[GHC] #13237: Extend TH with addModCStub

[GHC]

#13237: Extend TH with addModCStub
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        Reporter:                    |                Owner:
  facundo.dominguez                  |  facundo.dominguez
            Type:  feature request   |               Status:  patch
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Template Haskell  |              Version:  8.0.1
      Resolution:                    |             Keywords:  inline-c
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D3106
       Wiki Page:                    |
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Comment (by mboes):

 To clarify the context, a solution to this feature would lift a long
 standing usability problem for inline-c. That package generates C code,
 which then has to be linked with all the other object code from a project.
 Since GHC doesn't know about this, we have to lie to Cabal by listing the
 generated C file as an extra source file.

 But that's a very gross hack. Only meant to work around the fact that GHC
 has no direct support for appending arbitrary object code to the output of
 the current compilation unit. But in essence, what inline-c is doing is no
 different from what GHC already needs to do in when compiling modules with
 foreign exports or foreign import wrappers: it creates C stubs whose
 object code must be included with the rest of the object code for the
 module.

 There are now at least a dozen open source libraries that depend on
 inline-c, and likely many more closed source ones. But the current hack
 explained above causes problems: listing a generated file as a source file
 tends to confuse GHC's and Stack's recompilation checking. Worse, in some
 cases the generated C source file causes the build to fail. More details
 here: https://github.com/fpco/inline-c/issues/21.

 Being able to programmatically register C stubs in the current compilation
 unit would solve both problems at once.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13237#comment:6>
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