The Callback process plugin now handles callbacks with multiple arguments

The callback plugin, part of the Migrate API, can be used to apply a PHP function or class method as one step in a process pipeline. Before Drupal 9.2.0, this plugin was limited to functions or methods with exactly one argument.

As of Drupal 9.2.0, the plugin accepts the optional configuration argument unpack_source. When this argument is set, the value in the process pipeline must be an array and it is interpreted as an argument list.

Before Drupal 9.2.0

process:
  destination_field:
    plugin: callback
    callable: mb_strtolower
    source: source_field

The callback function mb_strtolower() takes one argument.

Starting with Drupal 9.2.0

The above example works as before. With the new unpack_source option, the callback plugin can now use a 2-variable function such as rtrim():

source:
  # plugin ...
  constants:
    slash: /
process:
  field_link_url:
    - plugin: callback
      callable: rtrim
      unpack_source: true
      source:
        - url
        - constants/slash

The callback function rtrim() takes two arguments. This example will remove the trailing /, if any, from the source URL.

Note: This system will also allow calling a function with no arguments by using unpack_source and using an empty array as a source:

process:
  time:
    plugin: callback
    callable: time
    unpack_source: true
    source: {  }