{-
(c) The University of Glasgow 2006
(c) The GRASP/AQUA Project, Glasgow University, 1992-1998

-}

{-# LANGUAGE TypeFamilies #-}

-- | Error-checking and other utilities for @deriving@ clauses or declarations.
module GHC.Tc.Deriv.Utils (
        DerivM, DerivEnv(..),
        DerivSpec(..), pprDerivSpec, DerivInstTys(..),
        DerivSpecMechanism(..), derivSpecMechanismToStrategy, isDerivSpecStock,
        isDerivSpecNewtype, isDerivSpecAnyClass, isDerivSpecVia,
        DerivContext(..), OriginativeDerivStatus(..),
        isStandaloneDeriv, isStandaloneWildcardDeriv, mkDerivOrigin,
        PredOrigin(..), ThetaOrigin(..), mkPredOrigin,
        mkThetaOrigin, mkThetaOriginFromPreds, substPredOrigin,
        checkOriginativeSideConditions, hasStockDeriving,
        canDeriveAnyClass,
        std_class_via_coercible, non_coercible_class,
        newDerivClsInst, extendLocalInstEnv
    ) where

import GHC.Prelude

import GHC.Data.Bag
import GHC.Types.Basic
import GHC.Core.Class
import GHC.Core.DataCon
import GHC.Driver.Session
import GHC.Utils.Error
import GHC.Driver.Types (lookupFixity, mi_fix)
import GHC.Hs
import GHC.Tc.Utils.Instantiate
import GHC.Core.InstEnv
import GHC.Iface.Load   (loadInterfaceForName)
import GHC.Unit.Module (getModule)
import GHC.Types.Name
import GHC.Utils.Outputable
import GHC.Builtin.Names
import GHC.Types.SrcLoc
import GHC.Tc.Deriv.Generate
import GHC.Tc.Deriv.Functor
import GHC.Tc.Deriv.Generics
import GHC.Tc.Types.Origin
import GHC.Tc.Utils.Monad
import GHC.Tc.Utils.TcType
import GHC.Builtin.Names.TH (liftClassKey)
import GHC.Core.TyCon
import GHC.Core.Multiplicity
import GHC.Core.TyCo.Ppr (pprSourceTyCon)
import GHC.Core.Type
import GHC.Utils.Misc
import GHC.Types.Var.Set

import Control.Monad.Trans.Reader
import Data.Maybe
import qualified GHC.LanguageExtensions as LangExt
import GHC.Data.List.SetOps (assocMaybe)

-- | To avoid having to manually plumb everything in 'DerivEnv' throughout
-- various functions in "GHC.Tc.Deriv" and "GHC.Tc.Deriv.Infer", we use 'DerivM', which
-- is a simple reader around 'TcRn'.
type DerivM = ReaderT DerivEnv TcRn

-- | Is GHC processing a standalone deriving declaration?
isStandaloneDeriv :: DerivM Bool
isStandaloneDeriv :: DerivM Bool
isStandaloneDeriv = (DerivEnv -> Bool) -> DerivM Bool
forall (m :: * -> *) r a. Monad m => (r -> a) -> ReaderT r m a
asks (DerivContext -> Bool
go (DerivContext -> Bool)
-> (DerivEnv -> DerivContext) -> DerivEnv -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. DerivEnv -> DerivContext
denv_ctxt)
  where
    go :: DerivContext -> Bool
    go :: DerivContext -> Bool
go (InferContext Maybe SrcSpan
wildcard) = Maybe SrcSpan -> Bool
forall a. Maybe a -> Bool
isJust Maybe SrcSpan
wildcard
    go (SupplyContext {})      = Bool
True

-- | Is GHC processing a standalone deriving declaration with an
-- extra-constraints wildcard as the context?
-- (e.g., @deriving instance _ => Eq (Foo a)@)
isStandaloneWildcardDeriv :: DerivM Bool
isStandaloneWildcardDeriv :: DerivM Bool
isStandaloneWildcardDeriv = (DerivEnv -> Bool) -> DerivM Bool
forall (m :: * -> *) r a. Monad m => (r -> a) -> ReaderT r m a
asks (DerivContext -> Bool
go (DerivContext -> Bool)
-> (DerivEnv -> DerivContext) -> DerivEnv -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. DerivEnv -> DerivContext
denv_ctxt)
  where
    go :: DerivContext -> Bool
    go :: DerivContext -> Bool
go (InferContext Maybe SrcSpan
wildcard) = Maybe SrcSpan -> Bool
forall a. Maybe a -> Bool
isJust Maybe SrcSpan
wildcard
    go (SupplyContext {})      = Bool
False

