The repetition is not what I was speaking of. As you say, including the same file name N times with successive line numbers just because you've localized the e

The repetition is not what I was speaking of. As you say, including the same file name N times with successive line numbers just because you've localized the error somewhere in that span means a bunch of noise. But where you are going to include a file location (and one is included), put it at the beginning of the line, to be friendly to existing to existing tooling. Putting the "-->" in front of the location is not what makes this format more readable. (Including multiple locations is great where they are actually distinct locations.)