[feature] handle route comments on line when using read_as_line

[Tristramg]

cf. ND-1075 and replaces #736

[woshilapin]

I'm a bit annoyed that generate_route_comment() might return a Comment either with an identifier prefixed with route: or line:. Then only after in read_routes(), the code is branching on read_as_line and decide to use this comment in a line or in a route. So in terms of code architecture, it's possible to add a comment route: in a line which would be wrong. I know both actions are conditioned to read_as_line so it won't happen at the moment but since the logic is in 2 different places, future maintenance of the code might break this invariant. I'm wondering how the code could be refactored to better reflect this.

I'm not sure if I'm very clear about what I'm trying to explain, so do not hesitate to ping me in private to better explain.

[woshilapin]

Suggested change

	id: prefix.to_string() + &route.id,
	id: format!("{}:{}", prefix, route.id),

And maybe remove the : from the prefix variable.

[Tristramg]

I think I understand what annoys you, but I’m not sure how to adress it.

First, we can rename it comment_from_gtfs_route to avoid some abiguity.
Secondly, would you prefer to duplicate the call?

[woshilapin]

I think I understand what annoys you, but I’m not sure how to adress it.

First, we can rename it comment_from_gtfs_route to avoid some abiguity.
Secondly, would you prefer to duplicate the call?

I propose this PR that might address the problem. Tell me what you think about it.

[woshilapin]

Good for me. Do not hesitate to squash/rebase if needed.

[Tristramg]

I just squashed you changes. Thank you!