Interpreter segfault when resuming fiber from nilable ivar

[ysbaddaden]

I identified the interpreter segfault from #16128 and #16209 and the following example reproduces: the interpreter segfaults when the scheduler tries to resume the fiber:

class Foo
  property fiber : Fiber?

  def enqueue
    @fiber.not_nil!("oops").enqueue
    # ^-- the scheduler segfaults when resuming the fiber
  end
end

foo = Foo.new
foo.fiber = Fiber.new { p "hello world" }
foo.enqueue

Fiber.yield

For the record, using a local variable works around the issue:

  def enqueue
    if fiber = @fiber
      fiber.enqueue
      # ^-- this is fine
    else
      raise NilAssertionError.new("oops")
    end
  end

[cyangle]

Looks like something's wrong with self keyword in interpreted mode:

Both Object#not_nil! and Object#not_nil!(message) just return self.

class Foo
  property x : String?
end

foo = Foo.new

foo.x = "hello"

bar = foo.x.not_nil!("test")

puts bar # => "test" in interpreted mode, "hello" in compiled mode

bar2 = foo.x.not_nil!
puts bar2 # => "hello" in both modes