-- | @'mkDerivOrigin' wc@ returns 'StandAloneDerivOrigin' if @wc@ is 'True',
-- and 'DerivClauseOrigin' if @wc@ is 'False'. Useful for error-reporting.
mkDerivOrigin :: Bool -> CtOrigin
mkDerivOrigin :: Bool -> CtOrigin
mkDerivOrigin Bool
standalone_wildcard
  | Bool
standalone_wildcard = CtOrigin
StandAloneDerivOrigin
  | Bool
otherwise           = CtOrigin
DerivClauseOrigin

-- | Contains all of the information known about a derived instance when
-- determining what its @EarlyDerivSpec@ should be.
-- See @Note [DerivEnv and DerivSpecMechanism]@.
data DerivEnv = DerivEnv
  { DerivEnv -> Maybe OverlapMode
denv_overlap_mode :: Maybe OverlapMode
    -- ^ Is this an overlapping instance?
  , DerivEnv -> [TyVar]
denv_tvs          :: [TyVar]
    -- ^ Universally quantified type variables in the instance
  , DerivEnv -> Class
denv_cls          :: Class
    -- ^ Class for which we need to derive an instance
  , DerivEnv -> [Type]
denv_inst_tys     :: [Type]
    -- ^ All arguments to 'denv_cls' in the derived instance.
  , DerivEnv -> DerivContext
denv_ctxt         :: DerivContext
    -- ^ @'SupplyContext' theta@ for standalone deriving (where @theta@ is the
    --   context of the instance).
    --   'InferContext' for @deriving@ clauses, or for standalone deriving that
    --   uses a wildcard constraint.
    --   See @Note [Inferring the instance context]@.
  , DerivEnv -> Maybe (DerivStrategy GhcTc)
denv_strat        :: Maybe (DerivStrategy GhcTc)
    -- ^ 'Just' if user requests a particular deriving strategy.
    --   Otherwise, 'Nothing'.
  }

instance Outputable DerivEnv where
  ppr :: DerivEnv -> SDoc
ppr (DerivEnv { denv_overlap_mode :: DerivEnv -> Maybe OverlapMode
denv_overlap_mode = Maybe OverlapMode
overlap_mode
                , denv_tvs :: DerivEnv -> [TyVar]
denv_tvs          = [TyVar]
tvs
                , denv_cls :: DerivEnv -> Class
denv_cls          = Class
cls
                , denv_inst_tys :: DerivEnv -> [Type]
denv_inst_tys     = [Type]
inst_tys
                , denv_ctxt :: DerivEnv -> DerivContext
denv_ctxt         = DerivContext
ctxt
                , denv_strat :: DerivEnv -> Maybe (DerivStrategy GhcTc)
denv_strat        = Maybe (DerivStrategy GhcTc)
mb_strat })
    = SDoc -> Int -> SDoc -> SDoc
hang (String -> SDoc
text String
"DerivEnv")
         Int
2 ([SDoc] -> SDoc
vcat [ String -> SDoc
text String
"denv_overlap_mode" SDoc -> SDoc -> SDoc
<+> Maybe OverlapMode -> SDoc
forall a. Outputable a => a -> SDoc
ppr Maybe OverlapMode
overlap_mode
                 , String -> SDoc
text String
"denv_tvs"          SDoc -> SDoc -> SDoc
<+> [TyVar] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [TyVar]
tvs
                 , String -> SDoc
text String
"denv_cls"          SDoc -> SDoc -> SDoc
<+> Class -> SDoc
forall a. Outputable a => a -> SDoc
ppr Class
cls
                 , String -> SDoc
text String
"denv_inst_tys"     SDoc -> SDoc -> SDoc
<+> [Type] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [Type]
inst_tys
                 , String -> SDoc
text String
"denv_ctxt"         SDoc -> SDoc -> SDoc
<+> DerivContext -> SDoc
forall a. Outputable a => a -> SDoc
ppr DerivContext
ctxt
                 , String -> SDoc
text String
"denv_strat"        SDoc -> SDoc -> SDoc
<+> Maybe (DerivStrategy GhcTc) -> SDoc
forall a. Outputable a => a -> SDoc
ppr Maybe (DerivStrategy GhcTc)
mb_strat ])

data DerivSpec theta = DS { forall theta. DerivSpec theta -> SrcSpan
ds_loc                 :: SrcSpan
                          , forall theta. DerivSpec theta -> Name
ds_name                :: Name         -- DFun name
                          , forall theta. DerivSpec theta -> [TyVar]
ds_tvs                 :: [TyVar]
                          , forall theta. DerivSpec theta -> theta
ds_theta               :: theta
                          , forall theta. DerivSpec theta -> Class
ds_cls                 :: Class
                          , forall theta. DerivSpec theta -> [Type]
ds_tys                 :: [Type]
                          , forall theta. DerivSpec theta -> Maybe OverlapMode
ds_overlap             :: Maybe OverlapMode
                          , forall theta. DerivSpec theta -> Maybe SrcSpan
ds_standalone_wildcard :: Maybe SrcSpan
                              -- See Note [Inferring the instance context]
                              -- in GHC.Tc.Deriv.Infer
                          , forall theta. DerivSpec theta -> DerivSpecMechanism
ds_mechanism           :: DerivSpecMechanism }
        -- This spec implies a dfun declaration of the form
        --       df :: forall tvs. theta => C tys
        -- The Name is the name for the DFun we'll build
        -- The tyvars bind all the variables in the theta

