[flutter_tools] provide more context for build_system invalidation (#77961)

packages/flutter_tools/lib/src/build_system/build_system.dart

@@ -1027,12 +1027,16 @@ class Node {
   /// One or more reasons why a task was invalidated.
   ///
   /// May be empty if the task was skipped.
-  final Set<InvalidatedReason> invalidatedReasons = <InvalidatedReason>{};
+  final Map<InvalidatedReasonKind, InvalidatedReason> invalidatedReasons = <InvalidatedReasonKind, InvalidatedReason>{};
 
   /// Whether this node needs an action performed.
   bool get dirty => _dirty;
   bool _dirty = false;
 
+  InvalidatedReason _invalidate(InvalidatedReasonKind kind) {
+    return invalidatedReasons[kind] ??= InvalidatedReason(kind);
+  }
+
   /// Collect hashes for all inputs to determine if any have changed.
   ///
   /// Returns whether this target can be skipped.
@@ -1060,7 +1064,8 @@ class Node {
       if (fileStore.currentAssetKeys.containsKey(absolutePath)) {
         final String currentHash = fileStore.currentAssetKeys[absolutePath];
         if (currentHash != previousAssetKey) {
-          invalidatedReasons.add(InvalidatedReason.inputChanged);
+          final InvalidatedReason reason = _invalidate(InvalidatedReasonKind.inputChanged);
+          reason.data.add(absolutePath);
           _dirty = true;
         }
       } else {
@@ -1074,13 +1079,15 @@ class Node {
       // output paths changed.
       if (!currentOutputPaths.contains(previousOutput)) {
         _dirty = true;
-        invalidatedReasons.add(InvalidatedReason.outputSetChanged);
+        final InvalidatedReason reason = _invalidate(InvalidatedReasonKind.outputSetChanged);
+        reason.data.add(previousOutput);
         // if this isn't a current output file there is no reason to compute the key.
         continue;
       }
       final File file = fileSystem.file(previousOutput);
       if (!file.existsSync()) {
-        invalidatedReasons.add(InvalidatedReason.outputMissing);
+        final InvalidatedReason reason = _invalidate(InvalidatedReasonKind.outputMissing);
+        reason.data.add(file.path);
         _dirty = true;
         continue;
       }
@@ -1089,7 +1096,8 @@ class Node {
       if (fileStore.currentAssetKeys.containsKey(absolutePath)) {
         final String currentHash = fileStore.currentAssetKeys[absolutePath];
         if (currentHash != previousHash) {
-          invalidatedReasons.add(InvalidatedReason.outputChanged);
+          final InvalidatedReason reason = _invalidate(InvalidatedReasonKind.outputChanged);
+          reason.data.add(absolutePath);
           _dirty = true;
         }
       } else {
@@ -1104,7 +1112,8 @@ class Node {
       _dirty = true;
       final String missingMessage = missingInputs.map((File file) => file.path).join(', ');
       logger.printTrace('invalidated build due to missing files: $missingMessage');
-      invalidatedReasons.add(InvalidatedReason.inputMissing);
+      final InvalidatedReason reason = _invalidate(InvalidatedReasonKind.inputMissing);
+      reason.data.addAll(missingInputs.map((File file) => file.path));
     }
 
     // If we have files to diff, compute them asynchronously and then
@@ -1112,7 +1121,8 @@ class Node {
     if (sourcesToDiff.isNotEmpty) {
       final List<File> dirty = fileStore.diffFileList(sourcesToDiff);
       if (dirty.isNotEmpty) {
-        invalidatedReasons.add(InvalidatedReason.inputChanged);
+        final InvalidatedReason reason = _invalidate(InvalidatedReasonKind.inputChanged);
+        reason.data.addAll(dirty.map((File file) => file.path));
         _dirty = true;
       }
     }
@@ -1120,8 +1130,35 @@ class Node {
   }
 }
 
+/// Data about why a target was re-run.
+class InvalidatedReason {
+  InvalidatedReason(this.kind);
+
+  final InvalidatedReasonKind kind;
+  /// Absolute file paths of inputs or outputs, depending on [kind].
+  final List<String> data = <String>[];
+
+  @override
+  String toString() {
+    switch (kind) {
+      case InvalidatedReasonKind.inputMissing:
+        return 'The following inputs were missing: ${data.join(',')}';
+      case InvalidatedReasonKind.inputChanged:
+        return 'The following inputs have updated contents: ${data.join(',')}';
+      case InvalidatedReasonKind.outputChanged:
+        return 'The following outputs have updated contents: ${data.join(',')}';
+      case InvalidatedReasonKind.outputMissing:
+        return 'The following outputs were missing: ${data.join(',')}';
+      case InvalidatedReasonKind.outputSetChanged:
+        return 'The following outputs were removed from the output set: ${data.join(',')}';
+    }
+    assert(false);
+    return null;
+  }
+}
+
 /// A description of why a target was rerun.
-enum InvalidatedReason {
+enum InvalidatedReasonKind {
   /// An input file that was expected is missing. This can occur when using
   /// depfile dependencies, or if a target is incorrectly specified.
   inputMissing,

packages/flutter_tools/test/general.shard/build_system/invalidated_reason_test.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// @dart = 2.8
+
+import 'package:flutter_tools/src/build_system/build_system.dart';
+
+import '../../src/common.dart';
+
+void main() {
+  testWithoutContext('InvalidatedReason formats message per invalidation kind', () {
+    final InvalidatedReason inputChanged = InvalidatedReason(InvalidatedReasonKind.inputChanged)
+      ..data.add('a.dart');
+    final InvalidatedReason outputChanged = InvalidatedReason(InvalidatedReasonKind.outputChanged)
+      ..data.add('b.dart');
+    final InvalidatedReason inputMissing = InvalidatedReason(InvalidatedReasonKind.inputMissing)
+      ..data.add('c.dart');
+    final InvalidatedReason outputMissing = InvalidatedReason(InvalidatedReasonKind.outputMissing)
+      ..data.add('d.dart');
+    final InvalidatedReason outputSetChanged = InvalidatedReason(InvalidatedReasonKind.outputSetChanged)
+      ..data.add('e.dart');
+
+    expect(inputChanged.toString(), 'The following inputs have updated contents: a.dart');
+    expect(outputChanged.toString(), 'The following outputs have updated contents: b.dart');
+    expect(inputMissing.toString(), 'The following inputs were missing: c.dart');
+    expect(outputMissing.toString(), 'The following outputs were missing: d.dart');
+    expect(outputSetChanged.toString(), 'The following outputs were removed from the output set: e.dart');
+  });
+}