Summary

When custom option saving is enabled, Select (save_options) and Checkbox (save_custom) can emit PHP warnings if the runtime field is JSON-only (no DB ID) or missing identifiers.

Affected areas

• includes/fields/class-acf-field-select.php (acf_field_select::update_value)
• includes/fields/class-acf-field-checkbox.php (acf_field_checkbox::update_value)

Problem

Current logic assumes a valid field identifier (ID or key) and a successful acf_get_field() lookup with a persisted ID. In JSON/local-field scenarios this may be false, which can lead to warnings (undefined array key / invalid array access) while trying to append custom choices.

Steps to reproduce

1. Configure a Select field with save_options = 1 (or Checkbox with save_custom = 1).
2. Use field data coming from JSON/local config (or with missing persisted ID).
3. Save a custom value not present in choices.
4. Observe warnings during update_value().

Expected behavior

No warnings should be emitted. Value should still be returned/saved, and custom-choice persistence should only run when a valid persisted field can be resolved.

Proposed fix

• Resolve selector defensively (ID -> key -> bail).
• Bail when lookup cannot run or acf_get_field() result is invalid/no ID.
• Normalize choices to an array before appending custom values.

Tests

Added regression tests:

• tests/php/includes/fields/test-class-acf-field-select.php
  • test_update_value_save_options_handles_json_field_without_id
  • test_update_value_save_options_handles_missing_field_identifier
• tests/php/includes/fields/test-class-acf-field-checkbox.php
  • test_update_value_save_custom_handles_json_field_without_id
  • test_update_value_save_custom_handles_missing_field_identifier

Patch reference

Commit: 34cfcb7
Branch: fix/select-checkbox-save-options-guards