Add --format github option

README.md

@@ -556,13 +556,14 @@ e.g., `codeclimate analyze -e duplication`
 
 ## Output formats
 
-Reek supports 5 output formats:
+Reek supports 6 output formats:
 
 * plain text (default)
-* HTML (`--format html`)
-* YAML (`--format yaml`, see also [YAML Reports](docs/YAML-Reports.md))
-* JSON (`--format json`)
-* XML  (`--format xml`)
+* HTML   (`--format html`)
+* YAML   (`--format yaml`, see also [YAML Reports](docs/YAML-Reports.md))
+* JSON   (`--format json`)
+* XML    (`--format xml`)
+* GitHub (`--format github`)
 
 ## Working with Rails
 

lib/reek/cli/options.rb

@@ -131,9 +131,9 @@ def set_generate_todo_list_options
       def set_alternative_formatter_options
         parser.separator "\nReport format:"
         parser.on(
-          '-f', '--format FORMAT', [:html, :text, :yaml, :json, :xml],
+          '-f', '--format FORMAT', [:html, :text, :yaml, :json, :xml, :github],
           'Report smells in the given format:',
-          '  html', '  text (default)', '  yaml', '  json', '  xml') do |opt|
+          '  html', '  text (default)', '  yaml', '  json', '  xml', '  github') do |opt|
           self.report_format = opt
         end
       end

lib/reek/report.rb

@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require_relative 'report/github_report'
 require_relative 'report/html_report'
 require_relative 'report/json_report'
 require_relative 'report/text_report'
@@ -16,11 +17,12 @@ module Reek
   # Reek reporting functionality.
   module Report
     REPORT_CLASSES = {
-      yaml: YAMLReport,
-      json: JSONReport,
-      html: HTMLReport,
-      xml:  XMLReport,
-      text: TextReport
+      yaml:   YAMLReport,
+      json:   JSONReport,
+      html:   HTMLReport,
+      xml:    XMLReport,
+      text:   TextReport,
+      github: GithubReport
     }.freeze
 
     LOCATION_FORMATTERS = {

lib/reek/report/github_report.rb

@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+require_relative 'base_report'
+
+module Reek
+  module Report
+    #
+    # Displays smells as GitHub Workflow commands.
+    #
+    # @public
+    #
+    class GithubReport < BaseReport
+      def show(out = $stdout)
+        out.print(workflow_commands.join)
+      end
+
+      private
+
+      def workflow_commands
+        smells.map do |smell|
+          WorkflowCommand.new(smell)
+        end
+      end
+
+      # Represents a smell as a GitHub Workflow command.
+      class WorkflowCommand
+        def initialize(smell)
+          @smell = smell
+        end
+
+        def to_s
+          format(
+            "::warning file=%<file>s,line=%<line>d::%<message>s\n",
+            file: file,
+            line: line,
+            message: message)
+        end
+
+        private
+
+        def file
+          @smell.source
+        end
+
+        def line
+          @smell.lines.first
+        end
+
+        def message
+          @smell.base_message.gsub('%', '%25').gsub("\r", '%0D').gsub("\n", '%0A')
+        end
+      end
+    end
+  end
+end

spec/reek/report/github_report_spec.rb

@@ -0,0 +1,44 @@
+require_relative '../../spec_helper'
+require_lib 'reek/examiner'
+require_lib 'reek/report/json_report'
+
+RSpec.describe Reek::Report::GithubReport do
+  let(:instance) do
+    described_class.new
+  end
+
+  let(:examiner) do
+    Reek::Examiner.new(source)
+  end
+
+  context 'with empty source' do
+    let(:source) do
+      ''
+    end
+
+    it 'prints empty string' do
+      instance.add_examiner(examiner)
+      expect { instance.show }.not_to output.to_stdout
+    end
+  end
+
+  context 'with smelly source' do
+    let(:source) do
+      <<~RUBY
+        def simple(a)
+          a[3]
+        end
+      RUBY
+    end
+
+    it 'prints smells as GitHub Workflow commands' do
+      instance.add_examiner(examiner)
+      expect { instance.show }.to output(
+        <<~TEXT
+          ::warning file=string,line=1::UncommunicativeParameterName: simple has the parameter name 'a'
+          ::warning file=string,line=1::UtilityFunction: simple doesn't depend on instance state (maybe move it to another class?)
+        TEXT
+      ).to_stdout
+    end
+  end
+end