Spawn child logger

CHANGELOG.md

@@ -1,6 +1,9 @@
 # Changelog
 All notable changes to this project will be documented in this file.
 
+## [2.3.2] - 2025-12-23
+- Add 'spawn_child_logger' method to allow other processes to inherit the current logger's configuration
+
 ## [2.3.1] - 2025-11-21
 - Fixed issue with output_path in create_logger, will now make a directory if it did not exist
 

README.md

@@ -102,6 +102,22 @@ You can call `new_scenario` with the identifier just before each scenario to cre
 logger.new_scenario('Scenario Id')
 ```
 
+### spawn_child_logger method
+You can call `spawn_child_logger` with a new system_name which will retain the current logger's config.
+This enables you to pass loggers to other tools and maintain the same colourisation and output_path.
+
+```ruby
+config = DVLA::Herodotus.config do |configuration|
+  configuration.display_pid = false
+  configuration.main = true
+  configuration.prefix_colour = {
+    overall: %w[blue bold],
+  }
+end
+LOG = DVLA::Herodotus.logger('<system-name>', config:, output_path: -> { "log.txt" })
+NewTool.new(logger: LOG.spawn_child_logger(system_name: 'new gem'))
+```
+
 ---
 ### Strings
 

lib/dvla/herodotus/herodotus_logger.rb

@@ -58,6 +58,16 @@ def sync_correlation_ids
         end
       end
 
+      # Creates a new logger with a different system name but inherits config and output path
+      def spawn_child_logger(system_name:)
+        config = DVLA::Herodotus.config do |c|
+          c.display_pid = @display_pid
+          c.main = false
+          c.prefix_colour = @prefix_colour
+        end
+        HerodotusLogger.new(system_name, @logdev.dev, config: config)
+      end
+
       %i[debug info warn error fatal].each do |log_level|
         define_method log_level do |progname = nil, &block|
           set_proc_writer_scenario

lib/dvla/herodotus/version.rb

@@ -1,5 +1,5 @@
 module DVLA
   module Herodotus
-    VERSION = '2.3.1'.freeze
+    VERSION = '2.3.2'.freeze
   end
 end

spec/dvla/herodotus/herodotus_logger_spec.rb

@@ -2,6 +2,11 @@
 
 RSpec.describe DVLA::Herodotus::HerodotusLogger do
   let(:logger) { DVLA::Herodotus.logger('rspec') }
+  let(:logger_with_colour) do
+    logger = DVLA::Herodotus.logger('colour-rspec')
+    logger.instance_variable_set(:@prefix_colour, { system: %w[red] })
+    logger
+  end
 
   after(:each) do
     DVLA::Herodotus.main_logger = nil
@@ -286,4 +291,53 @@
       expect { logger.info('test') }.to output(expected_output).to_stdout_from_any_process
     end
   end
+
+  context '#spawn_child_logger' do
+    it 'should create a child logger with different system name' do
+      child_logger = logger.spawn_child_logger(system_name: 'child-rspec')
+      expect(child_logger.system_name).to eq('child-rspec')
+    end
+
+    it 'should inherit display_pid config from parent' do
+      logger_with_pid = DVLA::Herodotus.logger('parent-rspec', config: DVLA::Herodotus.config { |c| c.display_pid = true })
+      child_logger = logger_with_pid.spawn_child_logger(system_name: 'child-rspec')
+      expect(child_logger.display_pid).to eq(true)
+    end
+
+    it 'should set main to false regardless of parent' do
+      main_logger = DVLA::Herodotus.logger('main-parent-rspec', config: DVLA::Herodotus.config { |c| c.main = true })
+      child_logger = main_logger.spawn_child_logger(system_name: 'child-rspec')
+      expect(child_logger.main).to eq(false)
+    end
+
+    it 'should share the same output device as parent' do
+      output_device = StringIO.new
+      parent_logger = DVLA::Herodotus::HerodotusLogger.new('parent-rspec', output_device)
+      child_logger = parent_logger.spawn_child_logger(system_name: 'child-rspec')
+
+      parent_logger.info('parent message')
+      child_logger.info('child message')
+
+      expect(output_device.string).to include('parent message')
+      expect(output_device.string).to include('child message')
+    end
+
+    it 'should inherit prefix_colour from parent when set' do
+      allow(Time).to receive(:now).and_return(Time.new(2022))
+      allow(SecureRandom).to receive(:uuid).and_return('123e4567-e89b-12d3-a456-426614174000')
+
+      child_logger = logger_with_colour.spawn_child_logger(system_name: 'child-rspec')
+      expect { child_logger.info('test') }.to output("[\e[31mchild-rspec\e[39m 2022-01-01 00:00:00 123e4567] INFO -- : test\n")
+                                                .to_stdout_from_any_process
+    end
+
+    it 'should not set prefix_colour when parent has none' do
+      allow(Time).to receive(:now).and_return(Time.new(2022))
+      allow(SecureRandom).to receive(:uuid).and_return('123e4567-e89b-12d3-a456-426614174000')
+
+      child_logger = logger.spawn_child_logger(system_name: 'child-rspec')
+      expect { child_logger.info('test') }.to output("[child-rspec 2022-01-01 00:00:00 123e4567] INFO -- : test\n")
+                                                .to_stdout_from_any_process
+    end
+  end
 end