        -- the theta is either the given and final theta, in standalone deriving,
        -- or the not-yet-simplified list of constraints together with their origin

        -- ds_mechanism specifies the means by which GHC derives the instance.
        -- See Note [Deriving strategies] in GHC.Tc.Deriv

{-
Example:

     newtype instance T [a] = MkT (Tree a) deriving( C s )
==>
     axiom T [a] = :RTList a
     axiom :RTList a = Tree a

     DS { ds_tvs = [a,s], ds_cls = C, ds_tys = [s, T [a]]
        , ds_mechanism = DerivSpecNewtype (Tree a) }
-}

pprDerivSpec :: Outputable theta => DerivSpec theta -> SDoc
pprDerivSpec :: forall theta. Outputable theta => DerivSpec theta -> SDoc
pprDerivSpec (DS { ds_loc :: forall theta. DerivSpec theta -> SrcSpan
ds_loc = SrcSpan
l, ds_name :: forall theta. DerivSpec theta -> Name
ds_name = Name
n, ds_tvs :: forall theta. DerivSpec theta -> [TyVar]
ds_tvs = [TyVar]
tvs, ds_cls :: forall theta. DerivSpec theta -> Class
ds_cls = Class
c,
                   ds_tys :: forall theta. DerivSpec theta -> [Type]
ds_tys = [Type]
tys, ds_theta :: forall theta. DerivSpec theta -> theta
ds_theta = theta
rhs,
                   ds_standalone_wildcard :: forall theta. DerivSpec theta -> Maybe SrcSpan
ds_standalone_wildcard = Maybe SrcSpan
wildcard, ds_mechanism :: forall theta. DerivSpec theta -> DerivSpecMechanism
ds_mechanism = DerivSpecMechanism
mech })
  = SDoc -> Int -> SDoc -> SDoc
hang (String -> SDoc
text String
"DerivSpec")
       Int
2 ([SDoc] -> SDoc
vcat [ String -> SDoc
text String
"ds_loc                  =" SDoc -> SDoc -> SDoc
<+> SrcSpan -> SDoc
forall a. Outputable a => a -> SDoc
ppr SrcSpan
l
               , String -> SDoc
text String
"ds_name                 =" SDoc -> SDoc -> SDoc
<+> Name -> SDoc
forall a. Outputable a => a -> SDoc
ppr Name
n
               , String -> SDoc
text String
"ds_tvs                  =" SDoc -> SDoc -> SDoc
<+> [TyVar] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [TyVar]
tvs
               , String -> SDoc
text String
"ds_cls                  =" SDoc -> SDoc -> SDoc
<+> Class -> SDoc
forall a. Outputable a => a -> SDoc
ppr Class
c
               , String -> SDoc
text String
"ds_tys                  =" SDoc -> SDoc -> SDoc
<+> [Type] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [Type]
tys
               , String -> SDoc
text String
"ds_theta                =" SDoc -> SDoc -> SDoc
<+> theta -> SDoc
forall a. Outputable a => a -> SDoc
ppr theta
rhs
               , String -> SDoc
text String
"ds_standalone_wildcard  =" SDoc -> SDoc -> SDoc
<+> Maybe SrcSpan -> SDoc
forall a. Outputable a => a -> SDoc
ppr Maybe SrcSpan
wildcard
               , String -> SDoc
text String
"ds_mechanism            =" SDoc -> SDoc -> SDoc
<+> DerivSpecMechanism -> SDoc
forall a. Outputable a => a -> SDoc
ppr DerivSpecMechanism
mech ])

instance Outputable theta => Outputable (DerivSpec theta) where
  ppr :: DerivSpec theta -> SDoc
ppr = DerivSpec theta -> SDoc
forall theta. Outputable theta => DerivSpec theta -> SDoc
pprDerivSpec

