onebusaway-gtfs-modules
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Merging already merged feeds may create duplicate IDs
Summary:
Trying to merge multiple regional feeds together with another, already merged feed resulted in duplicate schedule_ids for calendar.txt entries.
Steps to reproduce: Merge a feed with two schedules with IDs T0, a-T0 with another feed with another, different schedule with ID T0.
Expected behavior: Resulting feed has calendar entries with unique IDs.
Observed behavior: Resulting feed has calendar entries with duplicate IDs a-T0.
Root cause This behavior is caused by MergeSupport.renameAgencyAndId which prepends a prefix without further checking for uniqueness which might result in duplicates.
As long as no feed contains IDs starting with single letters followed by a hyphen (e.g. "a-"), this will not cause an issue. However, the documentation should describe this duplicate resolution strategy.