Merge branch '21247-mergerequestscontroller-conflicts-may-fail-with-iso-8859-data' into 'master'

Handle non-UTF-8 conflicts gracefully

## What does this MR do?

If a conflict file isn't in a UTF-8-compatible encoding, we can't resolve it in the UI.

## What are the relevant issue numbers?

Closes #21247. 

See merge request !5961

1 files changed, 9 insertions, 0 deletions

diff --git a/lib/gitlab/conflict/parser.rb b/lib/gitlab/conflict/parser.rb
index 6eccded7872..2d4d55daeeb 100644
--- a/lib/gitlab/conflict/parser.rb
+++ b/lib/gitlab/conflict/parser.rb
@@ -13,10 +13,19 @@ module Gitlab
       class UnmergeableFile < ParserError
       end
 
+      class UnsupportedEncoding < ParserError
+      end
+
       def parse(text, our_path:, their_path:, parent_file: nil)
         raise UnmergeableFile if text.blank? # Typically a binary file
         raise UnmergeableFile if text.length > 102400
 
+        begin
+          text.to_json
+        rescue Encoding::UndefinedConversionError
+          raise UnsupportedEncoding
+        end
+
         line_obj_index = 0
         line_old = 1
         line_new = 1