Prefer stable versions over pre-release versions in the solver.

sdk/lib/_internal/pub/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.
 
 library pub_upgrade_test;
 
 import 'dart:async';
 
 import 'package:unittest/unittest.dart';
 
@@ skipping 22 matching lines @@
   sdk.version = new Version(1, 2, 3);
 
   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('pre-release', prerelease);
 }
 
 void basicGraph() {
   testResolve('no dependencies', {
     'myapp 0.0.0': {}
   }, result: {
     'myapp from root': '0.0.0'
   });
 
   testResolve('simple dependency tree', {
@@ skipping 740 matching lines @@
     'bar': '2.0.0'
   }, maxTries: 3);
 
   testResolve('ignores SDK constraints on bleeding edge', {
     'myapp 0.0.0': {'sdk': badVersion }
   }, result: {
     'myapp from root': '0.0.0'
   }, useBleedingEdgeSdkVersion: true);
 }
 
+void prerelease() {
+  testResolve('prefer stable versions over unstable', {
+    'myapp 0.0.0': {
+      'a': 'any'
+    },
+    'a 1.0.0': {},
+    'a 1.1.0-dev': {},
+    'a 2.0.0-dev': {},
+    'a 3.0.0-dev': {}
+  }, result: {
+    'myapp from root': '0.0.0',
+    'a': '1.0.0'
+  });
+
+  testResolve('use latest allowed prerelease if no stable versions match', {
+    'myapp 0.0.0': {
+      'a': '<2.0.0'
+    },
+    'a 1.0.0-dev': {},
+    'a 1.1.0-dev': {},
+    'a 2.0.0-dev': {},
+    'a 3.0.0': {}
+  }, result: {
+    'myapp from root': '0.0.0',
+    'a': '2.0.0-dev'
+  });
+
+  testResolve('use an earlier stable version on a < constraint', {
+    'myapp 0.0.0': {
+      'a': '<2.0.0'
+    },
+    'a 1.0.0': {},
+    'a 1.1.0': {},
+    'a 2.0.0-dev': {},
+    'a 2.0.0': {}
+  }, result: {
+    'myapp from root': '0.0.0',
+    'a': '1.1.0'
+  });
+
+  testResolve('prefer a stable version even if constraint mentions unstable', {
+    'myapp 0.0.0': {
+      'a': '<=2.0.0-dev'
+    },
+    'a 1.0.0': {},
+    'a 1.1.0': {},
+    'a 2.0.0-dev': {},
+    'a 2.0.0': {}
+  }, result: {
+    'myapp from root': '0.0.0',
+    'a': '1.1.0'
+  });
+}
+
 testResolve(description, packages, {
              lockfile, result, FailMatcherBuilder error, int maxTries,
              bool useBleedingEdgeSdkVersion}) {
   _testResolve(test, description, packages, lockfile: lockfile, result: result,
       error: error, maxTries: maxTries,
       useBleedingEdgeSdkVersion: useBleedingEdgeSdkVersion);
 }
 
 solo_testResolve(description, packages, {
              lockfile, result, FailMatcherBuilder error, int maxTries,
@@ skipping 375 matching lines @@
   var source = "mock1";
   var match = new RegExp(r"(.*) from (.*)").firstMatch(description);
   if (match != null) {
     name = match[1];
     source = match[2];
     if (source == "root") source = null;
   }
 
   callback(isDev, name, source);
 }