Fix symlink test

build_runner_core/lib/src/asset/writer.dart

@@ -44,7 +44,17 @@ class DelayedAssetWriter implements RunnerAssetWriter {
   /// Obtain a [RunnerAssetReader] capable of reading pending writes of this
   /// writer (before they are persisted with [onBuildComplete]).
   RunnerAssetReader reader(RunnerAssetReader delegate, String rootPackage) {
-    return _DelayAwareReader(delegate, this, rootPackage);
+    final reader = _DelayAwareReader(delegate, this, rootPackage);
+
+    if (delegate is PathProvidingAssetReader) {
+      // `createMergedOutputDirectories` needs a path providing asset reader, so
+      // keep that interface intact if we're wrapping a reader capable of doing
+      // that.
+      return _PathProvidingDelayAwareReader(
+          reader, delegate as PathProvidingAssetReader);
+    } else {
+      return reader;
+    }
   }
 
   @override
@@ -136,3 +146,37 @@ class _DelayAwareReader extends AssetReader implements RunnerAssetReader {
     return encoding.decode(await readAsBytes(id));
   }
 }
+
+class _PathProvidingDelayAwareReader extends AssetReader
+    with RunnerAssetReader
+    implements PathProvidingAssetReader {
+  final _DelayAwareReader _reader;
+  final PathProvidingAssetReader _original;
+
+  _PathProvidingDelayAwareReader(this._reader, this._original);
+
+  @override
+  Future<bool> canRead(AssetId id) {
+    return _reader.canRead(id);
+  }
+
+  @override
+  Stream<AssetId> findAssets(Glob glob, {String? package}) {
+    return _reader.findAssets(glob, package: package);
+  }
+
+  @override
+  String pathTo(AssetId id) {
+    return _original.pathTo(id);
+  }
+
+  @override
+  Future<List<int>> readAsBytes(AssetId id) {
+    return _reader.readAsBytes(id);
+  }
+
+  @override
+  Future<String> readAsString(AssetId id, {Encoding encoding = utf8}) {
+    return _reader.readAsString(id, encoding: encoding);
+  }
+}