Allow programmatic construction of style even when one is not passed in initially ( h/t @stepankuzmin )

src/style-spec/empty.js

@@ -0,0 +1,29 @@
+import latest from './reference/latest';
+
+export default function emptyStyle() {
+    const style = {};
+
+    const version = latest['$version'];
+    for (const styleKey in latest['$root']) {
+        const spec = latest['$root'][styleKey];
+
+        if (spec.required) {
+            let value = null;
+            if (styleKey === 'version') {
+                value = version;
+            } else {
+                if (spec.type === 'array') {
+                    value = [];
+                } else {
+                    value = {};
+                }
+            }
+
+            if (value != null) {
+                style[styleKey] = value;
+            }
+        }
+    }
+
+    return style;
+}

src/style/style.js

@@ -27,6 +27,7 @@ import GeoJSONSource from '../source/geojson_source';
 import styleSpec from '../style-spec/reference/latest';
 import getWorkerPool from '../util/global_worker_pool';
 import deref from '../style-spec/deref';
+import emptyStyle from '../style-spec/empty';
 import diffStyles, {operations as diffOperations} from '../style-spec/diff';
 import {
     registerForPluginStateChange,
@@ -88,6 +89,8 @@ const ignoredDiffOperations = pick(diffOperations, [
     'setPitch'
 ]);
 
+const empty = emptyStyle();
+
 export type StyleOptions = {
     validate?: boolean,
     localIdeographFontFamily?: string
@@ -229,6 +232,11 @@ class Style extends Evented {
         });
     }
 
+    loadEmpty() {
+        this.fire(new Event('dataloading', {dataType: 'style'}));
+        this._load(empty, false);
+    }
+
     _load(json: StyleSpecification, validate: boolean) {
         if (validate && emitValidationErrors(this, validateStyle(json))) {
             return;

src/ui/map.js

@@ -1210,6 +1210,14 @@ class Map extends Camera {
         return this;
     }
 
+    _lazyInitEmptyStyle() {
+        if (!this.style) {
+            this.style = new Style(this, {});
+            this.style.setEventedParent(this, {style: this.style});
+            this.style.loadEmpty();
+        }
+    }
+
     _diffStyle(style: StyleSpecification | string,  options?: {diff?: boolean} & StyleOptions) {
         if (typeof style === 'string') {
             const url = this._requestManager.normalizeStyleURL(style);
@@ -1301,6 +1309,7 @@ class Map extends Camera {
      * @see Raster DEM source: [Add hillshading](https://docs.mapbox.com/mapbox-gl-js/example/hillshade/)
      */
     addSource(id: string, source: SourceSpecification) {
+        this._lazyInitEmptyStyle();
         this.style.addSource(id, source);
         return this._update(true);
     }
@@ -1353,6 +1362,7 @@ class Map extends Camera {
      * @param {Function} callback Called when the source type is ready or with an error argument if there is an error.
      */
     addSourceType(name: string, SourceType: any, callback: Function) {
+        this._lazyInitEmptyStyle();
         return this.style.addSourceType(name, SourceType, callback);
     }
 
@@ -1433,7 +1443,7 @@ class Map extends Camera {
     addImage(id: string,
              image: HTMLImageElement | ImageData | {width: number, height: number, data: Uint8Array | Uint8ClampedArray} | StyleImageInterface,
              {pixelRatio = 1, sdf = false, stretchX, stretchY, content}: $Shape<StyleImageMetadata> = {}) {
-
+        this._lazyInitEmptyStyle();
         const version = 0;
 
         if (image instanceof HTMLImageElement) {
@@ -1621,6 +1631,7 @@ class Map extends Camera {
      * @see [Add a WMS source](https://www.mapbox.com/mapbox-gl-js/example/wms/)
      */
     addLayer(layer: LayerSpecification | CustomLayerInterface, beforeId?: string) {
+        this._lazyInitEmptyStyle();
         this.style.addLayer(layer, beforeId);
         return this._update(true);
     }
@@ -1802,6 +1813,7 @@ class Map extends Camera {
      * @returns {Map} `this`
      */
     setLight(light: LightSpecification, options: StyleSetterOptions = {}) {
+        this._lazyInitEmptyStyle();
         this.style.setLight(light, options);
         return this._update(true);
     }

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

@@ -0,0 +1,15 @@
+import {test} from '../../util/test';
+import emptyStyle from '../../../src/style-spec/empty';
+import validateStyleMin from '../../../src/style-spec/validate_style.min';
+
+test('it generates something', (t) => {
+    const style = emptyStyle();
+    t.ok(style);
+    t.end();
+});
+
+test('generated empty style is a valid style', (t) => {
+    const errors = validateStyleMin(emptyStyle());
+    t.equal(errors.length, 0);
+    t.end();
+});

test/unit/ui/map.test.js

@@ -388,6 +388,23 @@ test('Map', (t) => {
             });
         });
 
+        t.test('a layer can be added even if a map is created without a style', (t) => {
+            const map = createMap(t, {deleteStyle: true});
+            const layer = {
+                id: 'background',
+                type: 'background'
+            };
+            map.addLayer(layer);
+            t.end();
+        });
+
+        t.test('a source can be added even if a map is created without a style', (t) => {
+            const map = createMap(t, {deleteStyle: true});
+            const source = createStyleSource();
+            map.addSource('fill', source);
+            t.end();
+        });
+
         t.test('returns the style with added source and layer', (t) => {
             const style = createStyle();
             const map = createMap(t, {style});

test/util/index.js

@@ -4,13 +4,7 @@ import {extend} from '../../src/util/util';
 
 export function createMap(t, options, callback) {
     const container = window.document.createElement('div');
-
-    Object.defineProperty(container, 'clientWidth', {value: 200, configurable: true});
-    Object.defineProperty(container, 'clientHeight', {value: 200, configurable: true});
-
-    if (!options || !options.skipCSSStub) t.stub(Map.prototype, '_detectMissingCSS');
-
-    const map = new Map(extend({
+    const defaultOptions = {
         container,
         interactive: false,
         attributionControl: false,
@@ -20,8 +14,15 @@ export function createMap(t, options, callback) {
             "sources": {},
             "layers": []
         }
-    }, options));
+    };
+
+    Object.defineProperty(container, 'clientWidth', {value: 200, configurable: true});
+    Object.defineProperty(container, 'clientHeight', {value: 200, configurable: true});
+
+    if (!options || !options.skipCSSStub) t.stub(Map.prototype, '_detectMissingCSS');
+    if (options && options.deleteStyle) delete defaultOptions.style;
 
+    const map = new Map(extend(defaultOptions, options));
     if (callback) map.on('load', () => {
         callback(null, map);
     });