Clarify pub.dart messages (#6856)

packages/flutter_tools/lib/src/dart/pub.dart

@@ -58,20 +58,22 @@ Future<Null> pubGet({
       throwToolExit('pub $command failed ($code)', exitCode: code);
   }
 
-  if (dotPackages.existsSync() && dotPackages.lastModifiedSync().isAfter(pubSpecYaml.lastModifiedSync()))
-    return;
+  if (!dotPackages.existsSync())
+    throwToolExit('$directory: pub did not create .packages file');
 
-  throwToolExit('$directory: pubspec.yaml and .packages are in an inconsistent state');
+  if (dotPackages.lastModifiedSync().isBefore(pubSpecYaml.lastModifiedSync()))
+    throwToolExit('$directory: pub did not update .packages file (pubspec.yaml file has a newer timestamp)');
 }
 
-String _filterOverrideWarnings(String str) {
-  // Warning: You are using these overridden dependencies:
-  // ! analyzer 0.29.0-alpha.0 from path ../../bin/cache/dart-sdk/lib/analyzer
+final RegExp _analyzerWarning = new RegExp(r'^! analyzer [^ ]+ from path \.\./\.\./bin/cache/dart-sdk/lib/analyzer$');
 
-  if (str.contains('overridden dependencies:'))
+String _filterOverrideWarnings(String message) {
+  // This function filters out these two messages:
+  //   Warning: You are using these overridden dependencies:
+  //   ! analyzer 0.29.0-alpha.0 from path ../../bin/cache/dart-sdk/lib/analyzer
+  if (message == 'Warning: You are using these overridden dependencies:')
     return null;
-  if (str.startsWith('! analyzer '))
+  if (message.contains(_analyzerWarning))
     return null;
-
-  return str;
+  return message;
 }