Cart editing

If we make a new superTrack and move an existing track into it, then we have a problem with old sessions, ones that predate this change:

• If you load an old saved session with a certain track on and it was saved before the superTrack-move, then the track disappears. There is no error at all.

This is because the superTrack is not set to "show" in the old cart. Cart editing with "cartVersion" solves this. Cart editing consists of two parts:

• A version number for trackDb, always written into all saved carts, so we can distinguish old from new carts.
• A piece of C code that adds a new cart variable, always when a cart that is loaded, anytime or anywhere from any CGI and that cart is is older than the current trackDb. It's called from cart.c

 ~/kent/src/hg/lib/cartRewrite.c

• hg.conf statement to turn on cartVersion edits

Process:

1. QA makes list of tracks to change and supertrack names
2. QA creates a session with each track on
3. QA adds those tracks to a new supertrack in trackDb
   • Add release tags to keep any changes from sneaking out to the RR
   • Do NOT add the cartVersion N line to the supertrack as it will cause errors if added before the code changes are added!
4. Engineer adds code to cartRewrite.c
5. Engineer adds the cartVersion N line to each new supertrack
6. QA checks their old session to validate engineer's change worked

Then wait until the code goes out the normal way to the RR. After the release, any time, you can do these two things:

1. increase the version number in the top-level trackDb.ra file for that track, at the top
2. add the superTrack and move the old track into it

See ticket:

https://redmine.soe.ucsc.edu/issues/26719

See slideshow:

http://genomewiki.ucsc.edu/images/9/99/CartVersion_and_cartRewrite.c.pdf