Use a combined inputs hash to check if we need to run a build

build_compilers/lib/src/summary_builder.dart

@@ -115,6 +115,8 @@ Future createLinkedSummary(Module module, BuildStep buildStep,
   var scratchSpace = await buildStep.fetchResource(scratchSpaceResource);
 
   var allAssetIds = new Set<AssetId>()
+    // TODO: Why can't we just add the unlinked summary?
+    // That would help invalidation.
     ..addAll(module.sources)
     ..addAll(transitiveLinkedSummaryDeps)
     ..addAll(transitiveUnlinkedSummaryDeps);
@@ -141,7 +143,8 @@ Future createLinkedSummary(Module module, BuildStep buildStep,
   request.arguments.addAll(_analyzerSourceArgsForModule(module, scratchSpace));
   var analyzer = await buildStep.fetchResource(analyzerDriverResource);
   var response = await analyzer.doWork(request);
-  if (response.exitCode == EXIT_CODE_ERROR) {
+  var summaryFile = scratchSpace.fileFor(module.linkedSummaryId);
+  if (response.exitCode == EXIT_CODE_ERROR || !await summaryFile.exists()) {
     throw new AnalyzerSummaryException(module.linkedSummaryId, response.output);
   }
 

build_runner/lib/src/asset/reader.dart

@@ -45,7 +45,7 @@ abstract class Md5DigestReader implements DigestAssetReader {
 ///
 /// Tracks the assets and globs read during this step for input dependency
 /// tracking.
-class SingleStepReader implements AssetReader {
+class SingleStepReader implements DigestAssetReader {
   final AssetGraph _assetGraph;
   final _assetsRead = new Set<AssetId>();
   final DigestAssetReader _delegate;
@@ -95,6 +95,13 @@ class SingleStepReader implements AssetReader {
     return result;
   }
 
+  @override
+  Future<Digest> digest(AssetId id) async {
+    if (!_isReadable(id)) throw new AssetNotFoundException(id);
+    await _ensureAssetIsBuilt(id);
+    return _ensureDigest(id);
+  }
+
   @override
   Future<List<int>> readAsBytes(AssetId id) async {
     if (!_isReadable(id)) throw new AssetNotFoundException(id);
@@ -135,8 +142,8 @@ class SingleStepReader implements AssetReader {
     }
   }
 
-  Future<Null> _ensureDigest(AssetId id) async {
+  Future<Digest> _ensureDigest(AssetId id) async {
     var node = _assetGraph.get(id);
-    node.lastKnownDigest ??= await _delegate.digest(id);
+    return node.lastKnownDigest ??= await _delegate.digest(id);
   }
 }

build_runner/lib/src/asset_graph/graph.dart

@@ -66,7 +66,9 @@ class AssetGraph {
     var existing = get(node.id);
     if (existing != null) {
       if (existing is SyntheticAssetNode) {
-        _remove(existing.id);
+        // Don't call _removeRecursive, that recursively removes all transitive
+        // primary outputs. We only want to remove this node.
+        _nodesByPackage[existing.id.package].remove(existing.id.path);
         node.outputs.addAll(existing.outputs);
         node.primaryOutputs.addAll(existing.primaryOutputs);
       } else {
@@ -100,14 +102,16 @@ class AssetGraph {
   /// Removes the node representing [id] from the graph, and all of its
   /// `primaryOutput`s.
   ///
+  /// Also removes all edges between all removed nodes and other nodes.
+  ///
   /// Returns a [Set<AssetId>] of all removed nodes.
-  Set<AssetId> _remove(AssetId id, {Set<AssetId> removedIds}) {
+  Set<AssetId> _removeRecursive(AssetId id, {Set<AssetId> removedIds}) {
     removedIds ??= new Set<AssetId>();
     var node = get(id);
     if (node == null) return removedIds;
     removedIds.add(id);
     for (var output in node.primaryOutputs) {
-      _remove(output, removedIds: removedIds);
+      _removeRecursive(output, removedIds: removedIds);
     }
     for (var output in node.outputs) {
       var generatedNode = get(output) as GeneratedAssetNode;
@@ -146,30 +150,24 @@ class AssetGraph {
       Future delete(AssetId id),
       DigestAssetReader digestReader) async {
     var invalidatedIds = new Set<AssetId>();
-    // All the assets that should be deleted.
-    var idsToDelete = new Set<AssetId>();
 
