add --offline to flutter packages get (#8707)

packages/flutter_tools/lib/src/commands/packages.dart

@@ -40,7 +40,12 @@ class PackagesGetCommand extends FlutterCommand {
 
   final bool upgrade;
 
-  PackagesGetCommand(this.name, this.upgrade);
+  PackagesGetCommand(this.name, this.upgrade) {
+    argParser.addFlag('offline',
+      negatable: false,
+      help: 'Use cached packages instead of accessing the network.'
+    );
+  }
 
   // TODO: implement description
   @override
@@ -68,6 +73,11 @@ class PackagesGetCommand extends FlutterCommand {
 
     // TODO: If the user is using a local build, we should use the packages from their build instead of the cache.
 
-    await pubGet(directory: target, upgrade: upgrade, checkLastModified: false);
+    await pubGet(
+      directory: target,
+      upgrade: upgrade,
+      offline: argResults['offline'],
+      checkLastModified: false
+    );
   }
 }

packages/flutter_tools/lib/src/dart/pub.dart

@@ -29,6 +29,7 @@ Future<Null> pubGet({
   String directory,
   bool skipIfAbsent: false,
   bool upgrade: false,
+  bool offline: false,
   bool checkLastModified: true
 }) async {
   if (directory == null)
@@ -47,8 +48,10 @@ Future<Null> pubGet({
     final String command = upgrade ? 'upgrade' : 'get';
     final Status status = logger.startProgress("Running 'flutter packages $command' in ${fs.path.basename(directory)}...",
         expectSlowOperation: true);
-    final int code = await runCommandAndStreamOutput(
-      <String>[sdkBinaryName('pub'), '--verbosity=warning', command, '--no-packages-dir', '--no-precompile'],
+    final List<String> args = <String>[sdkBinaryName('pub'), '--verbosity=warning', command, '--no-packages-dir', '--no-precompile'];
+    if (offline)
+      args.add('--offline');
+    final int code = await runCommandAndStreamOutput(args,
       workingDirectory: directory,
       mapFunction: _filterOverrideWarnings,
       environment: <String, String>{ 'FLUTTER_ROOT': Cache.flutterRoot }

packages/flutter_tools/test/packages_test.dart

@@ -37,13 +37,18 @@ void main() {
       await runner.run(<String>['create', '--no-pub', temp.path]);
     }
 
-    Future<Null> runCommand(String verb) async {
+    Future<Null> runCommand(String verb, { List<String> args }) async {
       await createProject();
 
       final PackagesCommand command = new PackagesCommand();
       final CommandRunner<Null> runner = createTestCommandRunner(command);
 
-      await runner.run(<String>['packages', verb, temp.path]);
+      final List<String> commandArgs = <String>['packages', verb];
+      if (args != null)
+        commandArgs.addAll(args);
+      commandArgs.add(temp.path);
+
+      await runner.run(commandArgs);
     }
 
     void expectExists(String relPath) {
@@ -57,6 +62,12 @@ void main() {
       expectExists('.packages');
     });
 
+    testUsingContext('get --offline', () async {
+      await runCommand('get', args: <String>['--offline']);
+      expectExists('lib/main.dart');
+      expectExists('.packages');
+    });
+
     testUsingContext('upgrade', () async {
       await runCommand('upgrade');
       expectExists('lib/main.dart');