Add support for post-rewrite hooks

Add the PostRewrite hook context and base hook so that post-rewrite
hooks can be written.

We've purposely not implemented the reading of the lines passed to
STDIN, as it's not clear what kind of API would be useful here. Since
the only use of this right now is as a trigger for re-indexing tags,
we'll pass on implementing reading STDIN until a use case arises.

Change-Id: I6047c820e5f792d1bab5ef56971f9403e3cf022e
Reviewed-on: http://gerrit.causes.com/46988
Tested-by: jenkins <jenkins@brigade.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>

Author: sds

CHANGELOG.md

@@ -10,7 +10,7 @@
   `required_executable` option on the JsHint and Jscs pre-commit hooks
 * Add pre-commit hooks for [standard](https://github.com/feross/standard) and
   [semistandard](https://github.com/Flet/semistandard) JavaScript linters
-* Add support for `post-commit` and `post-merge` hooks
+* Add support for `post-commit`, `post-merge`, and `post-rewrite` hooks
 * Add `GitGuilt` `post-commit` hook to display changes in blame ownership for
   modified files
 * Change behavior of configuration options containing array values to always

config/default.yml

@@ -306,3 +306,9 @@ PostCommit:
     required_executable: 'git-guilt'
     flags: ['HEAD~', 'HEAD']
     install_command: 'npm install -g git-guilt'
+
+# Hooks that run every time a commit is modified by an amend or rebase.
+PostRewrite:
+  ALL:
+    requires_files: false
+    quiet: false

lib/overcommit/hook/post-rewrite/base.rb

@@ -0,0 +1,10 @@
+require 'forwardable'
+
+module Overcommit::Hook::PostRewrite
+  # Functionality common to all post-rewrite hooks.
+  class Base < Overcommit::Hook::Base
+    extend Forwardable
+
+    def_delegators :@context, :amend?, :rebase?
+  end
+end

lib/overcommit/hook_context/post_rewrite.rb

@@ -0,0 +1,18 @@
+module Overcommit::HookContext
+  # Contains helpers for contextual information used by post-rewrite hooks.
+  class PostRewrite < Base
+    # Returns whether this post-rewrite was triggered by `git commit --amend`.
+    #
+    # @return [true,false]
+    def amend?
+      @args[0] == 'amend'
+    end
+
+    # Returns whether this post-rewrite was triggered by `git rebase`.
+    #
+    # @return [true,false]
+    def rebase?
+      @args[0] == 'rebase'
+    end
+  end
+end

spec/overcommit/hook_context/post_rewrite_spec.rb

@@ -0,0 +1,39 @@
+require 'spec_helper'
+require 'overcommit/hook_context/post_rewrite'
+
+describe Overcommit::HookContext::PostRewrite do
+  let(:config) { double('config') }
+  let(:context) { described_class.new(config, args) }
+
+  describe '#amend?' do
+    subject { context.amend? }
+
+    context 'when rewrite was triggered by amend' do
+      let(:args) { ['amend'] }
+
+      it { should == true }
+    end
+
+    context 'when rewrite was triggered by rebase' do
+      let(:args) { ['rebase'] }
+
+      it { should == false }
+    end
+  end
+
+  describe '#rebase?' do
+    subject { context.rebase? }
+
+    context 'when rewrite was triggered by amend' do
+      let(:args) { ['amend'] }
+
+      it { should == false }
+    end
+
+    context 'when rewrite was triggered by rebase' do
+      let(:args) { ['rebase'] }
+
+      it { should == true }
+    end
+  end
+end

spec/overcommit/utils_spec.rb

@@ -108,13 +108,13 @@
   describe '.supported_hook_types' do
     subject { described_class.supported_hook_types }
 
-    it { should =~ %w[commit-msg pre-commit post-checkout post-commit post-merge] }
+    it { should =~ %w[commit-msg pre-commit post-checkout post-commit post-merge post-rewrite] }
   end
 
   describe '.supported_hook_type_classes' do
     subject { described_class.supported_hook_type_classes }
 
-    it { should =~ %w[CommitMsg PreCommit PostCheckout PostCommit PostMerge] }
+    it { should =~ %w[CommitMsg PreCommit PostCheckout PostCommit PostMerge PostRewrite] }
   end
 
   describe '.execute' do

template-dir/hooks/post-rewrite

@@ -0,0 +1 @@
+overcommit-hook