Steps to reproduce:

1. put this in some project's stack.yaml:

   packages:
   - '.'
   - location:
       git: git://github.com/tfausak/strive.git
       commit: cfbd995dacafb1242482c0b6ce23826fad505338
     extra-dep: true
   

2. stack build

3. change commit to c39704d5f008af42f5c3c2d5319476c7aa12e52d

4. stack build again

Expected results:

• the second stack build does just git remote update; git reset --hard

Actual results:

2016-01-07 14:06:07.661449: [debug] Run process: git clone git://github.com/tfausak/strive.git /home/tomi/src/strava-gear/.stack-work/downloaded/5727e3e6b7fab4ac5241b42c7d83482fbddc6f05b1b698540df4ab681225a8ee.git.tmp/ @(stack_1RV4odVDW2e8SkMJA1Z8Zb:System.Process.Read src/System/Process/Read.hs:255:3)
2016-01-07 14:06:13.978009: [debug] Run process: git reset --hard c39704d5f008af42f5c3c2d5319476c7aa12e52d @(stack_1RV4odVDW2e8SkMJA1Z8Zb:System.Process.Read src/System/Process/Read.hs:255:3)

This means whenever I want to update the dep, the entire git repository is cloned over the network again. That's not very good. :-(

I may use git submodules as a workaround, but it's not nice.