catch parse error from corrupt config (#45319)

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

@@ -3,15 +3,28 @@
 // found in the LICENSE file.
 
 import '../convert.dart';
+import '../globals.dart';
 import 'context.dart';
 import 'file_system.dart';
+import 'logger.dart';
 import 'utils.dart';
 
 class Config {
-  Config([File configFile]) {
+  Config([File configFile, Logger localLogger]) {
+    final Logger loggerInstance = localLogger ?? logger;
     _configFile = configFile ?? fs.file(fs.path.join(userHomePath(), '.flutter_settings'));
     if (_configFile.existsSync()) {
+      try {
         _values = castStringKeyedMap(json.decode(_configFile.readAsStringSync()));
+      } on FormatException {
+        loggerInstance
+          ..printError('Failed to decode preferences in ${_configFile.path}.')
+          ..printError(
+              'You may need to reapply any previously saved configuration '
+              'with the "flutter config" command.',
+          );
+        _configFile.deleteSync();
+      }
     }
   }
 

packages/flutter_tools/test/general.shard/config_test.dart

@@ -2,47 +2,43 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/config.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
+import 'package:flutter_tools/src/base/logger.dart';
 
 import '../src/common.dart';
 
 void main() {
   Config config;
-  Directory tempDir;
+  MemoryFileSystem memoryFileSystem;
 
   setUp(() {
-    tempDir = fs.systemTempDirectory.createTempSync('flutter_config_test.');
-    final File file = fs.file(fs.path.join(tempDir.path, '.settings'));
+    memoryFileSystem = MemoryFileSystem();
+    final File file = memoryFileSystem.file('example');
     config = Config(file);
   });
-
-  tearDown(() {
-    tryToDelete(tempDir);
-  });
-
-  group('config', () {
-    test('get set value', () async {
+  test('Config get set value', () async {
     expect(config.getValue('foo'), null);
     config.setValue('foo', 'bar');
     expect(config.getValue('foo'), 'bar');
     expect(config.keys, contains('foo'));
   });
 
-    test('get set bool value', () async {
+  test('Config get set bool value', () async {
     expect(config.getValue('foo'), null);
     config.setValue('foo', true);
     expect(config.getValue('foo'), true);
     expect(config.keys, contains('foo'));
   });
 
-    test('containsKey', () async {
+  test('Config containsKey', () async {
     expect(config.containsKey('foo'), false);
     config.setValue('foo', 'bar');
     expect(config.containsKey('foo'), true);
   });
 
-    test('removeValue', () async {
+  test('Config removeValue', () async {
     expect(config.getValue('foo'), null);
     config.setValue('foo', 'bar');
     expect(config.getValue('foo'), 'bar');
@@ -51,5 +47,14 @@ void main() {
     expect(config.getValue('foo'), null);
     expect(config.keys, isNot(contains('foo')));
   });
+
+  test('Config parse error', () {
+    final BufferLogger bufferLogger =BufferLogger();
+    final File file = memoryFileSystem.file('example')
+      ..writeAsStringSync('{"hello":"bar');
+    config = Config(file, bufferLogger);
+
+    expect(file.existsSync(), false);
+    expect(bufferLogger.errorText, contains('Failed to decode preferences'));
   });
 }