From d322c495c2abc7e01311311dd9ad39a41a445b50 Mon Sep 17 00:00:00 2001
From: Tim Otten <totten@civicrm.org>
Date: Tue, 30 Nov 2021 14:25:50 -0800
Subject: [PATCH] mixin/polyfill.php - Import. Update comments.

---
 mixin/polyfill.md  |  46 +++++++++++++++++++++
 mixin/polyfill.php | 101 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 147 insertions(+)
 create mode 100644 mixin/polyfill.md
 create mode 100644 mixin/polyfill.php

diff --git a/mixin/polyfill.md b/mixin/polyfill.md
new file mode 100644
index 0000000000..d8059fc284
--- /dev/null
+++ b/mixin/polyfill.md
@@ -0,0 +1,46 @@
+# Mixin Polyfill
+
+Mixins will have built-in support in a future version of CiviCRM (vTBD). However,
+for an extension to use a mixin on an older version of CiviCRM, it should
+include the polyfill ([mixin/polyfill.php](../mixin/polyfill.php)).
+
+## Usage
+
+The polyfill will be enabled in `civix` (vTBD).  To activate the polyfill in
+a bespoke extension (`myext`, `org.example.myextension`), copy `mixin/polyfill.php`.
+Load this file during a few key moments:
+
+```php
+function _myext_mixin_polyfill() {
+  if (!class_exists('CRM_Extension_MixInfo')) {
+    $polyfill = __DIR__ . '/mixin/polyfill.php';
+    (require $polyfill)('org.example.myextension', 'myext', __DIR__);
+  }
+}
+
+function myext_civicrm_config() {
+  _myext_mixin_polyfill();
+}
+
+function myext_civicrm_install() {
+  _myext_mixin_polyfill();
+}
+
+function myext_civicrm_enable() {
+  _myext_mixin_polyfill();
+}
+```
+
+## Limitations / Comparison
+
+The polyfill loader is not as sophisticated as the core loader. Here's a comparison to highlight some of the limitations:
+
+| Feature | Core Loader | Polyfill Loader |
+| -- | -- | -- |
+| Load mixins from files (`mixin/*.mixin.php`) | Yes | Yes |
+| Load mixins from subdirectories (`mixin/*/mixin.php`) | Yes | No |
+| Read annotations from mixin files (eg `@mixinVersion`) | Yes | No |
+| Activation - How does it decide to activate a mixin? | Read `info.xml` | Read `mixin/*.mixin.php` |
+| Boot cache - How does it store boot-cache? | All boot-caches combined into one file | Each extension has separate boot-cache file |
+| Deduplication - If two extensions include the same mixin, then only load one copy. | Yes | Partial - for exact version matches. |
+| Upgrade - If two extensions include different-but-compatible versions, always load the newer version. | Yes | No |
diff --git a/mixin/polyfill.php b/mixin/polyfill.php
new file mode 100644
index 0000000000..f57c5ebbf8
--- /dev/null
+++ b/mixin/polyfill.php
@@ -0,0 +1,101 @@
+<?php
+
+/**
+ * When deploying on systems that lack mixin support, fake it.
+ *
+ * @mixinFile polyfill.php
+ *
+ * This polyfill does some (persnickity) deduplication, but it doesn't allow upgrades or shipping replacements in core.
+ *
+ * Note: The polyfill.php is designed to be copied into extensions for interoperability. Consequently, this file is
+ * not used 'live' by `civicrm-core`. However, the file does need a canonical home, and it's convenient to keep it
+ * adjacent to the actual mixin files.
+ *
+ * @param string $longName
+ * @param string $shortName
+ * @param string $basePath
+ */
+return function ($longName, $shortName, $basePath) {
+  // Construct imitations of the mixin services. These cannot work as well (e.g. with respect to
+  // number of file-reads, deduping, upgrading)... but they should be OK for a few months while
+  // the mixin services become available.
+
+  // List of active mixins; deduped by version
+  $mixinVers = [];
+  foreach ((array) glob($basePath . '/mixin/*.mixin.php') as $f) {
+    [$name, $ver] = explode('@', substr(basename($f), 0, -10));
+    if (!isset($mixinVers[$name]) || version_compare($ver, $mixinVers[$name], '>')) {
+      $mixinVers[$name] = $ver;
+    }
+  }
+  $mixins = [];
+  foreach ($mixinVers as $name => $ver) {
+    $mixins[] = "$name@$ver";
+  }
+
+  // Imitate CRM_Extension_MixInfo.
+  $mixInfo = new class() {
+
+    /**
+     * @var string
+     */
+    public $longName;
+
+    /**
+     * @var string
+     */
+    public $shortName;
+
+    public $_basePath;
+
+    public function getPath($file = NULL) {
+      return $this->_basePath . ($file === NULL ? '' : (DIRECTORY_SEPARATOR . $file));
+    }
+
+    public function isActive() {
+      return \CRM_Extension_System::singleton()->getMapper()->isActiveModule($this->shortName);
+    }
+
+  };
+  $mixInfo->longName = $longName;
+  $mixInfo->shortName = $shortName;
+  $mixInfo->_basePath = $basePath;
+
+  // Imitate CRM_Extension_BootCache.
+  $bootCache = new class() {
+
+    public function define($name, $callback) {
+      $envId = \CRM_Core_Config_Runtime::getId();
+      $oldExtCachePath = \Civi::paths()->getPath("[civicrm.compile]/CachedExtLoader.{$envId}.php");
+      $stat = stat($oldExtCachePath);
+      $file = Civi::paths()->getPath('[civicrm.compile]/CachedMixin.' . md5($name . ($stat['mtime'] ?? 0)) . '.php');
+      if (file_exists($file)) {
+        return include $file;
+      }
+      else {
+        $data = $callback();
+        file_put_contents($file, '<' . "?php\nreturn " . var_export($data, 1) . ';');
+        return $data;
+      }
+    }
+
+  };
+
+  // Imitate CRM_Extension_MixinLoader::run()
+  // Parse all live mixins before trying to scan any classes.
+  global $_CIVIX_MIXIN_POLYFILL;
+  foreach ($mixins as $mixin) {
+    // If the exact same mixin is defined by multiple exts, just use the first one.
+    if (!isset($_CIVIX_MIXIN_POLYFILL[$mixin])) {
+      $_CIVIX_MIXIN_POLYFILL[$mixin] = include_once $basePath . '/mixin/' . $mixin . '.mixin.php';
+    }
+  }
+  foreach ($mixins as $mixin) {
+    // If there's trickery about installs/uninstalls/resets, then we may need to register a second time.
+    if (!isset(\Civi::$statics[__FUNCTION__][$mixin])) {
+      \Civi::$statics[__FUNCTION__][$mixin] = 1;
+      $func = $_CIVIX_MIXIN_POLYFILL[$mixin];
+      $func($mixInfo, $bootCache);
+    }
+  }
+};
-- 
2.25.1