DebugSubscriber - Fix activation check

[totten]

Overview

This component injects debug info about API calls. It only does so if XDebug is configured with the suitable mode (ie xdebug.mode=develop or XDEBUG_MODE=develop)

This requires a guard based on XDebug configuration. This guard is slightly wrong, which can sometimes raise spurious errors.

The key thing is that XDebug reads configuration from multiple sources (eg php.ini or env-var). A recent buildkit update relied on env-var working (civicrm/civicrm-buildkit#727).

Before

The guard only consults ini_get('xdebug.mode'). If an env-var exists (eg XDEBUG_MODE), then ini_get() does not correctly reveal the effective policy.

This sometimes leads to failures like this (where in xdebug.mode looked like it had develop enabled, but XDEBUG_MODE actually disabled it, so anything that relies on develop mode fails):

1) api_v3_ACLCachingTest::testActivityCreateCustomBefore with data set "APIv3" (3)
Failure in api call for custom_field getoptions:  Function must be enabled in php.ini by setting 'xdebug.mode' to 'develop'
#0 [internal function]: PHPUnit\Util\ErrorHandler->__invoke(2, 'Function must b...', '/home/jenkins/b...', 99)
#1 /home/jenkins/bknix-max/build/delme-2-2/web/sites/all/modules/civicrm/Civi/API/Subscriber/DebugSubscriber.php(99): xdebug_time_index()
#2 /home/jenkins/bknix-max/build/delme-2-2/web/sites/all/modules/civicrm/vendor/symfony/event-dispatcher/EventDispatcher.php(264): Civi\API\Subscriber\DebugSubscriber->onApiRespond(Object(Civi\API\Event\RespondEvent), 'civi.api.respon...',

After

The guard works with both php.ini's xdebug.mode and env-var XDEBUG_MODE. It does this by asking XDebug for the effective mode (rather than looking at specific config flags).

Technical Details

See also: https://xdebug.org/docs/all_functions#xdebug_info

The option will behave correctly on XDebug 3.1+. On 3.0, it falls back to the older (less-accurate) check. All the systems I care about have 3.1.+

[civibot]

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