(dev/core#3660) CRM_Extension_ClassLoader - Defend against redundant refreshes

[totten]

Overview

This is a follow-up to #23824 (c24dd7d) which addresses a regressive edge-case.

Steps to Reproduce

• Write an extension like wmf-civicrm which (a) calls System.flush (rebuildMenuAndCaches())
  during hook_install -- and then (b) loads some class from the same extension.

  function foo_civicrm_install() {
    civicrm_api3('System', 'flush', []);
    CRM_Foo_Helper::doStuff();
  }

• Try to install the extension.

Before

Crashes on loading the class CRM_Foo_Helper

After

Loads the class CRM_Foo_Helper.

Comments

(1) To see what's happening, consider CRM_Extension_Manager_Module::onPreInstall(). This registers the new classloader and then fires hook_install which eventually fires rebuildMenuAndCaches(). With c24dd7d, this resets the classloader again. But the extension isn't fully installed yet - so it forgets about the new extension.

(2) Is it safe to have some (temporarily) sticky items? Ish. You might say: "Ah, but what if we need to remove an extension? Won't this static variable retain stale things?" Doesn't matter. In PHP, classloading is a one-way-street. (You cannot unload.) So you'll still have old classes in memory, regardless of whether the ClassLoader has some old metadata about where to find classes.

(3) I'm on the fence about whether this patch is a good idea. Calling System.flush explicitly in this context seems like an invitation to trouble. OTOH, it worked before #23824, so it can be called a regression.

[civibot]

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[eileenmcnaughton]

I've tested this on our build & it fixes the issue for us

[eileenmcnaughton]

This resolved our build-issue - merging