calling functions from (ruby-)functions and puppet data types

[Peter Meier]

Hi All,

I'm stumbling over two problems, while trying to port over a custom
hiera backend from hiera 3 to hiera 5.

I was able to simplify the problem I have to a simple example and I
think it shows

a) Documentation is wrong
b) You can't use Puppet Data types in ruby functions, at least not in my
example.

Essentially, the simplification of my problem all boils down to call
lookup with a certain set of parameters.

I have pushed an example repository that shows within a very compressed
version what is failing:

https://github.com/duritong/puppet_function_and_types

The first 2 ways (line 9 & 10) of calling the lookup function just don't
match a potential signature of lookup. And based on the signature errors
I get, I can only conclude that the official documentation at

https://docs.puppet.com/puppet/5.0/functions_ruby_implementation.html#calling-other-functions

"The second argument must be an array containing any arguments to the
function."

is *wrong*! As you can read out of the signature matching error message.

=> assumption a)

So let's then try without the arguments being an array:

Line 46 => Oh, looks like it matches, but can't compare Ruby Hash to
puppet Hash type. :/

Line 74 => Oh, looks like the String 'Hash' is not detected as Type, so
it indicates that this way of calling the function is right, but I am
still not able to define a ValueType.

=> assumption b)

So the only way it works: Line 89 which does not enforce any ValueType,
but everything else works.

I'm still pretty new to the type system and not yet deep into puppet 4/5
functions, but from my current perspective a) and b) are true.

best

~pete

[Ryan Whitehurst]

Your assumption a) seems to be correct, based on the implementation of call_function. The docs list the signature as call_function(name, args, &block) but the actual signature is call_function(name, *args, &block), so you need multiple arguments, not an array argument like the docs say. The first example, however, works either way because the include function accepts any number of arguments and then calls flatten on the resulting array before using it.

Now, the reason your call on line 74

    call_function('lookup', key, 'Hash', 'hash',{})

fails is that you have to pass in a ruby object for the type, not a string representation of the type. There's probably a better way that would generate an appropriate object based on the string, but this works for this case:

    call_function('lookup', key, Puppet::Pops::Types::PHashType::DEFAULT, 'hash',{})

That invocation gives the expected error message:

    Evaluation Error: Error while evaluating a Function Call, Found value has wrong type, expects a Hash value, got String

I've filed DOCUMENT-703 to correct the docs. https://tickets.puppetlabs.com/browse/DOCUMENT-703

 

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[Peter Meier]

> Now, the reason your call on line 74
>
> call_function('lookup', key, 'Hash', 'hash',{})
>
> fails is that you have to pass in a ruby object for the type, not a
> string representation of the type. There's probably a better way that
> would generate an appropriate object based on the string, but this
> works for this case:
>
> call_function('lookup', key,
> Puppet::Pops::Types::PHashType::DEFAULT, 'hash',{})
>
> That invocation gives the expected error message:
>
> Evaluation Error: Error while evaluating a Function Call, Found
> value has wrong type, expects a Hash value, got String

Awesome, that works! :) I was navigating within the pops subsystem code
once into this direction, but it felt a bit too clumsy and I didn't
bother to try.

Thanks for the help!

I agree that there should be a better (and documented! ;) ) way that
would generate an appropriate object based on the string and if there
isn't there should probably be a user story about it.

> I've filed DOCUMENT-703 to correct the docs.
> https://tickets.puppetlabs.com/browse/DOCUMENT-703

Cool, thanks!

best

~pete

[Henrik Lindberg]

On 24 Jul 2017, at 22:29, Peter Meier <peter...@immerda.ch> wrote:

Now, the reason your call on line 74

   call_function('lookup', key, 'Hash', 'hash',{})

fails is that you have to pass in a ruby object for the type, not a
string representation of the type. There's probably a better way that
would generate an appropriate object based on the string, but this
works for this case:

   call_function('lookup', key,
Puppet::Pops::Types::PHashType::DEFAULT, 'hash',{})

That invocation gives the expected error message:

   Evaluation Error: Error while evaluating a Function Call, Found
value has wrong type, expects a Hash value, got String

Awesome, that works! :) I was navigating within the pops subsystem code
once into this direction, but it felt a bit too clumsy and I didn't
bother to try.

Thanks for the help!

I agree that there should be a better (and documented! ;) ) way that
would generate an appropriate object based on the string and if there
isn't there should probably be a user story about it.

Puppet::Pops::Types::TypeParser#parse can be used to get a data type object given a

type expressed as in the puppet language. As an example - this:

tparser = Puppet::Pops::Types::TypeParser.singleton

t = tparser.parse(‘Array[String]’, scope)

would assign a data type of Array type accepting String values to the

variable t.

An alternative is to use the Puppet::Pops::Types::TypeFactory to create

the same Array[String] datatype:

tf = Puppet::Pops::Types::TypeFactory

t = tf.array_of(tf.string)

Hope those help in the future

Best,

- henrik