Ban a bunch of unsafe C functions from the codebase

List is taken from the git codebase

kitty/banned.h

@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2021 Kovid Goyal <kovid at kovidgoyal.net>
+ *
+ * Distributed under terms of the GPL3 license.
+ */
+
+#pragma once
+
+
+#define BANNED(func) sorry_##func##_is_a_banned_function
+
+#undef strcpy
+#define strcpy(x,y) BANNED(strcpy)
+#undef strcat
+#define strcat(x,y) BANNED(strcat)
+#undef strncpy
+#define strncpy(x,y,n) BANNED(strncpy)
+#undef strncat
+#define strncat(x,y,n) BANNED(strncat)
+
+#undef sprintf
+#undef vsprintf
+#ifdef HAVE_VARIADIC_MACROS
+#define sprintf(...) BANNED(sprintf)
+#define vsprintf(...) BANNED(vsprintf)
+#else
+#define sprintf(buf,fmt,arg) BANNED(sprintf)
+#define vsprintf(buf,fmt,arg) BANNED(vsprintf)
+#endif
+
+#undef gmtime
+#define gmtime(t) BANNED(gmtime)
+#undef localtime
+#define localtime(t) BANNED(localtime)
+#undef ctime
+#define ctime(t) BANNED(ctime)
+#undef ctime_r
+#define ctime_r(t, buf) BANNED(ctime_r)
+#undef asctime
+#define asctime(t) BANNED(asctime)
+#undef asctime_r
+#define asctime_r(t, buf) BANNED(asctime_r)

kitty/data-types.h

@@ -14,6 +14,7 @@
 #include <poll.h>
 #include <pthread.h>
 #include "glfw-wrapper.h"
+#include "banned.h"
 // Required minimum OpenGL version
 #define OPENGL_REQUIRED_VERSION_MAJOR 3
 #define OPENGL_REQUIRED_VERSION_MINOR 3