-- | Information about the arguments to the class in a stock- or
-- newtype-derived instance.
-- See @Note [DerivEnv and DerivSpecMechanism]@.
data DerivInstTys = DerivInstTys
  { DerivInstTys -> [Type]
dit_cls_tys     :: [Type]
    -- ^ Other arguments to the class except the last
  , DerivInstTys -> TyCon
dit_tc          :: TyCon
    -- ^ Type constructor for which the instance is requested
    --   (last arguments to the type class)
  , DerivInstTys -> [Type]
dit_tc_args     :: [Type]
    -- ^ Arguments to the type constructor
  , DerivInstTys -> TyCon
dit_rep_tc      :: TyCon
    -- ^ The representation tycon for 'dit_tc'
    --   (for data family instances). Otherwise the same as 'dit_tc'.
  , DerivInstTys -> [Type]
dit_rep_tc_args :: [Type]
    -- ^ The representation types for 'dit_tc_args'
    --   (for data family instances). Otherwise the same as 'dit_tc_args'.
  }

instance Outputable DerivInstTys where
  ppr :: DerivInstTys -> SDoc
ppr (DerivInstTys { dit_cls_tys :: DerivInstTys -> [Type]
dit_cls_tys = [Type]
cls_tys, dit_tc :: DerivInstTys -> TyCon
dit_tc = TyCon
tc, dit_tc_args :: DerivInstTys -> [Type]
dit_tc_args = [Type]
tc_args
                    , dit_rep_tc :: DerivInstTys -> TyCon
dit_rep_tc = TyCon
rep_tc, dit_rep_tc_args :: DerivInstTys -> [Type]
dit_rep_tc_args = [Type]
rep_tc_args })
    = SDoc -> Int -> SDoc -> SDoc
hang (String -> SDoc
text String
"DITTyConHead")
         Int
2 ([SDoc] -> SDoc
vcat [ String -> SDoc
text String
"dit_cls_tys"     SDoc -> SDoc -> SDoc
<+> [Type] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [Type]
cls_tys
                 , String -> SDoc
text String
"dit_tc"          SDoc -> SDoc -> SDoc
<+> TyCon -> SDoc
forall a. Outputable a => a -> SDoc
ppr TyCon
tc
                 , String -> SDoc
text String
"dit_tc_args"     SDoc -> SDoc -> SDoc
<+> [Type] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [Type]
tc_args
                 , String -> SDoc
text String
"dit_rep_tc"      SDoc -> SDoc -> SDoc
<+> TyCon -> SDoc
forall a. Outputable a => a -> SDoc
ppr TyCon
rep_tc
                 , String -> SDoc
text String
"dit_rep_tc_args" SDoc -> SDoc -> SDoc
<+> [Type] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [Type]
rep_tc_args ])

-- | What action to take in order to derive a class instance.
-- See @Note [DerivEnv and DerivSpecMechanism]@, as well as
-- @Note [Deriving strategies]@ in "GHC.Tc.Deriv".
data DerivSpecMechanism
    -- | \"Standard\" classes
  = DerivSpecStock
    { DerivSpecMechanism -> DerivInstTys
dsm_stock_dit    :: DerivInstTys
      -- ^ Information about the arguments to the class in the derived
      -- instance, including what type constructor the last argument is
      -- headed by. See @Note [DerivEnv and DerivSpecMechanism]@.
    , DerivSpecMechanism
-> SrcSpan
-> TyCon
-> [Type]
-> TcM (LHsBinds GhcPs, BagDerivStuff, [Name])
dsm_stock_gen_fn ::
        SrcSpan -> TyCon
                -> [Type]
                -> TcM (LHsBinds GhcPs, BagDerivStuff, [Name])
      -- ^ This function returns three things:
      --
      -- 1. @LHsBinds GhcPs@: The derived instance's function bindings
      --    (e.g., @compare (T x) (T y) = compare x y@)
      --
      -- 2. @BagDerivStuff@: Auxiliary bindings needed to support the derived
      --    instance. As examples, derived 'Generic' instances require
      --    associated type family instances, and derived 'Eq' and 'Ord'
      --    instances require top-level @con2tag@ functions.
      --    See @Note [Auxiliary binders]@ in "GHC.Tc.Deriv.Generate".
      --
      -- 3. @[Name]@: A list of Names for which @-Wunused-binds@ should be
      --    suppressed. This is used to suppress unused warnings for record
      --    selectors when deriving 'Read', 'Show', or 'Generic'.
      --    See @Note [Deriving and unused record selectors]@.
    }

    -- | @GeneralizedNewtypeDeriving@
  | DerivSpecNewtype
    { DerivSpecMechanism -> DerivInstTys
dsm_newtype_dit    :: DerivInstTys
      -- ^ Information about the arguments to the class in the derived
      -- instance, including what type constructor the last argument is
      -- headed by. See @Note [DerivEnv and DerivSpecMechanism]@.
    , DerivSpecMechanism -> Type
dsm_newtype_rep_ty :: Type
      -- ^ The newtype rep type.
    }

    -- | @DeriveAnyClass@
  | DerivSpecAnyClass

    -- | @DerivingVia@
  | DerivSpecVia
    { DerivSpecMechanism -> [Type]
dsm_via_cls_tys :: [Type]
      -- ^ All arguments to the class besides the last one.
    , DerivSpecMechanism -> Type
dsm_via_inst_ty :: Type
      -- ^ The last argument to the class.
    , DerivSpecMechanism -> Type
dsm_via_ty      :: Type
      -- ^ The @via@ type
    }

