wallet: change _requests_addr_to_key map to multi-map

I find this easier to reason about than occasionally overwriting the items.
get_request_by_addr still only returns a single invoice for simplicity,
but now all logic regarding how to handle collisions is inside that method.

electrum/wallet.py

@@ -1058,14 +1058,10 @@ class Abstract_Wallet(ABC, Logger, EventListener):
     def _init_requests_rhash_index(self):
         # self._requests_addr_to_key may contain addresses that can be reused
         # this is checked in get_request_by_address
-        self._requests_addr_to_key = {}
+        self._requests_addr_to_key = defaultdict(set)  # type: Dict[str, Set[str]]
         for req in self._receive_requests.values():
-            if req.is_lightning() and (addr:=req.get_address()):
-                # give priority to not-yet-expired requests, to postpone reusing the address
-                # FIXME maybe self._receive_requests should be a multi-map instead
-                if req.has_expired() and addr in self._requests_addr_to_key:
-                    continue
-                self._requests_addr_to_key[addr] = req.get_id()
+            if addr := req.get_address():
+                self._requests_addr_to_key[addr].add(req.get_id())
 
     def _prepare_onchain_invoice_paid_detection(self):
         self._invoices_from_txid_map = defaultdict(set)  # type: Dict[str, Set[str]]
@@ -2367,18 +2363,27 @@ class Abstract_Wallet(ABC, Logger, EventListener):
         return self.check_expired_status(invoice, status)
 
     def get_request_by_addr(self, addr: str) -> Optional[Invoice]:
-        """
-        Called in get_label_for_address and update_invoices_and_req_touched_by_tx
+        """Returns a relevant request for address, from an on-chain PoV.
+        (One that has been paid on-chain or is pending)
+
+        Called in get_label_for_address and update_invoices_and_reqs_touched_by_tx
         Returns None if the address can be reused (i.e. was paid by lightning or has expired)
         """
-        key = self._requests_addr_to_key.get(addr)
-        req = self._receive_requests.get(key)
-        if req is None:
+        keys = self._requests_addr_to_key.get(addr) or []
+        reqs = [self._receive_requests.get(key) for key in keys]
+        reqs = [req for req in reqs if req]  # filter None
+        if not reqs:
             return
-        status = self.get_invoice_status(req)
-        if (status == PR_PAID and not self.adb.is_used(addr)) or (status == PR_EXPIRED):
+        # filter out expired
+        reqs = [req for req in reqs if self.get_invoice_status(req) != PR_EXPIRED]
+        # filter out paid-with-lightning
+        if self.lnworker:
+            reqs = [req for req in reqs
+                    if not req.is_lightning() or self.lnworker.get_invoice_status(req) == PR_UNPAID]
+        if not reqs:
             return None
-        return req
+        # note: there typically should not be more than one relevant request for an address
+        return reqs[0]
 
     def get_request(self, request_id: str) -> Optional[Invoice]:
         return self._receive_requests.get(request_id)
@@ -2510,8 +2515,7 @@ class Abstract_Wallet(ABC, Logger, EventListener):
         request_id = req.get_id()
         self._receive_requests[request_id] = req
         if addr:=req.get_address():
-            # may overwrite expired or ln-paid request
-            self._requests_addr_to_key[addr] = request_id
+            self._requests_addr_to_key[addr].add(request_id)
         if write_to_disk:
             self.save_db()
         return request_id
@@ -2523,8 +2527,7 @@ class Abstract_Wallet(ABC, Logger, EventListener):
             return
         self._receive_requests.pop(request_id, None)
         if addr:=req.get_address():
-            if self._requests_addr_to_key.get(addr) == request_id:
-                self._requests_addr_to_key.pop(addr)
+            self._requests_addr_to_key[addr].discard(request_id)
         if req.is_lightning() and self.lnworker:
             self.lnworker.delete_payment_info(req.rhash)
         if write_to_disk: