Fix 'covariant' bit propagation in mixin applications

In the upstream CL the
'covariant' bit on parameters of class methods isn't propagated correctly in the
case of mixins.  Effectively, if it's used in a member of the superclass of the
mixin application, it won't be propagated to the mixin application or its
subclasses.  Consider the following:

class A {
  void foo(covariant num x) {}

class B {
  void foo(num x) {}

class C {
  void foo(num x) {}

class D extends A with B implements C {
  void foo(int x) {}

The program above doesn't have any errors, and overriding foo in D using int as
the type of the parameter is allowed, because D's superclass A declares the
parameter as 'covariant'.  Without the changes from this CL, the code will
result in a compile-time error.  With the change, the 'covariant' bit is
propagated correctly, and the program compiles.

An existing test already covers the described behavior: see class Mixed in

Change-Id: Ia508a224527c95f5ef04c1f1fb02614f8ff43714
Reviewed-by: Aske Simon Christensen <>
15 files changed
tree: a5169d04e60a57025f8daeee8fc4018880765dca
  1. .clang-format
  2. .gitattributes
  3. .gitconfig
  4. .github/
  5. .gitignore
  6. .gn
  7. .mailmap
  8. .packages
  9. .vpython
  14. DEPS
  18. README.dart-sdk
  21. build/
  22. client/
  23. codereview.settings
  24. docs/
  25. pkg/
  26. runtime/
  27. samples-dev/
  28. samples/
  29. sdk/
  30. tests/
  31. third_party/
  32. tools/
  33. utils/


A client-optimized language for fast apps on any platform

Dart is:

  • Optimized for UI: Develop with a programming language specialized around the needs of user interface creation

  • Productive: Make changes iteratively: use hot reload to see the result instantly in your running app

  • Fast on all platforms: Compile to ARM & x64 machine code for mobile, desktop, and backend. Or compile to JavaScript for the web

Dart has flexible compiler technology lets you run Dart code in different ways, depending on your target platform and goals:

  • Dart Native: For programs targeting devices (mobile, desktop, server, and more), Dart Native includes both a Dart VM with JIT (just-in-time) compilation and an AOT (ahead-of-time) compiler for producing machine code.

  • Dart Web: For programs targeting the web, Dart Web includes both a development time compiler (dartdevc) and a production time compiler (dart2js).

Dart platforms illustration

License & patents

Dart is free and open source.


Using Dart

Visit the to learn more about the language, tools, getting started, and more.

Browse for more packages and libraries contributed by the community and the Dart team.

Building Dart

If you want to build Dart yourself, here is a guide to getting the source, preparing your machine to build the SDK, and building.

There are more documents on our wiki.

Contributing to Dart

The easiest way to contribute to Dart is to file issues.

You can also contribute patches, as described in Contributing.