-- | Convert a 'DerivSpecMechanism' to its corresponding 'DerivStrategy'.
derivSpecMechanismToStrategy :: DerivSpecMechanism -> DerivStrategy GhcTc
derivSpecMechanismToStrategy :: DerivSpecMechanism -> DerivStrategy GhcTc
derivSpecMechanismToStrategy DerivSpecStock{}               = DerivStrategy GhcTc
forall pass. DerivStrategy pass
StockStrategy
derivSpecMechanismToStrategy DerivSpecNewtype{}             = DerivStrategy GhcTc
forall pass. DerivStrategy pass
NewtypeStrategy
derivSpecMechanismToStrategy DerivSpecMechanism
DerivSpecAnyClass              = DerivStrategy GhcTc
forall pass. DerivStrategy pass
AnyclassStrategy
derivSpecMechanismToStrategy (DerivSpecVia{dsm_via_ty :: DerivSpecMechanism -> Type
dsm_via_ty = Type
t}) = XViaStrategy GhcTc -> DerivStrategy GhcTc
forall pass. XViaStrategy pass -> DerivStrategy pass
ViaStrategy Type
XViaStrategy GhcTc
t

isDerivSpecStock, isDerivSpecNewtype, isDerivSpecAnyClass, isDerivSpecVia
  :: DerivSpecMechanism -> Bool
isDerivSpecStock :: DerivSpecMechanism -> Bool
isDerivSpecStock (DerivSpecStock{}) = Bool
True
isDerivSpecStock DerivSpecMechanism
_                  = Bool
False

isDerivSpecNewtype :: DerivSpecMechanism -> Bool
isDerivSpecNewtype (DerivSpecNewtype{}) = Bool
True
isDerivSpecNewtype DerivSpecMechanism
_                    = Bool
False

isDerivSpecAnyClass :: DerivSpecMechanism -> Bool
isDerivSpecAnyClass DerivSpecMechanism
DerivSpecAnyClass = Bool
True
isDerivSpecAnyClass DerivSpecMechanism
_                 = Bool
False

isDerivSpecVia :: DerivSpecMechanism -> Bool
isDerivSpecVia (DerivSpecVia{}) = Bool
True
isDerivSpecVia DerivSpecMechanism
_                = Bool
False

instance Outputable DerivSpecMechanism where
  ppr :: DerivSpecMechanism -> SDoc
ppr (DerivSpecStock{dsm_stock_dit :: DerivSpecMechanism -> DerivInstTys
dsm_stock_dit = DerivInstTys
dit})
    = SDoc -> Int -> SDoc -> SDoc
hang (String -> SDoc
text String
"DerivSpecStock")
         Int
2 ([SDoc] -> SDoc
vcat [ String -> SDoc
text String
"dsm_stock_dit" SDoc -> SDoc -> SDoc
<+> DerivInstTys -> SDoc
forall a. Outputable a => a -> SDoc
ppr DerivInstTys
dit ])
  ppr (DerivSpecNewtype { dsm_newtype_dit :: DerivSpecMechanism -> DerivInstTys
dsm_newtype_dit = DerivInstTys
dit, dsm_newtype_rep_ty :: DerivSpecMechanism -> Type
dsm_newtype_rep_ty = Type
rep_ty })
    = SDoc -> Int -> SDoc -> SDoc
hang (String -> SDoc
text String
"DerivSpecNewtype")
         Int
2 ([SDoc] -> SDoc
vcat [ String -> SDoc
text String
"dsm_newtype_dit"    SDoc -> SDoc -> SDoc
<+> DerivInstTys -> SDoc
forall a. Outputable a => a -> SDoc
ppr DerivInstTys
dit
                 , String -> SDoc
text String
"dsm_newtype_rep_ty" SDoc -> SDoc -> SDoc
<+> Type -> SDoc
forall a. Outputable a => a -> SDoc
ppr Type
rep_ty ])
  ppr DerivSpecMechanism
DerivSpecAnyClass = String -> SDoc
text String
"DerivSpecAnyClass"
  ppr (DerivSpecVia { dsm_via_cls_tys :: DerivSpecMechanism -> [Type]
dsm_via_cls_tys = [Type]
cls_tys, dsm_via_inst_ty :: DerivSpecMechanism -> Type
dsm_via_inst_ty = Type
inst_ty
                    , dsm_via_ty :: DerivSpecMechanism -> Type
dsm_via_ty = Type
via_ty })
    = SDoc -> Int -> SDoc -> SDoc
hang (String -> SDoc
text String
"DerivSpecVia")
         Int
2 ([SDoc] -> SDoc
vcat [ String -> SDoc
text String
"dsm_via_cls_tys" SDoc -> SDoc -> SDoc
<+> [Type] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [Type]
cls_tys
                 , String -> SDoc
text String
"dsm_via_inst_ty" SDoc -> SDoc -> SDoc
<+> Type -> SDoc
forall a. Outputable a => a -> SDoc
ppr Type
inst_ty
                 , String -> SDoc
text String
"dsm_via_ty"      SDoc -> SDoc -> SDoc
<+> Type -> SDoc
forall a. Outputable a => a -> SDoc
ppr Type
via_ty ])

