Fix default calculation for categorical zoom-and-property functions

src/style-spec/function/index.js

@@ -108,6 +108,7 @@ function createFunction(parameters, propertySpec) {
                         zoom: zoom,
                         type: parameters.type,
                         property: parameters.property,
+                        default: parameters.default,
                         stops: []
                     };
                     zoomStops.push(zoom);

test/integration/render-tests/regressions/mapbox-gl-js#4651/style.json

@@ -0,0 +1,50 @@
+{
+  "version": 8,
+  "metadata": {
+    "test": {
+      "height": 64,
+      "width": 64
+    }
+  },
+  "sources": {
+    "geojson": {
+      "type": "geojson",
+      "data": {
+        "type": "Feature",
+        "properties": {
+          "foo": "bar"
+        },
+        "geometry": {
+          "type": "Point",
+          "coordinates": [
+            0,
+            0
+          ]
+        }
+      }
+    }
+  },
+  "layers": [
+    {
+      "id": "circle",
+      "type": "circle",
+      "source": "geojson",
+      "paint": {
+        "circle-color": {
+          "type": "categorical",
+          "property": "foo",
+          "stops": [
+            [
+              {
+                "value": "nonesuch",
+                "zoom": 0
+              },
+              "red"
+            ]
+          ],
+          "default": "green"
+        }
+      }
+    }
+  ]
+}

test/unit/style-spec/function.test.js

@@ -715,6 +715,23 @@ test('categorical function', (t) => {
         t.end();
     });
 
+    t.test('string zoom-and-property function default', (t) => {
+        const f = createFunction({
+            property: 'foo',
+            type: 'categorical',
+            stops: [[{zoom: 0, value: 'bar'}, 'zero']],
+            default: 'default'
+        }, {
+            type: 'string'
+        });
+
+        t.equal(f(0, {}), 'default');
+        t.equal(f(0, {foo: 3}), 'default');
+        t.equal(f(0, {foo: 'bar'}), 'zero');
+
+        t.end();
+    });
+
     t.test('strict type checking', (t) => {
         const numberKeys = createFunction({
             property: 'foo',