Change location and refactor issue closing pattern documentation

Split into user and administrator docs:

- administration/issue_closing_pattern.md
- user/project/issues/automatic_issue_closing.md

[ci skip]

1 files changed, 49 insertions, 0 deletions

diff --git a/doc/administration/issue_closing_pattern.md b/doc/administration/issue_closing_pattern.md
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+# Issue closing pattern
+
+>**Note:**
+This is the administration documentation.
+There is a separate [user documentation] on issue closing pattern.
+
+When a commit or merge request resolves one or more issues, it is possible to
+automatically have these issues closed when the commit or merge request lands
+in the project's default branch.
+
+## Change the issue closing pattern
+
+In order to change the pattern you need to have access to the server that GitLab
+is installed on.
+
+The default pattern can be located in [gitlab.yml.example] under the
+"Automatic issue closing" section.
+
+> **Tip:**
+You are advised to use http://rubular.com to test the issue closing pattern.
+Because Rubular doesn't understand `%{issue_ref}`, you can replace this by
+`#\d+` when testing your patterns, which matches only local issue references like `#123`.
+
+**For Omnibus installations**
+
+1. Open `/etc/gitlab/gitlab.rb` with your editor.
+1. Change the value of `gitlab_rails['issue_closing_pattern']` to a regular
+   expression of your liking:
+
+    ```ruby
+    gitlab_rails['issue_closing_pattern'] = "((?:[Cc]los(?:e[sd]|ing)|[Ff]ix(?:e[sd]|ing)?) +(?:(?:issues? +)?%{issue_ref}(?:(?:, *| +and +)?))+)"
+    ```
+1. [Reconfigure] GitLab for the changes to take effect.
+
+**For installations from source**
+
+1. Open `gitlab.yml` with your editor.
+1. Change the value of `issue_closing_pattern`:
+
+    ```yaml
+    issue_closing_pattern: "((?:[Cc]los(?:e[sd]|ing)|[Ff]ix(?:e[sd]|ing)?) +(?:(?:issues? +)?%{issue_ref}(?:(?:, *| +and +)?))+)"
+    ```
+
+1. [Restart] GitLab for the changes to take effect.
+
+[gitlab.yml.example]: https://gitlab.com/gitlab-org/gitlab-ce/blob/master/config/gitlab.yml.example
+[reconfigure]: restart_gitlab.md#omnibus-gitlab-reconfigure
+[restart]: restart_gitlab.md#installations-from-source
+[user documentation]: ../user/project/issues/automatic_issue_closing.md