Fix 500 error when diff context line has broken encoding

Rugged sometimes chops a context line in between bytes, resulting in the context
line having an invalid encoding: https://github.com/libgit2/rugged/issues/716

When that happens, we will try to detect the encoding for the diff, and
sometimes we'll get it wrong. If that difference in encoding results in a
difference in string lengths between the diff and the underlying blobs, we'd
fail to highlight any inline diffs, and return a 500 status to the user.

As we're using the underlying blobs, the encoding is 'correct' anyway, so if the
string range is invalid, we can just discard the inline diff highlighting. We
still report to Sentry to ensure that we can investigate further in future.

1 files changed, 11 insertions, 1 deletions

diff --git a/lib/gitlab/diff/highlight.rb b/lib/gitlab/diff/highlight.rb
index 0f897e6316c..269016daac2 100644
--- a/lib/gitlab/diff/highlight.rb
+++ b/lib/gitlab/diff/highlight.rb
@@ -27,7 +27,17 @@ module Gitlab
           rich_line = highlight_line(diff_line) || diff_line.text
 
           if line_inline_diffs = inline_diffs[i]
-            rich_line = InlineDiffMarker.new(diff_line.text, rich_line).mark(line_inline_diffs)
+            begin
+              rich_line = InlineDiffMarker.new(diff_line.text, rich_line).mark(line_inline_diffs)
+            # This should only happen when the encoding of the diff doesn't
+            # match the blob, which is a bug. But we shouldn't fail to render
+            # completely in that case, even though we want to report the error.
+            rescue RangeError => e
+              if Gitlab::Sentry.enabled?
+                Gitlab::Sentry.context
+                Raven.capture_exception(e)
+              end
+            end
           end
 
           diff_line.text = rich_line