#2142. Add Subtyping tests for extension types

[sgrekhov]

Subtyping tests needs some comments, as usual. It makes sense to review extension_type_* files in the folders:
/Subtyping/test_types/
/Subtyping/static/test_types/
/Subtyping/dynamic/test_types/
All other tests are generated.

Tests in /Subtyping/static/test_types/ test static behaviour. Generated tests will look like

T0 t = t1; // Expect a compile-time error if static type of t1 is not subtype of T0

Tests in /Subtyping/dynamic/test_types/ test runtime behaviour. Generated tests will look like

dynamic forgetType(dynamic d) => d;

T0 t = forgetType(t1); // Expect a run-time error if run-time type of t1 is not subtype of T0

Tests in /Subtyping/test_types/ test both static and runtime behavior. In case of extension types we have to test some cases dynamically or statically only. For example

  extensuin type V(int id) {}
  int i1 = V(42); // Error at compile time
  int i2 = forgetType(V(42)); // No error at run time

So we have to test that extension type V is not assignable to int in static tests only. In dynamic tests we check that forgetType(V(...)) is assignable to int and vice-versa.

Please review

[eernstg]

Having looked at the libraries you suggested, I'm not sure about implements relations: Do we have subtype tests confirming that E1 <: E2, E0 <: int, and not E2 <: E1 and not int <: E0 (and similarly for some generic types):

extension type E2(int i) {}
extension type E1(int i) implements E2 {}
extension type E0(int i) implements int {}

[eernstg]

Looks good! I just have a couple of questions.

[sgrekhov]

Added missing cases. Please take another look

[eernstg]

I'm afraid there's a lot of trailing whitespace. I suppose it can be grepped where it occurs in non-generated files (or is created by the generator)? Otherwise it's good!

[sgrekhov]

Updated. Trailing whitespaces removed (yes, it was generator issue and fix affected all tests). But we need to review /test_types/ only. Please note, that one more test type added. /Subtyping/test_types/extension_type_A08.dart

[eernstg]

Please note, that one more test type added. /Subtyping/test_types/extension_type_A08.dart

OK, thanks! It's very helpful to know which parts are actually changed.

However, I'm confused about the changes overall anyway: It used to say (I think) hundred-and-fifty-something files changed; next time it said 253 files changed (I think); but now it says 2840 files changed.

What's going on that changes so many files?

[eernstg]

Ah, it's because almost everything had those trailing spaces, and now they have been regenerated without them. OK!

[eernstg]

LGTM.