Add write caching.

Author: davidmorgan

_test_common/lib/runner_asset_writer_spy.dart

@@ -23,7 +23,4 @@ class RunnerAssetWriterSpy extends AssetWriterSpy implements RunnerAssetWriter {
 
   @override
   Future<void> deleteDirectory(AssetId id) => _delegate.deleteDirectory(id);
-
-  @override
-  Future<void> completeBuild() async {}
 }

build/lib/src/state/filesystem_cache.dart

@@ -18,6 +18,8 @@ abstract interface class FilesystemCache {
   /// Waits for any pending reads to complete first.
   Future<void> invalidate(Iterable<AssetId> ids);
 
+  Future<void> flush();
+
   /// Whether [id] exists.
   ///
   /// Returns a cached result if available, or caches and returns `ifAbsent()`.
@@ -31,6 +33,12 @@ abstract interface class FilesystemCache {
     required Future<Uint8List> Function() ifAbsent,
   });
 
+  Future<void> writeAsBytes(
+    AssetId id,
+    List<int> contents, {
+    required Future<void> Function() writer,
+  });
+
   /// Reads [id] as a `String`.
   ///
   /// Returns a cached result if available, or caches and returns `ifAbsent()`.
@@ -39,6 +47,15 @@ abstract interface class FilesystemCache {
     Encoding encoding = utf8,
     required Future<Uint8List> Function() ifAbsent,
   });
+
+  Future<void> writeAsString(
+    AssetId id,
+    String contents, {
+    Encoding encoding = utf8,
+    required Future<void> Function() writer,
+  });
+
+  Future<void> delete(AssetId id, {required Future<void> Function() deleter});
 }
 
 /// [FilesystemCache] that always reads from the underlying source.
@@ -48,6 +65,9 @@ class PassthroughFilesystemCache implements FilesystemCache {
   @override
   Future<void> invalidate(Iterable<AssetId> ids) async {}
 
+  @override
+  Future<void> flush() => Future<void>.value();
+
   @override
   Future<bool> exists(
     AssetId id, {
@@ -66,6 +86,25 @@ class PassthroughFilesystemCache implements FilesystemCache {
     Encoding encoding = utf8,
     required Future<Uint8List> Function() ifAbsent,
   }) async => encoding.decode(await ifAbsent());
+
+  @override
+  Future<void> writeAsBytes(
+    AssetId id,
+    List<int> contents, {
+    required Future<void> Function() writer,
+  }) => writer();
+
+  @override
+  Future<void> writeAsString(
+    AssetId id,
+    String contents, {
+    Encoding encoding = utf8,
+    required Future<void> Function() writer,
+  }) => writer();
+
+  @override
+  Future<void> delete(AssetId id, {required Future<void> Function() deleter}) =>
+      deleter();
 }
 
 /// [FilesystemCache] that stores data in memory.
@@ -99,6 +138,8 @@ class InMemoryFilesystemCache implements FilesystemCache {
   /// Pending `readAsString` operations.
   final _pendingStringContentCache = <AssetId, Future<String>>{};
 
+  final _pendingWrites = <AssetId, Future<void> Function()>{};
+
   @override
   Future<void> invalidate(Iterable<AssetId> ids) async {
     // First finish all pending operations, as they will write to the cache.
@@ -113,6 +154,14 @@ class InMemoryFilesystemCache implements FilesystemCache {
     }
   }
 
+  @override
+  Future<void> flush() async {
+    for (final write in _pendingWrites.values) {
+      await write();
+    }
+    _pendingWrites.clear();
+  }
+
   @override
   Future<bool> exists(
     AssetId id, {
@@ -127,6 +176,11 @@ class InMemoryFilesystemCache implements FilesystemCache {
     var cached = _bytesContentCache[id];
     if (cached != null) return Future.value(cached);
 
+    // TODO(davidmorgan): ensure these can't be evicted.
+    if (_pendingWrites.containsKey(id)) {
+      throw StateError('Whoops, should have been cached: $id');
+    }
+
     return _pendingBytesContentCache.putIfAbsent(id, () async {
       final result = await ifAbsent();
       _bytesContentCache[id] = result;
@@ -149,11 +203,54 @@ class InMemoryFilesystemCache implements FilesystemCache {
     var cached = _stringContentCache[id];
     if (cached != null) return cached;
 
+    // TODO(davidmorgan): ensure these can't be evicted.
+    if (_pendingWrites.containsKey(id)) {
+      throw StateError('Whoops, should have been cached: $id');
+    }
+
     return _pendingStringContentCache.putIfAbsent(id, () async {
       final bytes = await ifAbsent();
       final result = _stringContentCache[id] = utf8.decode(bytes);
       unawaited(_pendingStringContentCache.remove(id));
       return result;
     });
   }
+
+  @override
+  Future<void> writeAsBytes(
+    AssetId id,
+    List<int> contents, {
+    required Future<void> Function() writer,
+  }) {
+    _bytesContentCache[id] =
+        contents is Uint8List ? contents : Uint8List.fromList(contents);
+    _stringContentCache[id] = utf8.decode(contents);
+    _canReadCache[id] = Future.value(true);
+
+    _pendingWrites[id] = writer;
+    return Future.value(null);
+  }
+
+  @override
+  Future<void> writeAsString(
+    AssetId id,
+    String contents, {
+    Encoding encoding = utf8,
+    required Future<void> Function() writer,
+  }) {
+    // TODO: encoding?
+    _stringContentCache[id] = contents;
+    _bytesContentCache[id] = utf8.encode(contents);
+    _canReadCache[id] = Future.value(true);
+
+    _pendingWrites[id] = writer;
+    return Future.value(null);
+  }
+
+  @override
+  Future<void> delete(AssetId id, {required Future<void> Function() deleter}) {
+    _pendingWrites[id] = deleter;
+    _canReadCache[id] = Future.value(false);
+    return Future.value(null);
+  }
 }

build_runner_core/lib/src/asset/batch.dart

@@ -130,7 +130,13 @@ class ReaderWriter extends AssetReader
   @override
   Future<void> writeAsBytes(AssetId id, List<int> bytes) async {
     final path = _pathFor(id);
-    await filesystem.writeAsBytes(path, bytes);
+    await cache.writeAsBytes(
+      id,
+      bytes,
+      writer: () {
+        return filesystem.writeAsBytes(path, bytes);
+      },
+    );
   }
 
   @override
@@ -140,7 +146,14 @@ class ReaderWriter extends AssetReader
     Encoding encoding = utf8,
   }) async {
     final path = _pathFor(id);
-    await filesystem.writeAsString(path, contents, encoding: encoding);
+    await cache.writeAsString(
+      id,
+      contents,
+      encoding: encoding,
+      writer: () {
+        return filesystem.writeAsString(path, contents, encoding: encoding);
+      },
+    );
   }
 
   @override
@@ -160,19 +173,19 @@ class ReaderWriter extends AssetReader
         'Should not delete assets outside of $rootPackage',
       );
     }
-    await filesystem.delete(path);
+    await cache.delete(
+      id,
+      deleter: () {
+        return filesystem.delete(path);
+      },
+    );
   }
 
   @override
   Future<void> deleteDirectory(AssetId id) async {
     final path = _pathFor(id);
     await filesystem.deleteDirectory(path);
   }
-
-  @override
-  Future<void> completeBuild() async {
-    // TODO(davidmorgan): add back write caching, "batching".
-  }
 }
 
 /// [AssetFinder] that uses [PackageGraph] to map packages to paths, then