Lazily download artifacts (III) (#27903)

packages/flutter_tools/bin/fuchsia_attach.dart

@@ -134,4 +134,7 @@ class _FuchsiaAttachCommand extends AttachCommand {
     Cache.flutterRoot = '$originalWorkingDirectory/third_party/dart-pkg/git/flutter';
     return super.runCommand();
   }
+
+  @override
+  Future<void> updateCache() async {}
 }

packages/flutter_tools/bin/xcode_backend.sh

@@ -84,7 +84,6 @@ BuildApp() {
 
   local framework_path="${FLUTTER_ROOT}/bin/cache/artifacts/engine/${artifact_variant}"
 
-  AssertExists "${framework_path}"
   AssertExists "${project_path}"
 
   local derived_dir="${SOURCE_ROOT}/Flutter"
@@ -123,6 +122,12 @@ BuildApp() {
     flutter_podspec="${FLUTTER_ENGINE}/out/${LOCAL_ENGINE}/Flutter.podspec"
   fi
 
+  # If the framework path does not exist, ensure that it is downloaded.
+  if [[ ! -e "$1" ]]; then
+    FLUTTER_ALREADY_LOCKED = "true"
+    RunCommand "${FLUTTER_ROOT}/bin/flutter" precache --suppress-analytics
+  fi
+
   if [[ -e "${project_path}/.ios" ]]; then
     RunCommand rm -rf -- "${derived_dir}/engine"
     mkdir "${derived_dir}/engine"

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

@@ -37,7 +37,8 @@ Future<List<int>> _attempt(Uri url, { bool onlyHeaders = false }) async {
   printTrace('Downloading: $url');
   HttpClient httpClient;
   if (context[HttpClientFactory] != null) {
-    httpClient = (context[HttpClientFactory] as HttpClientFactory)(); // ignore: avoid_as
+    final HttpClientFactory httpClientFactory = context[HttpClientFactory];
+    httpClient = httpClientFactory();
   } else {
     httpClient = HttpClient();
   }
@@ -64,9 +65,9 @@ Future<List<int>> _attempt(Uri url, { bool onlyHeaders = false }) async {
   // If we're making a HEAD request, we're only checking to see if the URL is
   // valid.
   if (onlyHeaders) {
-    return (response.statusCode == 200) ? <int>[] : null;
+    return (response.statusCode == HttpStatus.ok) ? <int>[] : null;
   }
-  if (response.statusCode != 200) {
+  if (response.statusCode != HttpStatus.ok) {
     if (response.statusCode > 0 && response.statusCode < 500) {
       throwToolExit(
         'Download failed.\n'

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

@@ -49,9 +49,15 @@ class BuildIOSCommand extends BuildSubCommand {
   final String description = 'Build an iOS application bundle (Mac OS X host only).';
 
   @override
-  Future<FlutterCommandResult> runCommand() async {
-    final bool forSimulator = argResults['simulator'];
+  Future<void> validateCommand() async {
     defaultBuildMode = forSimulator ? BuildMode.debug : BuildMode.release;
+    return super.validateCommand();
+  }
+
+  bool get forSimulator => argResults['simulator'];
+
+  @override
+  Future<FlutterCommandResult> runCommand() async {
 
     if (getCurrentHostPlatform() != HostPlatform.darwin_x64)
       throwToolExit('Building for iOS is only supported on the Mac.');

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

@@ -212,8 +212,6 @@ class CreateCommand extends FlutterCommand {
       throwToolExit('Neither the --flutter-root command line flag nor the FLUTTER_ROOT environment '
         'variable was specified. Unable to find package:flutter.', exitCode: 2);
 
-    await Cache.instance.updateAll();
-
     final String flutterRoot = fs.path.absolute(Cache.flutterRoot);
 
     final String flutterPackagesDirectory = fs.path.join(flutterRoot, 'packages');

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

@@ -223,8 +223,6 @@ class IdeConfigCommand extends FlutterCommand {
       throwToolExit('Currently, the only supported IDE is IntelliJ\n$usage', exitCode: 2);
     }
 
