-.. _release-9-14-1:

-

-Version 9.14.1

-==============

-

-The significant changes to the various parts of the compiler are listed in the

-following sections. See the `migration guide

-<https://gitlab.haskell.org/ghc/ghc/-/wikis/migration/9.14>`_ on the GHC Wiki

-for specific guidance on migrating programs to this release.

-

-Language

-~~~~~~~~

-

-* `GHC proposal 493: allow expressions in SPECIALISE pragmas <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0493-specialise-expressions.rst>`_

-  has been implemented. SPECIALISE pragmas now allow arbitrary expressions such as: ::

-

-    {-# SPECIALISE f @Int False :: Int -> Char #-}

-

-  The ability to specify multiple specialisations in a single SPECIALISE pragma,

-  with syntax of the form (note the comma between the type signatures): ::

-

-    {-# SPECIALISE g : Int -> Int, Float -> Float #-}

-

-  has been deprecated, and is scheduled to be removed in GHC 9.18.

-  This deprecation is controlled by the newly introduced ``-Wdeprecated-pragmas``

-  flag in ``-Wdefault``.

-

-* ``-Wincomplete-record-selectors`` is now part of `-Wall`, as specified

-  by `GHC Proposal 516: add warning for incomplete record selectors <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0516-incomplete-record-selectors.rst>`_.

-  Hence, if a library is compiled with ``-Werror``, compilation may now fail. Solution: fix the library.

-  Workaround: add ``-Werror=no-incomplete-record-selectors``.

-

-  Note that this warning is at least

-  as serious as a warning about missing patterns from a function definition, perhaps even

-  more so, since it is invisible in the source program.

-

-* The combination of :extension:`ScopedTypeVariables` and :extension:`TypeApplications`

-  no longer enables type applications in patterns, which now always requires

-  :extension:`TypeAbstractions`. The warning flag``deprecated-type-abstractions``

-  has also been removed from the compiler.

-

-* :extension:`OverloadedRecordUpdate` now passes the arguments to a ``setField`` function

-  in the flipped order, as specified by `GHC Proposal 583: HasField redesign <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0583-hasfield-redesign.rst>`_.

-

-  Previously GHC expected ``setField`` to have this type: ::

-

-    setField :: forall (fld :: Symbol) a r. r -> a -> r

-

-  And that's what GHC expects now: ::

-

-    setField :: forall (fld :: Symbol) a r. a -> r -> r

-

-  That will break the combination of :extension:`OverloadedRecordUpdate` with :extension:`RebindableSyntax`.

-

-* Multiline strings are now accepted in foreign imports. (#25157)

-

-* GHC now does a better job at inferring types in calls to ``coerce``: instead of

-  complaining about ambiguous type variables, GHC will consider that such type

-  variables are determined by the ``Coercible`` constraints they appear in.

-

-* With :extension:`LinearTypes` record fields can now be non-linear. This means that

-  the following record declaration is now valid:

-

-  ::

-

-      data Record = Rec { x %'Many :: Int, y :: Char }

-

-  This causes the constructor to have type ``Rec :: Int %'Many -> Char %1 -> Record``.

-

-* The :extension:`ExplicitNamespaces` extension now allows the ``data``

-  namespace specifier in import and export lists.

-

-* The ``-Wdata-kinds-tc`` warning has been deprecated, and the use of promoted

-  data types in kinds is now an error (rather than a warning) unless the

-  :extension:`DataKinds` extension is enabled. For example, the following code

-  will be rejected unless :extension:`DataKinds` is on:

-

-    import Data.Kind (Type)

-    import GHC.TypeNats (Nat)

-

-    -- Nat shouldn't be allowed here without DataKinds

-    data Vec :: Nat -> Type -> Type

-

-  (The ``-Wdata-kinds-tc`` warning was introduced in GHC 9.10 as part of a fix

-  for an accidental oversight in which programs like the one above were

-  mistakenly accepted without the use of :extension:`DataKinds`.)

-

-* The :extension:`MonadComprehensions` extension now implies :extension:`ParallelListComp` as was originally intended (see `Monad Comprehensions <https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/monad_comprehensions.html>`_).

