feat: SetChatMemberTag

messages.editChatParticipantRank sets a custom tag/rank on any supergroup or
channel member (the dedicated rank RPC, no admin-rights round-trip). Mapping
confirmed against telegram-bot-api 10.1. Hermetic test; lint clean.

Author: ernado

chat_admin_methods_test.go

@@ -183,3 +183,24 @@ func TestSetChatAdministratorCustomTitle(t *testing.T) {
 		t.Fatalf("rank = %q", req.Rank)
 	}
 }
+
+func TestSetChatMemberTag(t *testing.T) {
+	inv := newMockInvoker()
+	inv.reply(tg.MessagesEditChatParticipantRankRequestTypeID, okUpdates())
+
+	if err := newMockBot(inv).SetChatMemberTag(context.Background(), tdlibChannel(50), 60, "VIP"); err != nil {
+		t.Fatalf("SetChatMemberTag: %v", err)
+	}
+
+	var req tg.MessagesEditChatParticipantRankRequest
+
+	inv.decode(t, tg.MessagesEditChatParticipantRankRequestTypeID, &req)
+
+	if req.Rank != "VIP" {
+		t.Fatalf("rank = %q", req.Rank)
+	}
+
+	if _, ok := req.Participant.(*tg.InputPeerUser); !ok {
+		t.Fatalf("participant = %#v, want user", req.Participant)
+	}
+}

chat_member_methods.go

@@ -297,3 +297,28 @@ func (b *Bot) SetChatAdministratorCustomTitle(ctx context.Context, chat ChatID,
 
 	return nil
 }
+
+// SetChatMemberTag sets a custom tag (rank) for a member of a supergroup or
+// channel. An empty tag removes it. The bot must be an administrator with the
+// appropriate rights.
+func (b *Bot) SetChatMemberTag(ctx context.Context, chat ChatID, userID int64, tag string) error {
+	peer, err := b.resolveInputPeer(ctx, chat)
+	if err != nil {
+		return err
+	}
+
+	user, err := b.resolveInputUser(ctx, userID)
+	if err != nil {
+		return err
+	}
+
+	if _, err := b.raw.MessagesEditChatParticipantRank(ctx, &tg.MessagesEditChatParticipantRankRequest{
+		Peer:        peer,
+		Participant: userToInputPeer(user),
+		Rank:        tag,
+	}); err != nil {
+		return asAPIError(err)
+	}
+
+	return nil
+}