Add CapitalizedSubject commit message hook

It is considered good form to start your commit messages with a
capitalized subject. This commit adds a commit message hook that
enforces this practice.

Change-Id: I447ba091978b3c62f480967a1c5df36b8ffa50eb
Reviewed-on: http://gerrit.causes.com/47631
Tested-by: jenkins <jenkins@brigade.com>
Reviewed-by: Henric Trotzig <henric.trotzig@brigade.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>

Author: lencioni

CHANGELOG.md

@@ -23,6 +23,7 @@
   [ruby-lint](https://github.com/YorickPeterse/ruby-lint)
 * Add `Jsl` pre-commit hook that checks the style of JavaScript files with
   [JavaScript Lint](http://www.javascriptlint.com/)
+* Add `CapitalizedSubject` commit message hook
 
 ## 0.23.0
 

config/default.yml

@@ -22,6 +22,9 @@ CommitMsg:
     requires_files: false
     quiet: false
 
+  CapitalizedSubject:
+    description: 'Checking subject capitalization'
+
   GerritChangeId:
     enabled: false
     description: 'Ensuring Gerrit Change-Id is present'

lib/overcommit/hook/commit_msg/capitalized_subject.rb

@@ -0,0 +1,13 @@
+module Overcommit::Hook::CommitMsg
+  # Ensures commit message subject lines are followed by a blank line.
+  class CapitalizedSubject < Base
+    def run
+      first_letter = commit_message_lines[0].to_s.match(/^[[:punct:]]*(.)/)[1]
+      unless first_letter.match(/[[:upper:]]/)
+        return :warn, 'Subject should start with a capital letter'
+      end
+
+      :pass
+    end
+  end
+end

spec/overcommit/hook/commit_msg/capitalized_subject_spec.rb

@@ -0,0 +1,74 @@
+require 'spec_helper'
+
+describe Overcommit::Hook::CommitMsg::CapitalizedSubject do
+  let(:config)  { Overcommit::ConfigurationLoader.default_configuration }
+  let(:context) { double('context') }
+  subject { described_class.new(config, context) }
+
+  before do
+    subject.stub(:commit_message_lines).and_return(commit_msg.split("\n"))
+  end
+
+  context 'when subject starts with a capital letter' do
+    let(:commit_msg) { <<-MSG }
+Initial commit
+
+Mostly cats so far.
+    MSG
+
+    it { should pass }
+  end
+
+  context 'when subject starts with a utf-8 capital letter' do
+    let(:commit_msg) { <<-MSG }
+Årsgång
+
+Mostly cats so far.
+    MSG
+
+    it { should pass }
+  end
+
+  context 'when subject starts with punctuation and a capital letter' do
+    let(:commit_msg) { <<-MSG }
+"Initial" commit
+
+Mostly cats so far.
+    MSG
+
+    it { should pass }
+  end
+
+  context 'when subject starts with a lowercase letter' do
+    let(:commit_msg) { <<-MSG }
+initial commit
+
+I forget about commit message standards and decide to not capitalize my
+subject. Still mostly cats so far.
+    MSG
+
+    it { should warn }
+  end
+
+  context 'when subject starts with a utf-8 lowercase letter' do
+    let(:commit_msg) { <<-MSG }
+årsgång
+
+I forget about commit message standards and decide to not capitalize my
+subject. Still mostly cats so far.
+    MSG
+
+    it { should warn }
+  end
+
+  context 'when subject starts with punctuation and a lowercase letter' do
+    let(:commit_msg) { <<-MSG }
+"initial" commit
+
+I forget about commit message standards and decide to not capitalize my
+subject. Still mostly cats so far.
+    MSG
+
+    it { should warn }
+  end
+end