Form definitions in XML allow the usage of add(field|form|filter|rule)(path|prefix) to add form fields, forms, filters and rules from specified paths. Right now, this only works for single values. This means, if you want to import fields from two different locations, you need to specify them for example like this:

<fields name="params" addfieldpath="path/to/first/fields">
  <fieldset name="basic" addfieldpath="path/to/second/fields">

This separation of the two paths is not logically motivated. Second, it introduces a limitation on the number of paths you can add. If you have a structure form > fields > fieldset, you can enter at most three paths. To add more, you'd have to introduce empty dummy fieldsets at the end of the file.

Summary of Changes

This PR introduces the possibility to add multiple paths in a single argument, separated by comma. This reduces the above example to:

<fields name="params">
  <fieldset name="basic" addfieldpath="path/to/first/fields,path/to/second/fields">

Testing Instructions

1. Make sure all forms using addfieldpath, addfieldprefix, addfilterpath, addfilterprefix, addformpath, addformprefix, addrulepath, and addruleprefix still work as before.
2. Either write your own forms using two values for these attributes, or use the plugins I wrote:

Demo Plugins

I wrote https://github.com/Harmageddon/plg_demo_addfieldpath and https://github.com/Harmageddon/plg_demo_addfieldprefix for testing. As they use cross-references between each other, both need to be installed at the same time.

plg_demo_addfieldpath

This plugin aims to test the add*path functionalities. The form should contain the following fields:

• An article modal field to test the first value of addfieldpath.
• A menu item modal field to test the second value of addfieldpath.
• A "Filter and Rule test" field that requires an "a" to be entered by the rule. The filter converts text from lower to upper case. This tests the first value of addfilterpath and addrulepath.
• A "Filter and Rule test 2" field that requires a "b" to be entered by the rule. The filter converts text from upper to lower case. This tests the second value of addfilterpath and addrulepath.
• Two subform fields, one with color values and one with numbers to test both values for addformpath.

plg_demo_addfieldprefix

This plugin aims to test the add*prefix functionalities. The form should contain the following fields:

• An article modal field to test the first value of addfieldprefix.
• A menu item modal field to test the first value of addfieldprefix.
• A "Filter and Rule test" field that requires a number to be entered by the rule. The filter converts text from lower to upper case. This tests the first value of addfilterprefix and addruleprefix.
• A "Filter and Rule test 2" field that requires an "a" to be entered by the rule. The filter converts text from upper to lower case. This tests the second value of addfilterprefix and addruleprefix.

I couldn't find any usage of addformprefix, so if someone has an idea how to test this, I'm open for suggestions.

Documentation Changes Required

Could be noted at https://docs.joomla.org/Creating_a_custom_form_field_type#Linked_with_a_form or https://docs.joomla.org/Advanced_form_guide.