[GHC] #8983: sync-all get should respect branches

[GHC]

#8983: sync-all get should respect branches
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       Reporter:  ezyang            |             Owner:
           Type:  bug               |            Status:  new
       Priority:  low               |         Milestone:
      Component:  Build System      |           Version:  7.9
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
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 If I have ghc-7.8 checked out and I do a './sync-all get', I might expect
 the repositories that are retrieved would also be set for ghc-7.8.
 However, this does not currently appear to be the case.

 This may be a little trickier, since if you're on a topic branch but you
 are mostly based off of master, then 'sync-all get' will fail, since the
 topic branch in question won't exist. So we should probably fall back in
 some way, rather than fail if the specified branch is not available.

 At the very least, we should print a warning if we sync-all get, the main
 branch is not master but we checked out a copy of master in the subrepo.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8983>
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