[GHC] #8144: Interface hashes include time stamp of included .h file when CPP is used

[GHC]

#8144: Interface hashes include time stamp of included .h file when CPP is used
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        Reporter:  nh2                           |            Owner:
            Type:  bug                           |           Status:  new
        Priority:  normal                        |        Milestone:
       Component:  Compiler                      |          Version:  7.6.3
      Resolution:                                |         Keywords:
Operating System:  Unknown/Multiple              |     Architecture:
 Type of failure:  Compile-time performance bug  |  Unknown/Multiple
       Test Case:                                |       Difficulty:
        Blocking:                                |  Unknown
                                                 |       Blocked By:
                                                 |  Related Tickets:
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Comment (by nh2):

 http://www.haskell.org/ghc/docs/7.6.3/html/libraries/ghc/HscTypes.html#t:Usage
 see

 {{{
 UsageFile { usg_file_path :: FilePath
           , usg_mtime     :: UTCTime }
 }}}

 https://github.com/ghc/ghc/blame/9082111dc/compiler/iface/MkIface.lhs#L603

 {{{
 iface_hash <- computeFingerprint ...
 }}}

 where ''computeFingerprint'' just uses the ''instance Binary Usage'', so
 the mtime goes into the fingerprint.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8144#comment:4>
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