chs: fix GHC 9.2+ prim ambiguity in c2hs-processed source files#86
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chs: fix GHC 9.2+ prim ambiguity in c2hs-processed source files#86mgajda wants to merge 1 commit into
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c2hs processes .chs files with its own C preprocessor, in which
`__GLASGOW_HASKELL__` is not defined. Bare guards of the form
#if __GLASGOW_HASKELL__ < N
therefore evaluate to `0 < N` (TRUE), so local bridge definitions of
`wordToWord64#`, `word64ToWord#`, and `wordToWord8#` are emitted
unconditionally into the generated .hs output.
GHC 9.2 added these operations to `GHC.Prim` / `GHC.Base` / `GHC.Exts`,
so on GHC 9.2+ the generated code contains a duplicate definition that
the compiler correctly rejects as ambiguous:
Ambiguous occurrence `wordToWord64#'
It could refer to either `GHC.Base.wordToWord64#'
or `Foreign.CUDA.Driver.Stream.wordToWord64#'
Fix: rewrite bare guards as
#if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ < N
`defined(__GLASGOW_HASKELL__)` evaluates to FALSE under c2hs, suppressing
the local definition there. GHC's own CPP pass sees a defined macro and
evaluates the version comparison normally.
Affected files: Driver/Stream.chs, Driver/Marshal.chs, Driver/Module/Query.chs
Tested: c2hs 0.28.8, GHC 9.4.7 and 9.6.x, CUDA 12.0, Ubuntu 24.04.
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Branch:
fix/ghc94-prim-guardsCommit:
chs: fix GHC 9.2+ prim ambiguity in c2hs-processed source filesBuilding with GHC 9.2 or later fails with ambiguous occurrence errors:
The .chs files guard local bridge definitions with
#if __GLASGOW_HASKELL__ < N. c2hs processes .chs files with its own C preprocessor, in which__GLASGOW_HASKELL__is undefined (evaluates to0). The guard is therefore always TRUE, and the local definitions ofwordToWord64#,word64ToWord#, andwordToWord8#are emitted unconditionally into the generated .hs output. GHC 9.2+ exports these same operations fromGHC.Base/GHC.Exts, so the compiler sees a duplicate and correctly rejects it.The fix changes bare guards of the form
#if __GLASGOW_HASKELL__ < Nto#if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ < N. Under c2hs,defined(__GLASGOW_HASKELL__)is FALSE so the local definition is stripped. GHC's own CPP pass sees a defined macro and evaluates the version check normally.Affected:
Driver/Stream.chs,Driver/Marshal.chs,Driver/Module/Query.chs.Tested: c2hs 0.28.8, GHC 9.4.7, CUDA 12.0, Ubuntu 24.04.