Compiler bug on recursive generics (without alias)

[wolfgang371]

This is probably in relation to #13702 and #5155 , but without use of alias.

abstract class Base(T)
    abstract def mysize :  Array(Int32)
    def to_s
        if !(mysize.size>2)
        else
            raise("foo")
        end
        Array(Array(T)).new.map {|row| row.map {|el| el.to_s.size}.max}
    end
end

class Child(T) < Base(T)
    def mysize :  Array(Int32)
        [0]
    end
end

table = Child(Base(Int32)).new
table.to_s

Leads to...

BUG: `!(::raise("can't execute `().size` at /home/user/compiler-bug.cr:4:14: `` has no type"))` at /home/user/compiler-bug.cr:4:12 has no type (Exception)
  from /crystal/src/compiler/crystal/codegen/cond.cr:4 in 'codegen_cond'
  from /crystal/src/compiler/crystal/codegen/codegen.cr:909:7 in 'visit'
  from /crystal/src/compiler/crystal/syntax/visitor.cr:27:12 in 'accept'
[...]
  from /crystal/src/crystal/main.cr:129:5 in 'main'
  from src/env/__libc_start_main.c:95:2 in 'libc_start_main_stage2'
Error: you've found a bug in the Crystal compiler. Please open an issue, including source code that will allow us to reproduce the bug: https://github.com/crystal-lang/crystal/issues

I'm running

Crystal 1.9.2 [1908c816f] (2023-07-19)
LLVM: 15.0.7
Default target: x86_64-unknown-linux-gnu

on Ubuntu 18.04

[straight-shoota]

This looks completely unrelated to recursive aliases.

I have managed to reduce the reproduction a bit further. The conditional with empty then branch is very conspicuous. The condition needs to include negation.

abstract class Base(T)
  abstract def mysize :  Array(Int32)
  def to_s
    if !mysize.size
    end

    Array(T).new.map {|el| el.to_s.size}
  end
end

class Child(T) < Base(T)
  def mysize :  Array(Int32)
    [0]
  end
end

table = Child(Base(Int32)).new
table.to_s

Changing the condition to !mysize results in a slightly different error: BUG: `` at has no type. So it seems the cause of the problem lies with the implementations of Base(T)#mysize.