feat: add action_policy.init event

Author: palkan

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## master
 
+- Add `action_policy.init` instrumentation event. ([@palkan][])
+
+  Triggered every time a new policy object is initialized.
+
 - Fix policy memoization with explicit context. ([@palkan][])
 
   Explicit context (`authorize! context: {}`) wasn't considered during

docs/instrumentation.md

@@ -47,6 +47,17 @@ permitted to do that).
 
 The `action_policy.apply_rule` might have a large number of failures, 'cause it also tracks the usage of non-raising applications (i.e. `allowed_to?`).
 
+### `action_policy.init`
+
+This event is triggered every time a new policy object is initialized.
+
+The event contains the following information:
+
+- `:policy` – policy class name.
+
+This event is useful if you want to track the number of initialized policies per _action_ (for example, when you want to ensure that
+the [memoization](caching.md) works as expected).
+
 ## Turn off instrumentation
 
 Instrumentation is enabled by default. To turn it off add to your configuration:

lib/action_policy/rails/policy/instrumentation.rb

@@ -6,12 +6,19 @@ module Rails
       # Add ActiveSupport::Notifications support.
       #
       # Fires `action_policy.apply_rule` event on every `#apply` call.
+      # Fires `action_policy.init` event on every policy initialization.
       module Instrumentation
-        EVENT_NAME = "action_policy.apply_rule"
+        INIT_EVENT_NAME = "action_policy.init"
+        APPLY_EVENT_NAME = "action_policy.apply_rule"
+
+        def initialize(*)
+          event = {policy: self.class.name}
+          ActiveSupport::Notifications.instrument(INIT_EVENT_NAME, event) { super }
+        end
 
         def apply(rule)
           event = {policy: self.class.name, rule: rule.to_s}
-          ActiveSupport::Notifications.instrument(EVENT_NAME, event) do
+          ActiveSupport::Notifications.instrument(APPLY_EVENT_NAME, event) do
             res = super
             event[:cached] = result.cached?
             event[:value] = result.value

test/action_policy/rails/instrumentation_test.rb

@@ -62,6 +62,9 @@ def teardown
   def test_instrument_apply
     policy = TestPolicy.new false
 
+    # drop init event
+    events.shift
+
     refute policy.apply(:show?)
 
     assert_equal 1, events.size
@@ -78,6 +81,9 @@ def test_instrument_apply
   def test_instrument_cached_apply
     policy = TestPolicy.new true
 
+    # drop init event
+    events.shift
+
     assert policy.apply(:manage?)
 
     assert_equal 1, events.size
@@ -102,7 +108,11 @@ def test_instrument_authorize
     service = Service.new
 
     assert_equal "OK", service.call
-    assert_equal 2, events.size
+
+    assert_equal 3, events.size
+
+    # drop init event
+    events.shift
 
     event, data = events.shift
 
@@ -122,7 +132,10 @@ def test_instrument_authorize
 
     refute service.visible?(false)
 
-    assert_equal 1, events.size
+    assert_equal 2, events.size
+
+    # drop init event
+    events.shift
 
     event, data = events.shift
 
@@ -133,4 +146,14 @@ def test_instrument_authorize
     refute data[:value]
     refute data[:cached]
   end
+
+  def test_instrument_initialize
+    TestPolicy.new true
+    assert_equal 1, events.size
+
+    event, data = events.shift
+
+    assert_equal "action_policy.init", event
+    assert_equal TestPolicy.name, data[:policy]
+  end
 end