prepare-commit-message hook (sds#520)

* Add prepare-commit-msg hook

* This commit adds the ReplaceBranch prepare-commit-msg hook, which, when
correctly configured, automatically generates a commit message template based on
the branch name.

Groups captured in the branch_pattern regex can be used in replacement_text;
see the accompanying spec for details. Also, replacement_text can be a path to
a file, whose text will be processed following the same rules.

* Address code review comments relating to concurrency
and default.yml config file

* Updating ReplaceBranch hook

* Fixing CI errors

* Hopefully fixing Appveyor windows build

* Not removing test file in Appveyor due to build errors

* Fixing replace_branch with the new
commit_message_source API

Author: dcluna

config/default.yml

@@ -1143,6 +1143,20 @@ PostRewrite:
       - 'package.json'
       - 'yarn.lock'
 
+# Hooks that run during the `prepare-commit-msg` hook.
+PrepareCommitMsg:
+  ALL:
+    requires_files: false
+    required: false
+    quiet: false
+
+  ReplaceBranch:
+    enabled: false
+    description: 'Prepends the commit message with text based on the branch name'
+    branch_pattern: '\A.*\w+[-_](\d+).*\z'
+    replacement_text: '[#\1]'
+    on_fail: warn
+
 # Hooks that run during `git push`, after remote refs have been updated but
 # before any objects have been transferred.
 PrePush:

lib/overcommit/hook/prepare_commit_msg/base.rb

@@ -0,0 +1,23 @@
+require 'forwardable'
+
+module Overcommit::Hook::PrepareCommitMsg
+  # Functionality common to all prepare-commit-msg hooks.
+  class Base < Overcommit::Hook::Base
+    extend Forwardable
+
+    def_delegators :@context,
+                   :commit_message_filename, :commit_message_source, :commit, :lock
+
+    def modify_commit_message
+      raise 'This expects a block!' unless block_given?
+      # NOTE: this assumes all the hooks of the same type share the context's
+      # memory. If that's not the case, this won't work.
+      lock.synchronize do
+        contents = File.read(commit_message_filename)
+        File.open(commit_message_filename, 'w') do |f|
+          f << (yield contents)
+        end
+      end
+    end
+  end
+end

lib/overcommit/hook/prepare_commit_msg/replace_branch.rb

@@ -0,0 +1,50 @@
+module Overcommit::Hook::PrepareCommitMsg
+  # Prepends the commit message with a message based on the branch name.
+  # It's possible to reference parts of the branch name through the captures in
+  # the `branch_pattern` regex.
+  class ReplaceBranch < Base
+    def run
+      return :pass unless !commit_message_source ||
+        commit_message_source == :commit # NOTE: avoid 'merge' and 'rebase'
+      Overcommit::Utils.log.debug(
+        "Checking if '#{Overcommit::GitRepo.current_branch}' matches #{branch_pattern}"
+      )
+      if branch_pattern.match(Overcommit::GitRepo.current_branch)
+        Overcommit::Utils.log.debug("Writing #{commit_message_filename} with #{new_template}")
+        modify_commit_message do |old_contents|
+          "#{new_template}\n#{old_contents}"
+        end
+        :pass
+      else
+        :warn
+      end
+    end
+
+    def new_template
+      @new_template ||= Overcommit::GitRepo.current_branch.gsub(branch_pattern, replacement_text)
+    end
+
+    def branch_pattern
+      @branch_pattern ||=
+        begin
+          pattern = config['branch_pattern']
+          Regexp.new((pattern || '').empty? ? '\A.*\w+[-_](\d+).*\z' : pattern)
+        end
+    end
+
+    def replacement_text
+      @replacement_text ||=
+        begin
+          if File.exist?(replacement_text_config)
+            File.read(replacement_text_config)
+          else
+            replacement_text_config
+          end
+        end
+    end
+
+    def replacement_text_config
+      @replacement_text_config ||= config['replacement_text']
+    end
+  end
+end

lib/overcommit/hook_context/prepare_commit_msg.rb

@@ -0,0 +1,32 @@
+module Overcommit::HookContext
+  # Contains helpers related to contextual information used by prepare-commit-msg
+  # hooks.
+  class PrepareCommitMsg < Base
+    # Returns the name of the file that contains the commit log message
+    def commit_message_filename
+      @args[0]
+    end
+
+    # Returns the source of the commit message, and can be: message (if a -m or
+    # -F option was given); template (if a -t option was given or the
+    # configuration option commit.template is set); merge (if the commit is a
+    # merge or a .git/MERGE_MSG file exists); squash (if a .git/SQUASH_MSG file
+    # exists); or commit, followed by a commit SHA-1 (if a -c, -C or --amend
+    # option was given)
+    def commit_message_source
+      @args[1].to_sym if @args[1]
+    end
+
+    # Returns the commit's SHA-1.
+    # If commit_message_source is :commit, it's passed through the command-line.
+    def commit_message_source_ref
+      @args[2] || `git rev-parse HEAD`
+    end
+
+    # Lock for the pre_commit_message file. Should be shared by all
+    # prepare-commit-message hooks
+    def lock
+      @lock ||= Monitor.new
+    end
+  end
+end