{-
Note [DerivEnv and DerivSpecMechanism]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
DerivEnv contains all of the bits and pieces that are common to every
deriving strategy. (See Note [Deriving strategies] in GHC.Tc.Deriv.) Some deriving
strategies impose stricter requirements on the types involved in the derived
instance than others, and these differences are factored out into the
DerivSpecMechanism type. Suppose that the derived instance looks like this:

  instance ... => C arg_1 ... arg_n

Each deriving strategy imposes restrictions on arg_1 through arg_n as follows:

* stock (DerivSpecStock):

  Stock deriving requires that:

  - n must be a positive number. This is checked by
    GHC.Tc.Deriv.expectNonNullaryClsArgs
  - arg_n must be an application of an algebraic type constructor. Here,
    "algebraic type constructor" means:

    + An ordinary data type constructor, or
    + A data family type constructor such that the arguments it is applied to
      give rise to a data family instance.

    This is checked by GHC.Tc.Deriv.expectAlgTyConApp.

  This extra structure is witnessed by the DerivInstTys data type, which stores
  arg_1 through arg_(n-1) (dit_cls_tys), the algebraic type constructor
  (dit_tc), and its arguments (dit_tc_args). If dit_tc is an ordinary data type
  constructor, then dit_rep_tc/dit_rep_tc_args are the same as
  dit_tc/dit_tc_args. If dit_tc is a data family type constructor, then
  dit_rep_tc is the representation type constructor for the data family
  instance, and dit_rep_tc_args are the arguments to the representation type
  constructor in the corresponding instance.

* newtype (DerivSpecNewtype):

  Newtype deriving imposes the same DerivInstTys requirements as stock
  deriving. This is necessary because we need to know what the underlying type
  that the newtype wraps is, and this information can only be learned by
  knowing dit_rep_tc.

* anyclass (DerivSpecAnyclass):

  DeriveAnyClass is the most permissive deriving strategy of all, as it
  essentially imposes no requirements on the derived instance. This is because
  DeriveAnyClass simply derives an empty instance, so it does not need any
  particular knowledge about the types involved. It can do several things
  that stock/newtype deriving cannot do (#13154):

  - n can be 0. That is, one is allowed to anyclass-derive an instance with
    no arguments to the class, such as in this example:

      class C
      deriving anyclass instance C

  - One can derive an instance for a type that is not headed by a type
    constructor, such as in the following example:

      class C (n :: Nat)
      deriving instance C 0
      deriving instance C 1
      ...

  - One can derive an instance for a data family with no data family instances,
    such as in the following example:

      data family Foo a
      class C a
      deriving anyclass instance C (Foo a)

* via (DerivSpecVia):

  Like newtype deriving, DerivingVia requires that n must be a positive number.
  This is because when one derives something like this:

    deriving via Foo instance C Bar

  Then the generated code must specifically mention Bar. However, in
  contrast with newtype deriving, DerivingVia does *not* require Bar to be
  an application of an algebraic type constructor. This is because the
  generated code simply defers to invoking `coerce`, which does not need to
  know anything in particular about Bar (besides that it is representationally
  equal to Foo). This allows DerivingVia to do some things that are not
  possible with newtype deriving, such as deriving instances for data families
  without data instances (#13154):

    data family Foo a
    newtype ByBar a = ByBar a
    class Baz a where ...
    instance Baz (ByBar a) where ...
    deriving via ByBar (Foo a) instance Baz (Foo a)
-}

-- | Whether GHC is processing a @deriving@ clause or a standalone deriving
-- declaration.
data DerivContext
  = InferContext (Maybe SrcSpan) -- ^ @'InferContext mb_wildcard@ is either:
                                 --
                                 -- * A @deriving@ clause (in which case
                                 --   @mb_wildcard@ is 'Nothing').
                                 --
                                 -- * A standalone deriving declaration with
                                 --   an extra-constraints wildcard as the
                                 --   context (in which case @mb_wildcard@ is
                                 --   @'Just' loc@, where @loc@ is the location
                                 --   of the wildcard.
                                 --
                                 -- GHC should infer the context.

  | SupplyContext ThetaType      -- ^ @'SupplyContext' theta@ is a standalone
                                 -- deriving declaration, where @theta@ is the
                                 -- context supplied by the user.

