Feature: #109366 - Hide form fields with no selectable items 

See forge#109366

Description 

Relational fields in FormEngine, such as type=select with foreign_table, type=category, or type=select with misconfigured empty items are now automatically handled when no selectable items are available. Additionally, type=language fields are hidden when only a single language is configured, since a dropdown with one choice serves no purpose.

For regular users, the field is removed entirely. When backend debug mode is enabled ( $GLOBALS['TYPO3_CONF_VARS']['BE']['debug'] = true ), the field is kept as read-only with an info badge, so admins can identify configuration issues such as missing records or restrictive TSconfig.

Common scenarios where this applies:

  • A categories field is displayed but no sys_category records exist.
  • A select field references fe_groups but no frontend user groups have been created.
  • All available items have been removed via TSconfig removeItems or keepItems configuration.
  • The backend user has no permissions for any of the available items.
  • A site has only one language configured.
  • A type=select field is misconfigured with no items at all.

Affected field types 

  • type=select (all render types including selectTree): hidden when no items available. For fields with foreign_table, static items like "Hide at login" are not counted — they only make sense when actual foreign records exist.
  • type=category: hidden when no items available
  • type=language: hidden when only one language is available (the special -1 "All languages" item is not counted as a meaningful choice)

Existing values 

Fields not rendered in the form are simply not submitted on save. DataHandler preserves the existing database value for non-submitted fields, so no data is lost when a field is hidden by this feature.

Opt-out 

The behavior can be disabled per field using the TCA configuration option showIfEmpty:

EXT:my_extension/Configuration/TCA/Overrides/tt_content.php 
$GLOBALS['TCA']['tt_content']['columns']['categories']['config']['showIfEmpty'] = true;
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Impact 

Fields without selectable items are now hidden by default. In backend debug mode, the fields are shown as read-only with an info badge instead. Extensions that rely on always showing empty fields should set showIfEmpty to true in their TCA configuration.