Make Flutter tooling work on Android without Xcode being installed (#15161)

diff --git a/packages/flutter_tools/lib/src/application_package.dart b/packages/flutter_tools/lib/src/application_package.dart
index ea4e9dc3..f8fd765 100644
--- a/packages/flutter_tools/lib/src/application_package.dart
+++ b/packages/flutter_tools/lib/src/application_package.dart
@@ -178,7 +178,7 @@
 
     final String plistPath = fs.path.join('ios', 'Runner', 'Info.plist');
     String id = plist.getValueFromFile(plistPath, plist.kCFBundleIdentifierKey);
-    if (id == null)
+    if (id == null || !xcodeProjectInterpreter.isInstalled)
       return null;
     final String projectPath = fs.path.join('ios', 'Runner.xcodeproj');
     final Map<String, String> buildSettings = xcodeProjectInterpreter.getBuildSettings(projectPath, 'Runner');
diff --git a/packages/flutter_tools/lib/src/ios/cocoapods.dart b/packages/flutter_tools/lib/src/ios/cocoapods.dart
index f9eebbb..e020c17 100644
--- a/packages/flutter_tools/lib/src/ios/cocoapods.dart
+++ b/packages/flutter_tools/lib/src/ios/cocoapods.dart
@@ -105,7 +105,7 @@
   /// contains a suitable `Podfile` and that its `Flutter/Xxx.xcconfig` files
   /// include pods configuration.
   void setupPodfile(String appDirectory) {
-    if (!xcodeProjectInterpreter.canInterpretXcodeProjects) {
+    if (!xcodeProjectInterpreter.isInstalled) {
       // Don't do anything for iOS when host platform doesn't support it.
       return;
     }
diff --git a/packages/flutter_tools/lib/src/ios/ios_workflow.dart b/packages/flutter_tools/lib/src/ios/ios_workflow.dart
index d407bd2..55b5ed3 100644
--- a/packages/flutter_tools/lib/src/ios/ios_workflow.dart
+++ b/packages/flutter_tools/lib/src/ios/ios_workflow.dart
@@ -68,10 +68,10 @@
 
       messages.add(new ValidationMessage('Xcode at ${xcode.xcodeSelectPath}'));
 
-      xcodeVersionInfo = xcode.xcodeVersionText;
+      xcodeVersionInfo = xcode.versionText;
       if (xcodeVersionInfo.contains(','))
         xcodeVersionInfo = xcodeVersionInfo.substring(0, xcodeVersionInfo.indexOf(','));
-      messages.add(new ValidationMessage(xcode.xcodeVersionText));
+      messages.add(new ValidationMessage(xcode.versionText));
 
       if (!xcode.isInstalledAndMeetsVersionCheck) {
         xcodeStatus = ValidationType.partial;
diff --git a/packages/flutter_tools/lib/src/ios/mac.dart b/packages/flutter_tools/lib/src/ios/mac.dart
index 0d48146..49eb677 100644
--- a/packages/flutter_tools/lib/src/ios/mac.dart
+++ b/packages/flutter_tools/lib/src/ios/mac.dart
@@ -104,7 +104,7 @@
 }
 
 class Xcode {
-  bool get isInstalledAndMeetsVersionCheck => isInstalled && xcodeVersionSatisfactory;
+  bool get isInstalledAndMeetsVersionCheck => isInstalled && isVersionSatisfactory;
 
   String _xcodeSelectPath;
   String get xcodeSelectPath {
@@ -121,11 +121,15 @@
   bool get isInstalled {
     if (xcodeSelectPath == null || xcodeSelectPath.isEmpty)
       return false;
-    if (xcodeVersionText == null || !xcodeVersionRegex.hasMatch(xcodeVersionText))
-      return false;
-    return true;
+    return xcodeProjectInterpreter.isInstalled;
   }
 
+  int get majorVersion => xcodeProjectInterpreter.majorVersion;
+
+  int get minorVersion => xcodeProjectInterpreter.minorVersion;
+
+  String get versionText => xcodeProjectInterpreter.versionText;
+
   bool _eulaSigned;
   /// Has the EULA been signed?
   bool get eulaSigned {
@@ -145,61 +149,17 @@
     return _eulaSigned;
   }
 
-  final RegExp xcodeVersionRegex = new RegExp(r'Xcode ([0-9.]+)');
-  void _updateXcodeVersion() {
-    try {
-      _xcodeVersionText = processManager.runSync(<String>['/usr/bin/xcodebuild', '-version']).stdout.trim().replaceAll('\n', ', ');
-      final Match match = xcodeVersionRegex.firstMatch(xcodeVersionText);
-      if (match == null)
-        return;
-
-      final String version = match.group(1);
-      final List<String> components = version.split('.');
-      _xcodeMajorVersion = int.parse(components[0]);
-      _xcodeMinorVersion = components.length == 1 ? 0 : int.parse(components[1]);
-    } on ProcessException {
-      // Ignore: leave values null.
-    }
-  }
-
-  String _xcodeVersionText;
-  String get xcodeVersionText {
-    if (_xcodeVersionText == null)
-      _updateXcodeVersion();
-    return _xcodeVersionText;
-  }
-
-  int _xcodeMajorVersion;
-  int get xcodeMajorVersion {
-    if (_xcodeMajorVersion == null)
-      _updateXcodeVersion();
-    return _xcodeMajorVersion;
-  }
-
-  int _xcodeMinorVersion;
-  int get xcodeMinorVersion {
-    if (_xcodeMinorVersion == null)
-      _updateXcodeVersion();
-    return _xcodeMinorVersion;
-  }
-
-  bool get xcodeVersionSatisfactory {
-    if (xcodeVersionText == null || !xcodeVersionRegex.hasMatch(xcodeVersionText))
+  bool get isVersionSatisfactory {
+    if (!xcodeProjectInterpreter.isInstalled)
       return false;
-    return _xcodeVersionCheckValid(xcodeMajorVersion, xcodeMinorVersion);
+    if (majorVersion > kXcodeRequiredVersionMajor)
+      return true;
+    if (majorVersion == kXcodeRequiredVersionMajor)
+      return minorVersion >= kXcodeRequiredVersionMinor;
+    return false;
   }
 }
 
