[GHC] #13375: ghc-pkg "cache is out of date" message breaks testsuite

[GHC]

#13375: ghc-pkg "cache is out of date" message breaks testsuite
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        Reporter:  bgamari           |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  highest           |            Milestone:  8.2.1
       Component:  ghc-pkg           |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Other             |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D3569
       Wiki Page:                    |
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Comment (by marinelli):

 Wouldn't it be better to rebuild it? We'll certainly obtain a
 package.cache file that is consistent.

 We could use something like this after that for-loop in ghc.mk:

 {{{
 "$(INSTALLED_GHC_PKG_REAL)" --global-package-db
 "$(INSTALLED_PACKAGE_CONF)" recache
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13375#comment:14>
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