Fix reachability analysis for intersection types

[Praetonus]

This change fixes a bug where methods on members of intersection types sometimes weren't being reached.

Closes #2102.

I haven't been able to produce a minimal test case for the bug.

[jemc]

This is only waiting on one of the OSX builds - all other Travis builds have passed. The remaining build seems to be Travis-stalled, so I'm going to go ahead and merge.

Bummer about not having a minimal repro, but it's great that you found a fix so quickly.

[dipinhora]

@Praetonus Minimal case:

use "debug"

actor Main
  var _p: (P | None) = None
  var _env: Env
  
  new create(env: Env) =>
    _env = env
    create_p()
    run_p()
  
  be create_p() =>
    let v = V
    _p = P(v)
  
  be run_p() =>
    try
      (_p as P).run()
    end

trait C

trait E
  be fun_p() => None

actor P
  var _r: R tag
  
  new create(r: R tag) =>
    _r = r
  
  be run() =>
    _r.fun_p()

type R is (C tag & E tag)

actor V is (C & E)
  new create() => 
    Debug.out("V created")

Tested against commit b1a5cf32be86a516cd58b920a76db1475c67ceee. This prints out "V created" twice. Passing env to V.create() causes a segfault on the second invocation of create. Changing the var _p: (P | None) = None to be var _p: P and assigning directly in the constructor makes the issue go away. As does combining the two behaviors in Main together. Same with changing V to only have one is instead of two.

[SeanTAllen]

Sounds like another release is coming

[dipinhora]

@SeanTAllen Why? That commit is from right after 0.16.0.

[SeanTAllen]

We already released 0.16.1

[dipinhora]

Yes. The minimal case is for @Praetonus since he wasn't able to create one when fixing the issue. I had assumed the desire for one was to be able to include it as part of the automated testing.

[SeanTAllen]

O I thought this was a new bug. Nice. Sorry, I didn't understand what you were saying.