[ruby/irb] respect NO_COLOR environment variable

When `NO_COLOR` is set to any non-nil value, output is not colorized.

See https://no-color.org/

https://github.com/ruby/irb/commit/401d0916fe

lib/irb/init.rb

@@ -44,7 +44,7 @@ module IRB # :nodoc:
     @CONF[:IRB_RC] = nil
 
     @CONF[:USE_SINGLELINE] = false unless defined?(ReadlineInputMethod)
-    @CONF[:USE_COLORIZE] = true
+    @CONF[:USE_COLORIZE] = !ENV['NO_COLOR']
     @CONF[:INSPECT_MODE] = true
     @CONF[:USE_TRACER] = false
     @CONF[:USE_LOADER] = false
@@ -301,11 +301,11 @@ module IRB # :nodoc:
         break
       end
     end
+
     load_path.collect! do |path|
       /\A\.\// =~ path ? path : File.expand_path(path)
     end
     $LOAD_PATH.unshift(*load_path)
-
   end
 
   # running config

test/irb/test_init.rb

@@ -67,6 +67,22 @@ module TestIRB
       Process.kill("SIGKILL", status.pid) if !status.exited? && !status.stopped? && !status.signaled?
     end
 
+    def test_no_color_environment_variable
+      orig = ENV['NO_COLOR']
+
+      assert IRB.conf[:USE_COLORIZE]
+
+      ENV['NO_COLOR'] = 'true'
+      IRB.setup(eval("__FILE__"))
+      refute IRB.conf[:USE_COLORIZE]
+
+      ENV['NO_COLOR'] = nil
+      IRB.setup(eval("__FILE__"))
+      assert IRB.conf[:USE_COLORIZE]
+    ensure
+      ENV['NO_COLOR'] = orig
+    end
+
     private
 
     def with_argv(argv)