When running phan on core or extensions with a php7.4 it can shows some suggestion for the code which are not usable, because CI is running with 7.2 as current required version.
Example:
PhanPluginDuplicateExpressionAssignmentOperation Can simplify this assignment to $attributes['class'] ??= '' (requires php version 7.4 or newer)
Should the config have '_target_php_version' or 'minimum__target_php_version'?
// The PHP version that the codebase will be checked for compatibility against.
// For best results, the PHP binary used to run Phan should have the same PHP version.
// (Phan relies on Reflection for some types, param counts,
// and checks for undefined classes/methods/functions)
//
// Supported values: `'5.6'`, `'7.0'`, `'7.1'`, `'7.2'`, `'7.3'`, `'7.4'`, `null`.
// If this is set to `null`,
// then Phan assumes the PHP version which is closest to the minor version
// of the php executable used to execute Phan.
//
// Note that the **only** effect of choosing `'5.6'` is to infer that functions removed in php 7.0 exist.
// (See `backward_compatibility_checks` for additional options)
'_target_php_version' => null,
// The PHP version that will be used for feature/syntax compatibility warnings.
//
// Supported values: `'5.6'`, `'7.0'`, `'7.1'`, `'7.2'`, `'7.3'`, `'7.4'`, `null`.
// If this is set to `null`, Phan will first attempt to infer the value from
// the project's composer.json's `{"require": {"php": "version range"}}` if possible.
// If that could not be determined, then Phan assumes `_target_php_version`.
'minimum__target_php_version' => null,