[GHC] #4955: increase error message detail for module lookups failure due to hi references

[GHC]

#4955: increase error message detail for module lookups failure due to hi
references
---------------------------------+------------------------------------------
    Reporter:  duncan            |       Owner:              
        Type:  bug               |      Status:  new         
    Priority:  normal            |   Component:  Compiler    
     Version:  6.12.1            |    Keywords:              
    Testcase:                    |   Blockedby:              
          Os:  Unknown/Multiple  |    Blocking:              
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown
---------------------------------+------------------------------------------
 Consider the following build log. In particular note that we start by
 cleaning any local build files (rm dist).

 Additionally, the user reports that `transformers` is not installed and
 `ghc-pkg check` reports no problems.

 {{{
 00:14:25 | morn at twi:~/dev/darcs/fastconvert -> rm -rf dist
 00:14:27 | morn at twi:~/dev/darcs/fastconvert -> cabal configure -v
 [...]
 Dependency attoparsec ==0.8.1.1: using attoparsec-0.8.1.1
 Dependency base ==4.2.0.0: using base-4.2.0.0
 Dependency bytestring ==0.9.1.5: using bytestring-0.9.1.5
 Dependency cmdlib ==0.3: using cmdlib-0.3
 Dependency containers ==0.3.0.0: using containers-0.3.0.0
 Dependency darcs ==2.5: using darcs-2.5
 Dependency datetime ==0.2: using datetime-0.2
 Dependency directory ==1.0.1.0: using directory-1.0.1.0
 Dependency filepath ==1.1.0.3: using filepath-1.1.0.3
 Dependency hashed-storage ==0.5.4: using hashed-storage-0.5.4
 Dependency mtl ==1.1.1.0: using mtl-1.1.1.0
 Dependency old-time ==1.0.0.3: using old-time-1.0.0.3
 Dependency utf8-string ==0.3.6: using utf8-string-0.3.6
 Using Cabal-1.8.0.2 compiled by ghc-6.12
 Using compiler: ghc-6.12.1
 [...]
 00:14:31 | morn at twi:~/dev/darcs/fastconvert -> cabal build -v
 [...]
 /usr/bin/ghc --make -o dist/build/darcs-fastconvert/darcs-fastconvert
 -hide-all-packages -fbuilding-cabal-package -package-conf
 dist/package.conf.inplace -i -idist/build/darcs-fastconvert/darcs-
 fastconvert-tmp -i. -idist/build/autogen -Idist/build/autogen -Idist/build
 /darcs-fastconvert/darcs-fastconvert-tmp -optP-include
 -optPdist/build/autogen/cabal_macros.h -odir dist/build/darcs-fastconvert
 /darcs-fastconvert-tmp -hidir dist/build/darcs-fastconvert/darcs-
 fastconvert-tmp -stubdir dist/build/darcs-fastconvert/darcs-fastconvert-
 tmp -package-id attoparsec-0.8.1.1-280af3ab9743111575ea0031e8a83455
 -package-id base-4.2.0.0-73995e854f236dc2acd577d7c791221d -package-id
 bytestring-0.9.1.5-2d4a9d624c3be86b70c04730e5f12aca -package-id
 cmdlib-0.3-3ef785632945f8811c8ebbd1d2e9345b -package-id
 containers-0.3.0.0-409fe3b8f0dda25b98e03716d26be411 -package-id
 darcs-2.5-47653bbe1982b022915b3fa65161767f -package-id
 datetime-0.2-6f38d66fddaaa0ccccffea38d6fe8d60 -package-id
 directory-1.0.1.0-10fc46e61b67ff4a83f3e553454d003c -package-id
 filepath-1.1.0.3-07812de93a673f50011d47451bcaac87 -package-id hashed-
 storage-0.5.4-8a6b02d90d8e1d05f233c1e31eb4a367 -package-id
 mtl-1.1.1.0-7772b7b72936d947193a773ada65461a -package-id old-
 time-1.0.0.3-b53830b41b1085071f61ca7772f44e0c -package-id
 utf8-string-0.3.6-a7e240d06fa0c09cfff1a5445b521d24 -O -Wall -fno-warn-
 unused-do-bind ./main.hs
 [1 of 5] Compiling Utils            ( Utils.hs, dist/build/darcs-
 fastconvert/darcs-fastconvert-tmp/Utils.o )
 [...]
 [3 of 5] Compiling Import           ( Import.hs, dist/build/darcs-
 fastconvert/darcs-fastconvert-tmp/Import.o )
 Failed to load interface for `Control.Monad.Trans.Error':
   no package matching `transformers-0.2.2.0' was found
 }}}

 The message
 {{{
 Failed to load interface for `Control.Monad.Trans.Error':
   no package matching `transformers-0.2.2.0' was found
 }}}
 appears to be due to a .hi file from one of the dependencies of the
 current compilation. This hi file references a module from the
 transformers package.

  1. it is hard for a user to know what is causing this module to be looked
 up (ie that it is a .hi file)
  2. it is almost impossible to work out which existing registered package
 contains a .hi file that refers to the non-existent `transformers`
 package.

 If the error message specified that it was a .hi file that caused the
 lookup and gave e.g. the file name (or package+ver+module) of the .hi file
 that caused the lookup of `transformers` then this would make it much
 easier for the user to work out what is going on and which registered
 package is at fault: e.g.

 {{{
 Failed to load interface for `Control.Monad.Trans.Error':
   the package `transformers-0.2.2.0' was found
   referenced by `Data.Foo` from `foo-1.0`.
 }}}

 Clearly there is a deeper problem here, that a registered package is out-
 of-sync with its registration information: the .hi refers to a package
 that is not mentioned in the package registration.

 One way this could happen is due to inplace registrations, since it is
 easy in that case to rebuild the inplace .hi files without also re-
 registering. It may be sensible to rethink how Cabal does inplace
 registrations to prevent it getting out of sync.

 We may also wish to have a ghc-pkg register/update/check mode that reads
 the .hi files and verifies them against the package registration info.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4955>
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