Fix invalid access when recording keys

<c-n>/<c-p> handling in insert was always dropping the last key in
the last_insert() vector (in order to replace it with the actual
completion text inserted), this was not valid for synthetized keys
that are not added to that vector in the first place.

Take the opportunity to merge insert completion handling code between
<c-n>/<c-p> and direct menu selection.

Fixes #5120

1 files changed, 7 insertions, 16 deletions

diff --git a/src/input_handler.cc b/src/input_handler.cc
index 9d81f711..5800a6a0 100644
--- a/src/input_handler.cc
+++ b/src/input_handler.cc
@@ -1191,7 +1191,7 @@ public:
         }
     }
 
-    void on_key(Key key, bool) override
+    void on_key(Key key, bool synthesized) override
     {
         auto& buffer = context().buffer();
 
@@ -1289,22 +1289,13 @@ public:
                 }, "enter register name", register_doc.str());
             update_completions = false;
         }
-        else if (key == ctrl('n'))
-        {
-            last_insert().keys.pop_back();
-            m_completer.select(1, true, last_insert().keys);
-            update_completions = false;
-        }
-        else if (key == ctrl('p'))
-        {
-            last_insert().keys.pop_back();
-            m_completer.select(-1, true, last_insert().keys);
-            update_completions = false;
-        }
-        else if (key.modifiers == Key::Modifiers::MenuSelect)
+        else if (key == ctrl('n') or key == ctrl('p') or key.modifiers == Key::Modifiers::MenuSelect)
         {
-            last_insert().keys.pop_back();
-            m_completer.select(key.key, false, last_insert().keys);
+            if (not synthesized)
+                last_insert().keys.pop_back();
+            bool relative = key.modifiers != Key::Modifiers::MenuSelect;
+            int index = relative ? (key == ctrl('n') ? 1 : -1) : key.key;
+            m_completer.select(index, relative, last_insert().keys);
             update_completions = false;
         }
         else if (key == ctrl('x'))