Handle malformed depfiles in Fingerprinter (#18321)

Fingerprinter.doesFingerprintMatch() now returns false rather than
throwing if a depfile is malformed.

packages/flutter_tools/lib/src/base/fingerprint.dart

@@ -50,6 +50,7 @@ class Fingerprinter {
   }
 
   Future<bool> doesFingerprintMatch() async {
+    try {
       final File fingerprintFile = fs.file(fingerprintPath);
       if (!fingerprintFile.existsSync())
         return false;
@@ -61,7 +62,6 @@ class Fingerprinter {
       if (!paths.every(fs.isFileSync))
         return false;
 
-    try {
       final Fingerprint oldFingerprint = new Fingerprint.fromJson(await fingerprintFile.readAsString());
       final Fingerprint newFingerprint = await buildFingerprint();
       return oldFingerprint == newFingerprint;
@@ -153,6 +153,9 @@ class Fingerprint {
   // Ignore map entries here to avoid becoming inconsistent with equals
   // due to differences in map entry order.
   int get hashCode => hash2(_properties.length, _checksums.length);
+
+  @override
+  String toString() => '{checksums: $_checksums, properties: $_properties}';
 }
 
 final RegExp _separatorExpr = new RegExp(r'([^\\]) ');
@@ -171,6 +174,7 @@ Future<Set<String>> readDepfile(String depfilePath) async {
   // Depfile format:
   // outfile1 outfile2 : file1.dart file2.dart file3.dart
   final String contents = await fs.file(depfilePath).readAsString();
+
   final String dependencies = contents.split(': ')[1];
   return dependencies
       .replaceAllMapped(_separatorExpr, (Match match) => '${match.group(1)}\n')

packages/flutter_tools/test/base/fingerprint_test.dart

@@ -31,6 +31,23 @@ void main() {
       FileSystem: () => fs,
     };
 
+    testUsingContext('throws when depfile is malformed', () async {
+      await fs.file('a.dart').create();
+      await fs.file('b.dart').create();
+      await fs.file('depfile').create();
+
+      final Fingerprinter fingerprinter = new Fingerprinter(
+        fingerprintPath: 'out.fingerprint',
+        paths: <String>['a.dart'],
+        depfilePaths: <String>['depfile'],
+        properties: <String, String>{
+          'bar': 'baz',
+          'wobble': 'womble',
+        },
+      );
+      expect(() async => await fingerprinter.buildFingerprint(), throwsA(anything));
+    }, overrides: contextOverrides);
+
     testUsingContext('creates fingerprint with specified properties and files', () async {
       await fs.file('a.dart').create();
 
@@ -110,6 +127,55 @@ void main() {
       expect(await fingerprinter2.doesFingerprintMatch(), isFalse);
     }, overrides: contextOverrides);
 
+    testUsingContext('fingerprint does not match if depfile is malformed', () async {
+      await fs.file('a.dart').create();
+      await fs.file('b.dart').create();
+      await fs.file('depfile').writeAsString('depfile : b.dart');
+
+      // Write a valid fingerprint
+      final Fingerprinter fingerprinter = new Fingerprinter(
+        fingerprintPath: 'out.fingerprint',
+        paths: <String>['a.dart', 'b.dart'],
+        depfilePaths: <String>['depfile'],
+        properties: <String, String>{
+          'bar': 'baz',
+          'wobble': 'womble',
+        },
+      );
+      await fingerprinter.writeFingerprint();
+
+      // Write a corrupt depfile.
+      await fs.file('depfile').writeAsString('');
+      final Fingerprinter badFingerprinter = new Fingerprinter(
+        fingerprintPath: 'out.fingerprint',
+        paths: <String>['a.dart', 'b.dart'],
+        depfilePaths: <String>['depfile'],
+        properties: <String, String>{
+          'bar': 'baz',
+          'wobble': 'womble',
+        },
+      );
+
+      expect(await badFingerprinter.doesFingerprintMatch(), isFalse);
+    }, overrides: contextOverrides);
+
+    testUsingContext('fingerprint does not match if previous fingerprint is malformed', () async {
+      await fs.file('a.dart').create();
+      await fs.file('b.dart').create();
+      await fs.file('out.fingerprint').writeAsString('** not JSON **');
+
+      final Fingerprinter fingerprinter = new Fingerprinter(
+        fingerprintPath: 'out.fingerprint',
+        paths: <String>['a.dart', 'b.dart'],
+        depfilePaths: <String>['depfile'],
+        properties: <String, String>{
+          'bar': 'baz',
+          'wobble': 'womble',
+        },
+      );
+      expect(await fingerprinter.doesFingerprintMatch(), isFalse);
+    }, overrides: contextOverrides);
+
     testUsingContext('fingerprint does match if identical', () async {
       await fs.file('a.dart').create();
       await fs.file('b.dart').create();