[FEATURE] Pre-commit hook: check for structural similarities with flay

README.md

@@ -496,6 +496,7 @@ issue](https://github.com/brigade/overcommit/issues/238) for more details.
 * [ExecutePermissions](lib/overcommit/hook/pre_commit/execute_permissions.rb)
 * [Fasterer](lib/overcommit/hook/pre_commit/fasterer.rb)
 * [FixMe](lib/overcommit/hook/pre_commit/fix_me.rb)
+* [Flay](lib/overcommit/hook/pre_commit/flay.rb)
 * [Foodcritic](lib/overcommit/hook/pre_commit/foodcritic.rb)
 * [ForbiddenBranches](lib/overcommit/hook/pre_commit/forbidden_branches.rb)
 * [GoLint](lib/overcommit/hook/pre_commit/go_lint.rb)

config/default.yml

@@ -283,6 +283,16 @@ PreCommit:
     flags: ['-IEHnw']
     keywords: ['BROKEN', 'BUG', 'ERROR', 'FIXME', 'HACK', 'NOTE', 'OPTIMIZE', 'REVIEW', 'TODO', 'WTF', 'XXX']
 
+  Flay:
+    enabled: false
+    description: 'Analyze ruby code for structural similarities with Flay'
+    required_executable: 'flay'
+    install_command: 'gem install flay'
+    mass_threshold: 16
+    fuzzy: 1
+    liberal: false
+    include: '**/*.rb'
+
   Foodcritic:
     enabled: false
     description: 'Analyze with Foodcritic'

lib/overcommit/hook/pre_commit/flay.rb

@@ -0,0 +1,36 @@
+module Overcommit::Hook::PreCommit
+  # Runs `flay` against any modified files.
+  #
+  # @see https://github.com/seattlerb/flay
+  class Flay < Base
+    # Flay prints two kinds of messages:
+    #
+    # 1) IDENTICAL code found in :defn (mass*2 = MASS)
+    # file_path_1.rb:LINE_1
+    # file_path_2.rb:LINE_2
+    #
+    # 2) Similar code found in :defn (mass = MASS)
+    # file_path_1.rb:LINE_1
+    # file_path_2.rb:LINE_2
+    #
+
+    def run
+      command = ['flay', '--mass', @config['mass_threshold'].to_s, '--fuzzy', @config['fuzzy'].to_s]
+      # Use a more liberal detection method
+      command += ['--liberal'] if @config['liberal']
+      messages = []
+      # Run the command for each file
+      applicable_files.each do |file|
+        result = execute(command, args: [file])
+        results = result.stdout.split("\n\n")
+        results.shift
+        unless results.empty?
+          error_message = results.join("\n").gsub(/^\d+\)\s*/, '')
+          message = Overcommit::Hook::Message.new(:error, nil, nil, error_message)
+          messages << message
+        end
+      end
+      messages
+    end
+  end
+end

spec/overcommit/hook/pre_commit/flay_spec.rb

@@ -0,0 +1,58 @@
+require 'spec_helper'
+
+describe Overcommit::Hook::PreCommit::Flay do
+  let(:config)  { Overcommit::ConfigurationLoader.default_configuration }
+  let(:context) { double('context') }
+  let(:applicable_files) { %w[file1.rb] }
+  subject { described_class.new(config, context) }
+
+  before do
+    subject.stub(:applicable_files).and_return(applicable_files)
+  end
+
+  around do |example|
+    repo do
+      example.run
+    end
+  end
+
+  before do
+    command = %w[flay --mass 16 --fuzzy 1]
+    subject.stub(:execute).with(command, args: applicable_files).and_return(result)
+  end
+
+  context 'flay discovered two issues' do
+    let(:result) do
+      double(
+        success?: false,
+        stdout: <<-MSG
+Total score (lower is better) = 268
+
+1) IDENTICAL code found in :defn (mass*2 = 148)
+  app/whatever11.rb:105
+  app/whatever12.rb:76
+
+2) Similar code found in :defn (mass = 120)
+  app/whatever21.rb:105
+  app/whatever22.rb:76
+
+MSG
+      )
+    end
+
+    it { should fail_hook }
+  end
+
+  context 'flay discovered no issues' do
+    let(:result) do
+      double(
+        success?: false,
+        stdout: <<-MSG
+Total score (lower is better) = 0
+MSG
+      )
+    end
+
+    it { should pass }
+  end
+end