Add after_compile hook

Author: jsolas

docs/CHANGELOG.md

@@ -10,6 +10,12 @@ nav_order: 6
 
 ## main
 
+## 4.0.0.rc6
+
+* Add `compile.view_component` ActiveSupport::Notifications instrumentation, enabling gems to safely extend the compiler without monkey-patching.
+
+    *Jose Solás*
+
 * Setup Trusted Publishing to RubyGems to improve software supply chain safety.
 
     *Hans Lemuet*

lib/view_component/base.rb

@@ -588,6 +588,18 @@ def __vc_compiled?
         __vc_compiler.compiled?
       end
 
+      # Called after a component class has been compiled.
+      #
+      # Extensions can override this instance method to run logic after
+      # compilation (e.g., generate helpers, register metadata, etc.).
+      #
+      # By default, this is a no-op. The compiler will invoke this method on an
+      # uninitialized instance using `allocate` to avoid requiring initializer
+      # arguments.
+      def after_compile
+        # no-op by default
+      end
+
       # @private
       def __vc_ensure_compiled
         __vc_compile unless __vc_compiled?

lib/view_component/compiler.rb

@@ -24,8 +24,8 @@ def compile(raise_errors: false, force: false)
       return if @component == ViewComponent::Base
 
       @lock.synchronize do
-        # this check is duplicated so that concurrent compile calls can still
-        # early exit
+        # This check is duplicated so that concurrent compile calls can still
+        # early exit before we instrument.
         return if compiled? && !force
 
         gather_templates
@@ -52,6 +52,13 @@ def compile(raise_errors: false, force: false)
         @component.__vc_build_i18n_backend
 
         CompileCache.register(@component)
+
+        # Invoke instance-level after_compile hook without calling initialize.
+        begin
+          @component.allocate.after_compile
+        rescue NoMethodError
+          # no-op
+        end
       end
     end
 

test/sandbox/test/base_test.rb

@@ -195,4 +195,45 @@ def test_uses_module_configuration
     assert_equal false, TestAlreadyConfigurableModule::SomeComponent.instrumentation_enabled
     assert_equal false, TestAlreadyConfiguredModule::SomeComponent.instrumentation_enabled
   end
+
+  def test_after_compile_hook_called_on_compile
+    klass = Class.new(ViewComponent::Base) do
+      @@calls = 0
+      def self.calls = @@calls
+      def after_compile; @@calls += 1; end
+      erb_template ""
+    end
+
+    self.class.const_set("TempHookComponent", klass)
+    ViewComponent::CompileCache.invalidate_class!(klass)
+
+    ViewComponent::Compiler.new(klass).compile(force: true)
+    assert_equal 1, klass.calls
+  ensure
+    self.class.send(:remove_const, "TempHookComponent") if self.class.const_defined?("TempHookComponent")
+    ViewComponent::CompileCache.invalidate_class!(klass) if defined?(klass)
+  end
+
+  def test_after_compile_not_called_on_cached_compile
+    klass = Class.new(ViewComponent::Base) do
+      @@calls = 0
+      def self.calls = @@calls
+      def after_compile; @@calls += 1; end
+      erb_template ""
+    end
+
+    self.class.const_set("TempHookCachedComponent", klass)
+    ViewComponent::CompileCache.invalidate_class!(klass)
+
+    compiler = ViewComponent::Compiler.new(klass)
+    compiler.compile(force: true)
+    assert_equal 1, klass.calls
+
+    # compile again without force -> should not call hook again
+    compiler.compile
+    assert_equal 1, klass.calls
+  ensure
+    self.class.send(:remove_const, "TempHookCachedComponent") if self.class.const_defined?("TempHookCachedComponent")
+    ViewComponent::CompileCache.invalidate_class!(klass) if defined?(klass)
+  end
 end