Crystal: Block argument isn't seen inside macro code

[mperham]

      def sidekiq_options(&block : Sidekiq::Job -> Void)
        {% begin %}
        Sidekiq::Worker::OPTION_BLOCKS["{{@type.id}}"] = block
        {% end %}
      end

Error in ./examples/sidekiq.cr:11: instantiating 'sidekiq_options()'

  sidekiq_options do |job|
  ^~~~~~~~~~~~~~~

in macro 'macro_4614465168' /Users/mike/src/sidekiq.cr/src/sidekiq/worker.cr:132, line 2:

  1. 
  2.         Sidekiq::Worker::OPTION_BLOCKS["CrystalWorker"] = block
  3.         

        Sidekiq::Worker::OPTION_BLOCKS["CrystalWorker"] = block
                                                          ^~~~~

undefined local variable or method 'block'

What am I doing wrong?

[asterite]

Hmmm... it's kind of a bug, but I'm not sure.

The thing is, the compiler knows a block needs to be converted to a Proc when you use it. This is done at the parser level. But if the block is mentioned inside a macro it doesn't see this, because macro is just text with interpolation, no meaning inside it until it's parsed.

A workaround is to assign block to another variable, and then use it inside the macro:

def sidekiq_options(&block : Sidekiq::Job -> Void)
  captured_block = block
  {% begin %}
  Sidekiq::Worker::OPTION_BLOCKS["{{@type.id}}"] = captured_block
  {% end %}
end

Until we think of a way to solve this, I'd use the workaround.

[mperham]

Thanks, that works perfectly!

[miketheman]

codetriage

This came up today, and we still get a similar message of:

undefined local variable or method 'block'

from this kind of example - so it hasn't been handled yet.

Is this something worth continuing to consider, or should the macro docs be updated to account for this behavior?

[vlazar]

Tried it in Crystal 0.31.1 on MacOS with sidekiq.cr from master branch and it works for me.

(I assume the error was happening when running https://github.com/mperham/sidekiq.cr/blob/25b1abcb4791d2b33d76286cd5ee049fcf45bbfd/examples/sidekiq.crr.)

$ crystal --version
Crystal 0.31.1 (2019-10-02)

LLVM: 8.0.1
Default target: x86_64-apple-macosx

Output

$ crystal lib/sidekiq/examples/sidekiq.cr
2019-10-13T13:22:57.466Z 21667 TID-1zj91kg  INFO: Pushing job 8e75d30b7499ce190963c5a9
2019-10-13T13:22:57.468Z 21667 TID-1zj91kg  INFO: Pushing job 3474e2fb67aeee3189919253


         m,
         `$b
    .ss,  $$:         .,d$
    `$$P,d$P'    .,md$P"'
     ,$$$$$bmmd$$$P^'
   .d$$$$$$$$$$P'
   $$^' `"^$$$'       ____  _     _      _    _
   $:     ,$$:       / ___|(_) __| | ___| | _(_) __ _
   `b     :$$        \___ \| |/ _` |/ _ \ |/ / |/ _` |
          $$:         ___) | | (_| |  __/   <| | (_| |
          $$         |____/|_|\__,_|\___|_|\_\_|\__, |
        .d$$                                       |_|

2019-10-13T13:22:57.469Z 21667 TID-1zj91kg  INFO: Sidekiq v0.6.1 in Crystal 0.31.1
2019-10-13T13:22:57.469Z 21667 TID-1zj91kg  INFO: Licensed for use under the terms of the GNU LGPL-3.0 license.
2019-10-13T13:22:57.469Z 21667 TID-1zj91kg  INFO: Upgrade to Sidekiq Enterprise for more features and support: http://sidekiq.org
2019-10-13T13:22:57.469Z 21667 TID-1zj91kg  INFO: Starting processing with 25 workers
2019-10-13T13:22:57.469Z 21667 TID-1zj91kg  INFO: Press Ctrl-C to stop
2019-10-13T13:22:57.472Z 21667 TID-1zj90gg  JID=8e75d30b7499ce190963c5a9 INFO: Start
2019-10-13T13:22:57.472Z 21667 TID-1zj90gg  JID=8e75d30b7499ce190963c5a9 INFO: Executing job 8e75d30b7499ce190963c5a9
2019-10-13T13:22:57.472Z 21667 TID-1zj90gg  JID=8e75d30b7499ce190963c5a9 INFO: hello!
2019-10-13T13:22:57.473Z 21667 TID-1zj90gg  JID=8e75d30b7499ce190963c5a9 INFO: Done: 0.000301 sec
2019-10-13T13:22:57.474Z 21667 TID-1zj90gg  JID=3474e2fb67aeee3189919253 INFO: Start
2019-10-13T13:22:57.475Z 21667 TID-1zj90gg  JID=3474e2fb67aeee3189919253 INFO: Executing job 3474e2fb67aeee3189919253
2019-10-13T13:22:57.475Z 21667 TID-1zj90gg  JID=3474e2fb67aeee3189919253 INFO: hello!
2019-10-13T13:22:57.475Z 21667 TID-1zj90gg  JID=3474e2fb67aeee3189919253 INFO: Done: 0.000244 sec

[asterite]

This is still broken. Minimal code to reproduce:

def callback(&block)
  {% begin %}
    block
  {% end %}
end

block = callback { puts 1 }
block.call

@vlazar By the way, thank you for looking at old issues! 🙏