Dart Editor: incomplete error reporting on typedefs mismatch

[kevmoo]

Start with a typedef: typedef EventHandler<T>(Object sender, T args);

Then a method with EventHandler<T> as a param:

class SomeClass<T> {
  void add(EventHandler<T> handler){
    ...
  }
}

Then usage:

var someClass = new SomeClass<int>();

Calling add w/ a valid handler makes the editor happy.
Calling add w/ a number someClass.add(5) shows an error: 'int is not assignable to EventHandler<int>' as expected.
Calling add w/ a random object `someClass.add(new Object()) shows no error in the editor, although it blows up wonderfully at runtime.

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Attachment:
[Screen Shot 2012-05-30 at 10.19.11 AM.png](https://storage.googleapis.com/google-code-attachments/dart/issue-3316/comment-0/Screen Shot 2012-05-30 at 10.19.11 AM.png) (22.21 KB)

[madsager]

Added Area-Editor, Triaged labels.

[clayberg]

Added this to the M1 milestone.
Removed Area-Editor label.
Added Area-Analyzer label.

[scheglov]

Is this really issue?
Isn't Object superclass for everything, so for any interface too?

Reduced sample:

interface I {}
main() {
  I v = new Object();
}

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Set owner to @gbracha.

[gbracha]

By design, the Dart static checker does not complain about all possible type problems. In particular, it tolerates assignment/parameter passing/return whenever a subtype relation exists in either direction. So, since EventHandler<int> <: Object, no warning is given for

someClass.add(new Object())

In contrast, no subtype relation exists between int and EventHandler<int> in either direction. See

http://www.dartlang.org/articles/optional-types/

for a discussion and rationale.

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Added AsDesigned label.