From 9d3344adbbfc84ef8abc96366bdfa695293cd6c0 Mon Sep 17 00:00:00 2001
From: Stan Hu <stanhu@gmail.com>
Date: Thu, 10 Sep 2015 08:23:10 -0700
Subject: Gracefully handle errors in syntax highlighting by leaving the block
 unformatted

Closes #2433
---
 CHANGELOG                                          |  1 +
 lib/gitlab/markdown/syntax_highlight_filter.rb     |  6 +++++-
 .../markdown/syntax_highlight_filter_spec.rb       | 22 ++++++++++++++++++++++
 3 files changed, 28 insertions(+), 1 deletion(-)
 create mode 100644 spec/lib/gitlab/markdown/syntax_highlight_filter_spec.rb

diff --git a/CHANGELOG b/CHANGELOG
index 36ee3e69ab3..2c135d3475c 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,6 +1,7 @@
 Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.0.0 (unreleased)
+  - Gracefully handle errors in syntax highlighting by leaving the block unformatted (Stan Hu)
   - Fix URL construction for merge requests, issues, notes, and commits for relative URL config (Stan Hu)
   - Fix emoji URLs in Markdown when relative_url_root is used (Stan Hu)
   - Omit filename in Content-Disposition header in raw file download to avoid RFC 6266 encoding issues (Stan HU)
diff --git a/lib/gitlab/markdown/syntax_highlight_filter.rb b/lib/gitlab/markdown/syntax_highlight_filter.rb
index 86f4385753a..f9527c7286e 100644
--- a/lib/gitlab/markdown/syntax_highlight_filter.rb
+++ b/lib/gitlab/markdown/syntax_highlight_filter.rb
@@ -21,7 +21,11 @@ module Gitlab
         language = node.attr('class')
         code     = node.text
 
-        highlighted = block_code(code, language)
+        begin
+          highlighted = block_code(code, language)
+        rescue
+          highlighted = "<pre>#{code}</pre>"
+        end
 
         # Replace the parent `pre` element with the entire highlighted block
         node.parent.replace(highlighted)
diff --git a/spec/lib/gitlab/markdown/syntax_highlight_filter_spec.rb b/spec/lib/gitlab/markdown/syntax_highlight_filter_spec.rb
new file mode 100644
index 00000000000..ecef31853f4
--- /dev/null
+++ b/spec/lib/gitlab/markdown/syntax_highlight_filter_spec.rb
@@ -0,0 +1,22 @@
+require 'spec_helper'
+
+module Gitlab::Markdown
+  describe SyntaxHighlightFilter do
+    include FilterSpecHelper
+
+    let(:project)   { create(:empty_project) }
+    let(:reference) { snippet.to_reference }
+
+    it 'highlights valid code blocks' do
+      result = filter('<pre><code>def fun end</code>')
+      expect(result.to_html).to eq("<pre class=\"code highlight js-syntax-highlight plaintext\"><code>def fun end</code></pre>\n")
+    end
+
+    it 'passes through invalid code blocks' do
+      allow_any_instance_of(SyntaxHighlightFilter).to receive(:block_code).and_raise(StandardError)
+
+      result = filter('<pre><code>This is a test</code></pre>')
+      expect(result.to_html).to eq('<pre>This is a test</pre>')
+    end
+  end
+end
-- 
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