instance decls via TH: dropped methods and stack overflows

[FSalad]

{-# LANGUAGE TemplateHaskell #-}

class C a where
    c :: a

$([d| instance C Int where c = 0 |] )

data D = D

$([d| instance C D where c = D |] )

$([d| instance Show D where show _ = "D" |] )

Loading this into GHCI:

/tmp/Foo.hs:6:3:
    Warning: No explicit method nor default method for `c'
    In the instance declaration for `C Int'

/tmp/Foo.hs:10:3:
    Warning: No explicit method nor default method for `c'
    In the instance declaration for `C D'
Ok, modules loaded: Main.
ghci> c :: Int
*** Exception: /tmp/Foo.hs:6:3-35: No instance nor default method for class operation Main.c

ghci> c :: D
*** Exception: stack overflow
ghci> show D
"*** Exception: stack overflow
ghci> 

I also tried putting C and/or D into separate modules, to no effect.

[simonpj]

Happily this is OK in HEAD; I fixed a related bug recently. I'll add a regression test though.

Simon