-

-* In accordance with `GHC Proposal #281 <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0281-visible-forall.rst>`_,

-  section 4.7 "Data constructors", the :extension:`RequiredTypeArguments`

-  extension now allows visible forall in types of data constructors

-  (:ghc-ticket:`25127`). The following declaration is now accepted by GHC:

-

-  ::

-

-    data T a where

-      Typed :: forall a -> a -> T a

-

-  See :ref:`visible-forall-in-gadts` for details.

-

-Compiler

-~~~~~~~~

-

-- An improved error message is introduced to refer users to the heap-controlling flags of the RTS when there is a heap overflow during compilation. (#25198)

-

-- The kind checker now does a better job of finding type family instances for

-  use in the kinds of other declarations in the same module. This fixes a number

-  of tickets:

-  :ghc-ticket:`12088`, :ghc-ticket:`12239`, :ghc-ticket:`14668`, :ghc-ticket:`15561`,

-  :ghc-ticket:`16410`, :ghc-ticket:`16448`, :ghc-ticket:`16693`, :ghc-ticket:`19611`,

-  :ghc-ticket:`20875`, :ghc-ticket:`21172`, :ghc-ticket:`22257`, :ghc-ticket:`25238`,

-  :ghc-ticket:`25834`.

-

-- The compiler no longer accepts invalid ``type`` namespace specifiers in

-  subordinate import lists (:ghc-ticket:`22581`).

-

-- A new flag, :ghc-flag:`-Wuseless-specialisations`, controls warnings emitted when GHC

-  determines that a SPECIALISE pragma would have no effect.

-

-- A new flag, :ghc-flag:`-Wrule-lhs-equalities`, controls warnings emitted for RULES

-  whose left-hand side attempts to quantify over equality constraints that

-  previous GHC versions accepted quantifying over. GHC will now drop such RULES,

-  emitting a warning message controlled by this flag.

-

-  This warning is intended to give visibility to the fact that the RULES that

-  previous GHC versions generated in such circumstances could never fire.

-

-- A new flag, :ghc-flag:`-Wunusable-unpack-pragmas`, controls warnings emitted

-  when GHC is unable to unpack a data constructor field annotated by the

-  ``{-# UNPACK #-}`` pragma.

-

-  Previous GHC versions issued this warning unconditionally. Now it is possible

-  to disable it with ``-Wno-unusable-unpack-pragmas`` or turn it into an error

-  with ``-Werror=unusable-unpack-pragmas``.

-

-- Introduce a new warning :ghc-flag:`-Wpattern-namespace-specifier` to detect

-  uses of the now deprecated ``pattern`` namespace specifier in import/export

-  lists. See `GHC Proposal #581, section 2.3 <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0581-namespace-specified-imports.rst#deprecate-use-of-pattern-in-import-export-lists>`_.

-

-- Code coverage (:ghc-flag:`-fhpc`) now treats uses of record fields

-  (including via :extension:`RecordWildCards` or :extension:`NamedFieldPuns`)

-  as if the fields were accessed using the generated record selector functions,

-  marking the fields as covered in coverage reports (:ghc-ticket:`17834`,

-  :ghc-ticket:`26191`). Note that this currently only works when record fields

-  (or values contained within them) are bound to variables, and usage of those

-  variables marks the record selectors as covered. That is, a pattern like

-  ``Foo{bar = Bar{baz = b}}`` will mark ``bar`` and ``baz`` as covered if ``b``

-  is used, but the similar pattern ``Foo{bar = Bar{baz = 42}}`` will mark

-  neither as covered.

-

-- SIMD support in the X86 native code generator has been extended with 128-bit

-  integer operations.  Also, ``shuffleFloatX4#`` and ``shuffleDoubleX2#`` no longer

-  require ``-mavx``.

-

-- JSON diagnostics produced with (:ghc-flag:`-fdiagnostics-as-json`) now

-  include the `rendered` diagnostics message, in the exact same format as what

-  GHC would have produced without -fdiagnostics-as-json (including ANSI escape

-  sequences).

