#481: Recompilation check fails for TH
------------------------------------------+---------------------------------
Reporter: simonpj | Owner: simonpj
Type: bug | Status: new
Priority: low | Milestone: _|_
Component: Template Haskell | Version: 6.4.1
Resolution: None | Keywords:
Difficulty: Unknown | Os: Unknown/Multiple
Testcase: TH_recompile | Architecture: Unknown/Multiple
Failure: Incorrect result at runtime |
------------------------------------------+---------------------------------
Description changed by igloo:
Old description:
> The recompilation check only recompiles a module when
> the *interface* of a module it imports changes. But
> with Template Haskell, it may need to be recompiled
> when the *implementation* changes.
>
> Concrete example below. It's quite awkward to fix.
>
> * Perhaps a module that contains any splices should be
> recompiled always.
> * Perhaps a module that exports any TH stuff (how
> would we tell?) should be flagged as changed if
> anything about it changes.
>
> Simon
>
> The following scenario reproduces this error
> (thanks to Bulat Ziganshin [email protected]):
>
> 1) create Main.hs containing code
>
> {{{
> module Main where
> import Sub
> main = print $x
> }}}
>
> and Sub.hs containing code
>
> {{{
> module Sub where
> x = [| 1 |]
> }}}
>
> 2) compile them with --make:
>
> {{{
> C:\!\Haskell\!>ghc --make -fth Main.hs
> Chasing modules from: Main.hs
> Compiling Sub ( ./Sub.hs, ./Sub.o )
> Compiling Main ( Main.hs, Main.o )
> Loading package base-1.0 ... linking ... done.
> Loading package haskell98-1.0 ... linking ... done.
> Loading package template-haskell-1.0 ... linking ...
> done.
> Linking ...
>
> C:\!\Haskell\!>main.exe
> 1
> }}}
>
> 3) now change Sub.hs to the following code:
>
> {{{
> module Sub where
> x = [| 2 |]
> }}}
>
> 4) and recompile program:
>
> {{{
> C:\!\Haskell\!>ghc --make -fth Main.hs
> Chasing modules from: Main.hs
> Compiling Sub ( ./Sub.hs, ./Sub.o )
> Skipping Main ( Main.hs, Main.o )
> Linking ...
>
> C:\!\Haskell\!>main.exe
> 1
> }}}
>
> As you see, Main.hs is not recompiled despite the fact
> that definition
> of x is changed and now program must print "2"
New description:
The recompilation check only recompiles a module when
the ''interface'' of a module it imports changes. But
with Template Haskell, it may need to be recompiled
when the ''implementation'' changes.
Concrete example below. It's quite awkward to fix.
* Perhaps a module that contains any splices should be recompiled always.
* Perhaps a module that exports any TH stuff (how would we tell?) should
be flagged as changed if anything about it changes.
Simon
The following scenario reproduces this error
(thanks to Bulat Ziganshin [email protected]):
1) create Main.hs containing code
{{{
module Main where
import Sub
main = print $x
}}}
and Sub.hs containing code
{{{
module Sub where
x = [| 1 |]
}}}
2) compile them with --make:
{{{
C:\!\Haskell\!>ghc --make -fth Main.hs
Chasing modules from: Main.hs
Compiling Sub ( ./Sub.hs, ./Sub.o )
Compiling Main ( Main.hs, Main.o )
Loading package base-1.0 ... linking ... done.
Loading package haskell98-1.0 ... linking ... done.
Loading package template-haskell-1.0 ... linking ...
done.
Linking ...
C:\!\Haskell\!>main.exe
1
}}}
3) now change Sub.hs to the following code:
{{{
module Sub where
x = [| 2 |]
}}}
4) and recompile program:
{{{
C:\!\Haskell\!>ghc --make -fth Main.hs
Chasing modules from: Main.hs
Compiling Sub ( ./Sub.hs, ./Sub.o )
Skipping Main ( Main.hs, Main.o )
Linking ...
C:\!\Haskell\!>main.exe
1
}}}
As you see, Main.hs is not recompiled despite the fact
that definition
of x is changed and now program must print "2"
--
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/481#comment:6>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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