Add support for Flutter SDK constraints.

test/version_solver_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
 
 import 'package:path/path.dart' as p;
 import 'package:scheduled_test/scheduled_test.dart';
 
 import 'package:pub/src/lock_file.dart';
@@ skipping 14 matching lines @@
 import 'test_pub.dart';
 
 main() {
   group('basic graph', basicGraph);
   group('with lockfile', withLockFile);
   group('root dependency', rootDependency);
   group('dev dependency', devDependency);
   group('unsolvable', unsolvable);
   group('bad source', badSource);
   group('backtracking', backtracking);
-  group('SDK constraint', sdkConstraint);
+  group('Dart SDK constraint', dartSdkConstraint);
+  group('Flutter SDK constraint', flutterSdkConstraint);
   group('pre-release', prerelease);
   group('override', override);
   group('downgrade', downgrade);
 }
 
 void basicGraph() {
   integration('no dependencies', () {
     d.appDir().create();
     expectResolves(result: {});
   });
@@ skipping 716 matching lines @@
       builder.serve('d', '2.0.0', deps: {'myapp': 'any'});
       builder.serve('d', '1.0.0', deps: {'myapp': '<1.0.0'}); 
     });
 
     d.appDir({"a": "any", "c": "any", "d": "any"}).create();
     expectResolves(
         result: {'a': '1.0.0', 'b': '1.0.0', 'c': '1.0.0', 'd': '2.0.0'});
   });
 }
 
-void sdkConstraint() {
+void dartSdkConstraint() {
   integration('root matches SDK', () {
     d.dir(appPath, [
       d.pubspec({
         'name': 'myapp',
         'environment': {'sdk': '0.1.2+3'}
       })
     ]).create();
 
     expectResolves(result: {});
   });
@@ skipping 76 matching lines @@
           pubspec: {'environment': {'sdk': '0.1.2+3'}});
       builder.serve('bar', '3.0.0', pubspec: {'environment': {'sdk': '0.0.0'}});
       builder.serve('bar', '4.0.0', pubspec: {'environment': {'sdk': '0.0.0'}});
     });
 
     d.appDir({'foo': 'any'}).create();
     expectResolves(result: {'foo': '2.0.0', 'bar': '2.0.0'}, tries: 3);
   });
 }
 
