Request the user upgrade if the Android SDK version is 24 (#8462)

* Request the user upgrade if the Android SDK version is 24

* Update android_sdk_test.dart

* Update android_sdk.dart

packages/flutter_tools/lib/src/android/android_sdk.dart

@@ -2,14 +2,13 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'package:pub_semver/pub_semver.dart';
-
 import '../base/common.dart';
 import '../base/context.dart';
 import '../base/file_system.dart';
 import '../base/os.dart';
 import '../base/platform.dart';
 import '../base/process_manager.dart';
+import '../base/version.dart';
 import '../globals.dart';
 
 AndroidSdk get androidSdk => context[AndroidSdk];
@@ -36,6 +35,9 @@ const Map<String, int> _namedVersionMap = const <String, int> {
   'android-stable': 24,
 };
 
+/// The minimum Android SDK version we support.
+const int minimumAndroidSdkVersion = 25;
+
 /// Locate ADB. Prefer to use one from an Android SDK, if we can locate that.
 /// This should be used over accessing androidSdk.adbPath directly because it
 /// will work for those users who have Android Platform Tools installed but
@@ -188,7 +190,7 @@ class AndroidSdk {
       return new AndroidSdkVersion(
         this,
         platformVersionName: platformName,
-        buildToolsVersionName: buildToolsVersion.toString()
+        buildToolsVersion: buildToolsVersion
       );
     }).where((AndroidSdkVersion version) => version != null).toList();
 
@@ -204,12 +206,13 @@ class AndroidSdk {
 class AndroidSdkVersion implements Comparable<AndroidSdkVersion> {
   AndroidSdkVersion(this.sdk, {
     this.platformVersionName,
-    this.buildToolsVersionName
+    this.buildToolsVersion,
   });
 
   final AndroidSdk sdk;
   final String platformVersionName;
-  final String buildToolsVersionName;
+  final Version buildToolsVersion;
+  String get buildToolsVersionName => buildToolsVersion.toString();
 
   int get sdkLevel {
     if (_namedVersionMap.containsKey(platformVersionName))
@@ -229,6 +232,10 @@ class AndroidSdkVersion implements Comparable<AndroidSdkVersion> {
   String get apksignerPath => getBuildToolsPath('apksigner');
 
   List<String> validateSdkWellFormed({bool requireApkSigner = true}) {
+    if (buildToolsVersion.major < minimumAndroidSdkVersion) {
+      return <String>['Minimum supported Android SDK version is $minimumAndroidSdkVersion '
+                      'but this system has ${buildToolsVersion.major}. Please upgrade.'];
+    }
     if (_exists(androidJarPath) != null)
       return <String>[_exists(androidJarPath)];
 

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

@@ -58,6 +58,20 @@ class Version implements Comparable<Version> {
     }
   }
 
+  /// Returns the primary version out of a list of candidates.
+  ///
+  /// This is the highest-numbered stable version.
+  static Version primary(List<Version> versions) {
+    Version primary;
+    for (Version version in versions) {
+      if (primary == null || (version > primary)) {
+        primary = version;
+      }
+    }
+    return primary;
+  }
+
+
   static Version get unknown => new Version(0, 0, 0, text: 'unknown');
 
   /// Two [Version]s are equal if their version numbers are. The version text

packages/flutter_tools/lib/src/ios/ios_workflow.dart

@@ -4,12 +4,11 @@
 
 import 'dart:async';
 
-import 'package:pub_semver/pub_semver.dart' show Version;
-
 import '../base/io.dart';
 import '../base/os.dart';
 import '../base/platform.dart';
 import '../base/process.dart';
+import '../base/version.dart';
 import '../doctor.dart';
 import 'mac.dart';
 

packages/flutter_tools/test/android_sdk_test.dart

@@ -4,6 +4,7 @@
 
 import 'package:flutter_tools/src/android/android_sdk.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
+import 'package:flutter_tools/src/base/version.dart';
 import 'package:test/test.dart';
 
 import 'src/context.dart';
@@ -37,14 +38,14 @@ void main() {
     testUsingContext('parse normal', () {
       final AndroidSdk sdk = new AndroidSdk('.');
       final AndroidSdkVersion ver = new AndroidSdkVersion(sdk,
-        platformVersionName: 'android-23', buildToolsVersionName: '23.0.0');
+        platformVersionName: 'android-23', buildToolsVersion: new Version.parse('23.0.0'));
       expect(ver.sdkLevel, 23);
     });
 
     testUsingContext('parse android n', () {
       final AndroidSdk sdk = new AndroidSdk('.');
       final AndroidSdkVersion ver = new AndroidSdkVersion(sdk,
-        platformVersionName: 'android-N', buildToolsVersionName: '24.0.0');
+        platformVersionName: 'android-N', buildToolsVersion: new Version.parse('24.0.0'));
       expect(ver.sdkLevel, 24);
     });
   });