CFE seems to omit the scope that enables generic function types to have F-bounds

[iarkh]

Dart SDK Version: 2.3.0-dev.0.5
OS: Windows 10 64 bit

The following source example declares a typedef AAlias with Function in the right part:

class A<X extends A<X>> {}
typedef AAlias = Function<X extends A<X>> ();
main() { print("OK"); }

Dart throws a compile time error here whereas analyzer passes without any errors or warnings. Sample output is:

$> dartanalyzer test.dart
$> dart test.dart
test.dart:2:39: Error: Type 'X' not found.
typedef AAlias = Function<X extends A> ();
$>

Seems like analyzer should throw an error here too.

[eernstg]

This is actually an issue with the front end (and the error is still reported with dart from 7621137):

It is not an error to use X in the bound A<X>, because any generic function type (including one that occurs on the right hand side of a typedef) should have a scope where its type parameters are introduced, such that the type parameters can be used in F-bounds.

Changed the labels and issue title to reflect this.

[eernstg]

Just checked, the issue arises independently of the type alias:

class A<X extends A<X>> {}
Function<X extends A<X>>() f = throw 1; // Error in CFE: Type `X` not found.
main() {}

So, apparently, function types never introduce the scope where X can be found when checking a bound like A<X>, or it does get created but it isn't made the current scope of the bounds.