+void flutterSdkConstraint() {
+  group('without a Flutter SDK', () {
+    integration('fails for the root package', () {
+      d.dir(appPath, [
+        d.pubspec({
+          'name': 'myapp',
+          'environment': {'flutter': '1.2.3'}
+        })
+      ]).create();
+
+      expectResolves(
+          error: 'Package myapp requires the Flutter SDK, which is not '
+                    'available.');
+    });
+
+    integration('fails for a dependency', () {
+      servePackages((builder) {
+        builder.serve('foo', '1.0.0',
+            pubspec: {'environment': {'flutter': '0.0.0'}});
+      });
+
+      d.appDir({'foo': 'any'}).create();
+      expectResolves(
+          error: 'Package foo requires the Flutter SDK, which is not '
+                    'available.');
+    });
+
+    integration("chooses a version that doesn't need Flutter", () {
+      servePackages((builder) {
+        builder.serve('foo', '1.0.0');
+        builder.serve('foo', '2.0.0');
+        builder.serve('foo', '3.0.0',
+            pubspec: {'environment': {'flutter': '0.0.0'}});
+      });
+
+      d.appDir({'foo': 'any'}).create();
+      expectResolves(result: {'foo': '2.0.0'});
+    });
+
+    integration('fails even with a matching Dart SDK constraint', () {
+      d.dir(appPath, [
+        d.pubspec({
+          'name': 'myapp',
+          'environment': {
+            'dart': '0.1.2+3',
+            'flutter': '1.2.3'
+          }
+        })
+      ]).create();
+
+      expectResolves(
+          error: 'Package myapp requires the Flutter SDK, which is not '
+                    'available.');
+    });
+  });
+
+  group('with a Flutter SDK', () {
+    setUp(() {
+      d.dir('flutter', [
+        d.file('version', '1.2.3')
+      ]).create();
+    });
+
+    integration('succeeds with a matching constraint', () {
+      d.dir(appPath, [
+        d.pubspec({
+          'name': 'myapp',
+          'environment': {'flutter': 'any'}
+        })
+      ]).create();
+
+      expectResolves(
+          environment: {'FLUTTER_ROOT': p.join(sandboxDir, 'flutter')},
+          result: {});
+    });
+
+    integration('fails with a non-matching constraint', () {
+      d.dir(appPath, [
+        d.pubspec({
+          'name': 'myapp',
+          'environment': {'flutter': '>1.2.3'}
+        })
+      ]).create();
+
+      expectResolves(
+          environment: {'FLUTTER_ROOT': p.join(sandboxDir, 'flutter')},
+          error: 'Package myapp requires Flutter SDK version >1.2.3 but the '
+                    'current SDK is 1.2.3.');
+    });
+
+    integration('succeeds if both Flutter and Dart SDKs match', () {
+      d.dir(appPath, [
+        d.pubspec({
+          'name': 'myapp',
+          'environment': {
+            'sdk': '0.1.2+3',
+            'flutter': '1.2.3'
+          }
+        })
+      ]).create();
+
+      expectResolves(
+          environment: {'FLUTTER_ROOT': p.join(sandboxDir, 'flutter')},
+          result: {});
+    });
+
+    integration("fails if Flutter SDK doesn't match but Dart does", () {
+      d.dir(appPath, [
+        d.pubspec({
+          'name': 'myapp',
+          'environment': {
+            'sdk': '0.1.2+3',
+            'flutter': '>1.2.3'
+          }
+        })
+      ]).create();
+
+      expectResolves(
+          environment: {'FLUTTER_ROOT': p.join(sandboxDir, 'flutter')},
+          error: 'Package myapp requires Flutter SDK version >1.2.3 but the '
+                    'current SDK is 1.2.3.');
+    });
+
+    integration("fails if Dart SDK doesn't match but Flutter does", () {
+      d.dir(appPath, [
+        d.pubspec({
+          'name': 'myapp',
+          'environment': {
+            'sdk': '>0.1.2+3',
+            'flutter': '1.2.3'
+          }
+        })
+      ]).create();
+
+      expectResolves(
+          environment: {'FLUTTER_ROOT': p.join(sandboxDir, 'flutter')},
+          error: 'Package myapp requires SDK version >0.1.2+3 but the current '
+                   'SDK is 0.1.2+3.');
+    });
+
+    integration('selects the latest dependency with a matching constraint', () {
+      servePackages((builder) {
+        builder.serve('foo', '1.0.0',
+            pubspec: {'environment': {'flutter': '^0.0.0'}});
+        builder.serve('foo', '2.0.0',
+            pubspec: {'environment': {'flutter': '^1.0.0'}});
+        builder.serve('foo', '3.0.0',
+            pubspec: {'environment': {'flutter': '^2.0.0'}});
+      });
+
+      d.appDir({'foo': 'any'}).create();
+      expectResolves(
+          environment: {'FLUTTER_ROOT': p.join(sandboxDir, 'flutter')},
+          result: {'foo': '2.0.0'});
+    });
+  });
+}
+
 void prerelease() {
   integration('prefer stable versions over unstable', () {
     servePackages((builder) {
       builder.serve('a', '1.0.0');
       builder.serve('a', '1.1.0-dev');
       builder.serve('a', '2.0.0-dev');
       builder.serve('a', '3.0.0-dev');
     });
 
     d.appDir({'a': 'any'}).create();
@@ skipping 230 matching lines @@
 /// If [result] is passed, it's parsed as a pubspec-style dependency map, and
 /// this asserts that the resulting lockfile matches those dependencies, and
 /// that it contains only packages listed in [result].
 ///
 /// If [error] is passed, this asserts that pub's error output matches the
 /// value. It may be a String, a [RegExp], or a [Matcher].
 ///
 /// Asserts that version solving looks at exactly [tries] solutions. It defaults
 /// to allowing only a single solution.
 ///
+/// If [environment] is passed, it's added to the OS environment when running
+/// pub.
+///
 /// If [downgrade] is `true`, this runs "pub downgrade" instead of "pub get".
-void expectResolves({Map result, error, int tries, bool downgrade: false}) {
+void expectResolves({Map result, error, int tries,
+    Map<String, String> environment, bool downgrade: false}) {
   schedulePub(
       args: [downgrade ? 'downgrade' : 'get'],
+      environment: environment,
       output: error == null
           ? anyOf(
               contains('Got dependencies!'),
               matches(new RegExp(r'Changed \d+ dependenc(ies|y)!')))
           : null,
       error: error,
       silent: contains('Tried ${tries ?? 1} solutions'),
       exitCode: error == null ? 0 : 1);
 
   if (result == null) return;
@@ skipping 16 matching lines @@
         dep = registry.hosted
             .refFor(dep.name, url: await globalPackageServer.url)
             .withConstraint(dep.constraint);
       }
       expect(dep.allows(id), isTrue, reason: "Expected $id to match $dep.");
     }
 
     expect(ids, isEmpty, reason: "Expected no additional packages.");
   });
 }