Build with ASAN on macOS by default.

Makefile.am

@@ -43,7 +43,8 @@ AM_CPPFLAGS += -DDEBUG
 endif
 AM_CPPFLAGS += -iquote.
 if IS_ASAN
-AM_CFLAGS += -fsanitize=address
+AM_CPPFLAGS += -DASAN
+AM_CFLAGS += -fsanitize=address -fno-omit-frame-pointer
 AM_LDFLAGS += -fsanitize=address
 endif
 endif

configure.ac

@@ -78,7 +78,7 @@ AC_ARG_ENABLE(
 	asan,
 	AS_HELP_STRING(--enable-asan, enable ASAN build flags),
 	,
-	enable_asan=no
+	[case "x$host_os" in *darwin*) enable_asan=yes;; esac]
 )
 AM_CONDITIONAL(IS_ASAN, test "x$enable_asan" = xyes)
 

grid.c

@@ -366,6 +366,9 @@ grid_create(u_int sx, u_int sy, u_int hlimit)
 	if (gd->sy != 0)
 		gd->linedata = xcalloc(gd->sy, sizeof *gd->linedata);
 
+#ifdef __APPLE__
+	assert(gd->hsize == 0);
+#endif
 	grid_check_is_clear(gd);
 	return (gd);
 }

tmux.c

@@ -49,6 +49,24 @@ static char		*make_label(const char *, char **);
 static int		 areshell(const char *);
 static const char	*getshell(void);
 
+#ifdef ASAN
+__attribute__((used)) const char *__asan_default_options(void);
+__attribute__((used)) const char *
+__asan_default_options(void)
+{
+	return (
+	    "abort_on_error=1:"
+	    "halt_on_error=1:"
+	    "detect_leaks=0:"
+	    "detect_stack_use_after_return=1:"
+	    "strict_string_checks=1:"
+	    "check_initialization_order=1:"
+	    "log_path=/tmp/tmux-asan:"
+	    "log_exe_name=1"
+	);
+}
+#endif
+
 static __dead void
 usage(int status)
 {