Adding call through to existing defiend handler

lib/rspec/sorbet/doubles.rb

@@ -11,6 +11,8 @@ def allow_doubles!
           inline_type_error_handler(error)
         end
 
+        @existing_handler = T::Configuration.instance_variable_get(:@call_validation_error_handler)
+
         T::Configuration.call_validation_error_handler = proc do |signature, opts|
           call_validation_error_handler(signature, opts)
         end
@@ -23,6 +25,13 @@ def allow_doubles!
       INLINE_DOUBLE_REGEX =
         /T.(?:let|cast): Expected type (?:T.(?<t_method>any|nilable|class_of)\()?(?<expected_types>[a-zA-Z0-9:: ,]*)(\))?, got (?:type .* with value )?#<(?<double_type>Instance|Class|Object)?Double([\(]|[ ])(?<doubled_type>[a-zA-Z0-9:: ,]*)(\))?/.freeze
 
+
+      def handle_call_validation_error(signature, opts)
+        raise TypeError, opts[:pretty_message] unless @existing_handler 
+
+        @existing_handler.call(signature, opts)
+      end
+
       def inline_type_error_handler(error)
         case error
         when TypeError
@@ -75,7 +84,7 @@ def typed_array_message?(message)
         message.match?(TYPED_ARRAY_MESSAGE)
       end
 
-      def call_validation_error_handler(_signature, opts)
+      def call_validation_error_handler(signature, opts)
         should_raise = true
 
         message = opts.fetch(:pretty_message, opts.fetch(:message, ''))
@@ -108,7 +117,7 @@ def call_validation_error_handler(_signature, opts)
           end
         end
 
-        raise TypeError, opts[:pretty_message] if should_raise
+        handle_call_validation_error(signature, opts) if should_raise
       end
     end
   end

spec/lib/rspec/sorbet_spec.rb

@@ -131,6 +131,33 @@ class Animal; end
         it_should_behave_like 'it allows an instance double'
       end
 
+      describe 'with an existing error handler' do
+        let(:handler) { proc {|_,_| } }
+
+        before do
+          T::Configuration.call_validation_error_handler  = handler
+          described_class.allow_doubles!
+        end
+
+
+        class PassthroughSig
+          extend T::Sig
+
+          sig { params(message: String).void }
+          def initialize(message)
+            @message = message
+          end
+        end
+
+        specify do
+          expect(handler).to receive(:call)
+
+          # Error is not rasied becasue handler is no-op
+          expect { PassthroughSig.new(123) }.not_to raise_error
+        end
+
+      end
+
       describe 'class doubles' do
         extend T::Sig