Merge branch 'feature/custom-highlighting' into 'master'

Add custom highlighting via .gitattributes

## What does this MR do?
Allows user control of language selection via a `gitlab-language` entry in `.gitattributes`

## Are there points in the code the reviewer needs to double check?
(paired with @stanhu)

## Why was this MR needed?
Guessing languages by filename is fraught and often wrong. In one project, `foo.pl` may be perl, and in another it may be prolog. Users might have a Thingfile that needs ruby highlighting, or depend on things that can't work in general, like `*.C` (capitalized) mapping to C++ instead of C.

This allows the user to override language choice so they never have to look at a mis-highlighted file.

## What are the relevant issue numbers?
https://github.com/jneen/rouge/issues/494
https://gitlab.com/gitlab-org/gitlab-ce/issues/13818 (*.tpl can't in general map to Smarty)
https://gitlab.com/gitlab-org/gitlab-ce/issues/13615 (in cases we don't have a language and mis-identify it, users could map to 'text' to turn off highlighting)

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] API support added (N/A)
- [x] Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !4606

1 files changed, 6 insertions, 0 deletions

diff --git a/app/models/snippet.rb b/app/models/snippet.rb
index 51f6ae7b25c..5ec933601ac 100644
--- a/app/models/snippet.rb
+++ b/app/models/snippet.rb
@@ -20,6 +20,7 @@ class Snippet < ActiveRecord::Base
     length: { within: 0..255 },
     format: { with: Gitlab::Regex.file_name_regex,
               message: Gitlab::Regex.file_name_regex_message }
+
   validates :content, presence: true
   validates :visibility_level, inclusion: { in: Gitlab::VisibilityLevel.values }
 
@@ -81,6 +82,11 @@ class Snippet < ActiveRecord::Base
     0
   end
 
+  # alias for compatibility with blobs and highlighting
+  def path
+    file_name
+  end
+
   def name
     file_name
   end