chore(changelog): add commit-msg hook to verify commit messages

This adds a Git commit-msg hook which runs after a commit message is
written. It verifies that is matches a certain spec as defined by the
AngularJS document here:
https://docs.google.com/document/d/1QrDFcIiPjSLDn3EL15IJygNPiHORgU1_OOAqWjiDU5Y/edit#
This will allow for autmoated generation of Changelog.md in the future.

Migration notes: Please run `ln -sf ../../validate-commit-msg.js
.git/hooks/commit-msg` to install the commit hook.

validate-commit-msg.js

@@ -0,0 +1,107 @@
+#!/usr/bin/env node
+
+/**
+ * Git COMMIT-MSG hook for validating commit message
+ * From: https://github.com/angular/angular.js
+ * See https://docs.google.com/document/d/1rk04jEuGfk9kYzfqCuOlPTSJw3hEDZJTBN5E5f1SALo/edit
+ *
+ * Installation:
+ * >> cd <angular-repo>
+ * >> ln -s ../../validate-commit-msg.js .git/hooks/commit-msg
+ */
+var fs = require('fs');
+var util = require('util');
+
+
+var MAX_LENGTH = 100;
+var PATTERN = /^(?:fixup!\s*)?(\w*)(\(([\w\$\.\-\*/]*)\))?\: (.*)$/;
+var IGNORED = /^WIP\:/;
+var TYPES = {
+  feat: true,
+  fix: true,
+  docs: true,
+  style: true,
+  refactor: true,
+  perf: true,
+  test: true,
+  chore: true,
+  revert: true
+};
+
+
+var error = function() {
+  // gitx does not display it
+  // http://gitx.lighthouseapp.com/projects/17830/tickets/294-feature-display-hook-error-message-when-hook-fails
+  // https://groups.google.com/group/gitx/browse_thread/thread/a03bcab60844b812
+  console.error('INVALID COMMIT MSG: ' + util.format.apply(null, arguments));
+};
+
+
+var validateMessage = function(message) {
+  var isValid = true;
+
+  if (IGNORED.test(message)) {
+    console.log('Commit message validation ignored.');
+    return true;
+  }
+
+  if (message.length > MAX_LENGTH) {
+    error('is longer than %d characters !', MAX_LENGTH);
+    isValid = false;
+  }
+
+  var match = PATTERN.exec(message);
+
+  if (!match) {
+    error('does not match "<type>(<scope>): <subject>" ! was: ' + message);
+    return false;
+  }
+
+  var type = match[1];
+  var scope = match[3];
+  var subject = match[4];
+
+  if (!TYPES.hasOwnProperty(type)) {
+    error('"%s" is not allowed type !', type);
+    return false;
+  }
+
+  // Some more ideas, do want anything like this ?
+  // - allow only specific scopes (eg. fix(docs) should not be allowed ?
+  // - auto correct the type to lower case ?
+  // - auto correct first letter of the subject to lower case ?
+  // - auto add empty line after subject ?
+  // - auto remove empty () ?
+  // - auto correct typos in type ?
+  // - store incorrect messages, so that we can learn
+
+  return isValid;
+};
+
+
+var firstLineFromBuffer = function(buffer) {
+  return buffer.toString().split('\n').shift();
+};
+
+
+
+// publish for testing
+exports.validateMessage = validateMessage;
+
+// hacky start if not run by jasmine :-D
+if (process.argv.join('').indexOf('jasmine-node') === -1) {
+  var commitMsgFile = process.argv[2];
+  var incorrectLogFile = commitMsgFile.replace('COMMIT_EDITMSG', 'logs/incorrect-commit-msgs');
+
+  fs.readFile(commitMsgFile, function(err, buffer) {
+    var msg = firstLineFromBuffer(buffer);
+
+    if (!validateMessage(msg)) {
+      fs.appendFile(incorrectLogFile, msg + '\n', function() {
+        process.exit(1);
+      });
+    } else {
+      process.exit(0);
+    }
+  });
+}