When the error_on_name_conflict option was introduced, the compiler produced one output file per message name, regardless of the message's namespace. So foo.Message1 and bar.Message1 would both yield a file named message1.js, and the compiler would overwrite this file and only keep the last generated file. The error_on_name_conflict option was added to allow a compile time check for duplicate file names instead of the compiler silently overwriting files.
When the
error_on_name_conflictoption was introduced, the compiler produced one output file per message name, regardless of the message's namespace. Sofoo.Message1andbar.Message1would both yield a file namedmessage1.js, and the compiler would overwrite this file and only keep the last generated file. Theerror_on_name_conflictoption was added to allow a compile time check for duplicate file names instead of the compiler silently overwriting files.This "last output file wins" behavior was removed in https://github.com/protocolbuffers/protobuf/commit/0894e07536af88065d462cdc9d8e807c0723ef4d (see js_generator.cc). Now, instead of overwriting existing files, the compiler will prefix otherwise duplicate filenames with the message namespace, ensuring unique file names.
Since this option is now a no-op, it should be removed.