HARP-15773 Fixes VisibleTileSet::markTilesDirty bug

@here/harp-mapview/lib/VisibleTileSet.ts

@@ -1318,6 +1318,11 @@ export class VisibleTileSet {
             const tileKey = DataSourceCache.getKeyForTile(tile);
             if (!retainedTiles.has(tileKey)) {
                 retainedTiles.add(tileKey);
+                // We need to cancel the loader first because if we don't then the call to
+                // tileLoader.loadAndDecode() inside Tile::load will return the existing promise (if
+                // the tile is still loading) and not re-request the tile data from the provider as
+                // required.
+                tile.tileLoader?.cancel();
                 this.addToTaskQueue(tile);
             }
         };

@here/harp-mapview/test/FakeOmvDataSource.ts

@@ -26,18 +26,29 @@ export class FakeTileLoader implements ITileLoader {
         geometries: []
     };
 
+    reject?: (reason?: any) => void;
+
     isFinished: boolean = false;
 
     loadAndDecode(): Promise<TileLoaderState> {
-        return Promise.resolve(TileLoaderState.Ready);
+        this.state = TileLoaderState.Loading;
+        return new Promise((resolve, reject) => {
+            this.reject = reject;
+            // We use setTimeout to delay the resolve
+            setTimeout(() => {
+                this.state = TileLoaderState.Loaded;
+                resolve(TileLoaderState.Ready);
+            });
+        });
     }
 
     waitSettled(): Promise<TileLoaderState> {
         return Promise.resolve(TileLoaderState.Ready);
     }
 
     cancel(): void {
-        // Not covered with tests yet
+        this.state = TileLoaderState.Canceled;
+        this.reject!(this.state);
     }
 }
 export class FakeOmvDataSource extends DataSource {

@here/harp-mapview/test/VisibleTileSetTest.ts

@@ -25,6 +25,7 @@ import { DataSource, DataSourceOptions } from "../lib/DataSource";
 import { FrustumIntersection, TileKeyEntry } from "../lib/FrustumIntersection";
 import { TileGeometryCreator } from "../lib/geometry/TileGeometryCreator";
 import { TileGeometryManager } from "../lib/geometry/TileGeometryManager";
+import { TileLoaderState } from "../lib/ITileLoader";
 import { MapView, TileTaskGroups } from "../lib/MapView";
 import { Tile } from "../lib/Tile";
 import { TileOffsetUtils } from "../lib/Utils";
@@ -430,6 +431,36 @@ describe("VisibleTileSet", function () {
         assert.equal(dataSourceTileList[0]?.visibleTiles[0].tileKey.mortonCode(), 1);
     });
 
+    it("#markTilesDirty cancels tileloader", async function () {
+        setupBerlinCenterCameraFromSamples();
+        const zoomLevel = 15;
+        const storageLevel = 14;
+        let dataSourceTileList = updateRenderList(zoomLevel, storageLevel).tileList;
+        let visibleTiles = dataSourceTileList[0].visibleTiles;
+
+        fixture.mapView.taskQueue.processNext(TileTaskGroups.FETCH_AND_DECODE, undefined, 2);
+        assert(visibleTiles.every(tile => tile.tileLoader?.state === TileLoaderState.Loading));
+
+        // See FakeTileLoader, this will take ~ 50ms.
+        await Promise.all(visibleTiles.map(tile => tile.tileLoader?.loadAndDecode()));
+
+        assert(visibleTiles.every(tile => tile.tileLoader?.state === TileLoaderState.Loaded));
+
+        // We need to reset the state.
+        fixture.vts.clearTileCache();
+        // Force the tiles to re-load.
+        dataSourceTileList = updateRenderList(zoomLevel, storageLevel).tileList;
+
+        visibleTiles = dataSourceTileList[0].visibleTiles;
+        assert(visibleTiles.every(tile => tile.tileLoader?.state === TileLoaderState.Loading));
+
+        // This is the crux of this test, we want to check that the loader state is cancelled.
+        fixture.vts.markTilesDirty();
+        assert(visibleTiles.every(tile => tile.tileLoader?.state === TileLoaderState.Canceled));
+        await Promise.all(visibleTiles.map(tile => tile.tileLoader?.loadAndDecode()));
+        assert(visibleTiles.every(tile => tile.tileLoader?.state === TileLoaderState.Loaded));
+    });
+
     it("#markTilesDirty properly handles cached & visible tiles", async function () {
         setupBerlinCenterCameraFromSamples();
         const zoomLevel = 15;