Mixin application cannot be used as mixin

[scheglov]

language/mixin_mixin_test

1. "It is a compile-time error if a mixin is derived from a class whose superclass is not Object."
2. "A mixin application of the form S with M1, …, Mk defines a class C whose superclass is the application of the mixin composition Mk * … * M1 to S."

So, in code
class M1 { foo() => 42; }
typedef M2 = Object with M1;

class S { }
typedef C = S with M2;

Superclass of M2 is "application of M1 to Object" != Object, so compilation error.

[kasperl]

I think the test is just fine. The language specification clearly states:

  "A mixin application of the form S with M defines a class C with superclass S."

That means that M2 is a class that has Object as superclass. The form of the M2 mixin application doesn't match (2) because you're only mixing in one class.

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cc @gbracha.
Set owner to @kasperl.
Added Invalid label.

[gbracha]

As Kasper notes, the superclass of M2 is object, and mixing in M2 is fine - though it is just the same mixing in M1.