instance Outputable DerivContext where
  ppr :: DerivContext -> SDoc
ppr (InferContext Maybe SrcSpan
standalone) = String -> SDoc
text String
"InferContext"  SDoc -> SDoc -> SDoc
<+> Maybe SrcSpan -> SDoc
forall a. Outputable a => a -> SDoc
ppr Maybe SrcSpan
standalone
  ppr (SupplyContext [Type]
theta)     = String -> SDoc
text String
"SupplyContext" SDoc -> SDoc -> SDoc
<+> [Type] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [Type]
theta

-- | Records whether a particular class can be derived by way of an
-- /originative/ deriving strategy (i.e., @stock@ or @anyclass@).
--
-- See @Note [Deriving strategies]@ in "GHC.Tc.Deriv".
data OriginativeDerivStatus
  = CanDeriveStock            -- Stock class, can derive
      (SrcSpan -> TyCon -> [Type]
               -> TcM (LHsBinds GhcPs, BagDerivStuff, [Name]))
  | StockClassError SDoc      -- Stock class, but can't do it
  | CanDeriveAnyClass         -- See Note [Deriving any class]
  | NonDerivableClass SDoc    -- Cannot derive with either stock or anyclass

-- A stock class is one either defined in the Haskell report or for which GHC
-- otherwise knows how to generate code for (possibly requiring the use of a
-- language extension), such as Eq, Ord, Ix, Data, Generic, etc.)

-- | A 'PredType' annotated with the origin of the constraint 'CtOrigin',
-- and whether or the constraint deals in types or kinds.
data PredOrigin = PredOrigin PredType CtOrigin TypeOrKind

-- | A list of wanted 'PredOrigin' constraints ('to_wanted_origins') to
-- simplify when inferring a derived instance's context. These are used in all
-- deriving strategies, but in the particular case of @DeriveAnyClass@, we
-- need extra information. In particular, we need:
--
-- * 'to_anyclass_skols', the list of type variables bound by a class method's
--   regular type signature, which should be rigid.
--
-- * 'to_anyclass_metas', the list of type variables bound by a class method's
--   default type signature. These can be unified as necessary.
--
-- * 'to_anyclass_givens', the list of constraints from a class method's
--   regular type signature, which can be used to help solve constraints
--   in the 'to_wanted_origins'.
--
-- (Note that 'to_wanted_origins' will likely contain type variables from the
-- derived type class or data type, neither of which will appear in
-- 'to_anyclass_skols' or 'to_anyclass_metas'.)
--
-- For all other deriving strategies, it is always the case that
-- 'to_anyclass_skols', 'to_anyclass_metas', and 'to_anyclass_givens' are
-- empty.
--
-- Here is an example to illustrate this:
--
-- @
-- class Foo a where
--   bar :: forall b. Ix b => a -> b -> String
--   default bar :: forall y. (Show a, Ix y) => a -> y -> String
--   bar x y = show x ++ show (range (y, y))
--
--   baz :: Eq a => a -> a -> Bool
--   default baz :: Ord a => a -> a -> Bool
--   baz x y = compare x y == EQ
--
-- data Quux q = Quux deriving anyclass Foo
-- @
--
-- Then it would generate two 'ThetaOrigin's, one for each method:
--
-- @
-- [ ThetaOrigin { to_anyclass_skols  = [b]
--               , to_anyclass_metas  = [y]
--               , to_anyclass_givens = [Ix b]
--               , to_wanted_origins  = [ Show (Quux q), Ix y
--                                      , (Quux q -> b -> String) ~
--                                        (Quux q -> y -> String)
--                                      ] }
-- , ThetaOrigin { to_anyclass_skols  = []
--               , to_anyclass_metas  = []
--               , to_anyclass_givens = [Eq (Quux q)]
--               , to_wanted_origins  = [ Ord (Quux q)
--                                      , (Quux q -> Quux q -> Bool) ~
--                                        (Quux q -> Quux q -> Bool)
--                                      ] }
-- ]
-- @
--
-- (Note that the type variable @q@ is bound by the data type @Quux@, and thus
-- it appears in neither 'to_anyclass_skols' nor 'to_anyclass_metas'.)
--
-- See @Note [Gathering and simplifying constraints for DeriveAnyClass]@
-- in "GHC.Tc.Deriv.Infer" for an explanation of how 'to_wanted_origins' are
-- determined in @DeriveAnyClass@, as well as how 'to_anyclass_skols',
-- 'to_anyclass_metas', and 'to_anyclass_givens' are used.
data ThetaOrigin
  = ThetaOrigin { ThetaOrigin -> [TyVar]
to_anyclass_skols  :: [TyVar]
                , ThetaOrigin -> [TyVar]
to_anyclass_metas  :: [TyVar]
                , ThetaOrigin -> [Type]
to_anyclass_givens :: ThetaType
                , ThetaOrigin -> [PredOrigin]
to_wanted_origins  :: [PredOrigin] }

