clients: Introduce xmalloc() and use it a few places

For the sample clients we introduce xmalloc() to simplify OOM-handling.
This patch only converts a few callsites, but this will be our strategy
going forward.

clients/clickdot.c

@@ -247,9 +247,7 @@ clickdot_create(struct display *display)
 {
 	struct clickdot *clickdot;
 
-	clickdot = malloc(sizeof *clickdot);
-	if (clickdot == NULL)
-		return clickdot;
+	clickdot = xmalloc(sizeof *clickdot);
 	memset(clickdot, 0, sizeof *clickdot);
 
 	clickdot->window = window_create(display);

clients/window.c

@@ -4190,10 +4190,7 @@ window_create_internal(struct display *display,
 	struct window *window;
 	struct surface *surface;
 
-	window = malloc(sizeof *window);
-	if (window == NULL)
-		return NULL;
-
+	window = xmalloc(sizeof *window);
 	memset(window, 0, sizeof *window);
 	wl_list_init(&window->subsurface_list);
 	window->display = display;
@@ -4206,6 +4203,7 @@ window_create_internal(struct display *display,
 		window->shell_surface =
 			wl_shell_get_shell_surface(display->shell,
 						   surface->surface);
+		fail_on_null(window->shell_surface);
 	}
 
 	window->type = type;
@@ -4251,13 +4249,7 @@ window_create(struct display *display)
 struct window *
 window_create_custom(struct display *display)
 {
-	struct window *window;
-
-	window = window_create_internal(display, NULL, TYPE_CUSTOM);
-	if (!window)
-		return NULL;
-
-	return window;
+	return window_create_internal(display, NULL, TYPE_CUSTOM);
 }
 
 struct window *
@@ -4268,8 +4260,6 @@ window_create_transient(struct display *display, struct window *parent,
 
 	window = window_create_internal(parent->display,
 					parent, TYPE_TRANSIENT);
-	if (!window)
-		return NULL;
 
 	window->x = x;
 	window->y = y;
@@ -5309,3 +5299,26 @@ keysym_modifiers_get_mask(struct wl_array *modifiers_map,
 
 	return 1 << index;
 }
+
+void *
+fail_on_null(void *p)
+{
+	if (p == NULL) {
+		fprintf(stderr, "wayland-scanner: out of memory\n");
+		exit(EXIT_FAILURE);
+	}
+
+	return p;
+}
+
+void *
+xmalloc(size_t s)
+{
+	return fail_on_null(malloc(s));
+}
+
+char *
+xstrdup(const char *s)
+{
+	return fail_on_null(strdup(s));
+}

clients/window.h

@@ -53,6 +53,13 @@ struct rectangle {
 	int32_t height;
 };
 
+void *
+fail_on_null(void *p);
+void *
+xmalloc(size_t s);
+char *
+xstrdup(const char *s);
+
 struct display *
 display_create(int *argc, char *argv[]);