-    await Cache.instance.updateAll();
-
     if (argResults['update-templates']) {
       _handleTemplateUpdate();
       return null;

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

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import '../cache.dart';
 import '../globals.dart';
 import '../runner/flutter_command.dart';
 
@@ -11,6 +12,8 @@ class PrecacheCommand extends FlutterCommand {
   PrecacheCommand() {
     argParser.addFlag('all-platforms', abbr: 'a', negatable: false,
         help: 'Precache artifacts for all platforms.');
+    argParser.addFlag('force', abbr: 'f', negatable: false,
+        help: 'Force download of new cached artifacts');
   }
 
   @override
@@ -24,14 +27,18 @@ class PrecacheCommand extends FlutterCommand {
 
   @override
   Future<FlutterCommandResult> runCommand() async {
-    if (argResults['all-platforms'])
+    if (argResults['all-platforms']) {
       cache.includeAllPlatforms = true;
-
-    if (cache.isUpToDate())
+    }
+    final UpdateResult result = cache.isUpToDate(skipUnknown: false);
+    if (result.isUpToDate && !result.clobber && !argResults['force']) {
       printStatus('Already up-to-date.');
-    else
-      await cache.updateAll();
-
-    return null;
+    } else {
+      await cache.updateAll(
+        skipUnknown: false,
+        clobber: argResults['force'] || result.clobber,
+      );
+    }
+    return const FlutterCommandResult(ExitStatus.success);
   }
 }

packages/flutter_tools/lib/src/runner/flutter_command.dart

@@ -327,30 +327,43 @@ abstract class FlutterCommand extends Command<void> {
   }
 
   BuildMode getBuildMode() {
-    final List<bool> modeFlags = <bool>[argResults['debug'], argResults['profile'], argResults['release']];
-    if (modeFlags.where((bool flag) => flag).length > 1)
+    bool debug;
+    bool profile;
+    bool release;
+    if (argParser.options.containsKey('debug')) {
+      debug = argResults['debug'];
+    } else {
+      debug = _defaultBuildMode == BuildMode.debug;
+    }
+    if (argParser.options.containsKey('profile')) {
+      profile = argResults['profile'];
+    } else {
+      profile = _defaultBuildMode == BuildMode.profile;
+    }
+    if (argParser.options.containsKey('release')) {
+      release = argResults['release'];
+    } else {
+      release = _defaultBuildMode == BuildMode.release;
+    }
+    if (debug && profile || debug && release || release && profile) {
       throw UsageException('Only one of --debug, --profile, or --release can be specified.', null);
+    }
     final bool dynamicFlag = argParser.options.containsKey('dynamic')
         ? argResults['dynamic']
         : false;
 
-    if (argResults['debug']) {
-      if (dynamicFlag)
+    if (debug) {
+      if (dynamicFlag) {
         throw ToolExit('Error: --dynamic requires --release or --profile.');
+      }
       return BuildMode.debug;
     }
-    if (argResults['profile'])
+    if (profile) {
       return dynamicFlag ? BuildMode.dynamicProfile : BuildMode.profile;
-    if (argResults['release'])
+    }
+    if (release) {
       return dynamicFlag ? BuildMode.dynamicRelease : BuildMode.release;
-
-    if (_defaultBuildMode == BuildMode.debug && dynamicFlag)
-      throw ToolExit('Error: --dynamic requires --release or --profile.');
-    if (_defaultBuildMode == BuildMode.release && dynamicFlag)
-      return BuildMode.dynamicRelease;
-    if (_defaultBuildMode == BuildMode.profile && dynamicFlag)
-      return BuildMode.dynamicProfile;
-
+    }
     return _defaultBuildMode;
   }
 
@@ -388,7 +401,7 @@ abstract class FlutterCommand extends Command<void> {
           '--patch-number (${argResults['patch-number']}) must be an int.', null);
     }
 
