Jira (PUP-11066) optional_param does not set Integer to optional for custom ruby functions

Josh Cooper (Jira) Mon, 27 Sep 2021 21:57:05 -0700

Title: Message Title

Josh Cooper commented on

I think this is a case where 'optional' means different things in optional_param and Optional[T]. The former marks the parameter as an optional positional argument, while the latter is the type specification for the parameter, and Optional[T] will match either T or surprisingly Undef. See https://puppet.com/docs/puppet/7/lang_data_undef.html and https://tickets.puppetlabs.com/browse/PUP-8101?focusedCommentId=502043&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-502043

So if I have a wait function:

Puppet::Functions.create_function(:wait, Puppet::Functions::InternalFunction) do

  dispatch :wait do

    optional_param 'Integer[1]', :timeout

end

  def wait(timeout = nil)

    puts "timeout #{timeout.inspect}"

end

end

Then I can omit the timeout parameter due to optional_param:

$ bx puppet apply -e 'wait()'

timeout nil

But passing nil as an explicit timeout parameter won't work, because it's not an instance of Integer:

$ bx puppet apply -e 'wait($nada)'

Warning: Unknown variable: 'nada'. (line: 1, column: 6)

Error: Evaluation Error: Error while evaluating a Function Call, 'wait' parameter 'timeout' expects an Integer value, got Undef (line: 1, column: 1) on node localhost

That's a little surprising given we defaulted the function signature to "timeout = nil".

As mentioned earlier, changing the function dispatch to Optional[Integer[1]] works because Optional[T] matches Undef:

$ bx puppet apply -e 'wait($nada)'

Warning: Unknown variable: 'nada'. (line: 1, column: 6)

timeout nil

As a module author I can imagine the current behavior is surprising. In theory, the optional_param method could automatically wrap the type specification:

    def optional_param(type, name)

      internal_param("Optional[#{type}]", name)

      @max += 1

end

That way passing undef behaves the same as omitting the parameter. I assume double wrapping as Optional is not an issue? There might be other reasons why that'd be a bad idea...

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Jira (PUP-11066) optional_param does not set Integer to optional for custom ruby functions

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