Make pub strong-mode clean.

lib/src/solver/backtracking_solver.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.
 
 /// A back-tracking depth-first solver.
 ///
 /// Attempts to find the best solution for a root package's transitive
 /// dependency graph, where a "solution" is a set of concrete package versions.
 /// A valid solution will select concrete versions for every package reached
 /// from the root package's dependency graph, and each of those packages will
@@ skipping 121 matching lines @@
       _forceLatest.add(package);
     }
 
     for (var override in root.dependencyOverrides) {
       _overrides[override.name] = override;
     }
   }
 
   /// Creates [_implicitPubspec].
   static Pubspec _makeImplicitPubspec(SystemCache systemCache) {
-    var dependencies = [];
+    var dependencies = <PackageDep>[];
     barback.pubConstraints.forEach((name, constraint) {
       dependencies.add(
           systemCache.sources.hosted.refFor(name)
               .withConstraint(constraint));
     });
 
     return new Pubspec("pub itself", dependencies: dependencies);
   }
 
   /// Run the solver.
@@ skipping 14 matching lines @@
 
       // Pre-cache the root package's known pubspec.
       var rootID = new PackageId.root(root);
       await _selection.select(rootID);
 
       _validateSdkConstraint(root.pubspec);
 
       logSolve();
       var packages = await _solve();
 
-      var pubspecs = {};
+      var pubspecs = <String, Pubspec>{};
       for (var id in packages) {
         pubspecs[id.name] = await _getPubspec(id);
       }
 
       return new SolveResult.success(systemCache.sources, root, lockFile,
           packages, overrides, pubspecs, _getAvailableVersions(packages),
           _attemptedSolutions);
     } on SolveFailure catch (error) {
       // Wrap a failure in a result so we can attach some other data.
       return new SolveResult.failure(systemCache.sources, root, lockFile,
           overrides, error, _attemptedSolutions);
     } finally {
       // Gather some solving metrics.
       var buffer = new StringBuffer();
       buffer.writeln('${runtimeType} took ${stopwatch.elapsed} seconds.');
       buffer.writeln('- Tried $_attemptedSolutions solutions');
       buffer.writeln(cache.describeResults());
       log.solver(buffer);
     }
   }
 
   /// Generates a map containing all of the known available versions for each
   /// package in [packages].
   ///
   /// The version list may not always be complete. If the package is the root
   /// root package, or if it's a package that we didn't unlock while solving
   /// because we weren't trying to upgrade it, we will just know the current
   /// version.
   Map<String, List<Version>> _getAvailableVersions(List<PackageId> packages) {
-    var availableVersions = new Map<String, List<Version>>();
+    var availableVersions = <String, List<Version>>{};
     for (var package in packages) {
       var cached = cache.getCachedVersions(package.toRef());
-      var versions;
-      if (cached != null) {
-        versions = cached.map((id) => id.version).toList();
-      } else {
-        // If the version list was never requested, just use the one known
-        // version.
-        versions = [package.version];
-      }
+      // If the version list was never requested, just use the one known
+      // version.
+      var versions = cached == null
+          ? [package.version]
+          : cached.map((id) => id.version).toList();
 
       availableVersions[package.name] = versions;
     }
 
     return availableVersions;
   }
 
   /// Gets the version of [package] currently locked in the lock file.
   ///
   /// Returns `null` if it isn't in the lockfile (or has been unlocked).
@@ skipping 437 matching lines @@
 
       if (!pubspec.flutterSdkConstraint.allows(flutter.version)) {
         throw new BadSdkVersionException(pubspec.name,
             'Package ${pubspec.name} requires Flutter SDK version '
             '${pubspec.flutterSdkConstraint} but the current SDK is '
             '${flutter.version}.');
       }
     }
   }
 }