Add wrapper process plugin to wrap/unwrap values in arrays

I think that wrapper with method: wrap can be replaced by the more flexible build_array plugin from ✨ Process plugin to build an array Active ; and method: unwrap can be replaced by callback with callable: array_pop.

For example, the pipeline from the issue description,

  -
    plugin: wrapper
    method: wrap
    source: my_array
    key: element
  -
    plugin: sub_process
    process:
      '0':
        plugin: flatten
        source: element # This should match the 'key' used when wrapping.
  -
    plugin: wrapper
    method: unwrap

is equivalent to

  - 
    plugin: build_array
    template:
      element: 'pipeline:'
    source: my_array
  -
    plugin: sub_process
    process:
      '0':
        plugin: flatten
        source: element
  - plugin: callback
    callable: array_pop

I verified that they give the same results on the example input using migrate_sandbox.

So I suggest we close this issue in favor of ✨ Process plugin to build an array Active .

I'm working my way through reviewing the related array_template process plugin.

I can confirm the part of comment #5 about replacing the wrap method using array_template.

I'm thinking about the array_pop as a replacement for unwrap...it's not exactly the same because the unwrap method fails if the argument is not a single-valued array, but that's not really a big deal.

So I'm convinced that the wrapper plugin could be completely reproduced as described by @benjifisher in #5

The only question is whether there's enough DX value in:
1. the symmetry that comes with wrap/subprocess/unwrap
2. the relative simplicity or the wrap syntax compared to the array_template syntax

> The only question is whether there's enough DX value in:
> 1. the symmetry that comes with wrap/subprocess/unwrap
> 2. the relative simplicity or the wrap syntax compared to the array_template syntax

For the syntax, the plugin from this issue is definitely nicer.

The MR from the other issue, ✨ Process plugin to build an array Active , has this example for migrating a paragraph reference:

 * @code
 * process:
 *   field_paragraph:
 *     - plugin: migration_lookup
 *       # ...
 *     - plugin: array_template
 *       template:
 *         target_id: pipeline:0
 *         target_revision_id: pipeline:1
 * @endcode

But with the plugin from this issue, my process array is simpler:

  field_paragraph:
    -
      plugin: migration_lookup
      # SNIP
    -
      plugin: wrapper
      method: wrap

The array_template plugin allows much more complexity and is much more powerful for other use cases, but for this particular use case, having to specify a template for the array feels a bit redundant when I just want to nest the values down a level feels like overkill.

> 1. the symmetry that comes with wrap/subprocess/unwrap

I'd actually prefer two plugins, called 'wrap' and 'unwrap'.

This would then match the symmetry of the 'multiple_values' / 'single_value' plugins.

(An thought which may muddy the waters, if so, ignore -- what about instead of adding a wrapper plugin, we add an option to work with nesting to the 'multiple_values' / 'single_value' plugins? The functionality of the 'key' property here would be covered by the more complex 'array_template' plugin from ✨ Process plugin to build an array Active .)

I just want to note that "wrap" is just syntactical sugar for

plugin: get
      source:
        - ~

and unwrap is just syntactical sugar for

plugin: extract
      index:
        - 0

With maybe some single_value, multiple_value plugins in there if you need them, though if the purpose is to pipe a value into a handle_multiples plugin that can't handle a single value, there will often not be much point, as those plugins don't care if the value is a multiple or not.

(BTW, I'm starting to come around to just documenting the 'hack' with the get plugin above and officially supporting it. I've found enough cases where it's useful)

Now that ✨ Process plugin to build an array Active is fixed (and part of the 6.0.5 release) I think we can close this issue.

@mikelutz:

(BTW, I'm starting to come around to just documenting the 'hack' with the get plugin above and officially supporting it. I've found enough cases where it's useful)

Your timing is interesting. Now that we have the array_template plugin, we can get the same functionality (a little more verbose, but perhaps easier to read/clearer intention). So now you decide to change your mind? ;)