Instruction for fork with exit should be handled like ramps

[daniel-j-h]

When type is fork and we do have exit information available, what we generate is the following:

which does not include the exits 9B; 9C at all and mentions that this is a fork.

Instead what we should do is:

• handle forks with exit information like ramps
• compile the exit information into the instruction

cc @1ec5 @willwhite @freenerd @bsudekum

[freenerd]

@daniel-j-h Can you share the location of the maneuver?

To clarify: This will become a Take the exit 9B towards I 880 North, right? LGTM.

[daniel-j-h]

The motorway junction we re-write the ref tag from is here.

[daniel-j-h]

Found some junction:ref sub-exits we classify as forks in the open before re-writing:

http://overpass-turbo.eu/s/qsP

http://map.project-osrm.org/?z=17&center=37.259482%2C-121.857879&loc=37.264106%2C-121.859118&loc=37.255798%2C-121.867025&hl=en&alt=0

Should be:

Take the exit 1B towards SR 85 North

instead of

Keep right at the fork towards SR 85 North

[1ec5]

Unless #127 is fixed first, I think fixing this issue could exacerbate #127 for routes like the one in Project-OSRM/osrm-backend#4295 (comment) (OSRM frontend). Instead of:

1. Take exit 1B on the left towards I 71 North
2. Keep right at the fork towards I 71 North
3. Keep right at the fork towards 2nd Street

you’d get:

1. Take exit 1B on the left towards I 71 North
2. Take exit 1B towards I 71 North (should be exit 1A, but now the user will think it’s 1B)
3. Keep right at the fork towards 2nd Street

[daniel-j-h]

Urgh. It's even worse than that: the tagging here is ref=1A; 1B + ref:left=1A + ref:right=1B. We only re-write the ref= tag so both adjacent ways splitting off there will get exits: 1A; 1B in the response. We should fix this asap mapbox/osrm-tag-rewriter#10.

[daniel-j-h]

Update here: re-writer got a fix to never re-write if there's a :left or :right ref tag present.