-    // Builds up `idsToDelete` and `idsToRemove` by recursively invalidating
-    // the outputs of `id`.
-    void clearNodeAndDeps(AssetId id, ChangeType rootChangeType) {
+    // Transitively invalidates all assets.
+    void invalidateNodeAndDeps(AssetId id, ChangeType rootChangeType) {
       var node = this.get(id);
       if (node == null) return;
       if (!invalidatedIds.add(id)) return;
 
       if (node is GeneratedAssetNode) {
-        idsToDelete.add(id);
         node.needsUpdate = true;
-        node.wasOutput = false;
-        node.globs = new Set();
       }
 
       // Update all outputs of this asset as well.
       for (var output in node.outputs) {
-        clearNodeAndDeps(output, rootChangeType);
+        invalidateNodeAndDeps(output, rootChangeType);
       }
     }
 
-    updates.forEach(clearNodeAndDeps);
+    updates.forEach(invalidateNodeAndDeps);
 
     var newIds = new Set<AssetId>();
     var modifyIds = new Set<AssetId>();
@@ -197,10 +195,33 @@ class AssetGraph {
         newAndModifiedNodes.where((node) => node.outputs.isNotEmpty),
         digestReader);
 
+    // Collects the set of all transitive ids to be removed from the graph,
+    // based on the removed `SourceAssetNode`s by following the
+    // `primaryOutputs`.
+    var transitiveRemovedIds = new Set<AssetId>();
+    addTransitivePrimaryOutputs(AssetId id) {
+      transitiveRemovedIds.add(id);
+      get(id).primaryOutputs.forEach(addTransitivePrimaryOutputs);
+    }
+
+    removeIds
+        .where((id) => get(id) is SourceAssetNode)
+        .forEach(addTransitivePrimaryOutputs);
+
+    // The generated nodes to actually delete from the file system.
+    var idsToDelete = new Set<AssetId>.from(transitiveRemovedIds)
+      ..removeAll(removeIds);
+
+    // For manually deleted generated outputs, we bash away their
+    // `previousInputsDigest` to make sure they actually get regenerated.
+    for (var deletedOutput
+        in removeIds.where((id) => get(id) is GeneratedAssetNode)) {
+      (get(deletedOutput) as GeneratedAssetNode).previousInputsDigest = null;
+    }
+
     var allNewAndDeletedIds =
         _addOutputsForSources(buildActions, newIds, rootPackage)
-          ..addAll(removeIds)
-          ..addAll(idsToDelete);
+          ..addAll(transitiveRemovedIds);
 
     // For all new or deleted assets, check if they match any globs.
     for (var id in allNewAndDeletedIds) {
@@ -211,7 +232,7 @@ class AssetGraph {
             .globs
             .any((glob) => glob.matches(id.path))) {
           // The change type is irrelevant here.
-          clearNodeAndDeps(node.id, null);
+          invalidateNodeAndDeps(node.id, null);
         }
       }
     }
@@ -223,7 +244,9 @@ class AssetGraph {
 
     // Remove all deleted source assets from the graph, which also recursively
     // removes all their primary outputs.
-    removeIds.where((id) => get(id) is SourceAssetNode).forEach(_remove);
+    removeIds
+        .where((id) => get(id) is SourceAssetNode)
+        .forEach(_removeRecursive);
 
     return invalidatedIds;
   }
@@ -290,7 +313,7 @@ class AssetGraph {
       // outputs, and replace them with a `GeneratedAssetNode`.
       if (contains(output)) {
         assert(get(output) is! GeneratedAssetNode);
-        _remove(output, removedIds: removed);
+        _removeRecursive(output, removedIds: removed);
       }
 
       _add(new GeneratedAssetNode(
@@ -304,5 +327,5 @@ class AssetGraph {
 
   // TODO remove once tests are updated
   void add(AssetNode node) => _add(node);
-  Set<AssetId> remove(AssetId id) => _remove(id);
+  Set<AssetId> remove(AssetId id) => _removeRecursive(id);
 }

build_runner/lib/src/asset_graph/node.dart

@@ -2,6 +2,8 @@
 // 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.
 
