From e58592f00a61fe05a238bc106cd108f8a57ad291 Mon Sep 17 00:00:00 2001
From: Maxime Coste <mawww@kakoune.org>
Date: Mon, 19 Jun 2023 12:55:55 +1000
Subject: [PATCH] Fix highlighters being applied to empty display buffers

In some cases such as with folding we can end-up with regions
not having any atoms to highlight which can trigger a crash as
we assume display buffers not to be empty

Fixes #4926
---
 src/highlighters.cc                                 | 3 +++
 test/regression/4926-crash-with-fold-and-ranges/cmd | 1 +
 test/regression/4926-crash-with-fold-and-ranges/in  | 4 ++++
 test/regression/4926-crash-with-fold-and-ranges/rc  | 6 ++++++
 4 files changed, 14 insertions(+)
 create mode 100644 test/regression/4926-crash-with-fold-and-ranges/cmd
 create mode 100644 test/regression/4926-crash-with-fold-and-ranges/in
 create mode 100644 test/regression/4926-crash-with-fold-and-ranges/rc

diff --git a/src/highlighters.cc b/src/highlighters.cc
index d2daa085..ee772469 100644
--- a/src/highlighters.cc
+++ b/src/highlighters.cc
@@ -1840,6 +1840,9 @@ struct ForwardHighlighterApplier
                 cur_atom = cur_line->begin();
         }
 
+        if (region_lines.empty())
+            return;
+
         region_display.compute_range();
         highlighter.highlight(context, region_display, {begin, end});
 
diff --git a/test/regression/4926-crash-with-fold-and-ranges/cmd b/test/regression/4926-crash-with-fold-and-ranges/cmd
new file mode 100644
index 00000000..8b137891
--- /dev/null
+++ b/test/regression/4926-crash-with-fold-and-ranges/cmd
@@ -0,0 +1 @@
+
diff --git a/test/regression/4926-crash-with-fold-and-ranges/in b/test/regression/4926-crash-with-fold-and-ranges/in
new file mode 100644
index 00000000..5c93113c
--- /dev/null
+++ b/test/regression/4926-crash-with-fold-and-ranges/in
@@ -0,0 +1,4 @@
+{[foo]}
+{[bar]}
+{[baz]}
+%( )
diff --git a/test/regression/4926-crash-with-fold-and-ranges/rc b/test/regression/4926-crash-with-fold-and-ranges/rc
new file mode 100644
index 00000000..62d98e01
--- /dev/null
+++ b/test/regression/4926-crash-with-fold-and-ranges/rc
@@ -0,0 +1,6 @@
+declare-option range-specs fold %val{timestamp} 1.1,3.8|folded
+
+add-highlighter buffer/regions regions
+add-highlighter buffer/regions/curly region \{ \} regions
+add-highlighter buffer/regions/curly/brace region \[ \] fill green
+add-highlighter buffer/fold replace-ranges fold