github-commit-link: Add support for repo@<SHA> and user/repo@<SHA>

Based on similar parsing in github-issue-link.coffee.  The main change
in the logic is that the initial .* is now the non-greedy .*?, so it
doesn't gobble up the repo-part of the regexp [1].  The user/repo
portion is [^\s@]+, which matches one or more characters that are
neither whitespace [2] nor @.

The non-capturing (?:...) block [3] around the optional repo@ or
user/repo@ qualifier allows us to group the qualifier with its @, even
though we only need the repo or user/repo (without the @) in our
internal logic.

I use CoffeeScript's block regular expressions to comment the regexp
[4], and CoffeeScript's existential operator '?' to check if
'msg.match[1]' is defined [5].

I also document the fact that lines matching 'commit/' are ignored.

[1]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions#special-questionmark
[2]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions#special-white-space
[3]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions#special-non-capturing-parentheses
[4]: http://coffeescript.org/#regexes
[5]: http://coffeescript.org/#operators

Author: wking

src/scripts/github-commit-link.coffee

@@ -8,6 +8,8 @@
 # Configuration:
 #   HUBOT_GITHUB_REPO
 #     The `user/repository` that you want to connect to. example: github/hubot-scripts
+#   HUBOT_GITHUB_USER
+#     The `user` that you want to connect to. example: github
 #   HUBOT_GITHUB_TOKEN
 #     You can retrieve your github token via:
 #       curl -i https://api.github.com/authorizations -d '{"scopes":["repo"]}' -u "yourusername"
@@ -21,18 +23,33 @@
 #     http[s]://yourdomain.com/api/v3/ for Enterprise installations.
 #
 # Commands:
-#   Listens for <SHA> and links to the commit for your default repo on github
+#   Listens for <SHA>s with at least seven characters:
+#     <SHA>            links to that commit in HUBOT_GITHUB_REPO
+#     repo@<SHA>       links to that commit in HUBOT_GITHUB_USER's repo
+#     user/repo@<SHA>  links to that commit in user/repo
+#   Unless the string 'commit/' shows up in the line, in which case it
+#   is ignored.
 #
 # Author:
 #   achiu
 
 module.exports = (robot) ->
   github = require("githubot")(robot)
-  robot.hear /.*(\b[0-9a-f]{7,40}\b).*/i, (msg) ->
+  robot.hear ///
+      ^.*?              # non-greedy pre-commit-reference text
+      \b                # word boundary before the commit reference
+      (?:([^\s@]+)@)?   # optional repo@ or user/repo@ qualifier
+      ([0-9a-f]{7,40})  # commit hash (>= 7 and <= 40 hex digits long)
+      \b                # word boundary after the commit reference
+      .*$               # post-commit-reference text
+      ///i, (msg) ->
     if process.env.HUBOT_GITHUB_REPO && process.env.HUBOT_GITHUB_TOKEN
       if !(msg.message.text.match(/commit\//))
-        commit_sha = msg.match[1].replace /\b/, ""
-        bot_github_repo = github.qualified_repo process.env.HUBOT_GITHUB_REPO
+        commit_sha = msg.match[2]
+        if msg.match[1]?
+          bot_github_repo = github.qualified_repo msg.match[1]
+        else
+          bot_github_repo = github.qualified_repo process.env.HUBOT_GITHUB_REPO
         issue_title = ""
         base_url = process.env.HUBOT_GITHUB_API || 'https://api.github.com'
         github.get "#{base_url}/repos/#{bot_github_repo}/commits/" + commit_sha, (commit_obj) ->