Correct handling of assets when no main asset is present (#11564)

packages/flutter/lib/src/services/image_resolution.dart

@@ -150,7 +150,6 @@ class AssetImage extends AssetBundleImageProvider {
     final SplayTreeMap<double, String> mapping = new SplayTreeMap<double, String>();
     for (String candidate in candidates)
       mapping[_parseScale(candidate)] = candidate;
-    mapping[_naturalResolution] = main;
     // TODO(ianh): implement support for config.locale, config.size, config.platform
     // (then document this over in the Image.asset docs)
     return _findNearest(mapping, config.devicePixelRatio);

packages/flutter/test/widgets/image_resolution_test.dart

@@ -34,9 +34,10 @@ class TestByteData implements ByteData {
   dynamic noSuchMethod(Invocation invocation) => null;
 }
 
-String testManifest = '''
+const String testManifest = '''
 {
   "assets/image.png" : [
+    "assets/image.png",
     "assets/1.5x/image.png",
     "assets/2.0x/image.png",
     "assets/3.0x/image.png",
@@ -46,6 +47,10 @@ String testManifest = '''
 ''';
 
 class TestAssetBundle extends CachingAssetBundle {
+  TestAssetBundle({ this.manifest: testManifest });
+
+  final String manifest;
+
   @override
   Future<ByteData> load(String key) {
     ByteData data;
@@ -53,6 +58,9 @@ class TestAssetBundle extends CachingAssetBundle {
       case 'assets/image.png':
         data = new TestByteData(1.0);
         break;
+      case 'assets/1.0x/image.png':
+        data = new TestByteData(10.0); // see "...with a main asset and a 1.0x asset"
+        break;
       case 'assets/1.5x/image.png':
         data = new TestByteData(1.5);
         break;
@@ -72,7 +80,7 @@ class TestAssetBundle extends CachingAssetBundle {
   @override
   Future<String> loadString(String key, { bool cache: true }) {
     if (key == 'AssetManifest.json')
-      return new SynchronousFuture<String>(testManifest);
+      return new SynchronousFuture<String>(manifest);
     return null;
   }
 
@@ -101,7 +109,7 @@ class TestAssetImage extends AssetImage {
   }
 }
 
-Widget buildImageAtRatio(String image, Key key, double ratio, bool inferSize) {
+Widget buildImageAtRatio(String image, Key key, double ratio, bool inferSize, [AssetBundle bundle]) {
   const double windowSize = 500.0; // 500 logical pixels
   const double imageSize = 200.0; // 200 logical pixels
 
@@ -112,7 +120,7 @@ Widget buildImageAtRatio(String image, Key key, double ratio, bool inferSize) {
       padding: const EdgeInsets.all(0.0)
     ),
     child: new DefaultAssetBundle(
-      bundle: new TestAssetBundle(),
+      bundle: bundle ?? new TestAssetBundle(),
       child: new Center(
         child: inferSize ?
           new Image(
@@ -231,4 +239,57 @@ void main() {
     expect(getTestImage(tester, key).scale, 4.0);
   });
 
+  testWidgets('Image for device pixel ratio 1.0, with no main asset', (WidgetTester tester) async {
+    const String manifest = '''
+    {
+      "assets/image.png" : [
+        "assets/1.5x/image.png",
+        "assets/2.0x/image.png",
+        "assets/3.0x/image.png",
+        "assets/4.0x/image.png"
+      ]
+    }
+    ''';
+    final AssetBundle bundle = new TestAssetBundle(manifest: manifest);
+
+    const double ratio = 1.0;
+    Key key = new GlobalKey();
+    await pumpTreeToLayout(tester, buildImageAtRatio(image, key, ratio, false, bundle));
+    expect(getRenderImage(tester, key).size, const Size(200.0, 200.0));
+    expect(getTestImage(tester, key).scale, 1.5);
+    key = new GlobalKey();
+    await pumpTreeToLayout(tester, buildImageAtRatio(image, key, ratio, true, bundle));
+    expect(getRenderImage(tester, key).size, const Size(48.0, 48.0));
+    expect(getTestImage(tester, key).scale, 1.5);
+  });
+
+  testWidgets('Image for device pixel ratio 1.0, with a main asset and a 1.0x asset', (WidgetTester tester) async {
+    // If both a main asset and a 1.0x asset are specified, then prefer
+    // the 1.0x asset.
+
+    const String manifest = '''
+    {
+      "assets/image.png" : [
+        "assets/image.png",
+        "assets/1.0x/image.png",
+        "assets/1.5x/image.png",
+        "assets/2.0x/image.png",
+        "assets/3.0x/image.png",
+        "assets/4.0x/image.png"
+      ]
+    }
+    ''';
+    final AssetBundle bundle = new TestAssetBundle(manifest: manifest);
+
+    const double ratio = 1.0;
+    Key key = new GlobalKey();
+    await pumpTreeToLayout(tester, buildImageAtRatio(image, key, ratio, false, bundle));
+    expect(getRenderImage(tester, key).size, const Size(200.0, 200.0));
+    expect(getTestImage(tester, key).scale, 10.0);
+    key = new GlobalKey();
+    await pumpTreeToLayout(tester, buildImageAtRatio(image, key, ratio, true, bundle));
+    expect(getRenderImage(tester, key).size, const Size(480.0, 480.0));
+    expect(getTestImage(tester, key).scale, 10.0);
+  });
+
 }

packages/flutter_tools/lib/src/asset.dart

@@ -98,6 +98,10 @@ class AssetBundle {
 
     final PackageMap packageMap = new PackageMap(packagesPath);
 
+    // The _assetVariants map contains an entry for each asset listed
+    // in the pubspec.yaml file's assets and font and sections. The
+    // value of each image asset is a list of resolution-specific "variants",
+    // see _AssetDirectoryCache.
     final Map<_Asset, List<_Asset>> assetVariants = _parseAssets(
       packageMap,
       manifestDescriptor,
@@ -112,14 +116,24 @@ class AssetBundle {
         manifestDescriptor.containsKey('uses-material-design') &&
         manifestDescriptor['uses-material-design'];
 
+    // Save the contents of each image, image variant, and font
+    // asset in entries.
     for (_Asset asset in assetVariants.keys) {
       if (!asset.assetFileExists && assetVariants[asset].isEmpty) {
         printStatus('Error detected in pubspec.yaml:', emphasis: true);
         printError('No file or variants found for $asset.\n');
         return 1;
       }
-      if (asset.assetFileExists)
-        entries[asset.assetEntry] = new DevFSFileContent(asset.assetFile);
+      // The file name for an asset's "main" entry is whatever appears in
+      // the pubspec.yaml file. The main entry's file must always exist for
+      // font assets. It need not exist for an image if resolution-specific
+      // variant files exist. An image's main entry is treated the same as a
+      // "1x" resolution variant and if both exist then the explicit 1x
+      // variant is preferred.
+      if (asset.assetFileExists) {
+        assert(!assetVariants[asset].contains(asset));
+        assetVariants[asset].insert(0, asset);
+      }
       for (_Asset variant in assetVariants[asset]) {
         assert(variant.assetFileExists);
         entries[variant.assetEntry] = new DevFSFileContent(variant.assetFile);