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]

2 files changed, 56 insertions, 1 deletions

diff --git a/doc/user/project/issues/automatic_issue_closing.md b/doc/user/project/issues/automatic_issue_closing.md
new file mode 100644
index 00000000000..d6f3a7d5555
--- /dev/null
+++ b/doc/user/project/issues/automatic_issue_closing.md
@@ -0,0 +1,55 @@
+# Automatic issue closing
+
+>**Note:**
+This is the user docs. In order to change the default issue closing pattern,
+follow the steps in the [administration docs].
+
+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.
+
+If a commit message or merge request description contains a sentence matching
+a certain regular expression, all issues referenced from the matched text will
+be closed. This happens when the commit is pushed to a project's **default**
+branch, or when a commit or merge request is merged into it.
+
+## Default closing pattern value
+
+When not specified, the default issue closing pattern as shown below will be
+used:
+
+```bash
+((?:[Cc]los(?:e[sd]?|ing)|[Ff]ix(?:e[sd]|ing)?|[Rr]esolv(?:e[sd]?|ing))(:?) +(?:(?:issues? +)?%{issue_ref}(?:(?:, *| +and +)?)|([A-Z][A-Z0-9_]+-\d+))+)
+```
+
+Note that `%{issue_ref}` is a complex regular expression defined inside GitLab's
+source code that can match a reference to 1) a local issue (`#123`),
+2) a cross-project issue (`group/project#123`) or 3) a link to an issue
+(`https://gitlab.example.com/group/project/issues/123`).
+
+---
+
+This translates to the following keywords:
+
+- Close, Closes, Closed, Closing, close, closes, closed, closing
+- Fix, Fixes, Fixed, Fixing, fix, fixes, fixed, fixing
+- Resolve, Resolves, Resolved, Resolving, resolve, resolves, resolved, resolving
+
+---
+
+For example the following commit message:
+
+```
+Awesome commit message
+
+Fix #20, Fixes #21 and Closes group/otherproject#22.
+This commit is also related to #17 and fixes #18, #19
+and https://gitlab.example.com/group/otherproject/issues/23.
+```
+
+will close `#18`, `#19`, `#20`, and `#21` in the project this commit is pushed
+to, as well as `#22` and `#23` in group/otherproject. `#17` won't be closed as
+it does not match the pattern. It works with multi-line commit messages as well
+as one-liners when used with `git commit -m`.
+
+[administration docs]: ../../../administration/issue_closing_pattern.md
diff --git a/doc/user/project/repository/web_editor.md b/doc/user/project/repository/web_editor.md
index 7c041d019bb..993c6bfb7e9 100644
--- a/doc/user/project/repository/web_editor.md
+++ b/doc/user/project/repository/web_editor.md
@@ -172,4 +172,4 @@ you commit the changes you will be taken to a new merge request form.
 
 ![New file button](basicsimages/file_button.png)
 [ce-2808]: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/2808
-[issue closing pattern]: ../customization/issue_closing.md
+[issue closing pattern]: ../user/project/issues/automatic_issue_closing.md