Splicing in constructors that are abstract from the point of view of the splice point is unreliable

[batterseapower]

Test1.hs:

{-# LANGUAGE TemplateHaskell #-}

module Main where

import Test2

main = putStrLn (show $(makeOne))

Test2.hs:

{-# LANGUAGE TemplateHaskell #-}

module Test2(ExportedAbstract, makeOne) where

data ExportedAbstract = Yay String | NonYay AnotherThing

data AnotherThing = Foo String

instance Show ExportedAbstract where
	show _ = "Shown"

makeOne = [| Yay "Yep" |]

Compile this with optimizations:

ghc Test2.hs -O2
ghc --make Test1.hs

Results in:

$ ./Test1
Shown

Compile this without optimizations:

ghc Test2.hs -O0
ghc --make Test1.hs

Results in:

$ ghc --make Test1.hs
[2 of 2] Compiling Main             ( Test1.hs, Test1.o )
Loading package base ... linking ... done.
Loading package pretty-1.0.0.0 ... linking ... done.
Loading package array-0.1.0.0 ... linking ... done.
Loading package packedstring-0.1.0.0 ... linking ... done.
Loading package containers-0.1.0.1 ... linking ... done.
Loading package template-haskell ... linking ... done.

Test1.hs:7:24:
    Can't find interface-file declaration for data constructor Test2.Yay
      Probable cause: bug in .hi-boot file, or inconsistent .hi file
      Use -ddump-if-trace to get an idea of which file caused the error
    In the first argument of `show', namely `$makeOne'
    In the first argument of `putStrLn', namely `(show ($makeOne))'
    In the expression: putStrLn (show ($makeOne))

Why is this? Because trimThing in TidyPgm? makes data types abstract in some circumstances, and it only happens if compiling a boot file or with -O0!

I think this program should compile as the splicing is not a violation of the abstractness of the data type: all the manipulation etc is still being done by the defining module.

[simonpj]

Good point. I'm fixing.

S

[simonpj]

Fixed by switching off data type pruning if -XTemplateHaskell is enabled.

Mon Jul  7 11:29:41 BST 2008  simonpj@microsoft.com
  * Fix Trac #2386: exceesive trimming of data types with Template Haskell

Merge to 6.8.4 if/when we release it.

Simon

[igloo]

We won't be releasing 6.8.4.