Make pub strong-mode clean.

lib/src/validator/dependency.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:pub_semver/pub_semver.dart';
 
 import '../entrypoint.dart';
 import '../log.dart' as log;
@@ skipping 18 matching lines @@
 class DependencyValidator extends Validator {
   /// Whether the SDK constraint guarantees that `^` version constraints are
   /// safe.
   bool get _caretAllowed => entrypoint.root.pubspec.dartSdkConstraint
       .intersect(_preCaretPubVersions).isEmpty;
 
   DependencyValidator(Entrypoint entrypoint)
     : super(entrypoint);
 
   Future validate() async {
-    var caretDeps = [];
+    var caretDeps = <PackageDep>[];
 
     for (var dependency in entrypoint.root.pubspec.dependencies) {
+      var constraint = dependency.constraint;
       if (dependency.source is! HostedSource) {
         await _warnAboutSource(dependency);
-      } else if (dependency.constraint.isAny) {
+      } else if (constraint.isAny) {
         _warnAboutNoConstraint(dependency);
-      } else if (dependency.constraint is Version) {
+      } else if (constraint is Version) {
         _warnAboutSingleVersionConstraint(dependency);
-      } else if (dependency.constraint is VersionRange) {
-        if (dependency.constraint.min == null) {
+      } else if (constraint is VersionRange) {
+        if (constraint.min == null) {
           _warnAboutNoConstraintLowerBound(dependency);
-        } else if (dependency.constraint.max == null) {
+        } else if (constraint.max == null) {
           _warnAboutNoConstraintUpperBound(dependency);
         }
 
-        if (dependency.constraint.toString().startsWith("^")) {
+        if (constraint.toString().startsWith("^")) {
           caretDeps.add(dependency);
         }
       }
     }
 
     if (caretDeps.isNotEmpty && !_caretAllowed) {
       _errorAboutCaretConstraints(caretDeps);
     }
   }
 
   /// Warn that dependencies should use the hosted source.
   Future _warnAboutSource(PackageDep dep) async {
-    var versions;
+    List<Version> versions;
     try {
       var ids = await entrypoint.cache.hosted
           .getVersions(entrypoint.cache.sources.hosted.refFor(dep.name));
       versions = ids.map((id) => id.version).toList();
     } catch (error) {
       versions = [];
     }
 
     var constraint;
     var primary = Version.primary(versions);
@@ skipping 126 matching lines @@
     errors.add(buffer.toString().trim());
   }
 
   /// Returns the suggested version constraint for a dependency that was tested
   /// against [version].
   String _constraintForVersion(Version version) {
     if (_caretAllowed) return "^$version";
     return '">=$version <${version.nextBreaking}"';
   }
 }