-bool _xcodeVersionCheckValid(int major, int minor) {
-  if (major > kXcodeRequiredVersionMajor)
-    return true;
-
-  if (major == kXcodeRequiredVersionMajor)
-    return minor >= kXcodeRequiredVersionMinor;
-
-  return false;
-}
-
 Future<XcodeBuildResult> buildXcodeProject({
   BuildableIOSApp app,
   BuildInfo buildInfo,
@@ -547,23 +507,19 @@
   final Map<String, String> buildSettings;
 }
 
-final RegExp _xcodeVersionRegExp = new RegExp(r'Xcode (\d+)\..*');
 final String _xcodeRequirement = 'Xcode $kXcodeRequiredVersionMajor.$kXcodeRequiredVersionMinor or greater is required to develop for iOS.';
 
 bool _checkXcodeVersion() {
   if (!platform.isMacOS)
     return false;
-  try {
-    final String version = runCheckedSync(<String>['xcodebuild', '-version']);
-    final Match match = _xcodeVersionRegExp.firstMatch(version);
-    if (int.parse(match[1]) < kXcodeRequiredVersionMajor) {
-      printError('Found "${match[0]}". $_xcodeRequirement');
-      return false;
-    }
-  } catch (e) {
+  if (!xcodeProjectInterpreter.isInstalled) {
     printError('Cannot find "xcodebuild". $_xcodeRequirement');
     return false;
   }
+  if (!xcode.isVersionSatisfactory) {
+    printError('Found "${xcodeProjectInterpreter.versionText}". $_xcodeRequirement');
+    return false;
+  }
   return true;
 }
 
diff --git a/packages/flutter_tools/lib/src/ios/simulators.dart b/packages/flutter_tools/lib/src/ios/simulators.dart
index f9d5b22..c2222df 100644
--- a/packages/flutter_tools/lib/src/ios/simulators.dart
+++ b/packages/flutter_tools/lib/src/ios/simulators.dart
@@ -477,7 +477,7 @@
   }
 
   bool get _xcodeVersionSupportsScreenshot {
-    return xcode.xcodeMajorVersion > 8 || (xcode.xcodeMajorVersion == 8 && xcode.xcodeMinorVersion >= 2);
+    return xcode.majorVersion > 8 || (xcode.majorVersion == 8 && xcode.minorVersion >= 2);
   }
 
   @override
diff --git a/packages/flutter_tools/lib/src/ios/xcodeproj.dart b/packages/flutter_tools/lib/src/ios/xcodeproj.dart
index 9a50d30..e35d6aa 100644
--- a/packages/flutter_tools/lib/src/ios/xcodeproj.dart
+++ b/packages/flutter_tools/lib/src/ios/xcodeproj.dart
@@ -7,7 +7,10 @@
 import '../artifacts.dart';
 import '../base/context.dart';
 import '../base/file_system.dart';
+import '../base/io.dart';
+import '../base/platform.dart';
 import '../base/process.dart';
+import '../base/process_manager.dart';
 import '../base/utils.dart';
 import '../build_info.dart';
 import '../cache.dart';
@@ -84,16 +87,58 @@
 
 XcodeProjectInterpreter get xcodeProjectInterpreter => context.putIfAbsent(
   XcodeProjectInterpreter,
-  () => const XcodeProjectInterpreter(),
+  () => new XcodeProjectInterpreter(),
 );
 
-/// Interpreter of Xcode projects settings.
+/// Interpreter of Xcode projects.
 class XcodeProjectInterpreter {
   static const String _executable = '/usr/bin/xcodebuild';
+  static final RegExp _versionRegex = new RegExp(r'Xcode ([0-9.]+)');
 
-  const XcodeProjectInterpreter();
+  void _updateVersion() {
+    if (!platform.isMacOS || !fs.file(_executable).existsSync()) {
+      return;
+    }
+    try {
+      final ProcessResult result = processManager.runSync(<String>[_executable, '-version']);
+      if (result.exitCode != 0) {
+        return;
+      }
+      _versionText = result.stdout.trim().replaceAll('\n', ', ');
+      final Match match = _versionRegex.firstMatch(versionText);
+      if (match == null)
+        return;
+      final String version = match.group(1);
+      final List<String> components = version.split('.');
+      _majorVersion = int.parse(components[0]);
+      _minorVersion = components.length == 1 ? 0 : int.parse(components[1]);
+    } on ProcessException {
+      // Ignore: leave values null.
+    }
+  }
 
-  bool get canInterpretXcodeProjects => fs.isFileSync(_executable);
+  bool get isInstalled => majorVersion != null;
+
+  String _versionText;
+  String get versionText {
+    if (_versionText == null)
+      _updateVersion();
+    return _versionText;
+  }
+
+  int _majorVersion;
+  int get majorVersion {
+    if (_majorVersion == null)
+      _updateVersion();
+    return _majorVersion;
+  }
+
+  int _minorVersion;
+  int get minorVersion {
+    if (_minorVersion == null)
+      _updateVersion();
+    return _minorVersion;
+  }
 
   Map<String, String> getBuildSettings(String projectPath, String target) {
     final String out = runCheckedSync(<String>[