Added pre-commit hook to check for line endings

Depending on the configured representation, this hook will verify if
only unix line endings (LF) or only windows line endings (CRLF) are
used.

Author: harmjanblok

config/default.yml

@@ -629,6 +629,11 @@ PreCommit:
     include:
       - '**/*.html'
 
+  LineEndings:
+    description: 'Check line endings'
+    enabled: false
+    eol: "\n"
+
   XmlLint:
     enabled: false
     description: 'Analyze with xmllint'

lib/overcommit/hook/pre_commit/line_endings.rb

@@ -0,0 +1,51 @@
+module Overcommit::Hook::PreCommit
+  # Checks for line endings in files.
+  class LineEndings < Base
+    def run
+      messages = []
+
+      offending_files.map do |file_name|
+        file = File.open(file_name)
+        file.each_line do |line|
+          # remove configured line-ending
+          line.gsub!(/#{config['eol']}/, '')
+
+          # detect any left over line-ending characters
+          next unless line.end_with?("\n", "\r")
+
+          messages << Overcommit::Hook::Message.new(
+            :error,
+            file_name,
+            file.lineno,
+            "#{file_name}:#{file.lineno}:#{line.inspect}"
+          )
+        end
+      end
+
+      messages
+    end
+
+    private
+
+    def offending_files
+      result = execute(%w[git ls-files --eol -z --], args: applicable_files)
+      raise 'Unable to access git tree' unless result.success?
+
+      result.stdout.split("\0").map do |file_info|
+        i, _w, _attr, path = file_info.split
+        next if i == 'l/-text' # ignore binary files
+        next if i == "l/#{eol}"
+        path
+      end.compact
+    end
+
+    def eol
+      @eol ||=  case config['eol']
+                when "\n"
+                  'lf'
+                when "\r\n"
+                  'crlf'
+                end
+    end
+  end
+end

spec/overcommit/hook/pre_commit/line_endings_spec.rb

@@ -0,0 +1,61 @@
+require 'spec_helper'
+
+describe Overcommit::Hook::PreCommit::LineEndings do
+  let(:config) do
+    Overcommit::ConfigurationLoader.default_configuration.merge(
+      Overcommit::Configuration.new(
+        'PreCommit' => {
+          'LineEndings' => {
+            'eol' => eol
+          }
+        }
+      )
+    )
+  end
+  let(:context) { double('context') }
+  subject { described_class.new(config, context) }
+  let(:eol) { "\n" }
+  let(:staged_file) { 'filename.txt' }
+
+  before do
+    subject.stub(:applicable_files).and_return([staged_file])
+  end
+
+  around do |example|
+    repo do
+      File.open(staged_file, 'w') { |f| f.write(contents) }
+      `git add #{staged_file}`
+      example.run
+    end
+  end
+
+  context 'when enforcing \n' do
+    context 'when file contains \r\n line endings' do
+      let(:contents) { "CR-LF\r\nline\r\nendings\r\n" }
+
+      it { should fail_hook }
+    end
+
+    context 'when file contains \n endings' do
+      let(:contents) { "LF\nline\nendings\n" }
+
+      it { should pass }
+    end
+  end
+
+  context 'when enforcing \r\n' do
+    let(:eol) { "\r\n" }
+
+    context 'when file contains \r\n line endings' do
+      let(:contents) { "CR-LF\r\nline\r\nendings\r\n" }
+
+      it { should pass }
+    end
+
+    context 'when file contains \n line endings' do
+      let(:contents) { "LF\nline\nendings\n" }
+
+      it { should fail_hook }
+    end
+  end
+end