Crystal: Closure bug

[firejox]

require "c/pthread"

class FooThread
  @@current_thread_key = uninitialized LibC::PthreadKeyT
  @@key_once : LibC::PthreadOnceT = 0

  def start
    ret = 0
    LibC.pthread_once(pointerof(@@key_once), -> {
      ret = LibC.pthread_key_create(pointerof(@@current_thread_key), ->(data : Void*) {
        data.as(Thread)
      })
    })
  end
end

FooThread.new.start

lib LibC
  alias PthreadOnceT = Int
  alias PthreadKeyT = UInt

  fun pthread_once(key : PthreadOnceT*, init_routine : -> Void) : Int
  fun pthread_key_create(key : PthreadKeyT*, destructor : Void* -> Void) : Int
end

result in compiler error

Missing hash key: "data"
0x752ed7: *CallStack::unwind:Array(Pointer(Void)) at ??
0x752e6a: *CallStack#initialize:Array(Pointer(Void)) at ??
0x752e3a: *CallStack::new:CallStack at ??
0x7461fe: *raise<KeyError>:NoReturn at ??
0xfdf75a: *Hash(String, Crystal::MetaVar) at ??
0xfdf656: *Hash(String, Crystal::MetaVar) at ??
0x137a6b9: *Crystal::CleanupTransformer::ClosuredVarsCollector#visit<Crystal::Var+>:(Array(Crystal::ASTNode+) | Nil) at ??
0xbd2541: *Crystal::ASTNode+ at ??
0xcf5aaa: *Crystal::Cast#accept_children<Crystal::CleanupTransformer::ClosuredVarsCollector>:Nil at ??
0xbd2825: *Crystal::ASTNode+ at ??
0xd7ed62: *Crystal::Def+ at ??
0xd7eb3f: *Crystal::Def+ at ??
0xd536fa: *Crystal::ProcLiteral#accept_children<Crystal::CleanupTransformer::ClosuredVarsCollector>:Nil at ??
0xbd2ad6: *Crystal::ASTNode+ at ??
0xedd801: *Crystal::Call#accept_children<Crystal::CleanupTransformer::ClosuredVarsCollector>:Nil at ??
0xbd2ffb: *Crystal::ASTNode+ at ??
0xeb081d: *Crystal::Assign#accept_children<Crystal::CleanupTransformer::ClosuredVarsCollector>:Nil at ??
0xbd2f47: *Crystal::ASTNode+ at ??
0xd7ed62: *Crystal::Def+ at ??
0xd7eb3f: *Crystal::Def+ at ??
0x137a527: *Crystal::CleanupTransformer::ClosuredVarsCollector::collect<Crystal::Def+>:Array(Crystal::ASTNode+) at ??
0x1374f16: *Crystal::CleanupTransformer#check_args_are_not_closure<Crystal::Call, String>:Array(Crystal::ASTNode+) at ??
0x1373849: *Crystal::CleanupTransformer#transform<Crystal::Call>:Crystal::ASTNode+ at ??
0xbd0e96: *Crystal::ASTNode+ at ??
0x136f99d: *Crystal::CleanupTransformer#transform<Crystal::Expressions>:Crystal::Expressions at ??
0xbd0d9c: *Crystal::ASTNode+ at ??
0x1373f0d: *Crystal::CleanupTransformer#transform<Crystal::Call>:Crystal::ASTNode+ at ??
0xbd0e96: *Crystal::ASTNode+ at ??
0x136f99d: *Crystal::CleanupTransformer#transform<Crystal::Expressions>:Crystal::Expressions at ??
0xbd0d9c: *Crystal::ASTNode+ at ??
0x893406: *Crystal::Program#cleanup<Crystal::ASTNode+>:Crystal::ASTNode+ at ??
0x8930c5: *Crystal::Program#visit_main<Crystal::ASTNode+, Crystal::MainVisitor, Bool>:Crystal::ASTNode+ at ??
0x892fee: *Crystal::Program#visit_main:process_finished_hooks<Crystal::ASTNode+, Bool>:Crystal::ASTNode+ at ??
0x888219: *Crystal::Program#semantic<Crystal::ASTNode+, Bool>:Crystal::ASTNode+ at ??
0xfd37e4: *Crystal::Compiler#compile<Array(Crystal::Compiler::Source), String>:Crystal::Compiler::Result at ??
0xfda219: *Crystal::Command::CompilerConfig#compile<String>:Crystal::Compiler::Result at ??
0x86018d: *Crystal::Command#run_command<Bool>:Nil at ??
0x85c281: *Crystal::Command#run:(Array(Crystal::ImplementationTrace) | Array(Crystal::Init::View+:Class) | Array(String) | Bool | Crystal::Compiler::Result | Hash(String, String) | IO::FileDescriptor | Nil) at ??
0x85b97b: *Crystal::Command::run<Array(String)>:(Array(Crystal::ImplementationTrace) | Array(Crystal::Init::View+:Class) | Array(String) | Bool | Crystal::Compiler::Result | Hash(String, String) | IO::FileDescriptor | Nil) at ??
0x85b939: *Crystal::Command::run:(Array(Crystal::ImplementationTrace) | Array(Crystal::Init::View+:Class) | Array(String) | Bool | Crystal::Compiler::Result | Hash(String, String) | IO::FileDescriptor | Nil) at ??
0x72ff49: ??? at ??
0x73eae9: main at ??
0x7f7a8eba1291: __libc_start_main at ??
0x72f0ca: _start at ??
0x0: ??? at ??

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

Crystal version

Crystal 0.20.3+2 [929a551] (2016-12-27)
Crystal 0.20.1 (2016-12-06)

[asterite]

Reduced:

lib LibFoo
  fun foo(init_routine : ->)
end

x = 0
LibFoo.foo(->{
  x = ->(data : Int32) {
    data
  }
})

[asterite]

@firejox Thank you for reporting! In the next version you will get a correct error:

Error in bar.cr:17: instantiating 'FooThread#start()'

FooThread.new.start
              ^~~~~

in bar.cr:9: can't send closure to C function (closured vars: ret)

    LibC.pthread_once(pointerof(@@key_once), ->{
                                             ^