Log error message if duplicate file is found instead of throwing fatal error
If an attempt is made by the content classifier to add a duplicate file to the content catalog from the content aggregate, Antora will throw a fatal error. This scenario can happen if two content source roots both claim the same component version and have the same files.
The main problem with the current behavior is that it's misinterpreted by users. That's because the error message always draws attention to a duplicate nav. Rather than sending a message that two content sources are trying to contribute files with the same identity, the user thinks this is a problem specific to the nav.
FATAL (antora): Duplicate nav in 3.1@antora: modules/ROOT/nav-component-versions.adoc
1: /path/to/worktree/docs/modules/ROOT/nav-component-versions.adoc
2: docs/modules/ROOT/nav-component-versions.adoc in https://gitlab.com/antora/antora.git (refname: main-mirror, start path: docs)
If these duplicates were reported as a non-fatal log message instead, the user would see that the problem is much broader. In the event there really are genuine overlaps in a distributed component, the user would be able to see that as well.
Another idea is to log the messages, then throw a fatal error at the end if any duplicates were found. That way, the user would still see all the messages, but Antora would not continue.