Instance var is incorrectly considered nil when class var initializer is involved

[bcardiff]

Given the following code for Bar

class Bar
  @baz = 0

  def initialize
    begin
      @baz = 42
    rescue
    end
  end
end

The following code won't compile:

class Foo
  @@bar = Bar.new
end

Error in foo.cr:13: instantiating 'Bar:Class#new()'

  @@bar = Bar.new
              ^~~

instance variable '@baz' of Bar must be Int32, not Nil

Error: instance variable '@baz' is initialized inside a begin-rescue, so it can potentially be left uninitialized if an exception is raised and rescued

Note that however the code

class Foo
  @bar = Bar.new
end

pp Foo.new # => #<Foo:0x10b1c9f00 @bar=#<Bar:0x10b1cefd0 @baz=42>>

does works as expected.

Might be related to #3706 , extracted from crystal-lang/crystal-mysql#22

$ crystal --version
Crystal 0.20.5 (2017-01-20)

[bcardiff]

reduced to the following code.

class Foo
  @@foo = Foo.new

  @never_nil = 0

  def initialize
    if false
      @never_nil = 0
    end
  end
end

$ crystal build foo.cr 
Error in foo.cr:2: instance variable '@never_nil' of Foo must be Int32, not Nil

  @@foo = Foo.new

$ crystal --version
Crystal 0.21.0 (2017-02-21)