more debug message for async x requests

ping #1516

Author: yshui

src/event.c

@@ -302,13 +302,15 @@ void ev_update_focused(struct session *ps) {
 		                     ps->atoms->a_NET_ACTIVE_WINDOW, XCB_ATOM_WINDOW, 0, 1)
 		        .sequence;
 		req->base.callback = update_ewmh_active_win;
+		req->base.name = "get_property";
 		req->ps = ps;
 		x_await_request(&ps->c, &req->base);
 		log_debug("Started async request to get _NET_ACTIVE_WINDOW");
 	} else {
 		auto req = ccalloc(1, struct ev_recheck_focus_request);
 		req->base.sequence = xcb_get_input_focus(ps->c.c).sequence;
 		req->base.callback = recheck_focus;
+		req->base.name = "get_input_focus";
 		req->ps = ps;
 		x_await_request(&ps->c, &req->base);
 		log_debug("Started async request to recheck focus");

src/picom.c

@@ -1440,6 +1440,7 @@ static void handle_new_windows(session_t *ps) {
 			req->base.callback = handle_new_window_attributes_reply,
 			req->base.sequence =
 			    xcb_get_window_attributes(ps->c.c, req->id.x).sequence;
+			req->base.name = "get_window_attributes";
 			x_await_request(&ps->c, &req->base);
 			break;
 		case WM_TREE_CHANGE_TOPLEVEL_KILLED:

src/wm/win.c

@@ -2067,6 +2067,7 @@ void win_map_start(struct session *ps, struct win *w) {
 	req->base = (struct x_async_request_base){
 	    .callback = win_handle_get_geometry_reply,
 	    .sequence = xcb_get_geometry(ps->c.c, win_id(w)).sequence,
+	    .name = "get_geometry",
 	};
 	req->wid = win_id(w);
 	req->ps = ps;

src/wm/wm.c

@@ -675,6 +675,7 @@ wm_handle_set_event_mask_reply(struct x_connection *c, struct x_async_request_ba
 	{
 		auto req2 = ccalloc(1, struct wm_query_tree_request);
 		req2->base.callback = wm_handle_query_tree_reply;
+		req2->base.name = "query_tree";
 		req2->wid = node->id.x;
 		req2->wm = wm;
 		req2->atoms = atoms;
@@ -686,6 +687,7 @@ wm_handle_set_event_mask_reply(struct x_connection *c, struct x_async_request_ba
 	{
 		auto req2 = ccalloc(1, struct wm_get_property_request);
 		req2->base.callback = wm_handle_get_wm_state_reply;
+		req2->base.name = "get_property (wm)";
 		req2->wm = wm;
 		req2->wid = node->id.x;
 		x_async_get_property(c, node->id.x, atoms->aWM_STATE, XCB_ATOM_ANY, 0, 2,
@@ -713,6 +715,7 @@ static void wm_import_start_inner(struct wm *wm, struct x_connection *c, struct
 
 	auto req = ccalloc(1, struct wm_set_event_mask_request);
 	req->base.callback = wm_handle_set_event_mask_reply;
+	req->base.name = "change_window_attributes";
 	req->wid = wid;
 	req->atoms = atoms;
 	req->wm = wm;

src/x.c

@@ -3,6 +3,7 @@
 
 #include <stdalign.h>
 #include <stdbool.h>
+#include <stdint.h>
 #include <stdlib.h>
 
 #include <X11/Xlib-xcb.h>
@@ -197,6 +198,7 @@ void x_set_error_action(struct x_connection *c, uint32_t sequence, enum x_error_
 	req->base.sequence = sequence;
 	req->base.callback = x_generic_async_callback;
 	req->base.no_reply = true;
+	req->base.name = "error_action";
 	x_await_request(c, &req->base);
 }
 
@@ -1118,6 +1120,18 @@ static inline void x_ingest_event(struct x_connection *c, xcb_generic_event_t *e
 
 static const xcb_raw_generic_event_t no_reply_success = {.response_type = 1};
 
+static inline void report_has_reply_assertion_failure(struct x_async_request_base *base,
+                                                      uint64_t seq, uint64_t head_seq) {
+	log_fatal("Already received reply/error for seq %lu", seq);
+	log_fatal("Reply to seq %lu should have come before, but we don't have it", head_seq);
+	log_fatal("seq %lu is a \"%s\"", head_seq, base->name);
+	if (strcmp(base->name, "error_action") == 0) {
+		auto req = (struct x_generic_async_request *)base;
+		log_fatal("error_action previous set at %s:%d, %s", req->file, req->line,
+		          req->func);
+	}
+}
+
 /// Complete all pending async requests that "come before" the given event.
 static void x_complete_async_requests(struct x_connection *c, xcb_generic_event_t *e) {
 	auto seq = x_widen_sequence(c, e->full_sequence);
@@ -1139,6 +1153,9 @@ static void x_complete_async_requests(struct x_connection *c, xcb_generic_event_
 			xcb_generic_error_t *err = NULL;
 			auto has_reply = xcb_poll_for_reply(
 			    c->c, i->sequence, (void **)&reply_or_error, &err);
+			if (!has_reply) {
+				report_has_reply_assertion_failure(i, seq, head_seq);
+			}
 			BUG_ON(has_reply == 0);
 			if (reply_or_error == NULL) {
 				reply_or_error = (xcb_raw_generic_event_t *)err;

src/x.h

@@ -219,6 +219,7 @@ void x_set_error_action(struct x_connection *c, uint32_t sequence, enum x_error_
 
 struct x_async_request_base {
 	struct list_node siblings;
+	const char *name;
 	/// The callback function to call when the reply is received. If `reply_or_error`
 	/// is NULL, it means the X connection is closed while waiting for the reply.
 	void (*callback)(struct x_connection *, struct x_async_request_base *,