-    String extraFrontEndOptions =
+    List<String> extraFrontEndOptions =
         argParser.options.containsKey(FlutterOptions.kExtraFrontEndOptions)
             ? argResults[FlutterOptions.kExtraFrontEndOptions]
             : null;
@@ -397,9 +410,9 @@ abstract class FlutterCommand extends Command<void> {
       for (String expFlag in argResults[FlutterOptions.kEnableExperiment]) {
         final String flag = '--enable-experiment=' + expFlag;
         if (extraFrontEndOptions != null) {
-          extraFrontEndOptions += ',' + flag;
+          extraFrontEndOptions.add(flag);
         } else {
-          extraFrontEndOptions = flag;
+          extraFrontEndOptions = <String>[flag];
         }
       }
     }
@@ -425,9 +438,9 @@ abstract class FlutterCommand extends Command<void> {
       baselineDir: argParser.options.containsKey('baseline-dir')
           ? argResults['baseline-dir']
           : null,
-      extraFrontEndOptions: extraFrontEndOptions,
+      extraFrontEndOptions: extraFrontEndOptions?.join(', '),
       extraGenSnapshotOptions: argParser.options.containsKey(FlutterOptions.kExtraGenSnapshotOptions)
-          ? argResults[FlutterOptions.kExtraGenSnapshotOptions]
+          ? argResults[FlutterOptions.kExtraGenSnapshotOptions]?.join(', ')
           : null,
       buildSharedLibrary: argParser.options.containsKey('build-shared-library')
         ? argResults['build-shared-library']
@@ -517,6 +530,33 @@ abstract class FlutterCommand extends Command<void> {
     );
   }
 
+  /// A hook called to populate the cache with a particular target platform
+  /// or build mode.
+  ///
+  /// If a command requires specific artifacts, it is it's responsibility to
+  /// request them here.
+  Future<void> updateCache() async {
+    // Download all artifacts unless told otherwise.
+    await cache.updateAll(
+      buildModes: <BuildMode>[
+        BuildMode.debug,
+        BuildMode.release,
+        BuildMode.profile,
+        BuildMode.dynamicProfile,
+        BuildMode.dynamicRelease,
+      ],
+      targetPlatforms: <TargetPlatform>[
+        TargetPlatform.android_arm,
+        TargetPlatform.android_arm64,
+        TargetPlatform.android_x64,
+        TargetPlatform.android_x86,
+        TargetPlatform.ios,
+      ],
+      clobber: false,
+      skipUnknown: true,
+    );
+  }
+
   /// Perform validation then call [runCommand] to execute the command.
   /// Return a [Future] that completes with an exit code
   /// indicating whether execution was successful.
@@ -527,11 +567,11 @@ abstract class FlutterCommand extends Command<void> {
   @mustCallSuper
   Future<FlutterCommandResult> verifyThenRunCommand(String commandPath) async {
     await validateCommand();
-
     // Populate the cache. We call this before pub get below so that the sky_engine
     // package is available in the flutter cache for pub to find.
-    if (shouldUpdateCache)
-      await cache.updateAll();
+    if (shouldUpdateCache) {
+      await updateCache();
+    }
 
     if (shouldRunPub) {
       await pubGet(context: PubContext.getVerifyContext(name));

packages/flutter_tools/test/runner/flutter_command_test.dart

@@ -42,7 +42,12 @@ void main() {
     testUsingContext('honors shouldUpdateCache true', () async {
       final DummyFlutterCommand flutterCommand = DummyFlutterCommand(shouldUpdateCache: true);
       await flutterCommand.run();
-      verify(cache.updateAll()).called(1);
+      verify(cache.updateAll(
+        buildModes: anyNamed('buildModes'),
+        clobber: anyNamed('clobber'),
+        skipUnknown: anyNamed('skipUnknown'),
+        targetPlatforms: anyNamed('targetPlatforms')
+      )).called(1);
     },
     overrides: <Type, Generator>{
       Cache: () => cache,