From eb0e9831330d3b1e1d3ddb2bc789000706e6e445 Mon Sep 17 00:00:00 2001
From: Maxime Coste <mawww@kakoune.org>
Date: Fri, 3 Feb 2023 11:31:13 +1100
Subject: [PATCH] Fix DisplayLine::trim_front quadratic behaviour

Erasing fully trimmed display atoms one by one means we have to
shift all the remaining ones every time. This is wasteful and we
can just erase all the fully trimmed atom in one go.

Fixes #4797
---
 src/display_buffer.cc | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/display_buffer.cc b/src/display_buffer.cc
index 02007d8f..0fd180b6 100644
--- a/src/display_buffer.cc
+++ b/src/display_buffer.cc
@@ -252,12 +252,15 @@ bool DisplayLine::trim_from(ColumnCount first_col, ColumnCount front, ColumnCoun
         }
     }
 
+    auto front_it = it;
     while (front > 0 and it != end())
     {
         front -= it->trim_begin(front);
+        kak_assert(it->empty() or front == 0);
         if (it->empty())
-            it = m_atoms.erase(it);
+            ++it;
     }
+    m_atoms.erase(front_it, it);
 
     it = begin();
     for (; it != end() and col_count > 0; ++it)