#4437: unregistered language extensions
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Reporter: duncan | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: | Keywords:
Testcase: | Blockedby:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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There is a central registry of language extensions in the module
`Language.Haskell.Extension` (which currently lives in the Cabal package).
This lists all the registered extensions for all compilers. Compiler
authors are expected to register their extensions there. It helps to avoid
people giving different names to the same thing (see e.g. `RecordPuns` vs
`NamedFieldPuns`) and provides a starting point for compiler authors to
implement extension supported by other compilers. It also provides a
resource for users trying to work out the name of the extension they need.
Hackage also consults this list of registered extensions and does not
allow distributed packages to use unknown extensions.
It is currently too easy to forget to register extensions that GHC
supports. Attached is a test program that lists unregistered extensions.
This should be integrated into the ghc testsuite.
The test currently fails with the message:
{{{
The following extensions are known to GHC but are not in the
extension registry in Language.Haskell.Extension.
TupleSections
GHCForeignImportPrim
DoRec
NPlusKPatterns
ExplicitForAll
MonoLocalBinds
DeriveFunctor
DeriveTraversable
DeriveFoldable
If these extensions are ready for public consumption then they
should be registered. If they are still experimental and you
think they are not ready to be registered then please add them
to the exceptions list in this test program along with an
explanation.
}}}
It seems clear that apart from `GHCForeignImportPrim`, all the other
extensions should be registered. Note that it may be necessary to register
the "No" form of some of these instead (see
http://hackage.haskell.org/trac/hackage/ticket/708).
Not all extensions need to be, or should be registered. It is OK to have
experimental or purely private extensions (e.g. perhaps might want to
restrict use to GHC core libs). To support this, the test program has a
list of exceptions. Currently the list is:
{{{
-- | A list of GHC extensions that are deliberately not registered,
-- e.g. due to being experimental and not ready for public consumption
--
exceptions = map readExtension
[ "PArr" -- still classed as experimental, will be renamed and
registered
]
}}}
A decision needs to be made about whether `GHCForeignImportPrim` should be
registered. One could argue that it should remain private. The key point
to consider is that it would prevent the extension being used in packages
distributed on hackage.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4437>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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