Fix to-rgba with zero opacity

src/style-spec/expression/definitions/index.js

@@ -123,8 +123,7 @@ CompoundExpression.register(expressions, {
         array(NumberType, 4),
         [ColorType],
         (ctx, [v]) => {
-            const {r, g, b, a} = v.evaluate(ctx);
-            return [255 * r / a, 255 * g / a, 255 * b / a, a];
+            return v.evaluate(ctx).toArray();
         }
     ],
     'rgb': [

src/style-spec/util/color.js

@@ -71,9 +71,18 @@ class Color {
      * translucentGreen.toString(); // = "rgba(26,207,26,0.73)"
      */
     toString(): string {
-        const transformRgb = (value: number) => Math.round(value * 255 / this.a);
-        const rgb = [this.r, this.g, this.b].map(transformRgb);
-        return `rgba(${rgb.concat(this.a).join(',')})`;
+        const [r, g, b, a] = this.toArray();
+        return `rgba(${Math.round(r)},${Math.round(g)},${Math.round(b)},${a})`;
+    }
+
+    toArray(): [number, number, number, number] {
+        const {r, g, b, a} = this;
+        return a === 0 ? [0, 0, 0, 0] : [
+            r * 255 / a,
+            g * 255 / a,
+            b * 255 / a,
+            a
+        ];
     }
 }
 

test/integration/expression-tests/to-rgba/zero/test.json

@@ -0,0 +1,16 @@
+{
+  "expression": ["to-rgba", ["rgba", 0, 0, 0, 0]],
+  "inputs": [
+    [{}, {}]
+  ],
+  "expected": {
+    "compiled": {
+      "result": "success",
+      "isFeatureConstant": true,
+      "isZoomConstant": true,
+      "type": "array<number, 4>"
+    },
+    "outputs": [[0, 0, 0, 0]],
+    "serialized": ["to-rgba", ["rgba", 0, 0, 0, 0]]
+  }
+}