PHP Compat to 8.3

[nateconley]

Description of the Change

• Update plugin compatibility PHP 8.3.
• Confirms compatibility with PHP 7.0.

Closes #3

How to test the Change

Environments

• Test in environment with PHP 8.3 (used Local WP)
• Test in environment with 7.0 (used WP Local Docker v2)

wp-config constants:

define( 'WP_DEBUG', true );
define( 'WP_DEBUG_DISPLAY', true );
define( 'WP_DEBUG_LOG', true );

Steps:

• Connect via API Key
• Update plugin settings
• Place a widget signup form (used Twenty Twenty-One theme)
• Sign up to list via frontend form

Acceptance

• Ensure no errors on display
• Ensure no errors in logs
  • If using Query Monitor, version 3.10 is the most recent version to support PHP 7.0

Changelog Entry

Added - PHP 8.3 compatibility
Added - Minimum PHP version of 7.0

Credits

@nateconley

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added tests to cover my change. - n/a, updated minimum PHP version
• All new and existing tests pass.

[jeffpaul]

https://github.com/mailchimp/wordpress/blob/ddcdcf7aeb7d095d311da7ac76b3b6fe9b326074/phpcs-compat.xml#L17C1-L17C43 might also need to be bumped here?

[dkotter]

This looks good to me but in testing, received one PHP warning when submitting the form: Undefined array key "phone_format" in /oss/app/public/wp-content/plugins/mailchimp/mailchimp.php on line 992

[nateconley]

This looks good to me but in testing, received one PHP warning when submitting the form: Undefined array key "phone_format" in /oss/app/public/wp-content/plugins/mailchimp/mailchimp.php on line 992

@dkotter I resolved this and another issue with options. One thing that I have noticed through testing this last bit of feedback is that we should be testing with multiple Mailchimp accounts.

I have added custom merge vars for testing on my own 10up Mailchimp account. Even after not including the phone field in the form, I do not see the reported error.

The OSS Mailchimp account does not have those additional merge vars, and it does throw that error.

Additionally, I found an issue where some settings are not saving properly due to strict comparisons and the output returned from get_option. This has been resolved and pushed to this branch.