Plugin#params should not return obsolete params

Fixes #4011

lib/logstash/config/mixin.rb

@@ -110,6 +110,16 @@ module LogStash::Config::Mixin
         I18n.t("logstash.agent.configuration.invalid_plugin_settings")
     end
 
+    # We remove any config options marked as obsolete,
+    # no code should be associated to them and their values should not bleed
+    # to the plugin context.
+    #
+    # This need to be done after fetching the options from the parents classed
+    params.reject! do |name, value|
+      opts = self.class.get_config[name]
+      opts.include?(:obsolete)
+    end
+
     # set instance variables like '@foo'  for each config value given.
     params.each do |key, value|
       next if key[0, 1] == "@"

spec/core/config_mixin_spec.rb

@@ -115,6 +115,14 @@ describe LogStash::Config::Mixin do
       end
     end
 
+    context "when using an obsolete settings from the parent class" do
+      it "should cause a configuration error" do
+        expect {
+          plugin_class.new("debug" => true)
+        }.to raise_error(LogStash::ConfigurationError)
+      end
+    end
+
     context "when not using an obsolete setting" do
       it "should not cause a configuration error" do
         expect {
@@ -123,4 +131,24 @@ describe LogStash::Config::Mixin do
       end
     end
   end
+
+  context "#params" do
+    let(:plugin_class) do
+      Class.new(LogStash::Filters::Base)  do
+        config_name "fake"
+        config :password, :validate => :password
+        config :bad, :validate => :string, :default => "my default", :obsolete => "not here"
+      end
+    end
+
+    subject { plugin_class.new({ "password" => "secret" }) }
+
+    it "should not return the obsolete options" do
+      expect(subject.params).not_to include("bad")
+    end
+
+    it "should include any other params" do
+      expect(subject.params).to include("password")
+    end
+  end
 end