From 43a5c8768263a63febe0653ff4aac395c2adbefe Mon Sep 17 00:00:00 2001
From: Benno Schulenberg <bensberg@telfort.nl>
Date: Sun, 16 Jul 2017 13:14:16 +0200
Subject: [PATCH] suspension: prevent entering an invalid byte upon resume
 (with S-Lang)

For some reason, when returning from suspension, SLang will produce
either a clipped error code (0xFF instead of 0xFFFF, when returning
from an externally induced suspension), or it will clip the code of
first subsequent keystroke to a single byte (when returning from a
normal, in-editor suspension: ^Z).

Side-step this by ignoring the clipped error code, and by using an
undefined control code as the first fake keystroke.  Ignoring the
clipped error code is not possible when using a single-byte locale,
otherwise the user would not be able to type the character with
code 0xFF (although it could still be entered with Esc Esc 255).

This fixes https://savannah.gnu.org/bugs/?51477.
---
 src/nano.c  | 2 +-
 src/nano.h  | 9 +++++++++
 src/winio.c | 5 ++++-
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/src/nano.c b/src/nano.c
index 25601058..b82245a5 100644
--- a/src/nano.c
+++ b/src/nano.c
@@ -1288,7 +1288,7 @@ RETSIGTYPE do_continue(int signal)
     terminal_init();
 #endif
     /* Tickle the input routine so it will update the screen. */
-    ungetch(KEY_F0);
+    ungetch(KEY_FLUSH);
 }
 
 #ifndef NANO_TINY
diff --git a/src/nano.h b/src/nano.h
index 2c1aef2a..c6ea016d 100644
--- a/src/nano.h
+++ b/src/nano.h
@@ -576,6 +576,15 @@ enum
 #define SHIFT_HOME 0x40f
 #define SHIFT_END 0x410
 
+#ifdef USE_SLANG
+#ifdef ENABLE_UTF8
+#define KEY_BAD 0xFF  /* Clipped error code. */
+#endif
+#define KEY_FLUSH 0x91  /* User-definable control code. */
+#else
+#define KEY_FLUSH KEY_F0  /* Nonexistent function key. */
+#endif
+
 #ifndef NANO_TINY
 /* An imaginary key for when we get a SIGWINCH (window resize). */
 #define KEY_WINCH -2
diff --git a/src/winio.c b/src/winio.c
index fc058ac0..d9bde426 100644
--- a/src/winio.c
+++ b/src/winio.c
@@ -704,7 +704,10 @@ int parse_kbinput(WINDOW *win)
 	/* Slang and SunOS 5.7-5.9 don't support KEY_RESIZE. */
 	case KEY_RESIZE:
 #endif
-	case KEY_F0:
+#if defined(USE_SLANG) && defined(ENABLE_UTF8)
+	case KEY_BAD:
+#endif
+	case KEY_FLUSH:
 	    return ERR;
     }