Add child loggers

Child loggers mean that we can create new instances of a logger for
subsystems or specific classes, but still only have a single set of
outputs.

Signed-off-by: Thom May <thom@chef.io>

4 files changed, 139 insertions, 1 deletions

diff --git a/lib/mixlib/log.rb b/lib/mixlib/log.rb
index 7152a90..c6dc839 100644
--- a/lib/mixlib/log.rb
+++ b/lib/mixlib/log.rb
@@ -19,6 +19,7 @@
 require "logger"
 require "mixlib/log/version"
 require "mixlib/log/formatter"
+require "mixlib/log/child"
 
 module Mixlib
   module Log
@@ -69,6 +70,19 @@ module Mixlib
       @configured = true
     end
 
+    def with_child
+      child = Child.new(self)
+      if block_given?
+        yield child
+      else
+        child
+      end
+    end
+
+    def pass(severity, args, progname = nil, &block)
+      add(severity, args, progname, &block)
+    end
+
     # Use Mixlib::Log.init when you want to set up the logger manually.  Arguments to this method
     # get passed directly to Logger.new, so check out the documentation for the standard Logger class
     # to understand what to do here.
@@ -82,6 +96,7 @@ module Mixlib
       @logger.formatter = Mixlib::Log::Formatter.new() if @logger.respond_to?(:formatter=)
       @logger.level = Logger::WARN
       @configured = true
+      @parent = nil
       @logger
     end
 
diff --git a/lib/mixlib/log/child.rb b/lib/mixlib/log/child.rb
new file mode 100644
index 0000000..2676b69
--- /dev/null
+++ b/lib/mixlib/log/child.rb
@@ -0,0 +1,63 @@
+#
+# Copyright:: Copyright (c) 2018 Chef Software, Inc.
+# License:: Apache License, Version 2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+module Mixlib
+  module Log
+    class Child
+      # include Mixlib::Log
+
+      attr_reader :parent
+      def initialize(parent)
+        @parent = parent
+      end
+
+      def level
+        parent.level
+      end
+
+      def pass(severity, args, progname = nil, &block)
+        parent.pass(severity, args, progname, &block)
+      end
+
+      # Define the methods to interrogate the logger for the current log level.
+      # Note that we *only* query the default logger (@logger) and not any other
+      # loggers that may have been added, even though it is possible to configure
+      # two (or more) loggers at different log levels.
+      [:debug?, :info?, :warn?, :error?, :fatal?].each do |method_name|
+        class_eval(<<-METHOD_DEFN, __FILE__, __LINE__)
+          def #{method_name}
+            parent.#{method_name}
+          end
+        METHOD_DEFN
+      end
+
+      # Define the standard logger methods on this class programmatically.
+      # No need to incur method_missing overhead on every log call.
+      [:debug, :info, :warn, :error, :fatal].each do |method_name|
+        class_eval(<<-METHOD_DEFN, __FILE__, __LINE__)
+        def #{method_name}(msg=nil, &block)
+          pass(:#{method_name}, msg, &block)
+        end
+        METHOD_DEFN
+      end
+
+      def add(severity, message = nil, progname = nil, &block)
+        parent.pass(severity, message, progname, &block)
+      end
+
+    end
+  end
+end
diff --git a/spec/mixlib/log/child_spec.rb b/spec/mixlib/log/child_spec.rb
new file mode 100644
index 0000000..daf3734
--- /dev/null
+++ b/spec/mixlib/log/child_spec.rb
@@ -0,0 +1,60 @@
+#
+# Copyright:: Copyright (c) 2018 Chef Software, Inc.
+# License:: Apache License, Version 2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+require "tempfile"
+require "stringio"
+require "spec_helper"
+
+RSpec.describe Mixlib::Log::Child do
+  before do
+    Logit.reset!
+    Logit.init(io)
+    Logit.level = :warn
+  end
+
+  let(:io) { StringIO.new }
+
+  let(:child) { Logit.with_child }
+
+  it "has a parent" do
+    expect(child.parent).to be(Logit)
+  end
+
+  it "accepts a message" do
+    Logit.with_child { |l| l.add(Logger::WARN, "a message") }
+    expect(io.string).to match(/a message$/)
+  end
+
+  context "sends a message to the parent" do
+    %i{ debug info warn error fatal }.each do |level|
+      it "at #{level}" do
+        expect(Logit).to receive(:pass).with(level, "a #{level} message", nil)
+        child.send(level, "a #{level} message")
+      end
+    end
+  end
+
+  context "can query the parent's level" do
+    %i{ debug info warn error fatal }.each do |level|
+      it "at #{level}" do
+        query = "#{level}?".to_sym
+        Logit.level = level
+        expect(child.send(query)).to be(true)
+      end
+    end
+  end
+end
diff --git a/spec/mixlib/log_spec.rb b/spec/mixlib/log_spec.rb
index 277035d..69eebd5 100644
--- a/spec/mixlib/log_spec.rb
+++ b/spec/mixlib/log_spec.rb
@@ -19,7 +19,7 @@
 
 require "tempfile"
 require "stringio"
-require File.expand_path(File.join(File.dirname(__FILE__), "..", "spec_helper"))
+require "spec_helper"
 
 class LoggerLike
   attr_accessor :level