Fix bug where outputs of outputs wouldn't get deleted

build_runner/test/generate/watch_test.dart

@@ -22,7 +22,10 @@ import 'package:watcher/watcher.dart';
 void main() {
   /// Basic phases/phase groups which get used in many tests
   final copyABuildApplication = applyToRoot(
-    TestBuilder(buildExtensions: appendExtension('.copy', from: '.txt')),
+    TestBuilder(
+      buildExtensions: appendExtension('.copy', from: '.txt'),
+      shouldSkip: (content) => content.contains('skip'),
+    ),
   );
   final defaultBuilderOptions = const BuilderOptions({});
   final packageConfigId = makeAssetId('a|.dart_tool/package_config.json');
@@ -862,6 +865,20 @@ void main() {
           outputs: {'a|web/a.txt.copy': 'b', 'a|web/a.txt.copy.copy': 'b'},
           readerWriter: readerWriter,
         );
+
+        await readerWriter.writeAsString(makeAssetId('a|web/a.txt'), 'skip');
+        result = await results.next;
+        checkBuild(result, outputs: {}, readerWriter: readerWriter);
+
+        // Derived outputs should no longer exist.
+        expect(
+          readerWriter.testing.exists(makeAssetId('a|web/a.txt.copy')),
+          isFalse,
+        );
+        expect(
+          readerWriter.testing.exists(makeAssetId('a|web/a.txt.copy.copy')),
+          isFalse,
+        );
       });
 
       test('adds propagate through all phases', () async {

build_runner_core/lib/src/generate/build_impl.dart

@@ -445,8 +445,6 @@ class _SingleBuild {
           if (input.state != NodeState.upToDate) {
             await _runLazyPhaseForInput(input.phaseNumber, input.primaryInput);
           }
-          if (!input.wasOutput) return;
-          if (input.isFailure) return;
         }
         ids.add(input.id);
       }),
@@ -598,24 +596,27 @@ class _SingleBuild {
             .add(actionDescription);
 
         var unusedAssets = <AssetId>{};
-        await tracker.trackStage(
-          'Build',
-          () => runBuilder(
-            builder,
-            [input],
-            wrappedReader,
-            wrappedWriter,
-            PerformanceTrackingResolvers(_resolvers, tracker),
-            logger: logger,
-            resourceManager: _resourceManager,
-            stageTracker: tracker,
-            reportUnusedAssetsForInput:
-                (_, assets) => unusedAssets.addAll(assets),
-            packageConfig: _packageGraph.asPackageConfig,
-          ).catchError((void _) {
-            // Errors tracked through the logger
-          }),
-        );
+        // Don't run for primary inputs which weren't output.
+        if (inputNode is! GeneratedAssetNode || inputNode.wasOutput) {
+          await tracker.trackStage(
+            'Build',
+            () => runBuilder(
+              builder,
+              [input],
+              wrappedReader,
+              wrappedWriter,
+              PerformanceTrackingResolvers(_resolvers, tracker),
+              logger: logger,
+              resourceManager: _resourceManager,
+              stageTracker: tracker,
+              reportUnusedAssetsForInput:
+                  (_, assets) => unusedAssets.addAll(assets),
+              packageConfig: _packageGraph.asPackageConfig,
+            ).catchError((void _) {
+              // Errors tracked through the logger
+            }),
+          );
+        }
         actionsCompletedCount++;
         hungActionsHeartbeat.ping();
         pendingActions[phaseNumber]!.remove(actionDescription);

build_test/CHANGELOG.md

@@ -14,6 +14,8 @@
 - Breaking change: Remove `StubAssetReader`. Use `TestReaderWriter` instead.
 - Support checks on reader state after a build action in `resolveSources`.
 - Start using `package:build/src/internal.dart`.
+- Add a `shouldSkip` parameter to `TestBuilder`, which allows it to skip certain
+  inputs based on their file content.
 - Refactor `BuildCacheReader` to `BuildCacheAssetPathProvider`.
 
 ## 2.2.3

build_test/lib/src/builder.dart

@@ -13,6 +13,10 @@ typedef BuildBehavior =
       Map<String, List<String>> buildExtensions,
     );
 
+/// Optional function to skip a build step based on the content
+/// of the primary input.
+typedef ShouldSkip = bool Function(String content);
+
 /// Copy the input asset to all possible output assets.
 Future<void> _defaultBehavior(
   BuildStep buildStep,
@@ -42,12 +46,11 @@ Future<void> _copyToAll(
   }
 
   return Future.wait(
-    outputs.map(
-      (id) => buildStep.writeAsString(
-        id,
-        read(buildStep, readFrom(buildStep.inputId)),
-      ),
-    ),
+    outputs.map((id) async {
+      final content = await read(buildStep, readFrom(buildStep.inputId));
+      if (content == 'ignore') return;
+      await buildStep.writeAsString(id, content);
+    }),
   );
 }
 
@@ -96,6 +99,7 @@ class TestBuilder implements Builder {
 
   final BuildBehavior _build;
   final BuildBehavior? _extraWork;
+  final ShouldSkip? _shouldSkip;
 
   /// A stream of all the [BuildStep.inputId]s that are seen.
   ///
@@ -113,16 +117,25 @@ class TestBuilder implements Builder {
     Map<String, List<String>>? buildExtensions,
     BuildBehavior? build,
     BuildBehavior? extraWork,
+    ShouldSkip? shouldSkip,
   }) : buildExtensions = buildExtensions ?? appendExtension('.copy'),
        _build = build ?? _defaultBehavior,
-       _extraWork = extraWork;
+       _extraWork = extraWork,
+       _shouldSkip = shouldSkip;
 
   @override
   Future build(BuildStep buildStep) async {
     if (!await buildStep.canRead(buildStep.inputId)) return;
     _buildInputsController.add(buildStep.inputId);
-    await _build(buildStep, buildExtensions);
-    await _extraWork?.call(buildStep, buildExtensions);
-    _buildsCompletedController.add(buildStep.inputId);
+    try {
+      if (_shouldSkip != null) {
+        final content = await buildStep.readAsString(buildStep.inputId);
+        if (_shouldSkip(content)) return;
+      }
+      await _build(buildStep, buildExtensions);
+      await _extraWork?.call(buildStep, buildExtensions);
+    } finally {
+      _buildsCompletedController.add(buildStep.inputId);
+    }
   }
 }