-

-GHCi

-~~~~

-

-- :ghci-cmd:`:info` now outputs type declarations with @-binders that are

-  considered semantically significant. See the documentation for :ghci-cmd:`:info`

-  itself for a more detailed explanation.

-

-- GHCi errors and warnings now have their own numeric error codes that are

-  displayed alongside the error.

-

-Runtime system

-~~~~~~~~~~~~~~

-

-- Add new runtime flag :rts-flag:`--optimistic-linking` which instructs the

-  runtime linker to continue in the presence of unknown symbols. By default this

-  flag is not passed, preserving previous behavior.

-

-Cmm

-~~~

-

-``base`` library

-~~~~~~~~~~~~~~~~

-

-``ghc-prim`` library

-~~~~~~~~~~~~~~~~~~~~

-

-``ghc`` library

-~~~~~~~~~~~~~~~

-

-* The `UnknownDiagnostic` constructor now takes an additional type argument

-  for the type of hints corresponding to the diagnostic, and an additional

-  value-level argument used for existential wrapping of the hints of the inner

-  diagnostic.

-

-* Changes to the HPT and HUG interface:

-

-  - `addToHpt` and `addListToHPT` were moved from `GHC.Unit.Home.ModInfo` to `GHC.Unit.Home.PackageTable` and deprecated in favour of `addHomeModInfoToHpt` and `addHomeModInfosToHpt`.

-  - `UnitEnvGraph` and operations `unitEnv_lookup_maybe`, `unitEnv_foldWithKey, `unitEnv_singleton`, `unitEnv_adjust`, `unitEnv_insert`, `unitEnv_new` were moved from `GHC.Unit.Env` to `GHC.Unit.Home.Graph`.

-  - The HomePackageTable (HPT) is now exported from `GHC.Unit.Home.PackageTable`,

-    and is now backed by an IORef to avoid by construction very bad memory leaks.

-    This means the API to the HPT now is for the most part in IO. For instance,

-    `emptyHomePackageTable` and `addHomeModInfoToHpt` are now in IO.

-  - `mkHomeUnitEnv` was moved to `GHC.Unit.Home.PackageTable`, and now takes two

-    extra explicit arguments. To restore previous behaviour, pass `emptyUnitState`

-    and `Nothing` as the first two arguments additionally.

-  - `hugElts` was removed. Users should prefer `allUnits` to get the keys of the

-    HUG (the typical use case), or `traverse` or `unitEnv_foldWithKey` in other

-    cases.

-

-* Changes to `Language.Haskell.Syntax.Expr`

-

-  - The `ParStmtBlock` list argument of the `ParStmt` constructor of `StmtLR` is now `NonEmpty`.

-

-* As part of the implementation of `GHC proposal 493 <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0493-specialise-expressions.rst>`_,

-  the `SpecSig` constructor of `Sig` has been deprecated. It is replaced by

-  the constructor `SpecSigE` which supports expressions at the head, rather than

-  a lone variable.

-

-``ghc-heap`` library

-~~~~~~~~~~~~~~~~~~~~

-

-* The functions `getClosureInfoTbl_maybe`, `getClosureInfoTbl`,

-  `getClosurePtrArgs` and `getClosurePtrArgs_maybe` have been added to allow

-  reading of the relevant Closure attributes without reliance on incomplete

-  selectors.

-

-``ghc-experimental`` library

-~~~~~~~~~~~~~~~~~~~~~~~~~~~~

-

-- ``ghc-experimental`` now exposes ``GHC.RTS.Flags`` and ``GHC.Stats`` as

-  ``GHC.RTS.Flags.Experimental`` and ``GHC.Stats.Experimental``. These are

-  *also* exposed in ``base``, however the ``base`` versions will be deprecated as

-  part of the split base project. See `CLC proposal 289

-  <https://github.com/haskell/core-libraries-committee/issues/289>`__.

-  Downstream consumers of these flags are encouraged to migrate to the

-  ``ghc-experimental`` versions.

