Make Asset.readAsString() async.

pkg/barback/test/utils.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library barback.test.utils;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:barback/barback.dart';
@@ skipping 309 matching lines @@
 
   Future<bool> isPrimary(AssetId asset) {
     return new Future.value(asset.extension == ".$from");
   }
 
   Future apply(Transform transform) {
     numRuns++;
     if (!_started.isCompleted) _started.complete();
     _runningTransforms++;
     return transform.primaryInput.then((input) {
-      for (var extension in to.split(" ")) {
+      return Future.wait(to.split(" ").map((extension) {
         var id = transform.primaryId.changeExtension(".$extension");
-        var content = input.readAsString() + ".$extension";
-        transform.addOutput(id, new MockAsset(id, content));
-
-      }
-
-      if (_wait != null) return _wait.future;
+        return input.readAsString().then((content) {
+          transform.addOutput(id, new MockAsset(id, "$content.$extension"));
+        });
+      })).then((_) {
+        if (_wait != null) return _wait.future;
+      });
     }).whenComplete(() {
       _runningTransforms--;
     });
   }
 
   String toString() => "$from->$to";
 }
 
 /// A [Transformer] that takes an input asset that contains a comma-separated
 /// list of paths and outputs a file for each path.
 class OneToManyTransformer extends Transformer {
   final String extension;
 
   /// The number of times the transformer has been applied.
   int numRuns = 0;
 
   /// Creates a transformer that consumes assets with [extension].
   ///
   /// That file contains a comma-separated list of paths and it will output
   /// files at each of those paths.
   OneToManyTransformer(this.extension);
 
   Future<bool> isPrimary(AssetId asset) {
     return new Future.value(asset.extension == ".$extension");
   }
 
   Future apply(Transform transform) {
     numRuns++;
     return transform.primaryInput.then((input) {
-      for (var line in input.readAsString().split(",")) {
-        var id = new AssetId(transform.primaryId.package, line);
-        transform.addOutput(id, new MockAsset(id, "spread $extension"));
-      }
+      return input.readAsString().then((lines) {
+        for (var line in lines.split(",")) {
+          var id = new AssetId(transform.primaryId.package, line);
+          transform.addOutput(id, new MockAsset(id, "spread $extension"));
+        }
+      });
     });
   }
 
   String toString() => "1->many $extension";
 }
 
 /// A transformer that uses the contents of a file to define the other inputs.
 ///
 /// Outputs a file with the same name as the primary but with an "out"
 /// extension containing the concatenated contents of all non-primary inputs.
 class ManyToOneTransformer extends Transformer {
   final String extension;
 
   /// The number of times the transformer has been applied.
   int numRuns = 0;
 
   /// Creates a transformer that consumes assets with [extension].
   ///
   /// That file contains a comma-separated list of paths and it will input
   /// files at each of those paths.
   ManyToOneTransformer(this.extension);
 
   Future<bool> isPrimary(AssetId asset) {
     return new Future.value(asset.extension == ".$extension");
   }
 
   Future apply(Transform transform) {
     numRuns++;
     return transform.primaryInput.then((primary) {
-      // Get all of the included inputs.
-      var inputs = primary.readAsString().split(",").map((path) {
-        var id = new AssetId(transform.primaryId.package, path);
-        return transform.getInput(id);
-      });
+      return primary.readAsString().then((contents) {
+        // Get all of the included inputs.
+        var inputs = contents.split(",").map((path) {
+          var id = new AssetId(transform.primaryId.package, path);
+          return transform.getInput(id);
+        });
 
-      // Concatenate them to one output.
-      return Future.wait(inputs).then((inputs) {
-        var id = transform.primaryId.changeExtension(".out");
-        var contents = inputs.map((input) => input.readAsString()).join();
-        transform.addOutput(id, new MockAsset(id, contents));
+        return Future.wait(inputs);
+      }).then((inputs) {
+        // Concatenate them to one output.
+        var output = "";
+        return Future.forEach(inputs, (input) {
+          return input.readAsString().then((contents) {
+            output += contents;

[nweiz, 2013/07/03 18:21:07]

Doing this imperatively seems less clean than the map/join you were doing
before.

[Bob Nystrom, 2013/07/03 19:45:23]

I know, but Future.forEach() doesn't actually return the resulting futures into
some sequence I can aggregate, and Future.wait() doesn't guarantee ordering. I
think this is about the best I can do.

[nweiz, 2013/07/03 20:11:16]

[Future.wait] had better guarantee ordering; we rely on the ordering all over
the place. We use the pattern of

    Future.wait([future1, future2]).then((results) {
      var result1 = results[0];
      var result2 = results[1];
      ...
    })

very frequently.

+          });
+        }).then((_) {
+          var id = transform.primaryId.changeExtension(".out");
+          transform.addOutput(id, new MockAsset(id, output));
+        });
       });
     });
   }
 
   String toString() => "many->1 $extension";
 }
 
 /// A transformer that throws an exception when run, after generating the
 /// given outputs.
 class BadTransformer extends Transformer {
@@ skipping 20 matching lines @@
   }
 }
 
 /// An implementation of [Asset] that never hits the file system.
 class MockAsset implements Asset {
   final AssetId _id;
   String _contents;
 
   MockAsset(this._id, this._contents);
 
-  String readAsString() => _contents;
+  Future<String> readAsString() => new Future.value(_contents);
   Stream<List<int>> read() => throw new UnimplementedError();
 
   serialize() => throw new UnimplementedError();
 
   String toString() => "MockAsset $_id $_contents";
 }