 
         let bs_rect = box_bounds.translate(box_offset)
                                 .inflate(inflate_amount, inflate_amount);
+        // If we have negative inflate amounts.
+        // Have to explicitly check this since euclid::TypedRect relies on negative rects
+        let bs_rect_empty = bs_rect.size.width <= 0.0 || bs_rect.size.height <= 0.0;
 
         // Just draw a rectangle
-        if blur_radius == 0.0 && spread_radius == 0.0 && clip_mode == BoxShadowClipMode::None {
+        if (blur_radius == 0.0 && spread_radius == 0.0 && clip_mode == BoxShadowClipMode::None)
+           || bs_rect_empty {
             self.add_solid_rectangle(clip_id,
                                      box_bounds,
                                      clip_region,

wrench/reftests/boxshadow/inset-spread-large-ref.yaml

@@ -0,0 +1,9 @@
+---
+root:
+  items:
+        - type: stacking-context
+          bounds: [50, 50, 100, 100]
+          items:
+            - type: rect
+              bounds: [ 10, 10, 80, 80 ]
+              color: [255, 0, 0]

wrench/reftests/boxshadow/inset-spread-large.yaml

@@ -0,0 +1,12 @@
+---
+root:
+  items:
+        - type: stacking-context
+          bounds: [50, 50, 100, 100]
+          items:
+            - type: box-shadow
+              bounds: [ 10, 10, 80, 80 ]
+              blur-radius: 5
+              clip-mode: inset
+              spread-radius: 200
+              color: [255, 0, 0]

wrench/reftests/boxshadow/reftest.list

@@ -1,6 +1,7 @@
 != inset-simple.yaml inset-simple-ref.yaml
 != inset-spread.yaml inset-spread-ref.yaml
 == inset-no-blur-radius.yaml inset-no-blur-radius-ref.png
+== inset-spread-large.yaml inset-spread-large-ref.yaml
 
 # fuzzy because the test is a blur. Just want to test that clip out works.
 fuzzy(7,13704) == inset-border-radius.yaml inset-border-radius-ref.yaml