#4961 - Fix read-only not having any effect on checkbox fields

[atanas-dev]

Description

Fixes #4961

The "readonly" attribute only prevents the "value" attribute from changing which is not what we want in the case of checkboxes as interacting with a checkbox changes its checked attribute instead which is why we need to do this:

1. Add disabled="DISABLED" to the checkbox.
2. As a consequence of 1, even if the checkbox default value is set to 1, the value stored will still be 0 since disabled inputs are not submitted.
3. To fix 2 we add a hidden input immediately after the checkbox only when the checkbox should be checked.
4. The hidden input will have the same name and value as the checkbox and will override it since it appears later in the html hierarchy. A bit hacky but avoids name clashes with other fields and the need for special-case back-end code.

Default value	Result	Stored Value
NONE	Checkbox is unchecked and disabled; no hidden input	0
0	Checkbox is unchecked and disabled; no hidden input	0
1	Checkbox is checked and disabled; hidden input is present	1

I decided not to include this lengthy explanation as an inline comment - let me know if I should try to condense it and add it.

Feedback is appreciated.

How Has This Been Tested?

Manually tested a read-only checkbox field with no default value, 0 and 1 as the default value.

Types of changes

Bug fix

ChangeLog

Fix: Checkbox fields not respecting their Make field "Read Only" in UI setting.

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows has proper inline documentation.

[sc0ttkclark]

Good first PR!

[sc0ttkclark]

@pglewis can you come back around on this PR branch with the DFV fix too?

[jimtrue]

QA Tests Passed:

• Yes/No Checkbox created with default of 0 and Read Only: Wrote 0
• Yes/No Checkbox created with default of 1 and Read Only: Wrote 1