spec/overcommit/hook/prepare_commit_msg/base_spec.rb

@@ -0,0 +1,45 @@
+require 'spec_helper'
+require 'overcommit/hook_context/prepare_commit_msg'
+
+describe Overcommit::Hook::PrepareCommitMsg::Base do
+  let(:config)  { Overcommit::ConfigurationLoader.default_configuration }
+  let(:context) { Overcommit::HookContext::PrepareCommitMsg.new(config, [], StringIO.new) }
+  let(:printer) { double('printer') }
+
+  context 'when multiple hooks run simultaneously' do
+    let(:hook_1) { described_class.new(config, context) }
+    let(:hook_2) { described_class.new(config, context) }
+
+    let(:tempfile) { 'test-prepare-commit-msg.txt' }
+
+    let(:initial_content) { "This is a test\n" }
+
+    before do
+      File.open(tempfile, 'w') do |f|
+        f << initial_content
+      end
+    end
+
+    after do
+      File.delete(tempfile)
+    end
+
+    it 'works well with concurrency' do
+      allow(context).to receive(:commit_message_filename).and_return(tempfile)
+      allow(hook_1).to receive(:run) do
+        hook_1.modify_commit_message do |contents|
+          "alpha\n" + contents
+        end
+      end
+      allow(hook_2).to receive(:run) do
+        hook_2.modify_commit_message do |contents|
+          contents + "bravo\n"
+        end
+      end
+      Thread.new { hook_1.run }
+      Thread.new { hook_2.run }
+      Thread.list.each { |t| t.join unless t == Thread.current }
+      expect(File.read(tempfile)).to match(/alpha\n#{initial_content}bravo\n/m)
+    end
+  end
+end

spec/overcommit/hook/prepare_commit_msg/replace_branch_spec.rb

@@ -0,0 +1,67 @@
+require 'spec_helper'
+require 'overcommit/hook_context/prepare_commit_msg'
+
+describe Overcommit::Hook::PrepareCommitMsg::ReplaceBranch do
+  let(:config) { Overcommit::ConfigurationLoader.default_configuration }
+  let(:context) do
+    Overcommit::HookContext::PrepareCommitMsg.new(
+      config, [prepare_commit_message_file, 'commit'], StringIO.new
+    )
+  end
+
+  let(:prepare_commit_message_file) { 'prepare_commit_message_file.txt' }
+
+  subject(:hook) { described_class.new(config, context) }
+
+  before do
+    File.open(prepare_commit_message_file, 'w')
+    allow(Overcommit::Utils).to receive_message_chain(:log, :debug)
+    allow(Overcommit::GitRepo).to receive(:current_branch).and_return(new_head)
+  end
+
+  after do
+    File.delete(prepare_commit_message_file) unless ENV['APPVEYOR']
+  end
+
+  let(:new_head) { 'userbeforeid-12345-branch-description' }
+
+  describe '#run' do
+    context 'when the checked out branch matches the pattern' do
+      it { is_expected.to pass }
+
+      context 'template contents' do
+        subject(:template) { hook.new_template }
+
+        before do
+          hook.stub(:replacement_text).and_return('Id is: \1')
+        end
+
+        it { is_expected.to eq('Id is: 12345') }
+      end
+    end
+
+    context 'when the checked out branch does not match the pattern' do
+      let(:new_head) { "this shouldn't match the default pattern" }
+
+      it { is_expected.to warn }
+    end
+  end
+
+  describe '#replacement_text' do
+    subject(:replacement_text) { hook.replacement_text }
+    let(:replacement_template_file) { 'valid_filename.txt' }
+    let(:replacement) { 'Id is: \1' }
+
+    context 'when the replacement text points to a valid filename' do
+      before do
+        hook.stub(:replacement_text_config).and_return(replacement_template_file)
+        File.stub(:exist?).and_return(true)
+        File.stub(:read).with(replacement_template_file).and_return(replacement)
+      end
+
+      describe 'it reads it as the replacement template' do
+        it { is_expected.to eq(replacement) }
+      end
+    end
+  end
+end

spec/overcommit/hook_context/prepare_commit_msg_spec.rb

@@ -0,0 +1,24 @@
+require 'spec_helper'
+require 'overcommit/hook_context/prepare_commit_msg'
+
+describe Overcommit::HookContext::PrepareCommitMsg do
+  let(:config) { double('config') }
+  let(:args) { [commit_message_filename, commit_message_source] }
+  let(:commit_message_filename) { 'message-template.txt' }
+  let(:commit_message_source) { :file }
+  let(:commit) { 'SHA-1 here' }
+  let(:input) { double('input') }
+  let(:context) { described_class.new(config, args, input) }
+
+  describe '#commit_message_filename' do
+    subject { context.commit_message_filename }
+
+    it { should == commit_message_filename }
+  end
+
+  describe '#commit_message_source' do
+    subject { context.commit_message_source }
+
+    it { should == commit_message_source }
+  end
+end

spec/overcommit/utils_spec.rb

@@ -118,15 +118,15 @@
     subject { described_class.supported_hook_types }
 
     # rubocop:disable Metrics/LineLength
-    it { should =~ %w[commit-msg pre-commit post-checkout post-commit post-merge post-rewrite pre-push pre-rebase] }
+    it { should =~ %w[commit-msg pre-commit post-checkout post-commit post-merge post-rewrite pre-push pre-rebase prepare-commit-msg] }
     # rubocop:enable Metrics/LineLength
   end
 
   describe '.supported_hook_type_classes' do
     subject { described_class.supported_hook_type_classes }
 
     # rubocop:disable Metrics/LineLength
-    it { should =~ %w[CommitMsg PreCommit PostCheckout PostCommit PostMerge PostRewrite PrePush PreRebase] }
+    it { should =~ %w[CommitMsg PreCommit PostCheckout PostCommit PostMerge PostRewrite PrePush PreRebase PrepareCommitMsg] }
     # rubocop:enable Metrics/LineLength
   end