Pull Request for #34233 (comment) point 6.

Summary of Changes

Currently we have three places where we use text fields to specify the path to a folder which has to exist and be below the Joomla root:

• Field "Attachments Folder" in the Mail Templates component (com_mails) options.
• Fields "Path to Files Folder" and "Path to Images Folder" in the Media Manager (com_media) options.

This is bad because text fields should only be used to define names for new files or folders to be created, and because there is no validation done if the folder really exists if we use text fields to define paths to existing folders.

But currently we have no comfortable way to recursively, i.e. including all sub folders, navigate through all folders in the Joomla root.

For the mean time, as long as we don't have a better solution, this PR here adds a new validation rule "FolderPathExistsRule" to be used in such cases and which checks if the folder exists below the Joomla root, in addition to the validation which is done by the "FilePathRule".

The FilePathRule validation should not be extended to check if a file or folder exists because it shall still be possible to use it for validating paths to not existing files or folders.

The new rule added by this PR should not be used with folderlist fields because 1. it doesn't make sense for them, the "OptionsRule" should be used to validate these fields, and 2. it would not work for these fields because the "directory" element of such fields is not handled by the new rule.

In addition to these changes, this PR removes the "bin" folder from the existing "exclude" elements of the 2 text fields "Path to Files Folder" and "Path to Images Folder" in the Media Manager (com_media) options, because in J4 there is no "bin" folder anymore, not even after updates from 3.10.

Testing Instructions

The test starts on an installation of current 4.0-dev branch or latest 4.0 nightly build without the patch of this PR applied.

All actions are performed in backend.

1. Go to media manager options.

2. In one or both of the fields "Path to Files Folder" and "Path to Images Folder", enter a path which is valid e.g. regarding forbidden characters but which doesn't exist below the Joomla root, e.g. "gaga" or "images/gaga".

3. Save and close.
   Result: Changes are saved, green success message shown.

4. Go to "System -> Templates -> Mail Templates" and edit the options.

5. In field "Attachments Folder", enter a path which is valid e.g. regarding forbidden characters but which doesn't exist below the Joomla root, e.g. "gaga" or "images/gaga".

6. Save the change.
   Result: Changes are saved, green success message shown.

7. Apply the patch of this PR.

8. Go to media manager options which have still the path to not existing folder(s) from step 2.

9. Without making any changes, use the "Save" button.
   Result: The form is not saved, you get an alert about invalid field.

10. Change the path(s) so they are valid and point to existing folder(s), and save and close.
    Result: Changes are saved, green success message shown.

11. Go to "System -> Templates -> Mail Templates" and edit the options which have still the path to not existing folder(s) from step 5.

12. Without making any changes, use the "Save" button.
    Result: The form is not saved, you get an alert about invalid field.

13. Change the path so it is valid and points to an existing folder which is in the exclude list, e.g. "administrator", and use the "Save" button.
    Result: The form is not saved, you get an alert about invalid field.

14. Change the path so it is valid and points to an existing folder, and save and close.
    Result: Changes are saved, green success message shown.

Actual result BEFORE applying this Pull Request

See section "What this PR does not fix" in PR #34233 : You can specify paths to not existing folder for the three fields.

Expected result AFTER applying this Pull Request

You can't specify paths to not existing folder for the three fields. The form can't be saved, and an alert is shown, telling which field is invalid.

When specifying paths to existing folders, the fields can be saved.

Documentation Changes Required

Documentation of form field validation rules in J4 needs to be extended by the new rule, including to mention that it only makes sense for text fields and will not work and not make sense with filelist or filderlist fields.