+import 'dart:collection';
+
 import 'package:build/build.dart';
 import 'package:crypto/crypto.dart';
 import 'package:glob/glob.dart';
@@ -74,13 +76,27 @@ class GeneratedAssetNode extends AssetNode {
 
   /// All the inputs that were read when generating this asset, or deciding not
   /// to generate it.
-  final Set<AssetId> inputs;
+  ///
+  /// This needs to be an ordered set because we compute combined input digests
+  /// using this later on.
+  final SplayTreeSet<AssetId> inputs;
+
+  /// A digest combining all digests of all previous inputs.
+  ///
+  /// Used to determine whether all the inputs to a build step are identical to
+  /// the previous run, indicating that the previous output is still valid.
+  Digest previousInputsDigest;
 
   GeneratedAssetNode(this.phaseNumber, this.primaryInput, this.needsUpdate,
       this.wasOutput, AssetId id,
-      {Digest lastKnownDigest, Set<Glob> globs, Iterable<AssetId> inputs})
+      {Digest lastKnownDigest,
+      Set<Glob> globs,
+      Iterable<AssetId> inputs,
+      this.previousInputsDigest})
       : this.globs = globs ?? new Set<Glob>(),
-        this.inputs = inputs?.toSet() ?? new Set<AssetId>(),
+        this.inputs = inputs != null
+            ? new SplayTreeSet.from(inputs)
+            : new SplayTreeSet<AssetId>(),
         super(id, lastKnownDigest: lastKnownDigest);
 
   @override

build_runner/lib/src/asset_graph/serialization.dart

@@ -8,7 +8,7 @@ part of 'graph.dart';
 ///
 /// This should be incremented any time the serialize/deserialize formats
 /// change.
-const _version = 10;
+const _version = 11;
 
 /// Deserializes an [AssetGraph] from a [Map].
 class _AssetGraphDeserializer {
@@ -57,9 +57,7 @@ class _AssetGraphDeserializer {
     var typeId = _NodeType.values[serializedNode[_Field.NodeType.index] as int];
     var id = _idToAssetId[serializedNode[_Field.Id.index] as int];
     var serializedDigest = serializedNode[_Field.Digest.index] as String;
-    var digest = serializedDigest == null
-        ? null
-        : new Digest(BASE64.decode(serializedDigest));
+    var digest = _deserializeDigest(serializedDigest);
     switch (typeId) {
       case _NodeType.Source:
         assert(serializedNode.length == _WrappedAssetNode._length);
@@ -72,16 +70,17 @@ class _AssetGraphDeserializer {
       case _NodeType.Generated:
         assert(serializedNode.length == _WrappedGeneratedAssetNode._length);
         node = new GeneratedAssetNode(
-          serializedNode[_Field.PhaseNumber.index] as int,
-          _idToAssetId[serializedNode[_Field.PrimaryInput.index] as int],
-          _deserializeBool(serializedNode[_Field.NeedsUpdate.index] as int),
-          _deserializeBool(serializedNode[_Field.WasOutput.index] as int),
-          id,
-          globs: (serializedNode[_Field.Globs.index] as Iterable<String>)
-              .map((pattern) => new Glob(pattern))
-              .toSet(),
-          lastKnownDigest: digest,
-        );
+            serializedNode[_Field.PhaseNumber.index] as int,
+            _idToAssetId[serializedNode[_Field.PrimaryInput.index] as int],
+            _deserializeBool(serializedNode[_Field.NeedsUpdate.index] as int),
+            _deserializeBool(serializedNode[_Field.WasOutput.index] as int),
+            id,
+            globs: (serializedNode[_Field.Globs.index] as Iterable<String>)
+                .map((pattern) => new Glob(pattern))
+                .toSet(),
+            lastKnownDigest: digest,
+            previousInputsDigest: _deserializeDigest(
+                serializedNode[_Field.PreviousInputsDigest.index] as String));
         break;
     }
     node.outputs.addAll(_deserializeAssetIds(
@@ -95,6 +94,10 @@ class _AssetGraphDeserializer {
       serializedIds.map((id) => _idToAssetId[id]).toList();
 
   bool _deserializeBool(int value) => value == 0 ? false : true;
+
+  Digest _deserializeDigest(String serializedDigest) => serializedDigest == null
+      ? null
+      : new Digest(BASE64.decode(serializedDigest));
 }
 
 /// Serializes an [AssetGraph] into a [Map].
@@ -159,7 +162,8 @@ enum _Field {
   WasOutput,
   PhaseNumber,
   Globs,
-  NeedsUpdate
+  NeedsUpdate,
+  PreviousInputsDigest
 }
 
 /// Wraps an [AssetNode] in a class that implements [List] instead of
@@ -253,6 +257,10 @@ class _WrappedGeneratedAssetNode extends _WrappedAssetNode {
         return generatedNode.globs.map((glob) => glob.pattern).toList();
       case _Field.NeedsUpdate:
         return _serializeBool(generatedNode.needsUpdate);
+      case _Field.PreviousInputsDigest:
+        return generatedNode.previousInputsDigest == null
+            ? null
+            : BASE64.encode(generatedNode.previousInputsDigest.bytes);
       default:
         throw new RangeError.index(index, this);
     }