Support for GTFS Flex

[fchabouis]

I never noticed, but the GTFS Flex extension has the specificity to add a geojson file in the GTFS specification.
This is still a proposal, so there is no rush here, but I am curious to know your opinion on how difficult it would be to adapt this crate to handle this new kind of format.
Thanks!

@Tristramg @antoine-de

[Tristramg]

I don’t think it would be a big problem. We already use serde for the csv, and its json support is very good.

[lolpro11]

This would be a small update but make stops.txt optional as well to support GTFS Flex

[robfitzgerald]

Hello, I have begun working on an implementation to add this feature to gtfs-structures and wanted to gauge interest. I'm a research software engineer at NRL in Colorado, USA (formerly NREL) where I support mobility science research with our open-source route planner and access model (RouteE Compass, BAMBAM). our business case is we are developing a GTFS-Flex access model and we currently use gtfs-structures for our transit access model.

my WIP has the following objectives:

• add GTFS-Flex data models and collections under a gtfs-flex compiler flag
• no API changes for users with feature disabled
• use this examples page as the source of truth (didn't find a spec page)
• add tests using new test fixtures from Brown County Heartland Express and Otter Express feeds

my main critique of my design is that the StopTime and Gtfs types gets a bit sliced up with #[cfg(feature)] macros in a way that affects readability. this feels more complicated with StopTime which sits in the middle of other types and methods that may or may not be connected based on the compiler flag. the tradeoff being that existing users can have the same API as they do now with the feature deactivated. i think this is the best way to accomplish this, but, i would worry about how this might explode if additional gtfs extensions took a similar approach.

once i wrap up a first draft i would submit it as a draft PR. noting in the discussion above there was some buy-in from a core contributor (@Tristramg), but, that was 3 years ago, so i first want to confirm that there would be interest in this proposed change.

edit: you can see my WIP changes here