From cb3512f01e7243919241eed80d975e1f08a0903d Mon Sep 17 00:00:00 2001
From: Maxime Coste <mawww@kakoune.org>
Date: Mon, 13 Mar 2023 22:45:19 +1100
Subject: [PATCH] Grow dual thread stack after pushing a thread on the next
 queue

The previous code was assuming it was fine to push_next without
growing, which used to be the case with the previous implementation
because we always have poped the current thread that we try to push.

However now that we use a ring-buffer, m_next_begin == m_next_end can
either mean full, or empty. We solve this by assuming it means empty
and never allowing the buffer to become full, which means we need
to grow after pushing to next if we get full.

Fixes #4859
---
 src/regex_impl.hh                                | 3 +--
 test/regression/4859-regex-invalid-behaviour/cmd | 1 +
 test/regression/4859-regex-invalid-behaviour/in  | 3 +++
 test/regression/4859-regex-invalid-behaviour/out | 1 +
 test/regression/4859-regex-invalid-behaviour/rc  | 1 +
 5 files changed, 7 insertions(+), 2 deletions(-)
 create mode 100644 test/regression/4859-regex-invalid-behaviour/cmd
 create mode 100644 test/regression/4859-regex-invalid-behaviour/in
 create mode 100644 test/regression/4859-regex-invalid-behaviour/out
 create mode 100644 test/regression/4859-regex-invalid-behaviour/rc

diff --git a/src/regex_impl.hh b/src/regex_impl.hh
index 9d1748bb..57f07c8b 100644
--- a/src/regex_impl.hh
+++ b/src/regex_impl.hh
@@ -504,7 +504,6 @@ private:
                 if (start_desc and m_threads.next_is_empty())
                     to_next_start(pos, config, *start_desc);
                 m_threads.push_next({first_inst, -1});
-                m_threads.grow_ifn(false);
             }
             m_threads.swap_next();
         }
@@ -632,7 +631,7 @@ private:
         void push_current(Thread thread) { m_data[decrement(m_current)] = thread; grow_ifn(true); }
         Thread pop_current() { return m_data[post_increment(m_current)]; }
 
-        void push_next(Thread thread) { m_data[post_increment(m_next_end)] = thread; }
+        void push_next(Thread thread) { m_data[post_increment(m_next_end)] = thread; grow_ifn(false); }
         Thread pop_next() { return m_data[decrement(m_next_end)]; }
 
         void swap_next()
diff --git a/test/regression/4859-regex-invalid-behaviour/cmd b/test/regression/4859-regex-invalid-behaviour/cmd
new file mode 100644
index 00000000..170cee79
--- /dev/null
+++ b/test/regression/4859-regex-invalid-behaviour/cmd
@@ -0,0 +1 @@
+ge<a-/><ret>d
diff --git a/test/regression/4859-regex-invalid-behaviour/in b/test/regression/4859-regex-invalid-behaviour/in
new file mode 100644
index 00000000..73573eb5
--- /dev/null
+++ b/test/regression/4859-regex-invalid-behaviour/in
@@ -0,0 +1,3 @@
+             ddddd
+             aaaaa
+             bbbbb
diff --git a/test/regression/4859-regex-invalid-behaviour/out b/test/regression/4859-regex-invalid-behaviour/out
new file mode 100644
index 00000000..df031279
--- /dev/null
+++ b/test/regression/4859-regex-invalid-behaviour/out
@@ -0,0 +1 @@
+            bbbbb
diff --git a/test/regression/4859-regex-invalid-behaviour/rc b/test/regression/4859-regex-invalid-behaviour/rc
new file mode 100644
index 00000000..fabf8e5f
--- /dev/null
+++ b/test/regression/4859-regex-invalid-behaviour/rc
@@ -0,0 +1 @@
+reg slash '(?S)((^ {13}d.*\n)(^ {13}.*\n)*?)?^.'