-

-

-

-``template-haskell`` library

-~~~~~~~~~~~~~~~~~~~~~~~~~~~~

-

-- As part of the implementation of `GHC proposal 493 <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0493-specialise-expressions.rst>`_,

-  the ``SpecialiseP`` constructor of the Template Haskell ``Pragma`` type, as

-  well as the helpers ``pragSpecD`` and ``pragSpecInlD``, have been deprecated.

-

-  They are replaced, respectively, by ``SpecialiseEP``, ``pragSpecED`` and

-  ``pragSpecInlED``.

-

-Included libraries

-~~~~~~~~~~~~~~~~~~

-

-The package database provided with this distribution also contains a number of

-packages other than GHC itself. See the changelogs provided with these packages

-for further change information.

-

-.. ghc-package-list::

-

-    libraries/array/array.cabal:                         Dependency of ``ghc`` library

-    libraries/base/base.cabal:                           Core library

-    libraries/binary/binary.cabal:                       Dependency of ``ghc`` library

-    libraries/bytestring/bytestring.cabal:               Dependency of ``ghc`` library

-    libraries/Cabal/Cabal/Cabal.cabal:                   Dependency of ``ghc-pkg`` utility

-    libraries/Cabal/Cabal-syntax/Cabal-syntax.cabal:     Dependency of ``ghc-pkg`` utility

-    libraries/containers/containers/containers.cabal:    Dependency of ``ghc`` library

-    libraries/deepseq/deepseq.cabal:                     Dependency of ``ghc`` library

-    libraries/directory/directory.cabal:                 Dependency of ``ghc`` library

-    libraries/exceptions/exceptions.cabal:               Dependency of ``ghc`` and ``haskeline`` library

-    libraries/filepath/filepath.cabal:                   Dependency of ``ghc`` library

-    compiler/ghc.cabal:                                  The compiler itself

-    libraries/ghci/ghci.cabal:                           The REPL interface

-    libraries/ghc-boot/ghc-boot.cabal:                   Internal compiler library

-    libraries/ghc-boot-th/ghc-boot-th.cabal:             Internal compiler library

-    libraries/ghc-compact/ghc-compact.cabal:             Core library

-    libraries/ghc-heap/ghc-heap.cabal:                   GHC heap-walking library

-    libraries/ghc-prim/ghc-prim.cabal:                   Core library

-    utils/haddock/haddock-api/haddock-api.cabal:         Dependency of ``haddock`` executable

-    utils/haddock/haddock-library/haddock-library.cabal: Dependency of ``haddock`` executable

-    libraries/haskeline/haskeline.cabal:                 Dependency of ``ghci`` executable

-    libraries/hpc/hpc.cabal:                             Dependency of ``hpc`` executable

-    libraries/integer-gmp/integer-gmp.cabal:             Core library

-    libraries/mtl/mtl.cabal:                             Dependency of ``Cabal`` library

-    libraries/parsec/parsec.cabal:                       Dependency of ``Cabal`` library

-    libraries/pretty/pretty.cabal:                       Dependency of ``ghc`` library

-    libraries/process/process.cabal:                     Dependency of ``ghc`` library

-    libraries/stm/stm.cabal:                             Dependency of ``haskeline`` library

-    libraries/template-haskell/template-haskell.cabal:   Core library

-    libraries/terminfo/terminfo.cabal:                   Dependency of ``haskeline`` library

-    libraries/text/text.cabal:                           Dependency of ``Cabal`` library

-    libraries/time/time.cabal:                           Dependency of ``ghc`` library

-    libraries/transformers/transformers.cabal:           Dependency of ``ghc`` library

-    libraries/unix/unix.cabal:                           Dependency of ``ghc`` library

-    libraries/Win32/Win32.cabal:                         Dependency of ``ghc`` library

-    libraries/xhtml/xhtml.cabal:                         Dependency of ``haddock`` executable

-    libraries/os-string/os-string.cabal:                 Dependency of ``filepath`` library

-    libraries/file-io/file-io.cabal:                     Dependency of ``directory`` library

-   9.14.1-notes