Crash from accessing instance variable in super before it's set in subclass

[manveru]

This happens with 0.24.1, 0.24.2, and master, but for completeness here's the version string of master:

Crystal 0.24.2 (2018-05-26)
LLVM: 5.0.1
Default target: x86_64-unknown-linux-gnu

The OS is NixOS.

class Base
  property last_value : String

  def initialize
    @last_value = data
  end
end

class Sub < Base
  property url : String

  def initialize
    super
    @url = ""
  end

  def data
    url
  end
end

pp Sub.new.last_value

Moving @url = "" before the super fixes the crash, but that should be caught by the compiler.

Backtrace is:

Invalid memory access (signal 11) at address 0x4
[0x446886] *CallStack::print_backtrace:Int32 +118
[0x43afbb] __crystal_sigfault_handler +75
[0x7f07fe4d0dd0] ???
[0x44b070] *String#chomp:String +352
[0x44c8b3] *String#pretty_print<PrettyPrint>:Nil +275
[0x485175] *PrettyPrint::format<String, IO::FileDescriptor, Int32, String, Int32>:IO::FileDescriptor +117
[0x4850f3] *PrettyPrint::format<String, IO::FileDescriptor, Int32>:IO::FileDescriptor +67
[0x43b010] *pp<String>:String +32
[0x42dea2] __crystal_main +1730
[0x483946] *Crystal::main_user_code<Int32, Pointer(Pointer(UInt8))>:Nil +6
[0x483812] *Crystal::main<Int32, Pointer(Pointer(UInt8))>:Int32 +50
[0x438e86] main +6
[0x7f07fd8b6020] __libc_start_main +240
[0x42d72a] _start +42
[0x0] ???

[wooster0]

Can this be reduced to

module Hello
  def self.hello
    print @@hello

    "hello"
  end
  
  @@hello : String = hello()
end

maybe?

[asterite]

No, the original example mentions an instance variable. It's just a different bug. I actually can make the second one compile but it will still crash with a stack overflow.

[manveru]

Well, just wanted to say this still happens on 1.9.2