[GHC] #13729: ghc does not pick up TH changes across package boundaries

19 May 2017

      #13729: ghc does not pick up TH changes across package boundaries
-------------------------------------+-------------------------------------
           Reporter:  Feuerbach      |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 I have the following three modules:

 {{{#!hs
 module Types where

 data Foo = Bar
 }}}
 {{{#!hs
 {-# LANGUAGE TemplateHaskell #-}
 module TH where

 import Language.Haskell.TH
 import Language.Haskell.TH.Syntax
 import Types

 th_string = lift . show =<< reify ''Foo
 }}}
 {{{#!hs
 {-# LANGUAGE TemplateHaskell #-}
 module Main where

 import TH

 main = putStrLn $(th_string)
 }}}

 The goal is to make Main recompile if the definition of Types.Foo changes.

 If I simply put the three files in the same directory and compile with
 ghc, it works.

 However, if I put Types and TH in package A and Main in package B, then
 ghc doesn't recompile B.Main if I change the definition of A.Types.Foo and
 reinstall the package A.

 I tried this with both stack and cabal-install. In both cases I compiled
 B.Main directly with ghc, so it's not Cabal that's hiding the changes. If
 I pass -fforce-recomp to ghc,  Main recompiles as expected.

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13729
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler