Fix expensive thinko: operator++ returns a reference, not a copy

This accounts for 45% of the row breaking time on the (huge) paragraph
of the MWE in bug #12598.

Fixes part of bug #12598.

diff --git a/src/TextMetrics.cpp b/src/TextMetrics.cpp
index 00fb217c0ad5628d8c628376288affe680c773e0..f58efa794beeee18760483f49f2cb402f745a4f2 100644 (file)
--- a/src/TextMetrics.cpp
+++ b/src/TextMetrics.cpp
@@ -979,7 +979,7 @@ class flexible_const_iterator {
 public:
 
        //
-       flexible_const_iterator operator++() {
+       flexible_const_iterator & operator++() {
                if (pile_.empty())
                        ++cit_;
                else