Add optional pretty printing

README.md

@@ -62,7 +62,7 @@ will get you something like
 }
 ```
 
-[Note: I've pretty-printed the output in these examples for easier reading. The actual log output will be on a single line without extra whitespace.]
+[_Note_: By default, `JsonTaggedLogger::Formatter` outputs logs as single lines without extra whitespace. Setting `JsonTaggedLogger::Formatter#pretty_print` to `true` will pretty print the logs, as I've done in these examples.]
 
 Importantly, if the controller action (or any code it calls along the way) has an explicit call to `Rails.logger.tagged("TAG").info("tagged log message")`, you'll get the same key/value tags (`request_id`, `host`, `my_param`, &c.) in the JSON document along with a `tags` key:
 

lib/json_tagged_logger/formatter.rb

@@ -3,6 +3,12 @@
 
 module JsonTaggedLogger
   class Formatter
+    attr_accessor :pretty_print
+
+    def initialize(pretty_print: false)
+      @pretty_pretty = pretty_print
+    end
+
     def call(severity, _time, _progname, message)
       log = {
         level: severity,
@@ -36,7 +42,7 @@ def call(severity, _time, _progname, message)
         end
       end
 
-      log.compact.to_json + "\n"
+      format_for_output(log)
     end
 
     private
@@ -69,5 +75,17 @@ def message_without_tags(message)
         message
       end
     end
+
+    def format_for_output(log_hash)
+      compacted_log = log_hash.compact
+
+      output_json = if pretty_print
+                      JSON.pretty_generate(compacted_log)
+                    else
+                      JSON.generate(compacted_log)
+                    end
+
+      output_json + "\n"
+    end
   end
 end

test/test_formatter.rb

@@ -140,4 +140,19 @@ def test_tags_merged_with_tags_in_json_message
     assert_equal "val1", results["key1"]
     assert_equal ["tag1", "tag2", "tag3", "tag4"], results["tags"]
   end
+
+  def test_optional_pretty_printing
+    @logger.formatter.pretty_print = true
+
+    @logger.info("hello world")
+
+    expected_output = <<~JSON
+    {
+      "level": "INFO",
+      "msg": "hello world"
+    }
+    JSON
+
+    assert_equal expected_output, @output.string
+  end
 end