[GHC] #8025: -fno-code and Template Haskell are incompatible

[GHC]

#8025: -fno-code and Template Haskell are incompatible
-------------------------------------+-------------------------------------
        Reporter:  mojojojo          |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  7.6.3
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:  x86
 Type of failure:  Incorrect         |            Test Case:
  warning at compile-time            |
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"53c78be0aab76a3107c4dacbb1d177afacdd37fa/ghc"
 53c78be0/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="53c78be0aab76a3107c4dacbb1d177afacdd37fa"
 Compile modules that are needed by template haskell, even with -fno-code.

 This patch relates to Trac #8025

 The goal here is to enable typechecking of packages that contain some
 template haskell. Prior to this patch, compilation of a package with
 -fno-code would fail if any functions in the package were called from
 within a splice.

 downsweep is changed to do an additional pass over the modules,
 targetting any ModSummaries transitively depended on by a module that
 has LangExt.TemplateHaskell enabled. Those targeted modules have
 hscTarget changed from HscNothing to the default target of the platform.

 There is a small change to the prevailing_target logic to enable this.

 A simple test is added.

 I have benchmarked with and without a patched haddock
 (available:https://github.com/duog/haddock/tree/wip-no-explicit-th-compi
 lation).  Running cabal haddock on the wreq package results in a 25%
 speedup on my machine:

 time output from patched cabal haddock:

 real    0m5.780s
 user    0m5.304s
 sys     0m0.496s
 time output from unpatched cabal haddock:

 real    0m7.712s
 user    0m6.888s
 sys     0m0.736s

 Reviewers: austin, bgamari, ezyang

 Reviewed By: bgamari

 Subscribers: bgamari, DanielG, rwbarton, thomie

 GHC Trac Issues: #8025

 Differential Revision: https://phabricator.haskell.org/D3441
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8025#comment:14>
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