Supertype cannot be assigned to subtype

[DartBot]

This issue was originally filed by alexei.kaigo...@gmail.com

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Consider following test:

class A<T, U extends T>
{
  T t;
  A(U u) {
     u=t;
  }
}

main() {
  new A<num, double>(1.0);
}

The spec 10.16 Assignment reads:

In checked mode, it is a dynamic type error if o is not null and the interface induced by the class of o is not a subtype of the actual type (13.8.1) of v.
It is a static type warning if the static type of e may not be assigned to the static type of v.

There is no other definition of "may not be assigned", except "interface induced by the class of o is not a subtype of the actual type (13.8.1) of v".

Since U is subtype of T, t may be assigned to u. Indeed, Dart VM in checked mode shows no dynamic error.

However, Dart compiler issues static warning:

WARNING|STATIC_TYPE|TYPE_NOT_ASSIGNMENT_COMPATIBLE|file:/home/kaigorodov/dash/dash/co19/tests/co19/src/Language/09_Generics/09_Generics_A04_t01.dart/09_Generics_A04_t01.dart|19|8|1|A.T is not assignable to A.U
    18: A(U u) {
    19: u=t;

Either spec or Dart Compiler should be fixed.

[madsager]

Added Area-Analyzer, Triaged labels.

[danrubel]

Added this to the M1 milestone.

[scheglov]

Set owner to @scheglov.
Added Accepted label.

[scheglov]

Issue #2480 has been merged into this issue.

[scheglov]

https://chromiumcodereview.appspot.com/10543089

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Added Started label.

[scheglov]

https://code.google.com/p/dart/source/detail?r=8498

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Added Fixed label.