Delay formatter setup until reporter needs to notify something

Author: JonRowe

lib/rspec/core/configuration.rb

@@ -930,7 +930,7 @@ def reporter
         @reporter_buffer || @reporter ||=
           begin
             @reporter_buffer = DeprecationReporterBuffer.new
-            formatter_loader.setup_default output_stream, deprecation_stream
+            formatter_loader.prepare_default output_stream, deprecation_stream
             @reporter_buffer.play_onto(formatter_loader.reporter)
             @reporter_buffer = nil
             formatter_loader.reporter

lib/rspec/core/formatters.rb

@@ -115,6 +115,11 @@ def initialize(reporter)
     # @return [String] the default formatter to setup, defaults to `progress`
     attr_accessor :default_formatter
 
+    # @private
+    def prepare_default(output_stream, deprecation_stream)
+      reporter.prepare_default(self, output_stream, deprecation_stream)
+    end
+
     # @private
     def setup_default(output_stream, deprecation_stream)
       add default_formatter, output_stream if @formatters.empty?

lib/rspec/core/reporter.rb

@@ -19,6 +19,8 @@ def initialize(configuration)
       @pending_examples = []
       @duration = @start = @load_time = nil
       @non_example_exception_count = 0
+      @setup_default = lambda {}
+      @setup = false
     end
 
     # @private
@@ -52,6 +54,13 @@ def register_listener(listener, *notifications)
       true
     end
 
+    # @private
+    def prepare_default(loader, output_stream, deprecation_stream)
+      @setup_default = lambda do
+        loader.setup_default output_stream, deprecation_stream
+      end
+    end
+
     # @private
     def registered_listeners(notification)
       @listeners[notification].to_a
@@ -200,6 +209,7 @@ def stop
 
     # @private
     def notify(event, notification)
+      ensure_listeners_ready
       registered_listeners(event).each do |formatter|
         formatter.__send__(event, notification)
       end
@@ -225,6 +235,13 @@ def fail_fast_limit_met?
 
   private
 
+    def ensure_listeners_ready
+      return if @setup
+
+      @setup_default.call
+      @setup = true
+    end
+
     def close
       notify :close, Notifications::NullNotification
     end

spec/rspec/core/configuration_spec.rb

@@ -1459,6 +1459,38 @@ def metadata_hash(*args)
       end
     end
 
+    describe '#reporter' do
+      before do
+        config.output_stream = StringIO.new
+        config.deprecation_stream = StringIO.new
+      end
+
+      it 'doesnt immediately trigger formatter setup' do
+        config.reporter
+
+        expect(config.formatters).to be_empty
+      end
+
+      it 'allows registering listeners without doubling up formatters' do
+        config.reporter.register_listener double(:message => nil), :message
+
+        expect {
+          config.formatter = :documentation
+        }.to change { config.formatters.size }.from(0).to(1)
+
+        expect {
+          config.reporter.notify :message, double(:message => 'Triggers formatter setup')
+        }.to change { config.formatters.size }.from(1).to(2)
+      end
+
+      it 'still configures a default formatter when none specified' do
+        config.reporter.register_listener double(:message => nil), :message
+        expect {
+          config.reporter.notify :message, double(:message => 'Triggers formatter setup')
+        }.to change { config.formatters.size }.from(0).to(2)
+      end
+    end
+
     describe "#default_formatter" do
       it 'defaults to `progress`' do
         expect(config.default_formatter).to eq('progress')
@@ -1480,8 +1512,13 @@ def metadata_hash(*args)
       end
 
       context 'when no other formatter has been set' do
+        before do
+          config.output_stream = StringIO.new
+        end
+
         it 'gets used' do
           config.default_formatter = 'doc'
+          config.reporter.notify :message, double(:message => 'Triggers formatter setup')
 
           expect(used_formatters).not_to include(an_instance_of Formatters::ProgressFormatter)
           expect(used_formatters).to include(an_instance_of Formatters::DocumentationFormatter)