Generic modules: is_a? returns incorrect value

[Ragmaanir]

https://carc.in/#/r/1uz9

module A
end

module B(T)
  include A
end

class C
  include B(Int32)
end

class D
  getter c : A
  
  def initialize(@c : A)
  end
end

d = D.new(C.new)

puts d.c.is_a?(C) # => false
puts d.c.class == C # => true

crystal -v: Crystal 0.21.1 [3c6c75e] (2017-03-06) LLVM 3.5.0

Both expressions at the bottom should return true. Removing the type parameter lets it return the correct values. Is this related to #2665 ?

[iSarCasm]

Reduced
https://carc.in/#/r/2wvl

module B(T)
end

class C
  include B(Int32)
end

class D
  def initialize(c : B(Int32))
    puts c.is_a?(C)   # => true
    puts c.class == C # => true
    @c = c
    puts @c.is_a?(C)   # => false
    puts @c.class == C # => true
  end
end

D.new(C.new)

[asterite]

Reduced:

module A
end

module B(T)
  include A
end

class C
  include B(Int32)
end

c = C.new.as(A)
p c.is_a?(C) # => false (but should be true)

[jbomanson]

I bumped into this bug myself recently using Crystal 0.23.1 [e2a1389] (2017-07-13) LLVM 3.8.1.

Reduced:

module B(T)
end

class C
  include B(Int32)
end

c = C.new.as(B(Int32))
p c.is_a?(C) # => false (but should be true)

[miketheman]

#codetriage This still appears today with 0.26.1 https://carc.in/#/r/589h