Track inputs for GeneratedAssetNodes

build_runner/lib/src/asset/reader.dart

@@ -57,7 +57,7 @@ class SingleStepReader implements AssetReader {
   SingleStepReader(this._delegate, this._assetGraph, this._phaseNumber,
       this._primaryPackage, this._runPhaseForInput);
 
-  Iterable<AssetId> get assetsRead => _assetsRead;
+  Set<AssetId> get assetsRead => _assetsRead;
 
   /// The [Glob]s which have been searched with [findAssets].
   ///

build_runner/lib/src/asset_graph/graph.dart

@@ -109,6 +109,12 @@ class AssetGraph {
     for (var output in node.primaryOutputs) {
       _remove(output, removedIds: removedIds);
     }
+    for (var output in node.outputs) {
+      var generatedNode = get(output) as GeneratedAssetNode;
+      if (generatedNode != null) {
+        generatedNode.inputs.remove(id);
+      }
+    }
     _nodesByPackage[id.package].remove(id.path);
     return removedIds;
   }
@@ -145,12 +151,10 @@ class AssetGraph {
 
     // Builds up `idsToDelete` and `idsToRemove` by recursively invalidating
     // the outputs of `id`.
-    void clearNodeAndDeps(AssetId id, ChangeType rootChangeType,
-        {bool rootIsSource}) {
+    void clearNodeAndDeps(AssetId id, ChangeType rootChangeType) {
       var node = this.get(id);
       if (node == null) return;
       if (!invalidatedIds.add(id)) return;
-      rootIsSource ??= node is SourceAssetNode;
 
       if (node is GeneratedAssetNode) {
         idsToDelete.add(id);
@@ -161,7 +165,7 @@ class AssetGraph {
 
       // Update all outputs of this asset as well.
       for (var output in node.outputs) {
-        clearNodeAndDeps(output, rootChangeType, rootIsSource: rootIsSource);
+        clearNodeAndDeps(output, rootChangeType);
       }
     }
 

build_runner/lib/src/asset_graph/node.dart

@@ -72,10 +72,15 @@ class GeneratedAssetNode extends AssetNode {
   /// Any new or deleted files matching this glob should invalidate this node.
   Set<Glob> globs;
 
+  /// All the inputs that were read when generating this asset, or deciding not
+  /// to generate it.
+  final Set<AssetId> inputs;
+
   GeneratedAssetNode(this.phaseNumber, this.primaryInput, this.needsUpdate,
       this.wasOutput, AssetId id,
-      {Digest lastKnownDigest, Set<Glob> globs})
+      {Digest lastKnownDigest, Set<Glob> globs, Iterable<AssetId> inputs})
       : this.globs = globs ?? new Set<Glob>(),
+        this.inputs = inputs?.toSet() ?? new Set<AssetId>(),
         super(id, lastKnownDigest: lastKnownDigest);
 
   @override

build_runner/lib/src/asset_graph/serialization.dart

@@ -32,10 +32,23 @@ class _AssetGraphDeserializer {
           new AssetId(descriptor[1] as String, descriptor[2] as String);
     }
 
+    // Read in all the nodes and their outputs.
+    //
+    // Note that this does not read in the inputs of generated nodes.
     for (var serializedItem in _serializedGraph['nodes']) {
       graph._add(_deserializeAssetNode(serializedItem as List));
     }
 
+    // Update the inputs of all generated nodes based on the outputs of the
+    // current nodes.
+    for (var node in graph.allNodes) {
+      for (var output in node.outputs) {
+        var generatedNode = graph.get(output) as GeneratedAssetNode;
+        assert(generatedNode != null, 'Asset Graph is missing $output');
+        generatedNode.inputs.add(node.id);
+      }
+    }
+
     return graph;
   }
 

build_runner/lib/src/generate/build_impl.dart

@@ -411,12 +411,38 @@ class BuildImpl {
       SingleStepReader reader, AssetWriterSpy writer) async {
     // Reset the state for each output, setting `wasOutput` to false for now
     // (will set to true in the next loop for written assets).
+    //
+    // Also updates the `inputs` set for each output, and the `outputs` sets for
+    // all inputs.
     for (var output in declaredOutputs) {
-      (_assetGraph.get(output) as GeneratedAssetNode)
+      var node = _assetGraph.get(output) as GeneratedAssetNode;
+      node
         ..needsUpdate = false
         ..wasOutput = false
         ..lastKnownDigest = null
         ..globs = reader.globsRan.toSet();
+
+      // Update dependencies that don't exist any more.
+      var removedInputs = node.inputs.difference(reader.assetsRead);
+      node.inputs.removeAll(removedInputs);
+      for (var input in removedInputs) {
+        // TODO: special type of dependency here? This means the primary input
+        // was never actually read.
+        if (input == node.primaryInput) continue;
+
+        var inputNode = _assetGraph.get(input);
+        assert(inputNode != null, 'Asset Graph is missing $input');
+        inputNode.outputs.remove(output);
+      }
+
+      // Add the new dependencies.
+      var newInputs = reader.assetsRead.difference(node.inputs);
+      node.inputs.addAll(newInputs);
+      for (var input in newInputs) {
+        var inputNode = _assetGraph.get(input);
+        assert(inputNode != null, 'Asset Graph is missing $input');
+        inputNode.outputs.add(output);
+      }
     }
 
     // Mark the actual outputs as output.
@@ -425,15 +451,6 @@ class BuildImpl {
         ..wasOutput = true
         ..lastKnownDigest = await _reader.digest(output);
     }));
-
-    // Update the asset graph based on the dependencies discovered.
-    for (var dependency in reader.assetsRead) {
-      var dependencyNode = _assetGraph.get(dependency);
-      assert(dependencyNode != null, 'Asset Graph is missing $dependency');
-      // We care about all builderOutputs, not just real outputs. Updates
-      // to dependencies may cause a file to be output which wasn't before.
-      dependencyNode.outputs.addAll(declaredOutputs);
-    }
   }
 
   Future _delete(AssetId id) {

build_runner/test/asset_graph/graph_test.dart

@@ -88,6 +88,8 @@ void main() {
             var syntheticNode = new SyntheticAssetNode(makeAssetId());
             syntheticNode.outputs.add(generatedNode.id);
 
+            generatedNode.inputs.addAll([node.id, syntheticNode.id]);
+
             graph.add(syntheticNode);
             graph.add(generatedNode);
           }

build_runner/test/common/matchers.dart

@@ -84,6 +84,14 @@ class _AssetGraphMatcher extends Matcher {
             ];
             matches = false;
           }
+          if (!unorderedEquals(node.inputs)
+              .matches(expectedNode.inputs, null)) {
+            matchState['Inputs of ${node.id}'] = [
+              node.inputs,
+              expectedNode.inputs
+            ];
+            matches = false;
+          }
         } else {
           matchState['Type of ${node.id}'] = [
             node.runtimeType,