[GHC] #13251: Must perform family consistency check on non-imported identifiers

[GHC]

#13251: Must perform family consistency check on non-imported identifiers
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        Reporter:  ezyang            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |
      Resolution:                    |             Keywords:  TypeFamilies
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC accepts       |  Unknown/Multiple
  invalid program                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by rwbarton):

 Not thoroughly thought out, but how about in `checkWiredInTyCon` (or
 something which wraps it) and in `tcLookupGlobal`, we check whether the
 thing lives in a module that was actually imported and, if not, add the
 relevant import information to `tcg_imports`, and either do the ensuing
 type family consistency checks immediately, or perhaps add them to
 `tcg_pending_fam_checks`?

 I mean, we also have this behavior:
 {{{#!hs
 {-# LANGUAGE TemplateHaskell #-}
 import Language.Haskell.TH.Syntax
 main = print $( return (VarE (Name (OccName "sigFPE")
                              (NameG VarName (PkgName "unix-2.7.0.1")
                                     (ModName "System.Posix.Signals")))) )
 }}}
 {{{
 rwbarton at morphism:~/ghc2$ ghc x/TH -fforce-recomp
 [1 of 1] Compiling Main             ( x/TH.hs, x/TH.o )
 Loading package ghc-prim ... linking ... done.
 Loading package integer-gmp ... linking ... done.
 Loading package base ... linking ... done.
 Loading package array-0.5.0.0 ... linking ... done.
 Loading package deepseq-1.3.0.2 ... linking ... done.
 Loading package containers-0.5.5.1 ... linking ... done.
 Loading package pretty-1.1.1.1 ... linking ... done.
 Loading package template-haskell ... linking ... done.
 Linking x/TH ...
 x/TH.o:(.text+0x4b): undefined reference to
 `unixzm2zi7zi0zi1_SystemziPosixziSignals_sigFPE_closure'
 x/TH.o: In function `S4hM_srt':
 (.data+0x48): undefined reference to
 `unixzm2zi7zi0zi1_SystemziPosixziSignals_sigFPE_closure'
 collect2: error: ld returned 1 exit status
 }}}
 If we updated the `ImportAvails` when we type checked the spliced thing,
 wouldn't that also create a dependency on the `unix` package at link time?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13251#comment:2>
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