type inheritance not taken into account depending on order of declaration

[gewang]

The following code should work, but does not:

public class Foo
{
    BarFactory.make() @=> Bar bar;
}

class Bar
{
    "i am bar" => string name;
}

class BarChild extends Bar
{
    "i extend bar" => name;
}

class BarFactory
{
    fun static BarChild make()
    {
        return new BarChild;
    }
}

compiler error:

error: cannot assign '@=>' on types 'BarChild' @=> 'Bar'...
[3]     BarFactory.make() @=> Bar bar;
        ^
error:  |- reason: incompatible types for assignment
[3]     BarFactory.make() @=> Bar bar;

Cause: class definitions are processed across several phase (scan0, scan1, scan2, type-checking, code-emission). While the new Type defined by the class (e.g., BarChild) is created during scan (scan0), the inheritance (class BarChild extends Bar) is not processed until the type-checking phase, where it is done in the order it appears in the code. In this case, since Foo's BarFactory.make() @=> Bar bar; occurs before class BarChild extends Bar, Bar and BarChild are known but that BarChild extends Bar is not yet known to the type system.

Possible Remedy:

1. move the class inheritance check earlier, from type-checking potentially into scan1 or scan2 (and leave the class body portion in type-checking)
2. need to check for circular extensions e.g., A extend B and B extends A

(FYI issue uncovered while addressing #348 cc @nshaheed @heuremh)

[heuermh]

See also related issue #107

[gewang]

addressed in dbcec84 and b620658; will be part of 1.5.2.0 release