always output the code/name part of the html entities if the placehol…

…ders are exhausted.

services/gitdiff/highlightdiff.go

@@ -169,7 +169,8 @@ func (hcd *highlightCodeDiff) convertToPlaceholders(htmlCode string) string {
 			hcd.placeholderOverflowCount++
 			if strings.HasPrefix(token, "&") {
 				// when the token is a html entity, something must be outputted even if there is no placeholder.
-				res.WriteRune(0xFFFD) // replacement character TODO: how to handle this case more gracefully?
+				res.WriteRune(0xFFFD)      // replacement character TODO: how to handle this case more gracefully?
+				res.WriteString(token[1:]) // still output the entity code part, otherwise there will be no diff result.
 			}
 		}
 	}

services/gitdiff/highlightdiff_test.go

@@ -63,7 +63,22 @@ func TestDiffWithHighlightPlaceholderExhausted(t *testing.T) {
 		``,
 	)
 	output := diffToHTML(nil, diffs, DiffLineDel)
-	expected := fmt.Sprintf(`<span class="removed-code">%s</span>`, "\uFFFD")
+	expected := fmt.Sprintf(`<span class="removed-code">%s#39;</span>`, "\uFFFD")
+	assert.Equal(t, expected, output)
+
+	hcd = newHighlightCodeDiff()
+	hcd.placeholderMaxCount = 0
+	diffs = hcd.diffWithHighlight(
+		"main.js", "",
+		"a < b",
+		"a > b",
+	)
+	output = diffToHTML(nil, diffs, DiffLineDel)
+	expected = fmt.Sprintf(`a %s<span class="removed-code">l</span>t; b`, "\uFFFD")
+	assert.Equal(t, expected, output)
+
+	output = diffToHTML(nil, diffs, DiffLineAdd)
+	expected = fmt.Sprintf(`a %s<span class="added-code">g</span>t; b`, "\uFFFD")
 	assert.Equal(t, expected, output)
 }