adding crosslist check so same time warnings doesnt come when crosslisted

backend/app/repositories/section.py

@@ -100,3 +100,19 @@ def double_booked(db: Session, assignments: list[FacultyAssignment], meeting_tim
         if section.time_block_id == meeting_time:
             return True
     return False
+
+
+def crosslist_group_section_ids(db: Session, section_id: int) -> set[int]:
+    ids: set[int] = {section_id}
+    section = get_by_id(db, section_id)
+    if section is None:
+        return ids
+
+    if section.crosslisted_section_id is not None:
+        ids.add(section.crosslisted_section_id)
+
+    reverse = db.query(Section).filter(Section.crosslisted_section_id == section_id).first()
+    if reverse is not None:
+        ids.add(reverse.section_id)
+
+    return ids

backend/app/services/section.py

@@ -318,6 +318,7 @@ def error_check(db: Session, section: Section, updates: SectionUpdate | None = N
         return []
     warnings = []
     faculty_nuids = section_repo.get_faculty_assignmnets(db, section.section_id)
+    crosslist_ids = section_repo.crosslist_group_section_ids(db, section.section_id)
 
     if section.time_block_id is not None:
         schedule = schedule_repo.get_by_id(db, section.schedule_id)
@@ -327,7 +328,7 @@ def error_check(db: Session, section: Section, updates: SectionUpdate | None = N
             warnings.append(WarningType.TIME_BLOCK_OVERLOAD)
 
     for nuid in faculty_nuids:
-        other_assignments = [a for a in faculty_repo.get_assignments(db, nuid, section.schedule_id) if a.section_id != section.section_id]
+        other_assignments = [a for a in faculty_repo.get_assignments(db, nuid, section.schedule_id) if a.section_id not in crosslist_ids]
         if section.time_block_id is not None:
             if not faculty_repo.find_meeting_time_preference(db, nuid, section.time_block_id):
                 warnings.append(WarningType.UNPREFERENCED_TIME)

backend/tests/test_section_service.py

@@ -397,6 +397,39 @@ def test_error_check_empty_faculty_nuids_no_warning(db_session):
     assert WarningType.FACULTY_OVERLOAD not in warnings
 
 
+def test_error_check_crosslisted_sections_not_double_booked(db_session):
+    campus = _make_campus(db_session)
+    semester = _make_semester(db_session)
+    schedule = _make_schedule(db_session, campus, semester)
+    course = _make_course(db_session, name="CS 2500", code=2500)
+    tb = _make_time_block(db_session, campus)
+    faculty = _make_faculty(db_session, campus, nuid=1001, email="f1@test.edu")
+
+    a = _make_section(db_session, schedule, course, tb, number=1)
+    b = _make_section(db_session, schedule, course, tb, number=2)
+    # Crosslist them as partners.
+    a.crosslisted_section_id = b.section_id
+    b.crosslisted_section_id = a.section_id
+
+    db_session.add(FacultyAssignment(faculty_nuid=faculty.nuid, section_id=a.section_id))
+    db_session.add(FacultyAssignment(faculty_nuid=faculty.nuid, section_id=b.section_id))
+    db_session.commit()
+
+    warnings_a = section_service.error_check(db_session, a, SectionUpdate(faculty_nuids=[faculty.nuid]))
+    warnings_b = section_service.error_check(db_session, b, SectionUpdate(faculty_nuids=[faculty.nuid]))
+
+    assert WarningType.FACULTY_DOUBLE_BOOKED not in warnings_a
+    assert WarningType.FACULTY_DOUBLE_BOOKED not in warnings_b
+
+    # A third, non-crosslisted section at the same time block should still trigger a real double-booking warning.
+    c = _make_section(db_session, schedule, course, tb, number=3)
+    db_session.add(FacultyAssignment(faculty_nuid=faculty.nuid, section_id=c.section_id))
+    db_session.commit()
+
+    warnings_c = section_service.error_check(db_session, c, SectionUpdate(faculty_nuids=[faculty.nuid]))
+    assert WarningType.FACULTY_DOUBLE_BOOKED in warnings_c
+
+
 # ---------------------------------------------------------------------------
 # update_section — basic behavior
 # ---------------------------------------------------------------------------