Add ability to have many post initialization callbacks

sentry-rails/lib/sentry/rails/configuration.rb

@@ -2,7 +2,7 @@ module Sentry
   class Configuration
     attr_reader :rails
 
-    def post_initialization_callback
+    add_post_initialization_callback do
       @rails = Sentry::Rails::Configuration.new
       @excluded_exceptions = @excluded_exceptions.concat(Sentry::Rails::IGNORE_DEFAULT)
     end

sentry-ruby/lib/sentry/configuration.rb

@@ -156,6 +156,10 @@ class Configuration
 
     AVAILABLE_BREADCRUMBS_LOGGERS = [:sentry_logger, :active_support_logger].freeze
 
+    # Post initialization callbacks are called at the end of initialization process
+    # allowing extending the configuration of sentry-ruby by multiple extensions
+    @@post_initialization_callbacks = []
+
     def initialize
       self.background_worker_threads = Concurrent.processor_count
       self.breadcrumbs_logger = []
@@ -182,7 +186,7 @@ def initialize
 
       @transport = Transport::Configuration.new
       @gem_specs = Hash[Gem::Specification.map { |spec| [spec.name, spec.version.to_s] }] if Gem::Specification.respond_to?(:map)
-      post_initialization_callback
+      run_post_initialization_callbacks
     end
 
     def dsn=(value)
@@ -386,7 +390,21 @@ def server_name_from_env
       end
     end
 
-    # allow extensions to extend the Configuration class
-    def post_initialization_callback; end
+    def run_post_initialization_callbacks
+      self.class.post_initialization_callbacks.each do |hook|
+        instance_eval(&hook)
+      end
+    end
+
+    # allow extensions to add their hooks to the Configuration class
+    def self.add_post_initialization_callback(&block)
+      self.post_initialization_callbacks << block
+    end
+
+    protected
+
+    def self.post_initialization_callbacks
+      @@post_initialization_callbacks
+    end
   end
 end

sentry-ruby/spec/sentry/configuration_spec.rb

@@ -367,4 +367,27 @@ class MyTestException < RuntimeError; end
       end
     end
   end
+
+  describe '.add_post_initialization_callback' do
+    class SentryConfigurationSample < Sentry::Configuration
+      attr_reader :var1, :var2
+
+      add_post_initialization_callback do
+        @var1 = 1
+      end
+
+      add_post_initialization_callback do
+        @var2 = 2
+      end
+    end
+
+    subject(:configuration) { SentryConfigurationSample }
+
+    it 'calls all hooks and initializes assigned variables' do
+      instance = configuration.new
+
+      expect(instance.var1). to eq 1
+      expect(instance.var2). to eq 2
+    end
+  end
 end