Fix 500 error when diff context line has broken encoding

changelogs/unreleased/42332-actionview-template-error-366-524-out-of-range.yml

+---
+title: Fix 500 error being shown when diff has context marker with invalid encoding
+merge_request:
+author:
+type: fixed

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

spec/lib/gitlab/diff/highlight_spec.rb

@@ -72,6 +72,28 @@ describe Gitlab::Diff::Highlight do
         expect(subject[5].text).to eq(code)
         expect(subject[5].text).to be_html_safe
       end
+
+      context 'when the inline diff marker has an invalid range' do
+        before do
+          allow_any_instance_of(Gitlab::Diff::InlineDiffMarker).to receive(:mark).and_raise(RangeError)
+        end
+
+        it 'keeps the original rich line' do
+          code = %q{+      raise RuntimeError, "System commands must be given as an array of strings"}
+
+          expect(subject[5].text).to eq(code)
+          expect(subject[5].text).not_to be_html_safe
+        end
+
+        it 'reports to Sentry if configured' do
+          allow(Gitlab::Sentry).to receive(:enabled?).and_return(true)
+
+          expect(Gitlab::Sentry).to receive(:context)
+          expect(Raven).to receive(:capture_exception)
+
+          subject
+        end
+      end
     end
   end
 end