When running ./vendor/bin/phpcs -p web/modules/contrib/migrate_plus/ --standard=PHPCompatibility --extensions=php,module,inc,install,test,profile,theme to check for PHP 7.4 compatibility:
FILE: web/modules/contrib/migrate_plus/migrate_example_advanced/migrate_example_advanced_setup/src/Plugin/rest/resource/PositionResource.php
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FOUND 0 ERRORS AND 1 WARNING AFFECTING 1 LINE
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3 | WARNING | 'resource' is a soft reserved keyword as of PHP version 7.0 and should not be used to name a class, interface or trait or as part of a namespace (T_NAMESPACE)
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FILE: web/modules/contrib/migrate_plus/migrate_example_advanced/migrate_example_advanced_setup/src/Plugin/rest/resource/VarietyItems.php
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FOUND 0 ERRORS AND 1 WARNING AFFECTING 1 LINE
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3 | WARNING | 'resource' is a soft reserved keyword as of PHP version 7.0 and should not be used to name a class, interface or trait or as part of a namespace (T_NAMESPACE)
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FILE: web/modules/contrib/migrate_plus/migrate_example_advanced/migrate_example_advanced_setup/src/Plugin/rest/resource/VarietyList.php
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FOUND 0 ERRORS AND 1 WARNING AFFECTING 1 LINE
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3 | WARNING | 'resource' is a soft reserved keyword as of PHP version 7.0 and should not be used to name a class, interface or trait or as part of a namespace (T_NAMESPACE)
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FILE: web/modules/contrib/migrate_plus/migrate_example_advanced/migrate_example_advanced_setup/src/Plugin/rest/resource/VarietyMultiFiles.php
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FOUND 0 ERRORS AND 1 WARNING AFFECTING 1 LINE
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3 | WARNING | 'resource' is a soft reserved keyword as of PHP version 7.0 and should not be used to name a class, interface or trait or as part of a namespace (T_NAMESPACE)
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Needs work
5.0
API
The issue particularly affects sites running on PHP version 7.4.0 or later.
Not all content is available!
It's likely this issue predates Contrib.social: some issue and comment data are missing.
Is this actually a problem? The conclusion in #2990879: 'resource' is a soft reserved keyword as of PHP version 7.0 and should not be used to name a class, interface or trait or as part of a namespace → was that this is a false positive from PHP compatibility checker.
Reserved words are allowed, in a namespace, with the exception of namespace. It means that a namespace like Drupal\migrate_plus\Plugin\rest\resource is allowed.