Subtraction underflow crash calculating backwards lane count

[dmfutcher]

Hi, I ran into a crash when trying to load Edinburgh, Scotland into A/B Street:
thread 'main' panicked at 'attempt to subtract with overflow', /home/david/.cargo/git/checkouts/osm2streets-fbbbdf753e406749/a55aef7/osm2streets/src/lanes/classic.rs:110:20

Did some debugging and saw here, n = 2 and num_driving_fwd=3, which doesn't make much sense, but was causing a crash.

I added a workaround to check for situations where that subtraction would underflow and default to 0 backward lanes, diff here: main...dmfutcher:osm2streets:fix-lanes-calculation-crash. This works and I successfully loaded Edinburgh, but I'm not sure if that's the "correct" way to fix it. I'd be happy to hack on this and submit a PR if you could give me some guidance on the correct way to handle this situation (I found this software looking for something to hack on for Hacktoberfest).

You can repro using this GeoJSON: https://gist.github.com/dmfutcher/2b906f1b2b953a62ea1da8b361ab2fed

[dabreegster]

Your fix looks good, please do send a PR! But also, could you print the osm id of the offending road? We should fix the data there too, something seems very wrong

…

On Sat, Oct 15, 2022, 6:01 PM David Futcher ***@***.***> wrote: Hi, I ran into a crash when trying to load Edinburgh, Scotland into A/B Street: thread 'main' panicked at 'attempt to subtract with overflow', /home/david/.cargo/git/checkouts/osm2streets-fbbbdf753e406749/a55aef7/osm2streets/src/lanes/classic.rs:110 :20 Did some debugging and saw here <https://github.com/a-b-street/osm2streets/blob/main/osm2streets/src/lanes/classic.rs#L110>, n = 2 and num_driving_fwd=3, which doesn't make much sense, but was causing a crash. I added a workaround to check for situations where that subtraction would underflow and default to 0 backward lanes, diff here: main...dmfutcher:osm2streets:fix-lanes-calculation-crash <main...dmfutcher:osm2streets:fix-lanes-calculation-crash> but wasn't sure if that's the "correct" way to fix it. I'd be happy to hack on this and submit a PR if you could give me some guidance on the correct way to handle this situation (I found this software looking for something to hack on for Hacktoberfest). You can repro using this GeoJSON: https://gist.github.com/dmfutcher/2b906f1b2b953a62ea1da8b361ab2fed — Reply to this email directly, view it on GitHub <#102>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAMWLF5E6RAEKCOR4HIHF73WDLPQHANCNFSM6AAAAAARF7NVFA> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[dmfutcher]

PR submitted. I found and fixed the issue in the OSM data (way 413519168).

[dabreegster]

Edinburgh looks alright after this fix! It's a huge area and slow to import / use, of course. The missing ocean is a-b-street/abstreet#32. If you hit more problems or get interested in working on anything, let me know -- thanks for trying stuff out and sending a fix!