instance Outputable PredOrigin where
  ppr :: PredOrigin -> SDoc
ppr (PredOrigin Type
ty CtOrigin
_ TypeOrKind
_) = Type -> SDoc
forall a. Outputable a => a -> SDoc
ppr Type
ty -- The origin is not so interesting when debugging

instance Outputable ThetaOrigin where
  ppr :: ThetaOrigin -> SDoc
ppr (ThetaOrigin { to_anyclass_skols :: ThetaOrigin -> [TyVar]
to_anyclass_skols  = [TyVar]
ac_skols
                   , to_anyclass_metas :: ThetaOrigin -> [TyVar]
to_anyclass_metas  = [TyVar]
ac_metas
                   , to_anyclass_givens :: ThetaOrigin -> [Type]
to_anyclass_givens = [Type]
ac_givens
                   , to_wanted_origins :: ThetaOrigin -> [PredOrigin]
to_wanted_origins  = [PredOrigin]
wanted_origins })
    = SDoc -> Int -> SDoc -> SDoc
hang (String -> SDoc
text String
"ThetaOrigin")
         Int
2 ([SDoc] -> SDoc
vcat [ String -> SDoc
text String
"to_anyclass_skols  =" SDoc -> SDoc -> SDoc
<+> [TyVar] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [TyVar]
ac_skols
                 , String -> SDoc
text String
"to_anyclass_metas  =" SDoc -> SDoc -> SDoc
<+> [TyVar] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [TyVar]
ac_metas
                 , String -> SDoc
text String
"to_anyclass_givens =" SDoc -> SDoc -> SDoc
<+> [Type] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [Type]
ac_givens
                 , String -> SDoc
text String
"to_wanted_origins  =" SDoc -> SDoc -> SDoc
<+> [PredOrigin] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [PredOrigin]
wanted_origins ])

mkPredOrigin :: CtOrigin -> TypeOrKind -> PredType -> PredOrigin
mkPredOrigin :: CtOrigin -> TypeOrKind -> Type -> PredOrigin
mkPredOrigin CtOrigin
origin TypeOrKind
t_or_k Type
pred = Type -> CtOrigin -> TypeOrKind -> PredOrigin
PredOrigin Type
pred CtOrigin
origin TypeOrKind
t_or_k

mkThetaOrigin :: CtOrigin -> TypeOrKind
              -> [TyVar] -> [TyVar] -> ThetaType -> ThetaType
              -> ThetaOrigin
mkThetaOrigin :: CtOrigin
-> TypeOrKind
-> [TyVar]
-> [TyVar]
-> [Type]
-> [Type]
-> ThetaOrigin
mkThetaOrigin CtOrigin
origin TypeOrKind
t_or_k [TyVar]
skols [TyVar]
metas [Type]
givens
  = [TyVar] -> [TyVar] -> [Type] -> [PredOrigin] -> ThetaOrigin
ThetaOrigin [TyVar]
skols [TyVar]
metas [Type]
givens ([PredOrigin] -> ThetaOrigin)
-> ([Type] -> [PredOrigin]) -> [Type] -> ThetaOrigin
forall b c a. (b -> c) -> (a -> b) -> a -> c
. (Type -> PredOrigin) -> [Type] -> [PredOrigin]
forall a b. (a -> b) -> [a] -> [b]
map (CtOrigin -> TypeOrKind -> Type -> PredOrigin
mkPredOrigin CtOrigin
origin TypeOrKind
t_or_k)

-- A common case where the ThetaOrigin only contains wanted constraints, with
-- no givens or locally scoped type variables.
mkThetaOriginFromPreds :: [PredOrigin] -> ThetaOrigin
mkThetaOriginFromPreds :: [PredOrigin] -> ThetaOrigin
mkThetaOriginFromPreds = [TyVar] -> [TyVar] -> [Type] -> [PredOrigin] -> ThetaOrigin
ThetaOrigin [] [] []

substPredOrigin :: HasCallStack => TCvSubst -> PredOrigin -> PredOrigin
substPredOrigin :: HasCallStack => TCvSubst -> PredOrigin -> PredOrigin
substPredOrigin TCvSubst
subst (PredOrigin Type
pred CtOrigin
origin TypeOrKind
t_or_k)
  = Type -> CtOrigin -> TypeOrKind -> PredOrigin
PredOrigin (HasCallStack => TCvSubst -> Type -> Type
TCvSubst -> Type -> Type
substTy TCvSubst
subst Type
pred) CtOrigin
origin TypeOrKind
t_or_k

{-
************************************************************************
*                                                                      *
                Class deriving diagnostics
*                                                                      *
************************************************************************

Only certain blessed classes can be used in a deriving clause (without the
assistance of GeneralizedNewtypeDeriving or DeriveAnyClass). These classes
are listed below in the definition of hasStockDeriving. The stockSideConditions
function determines the criteria that needs to be met in order for a particular
stock class to be able to be derived successfully.

A class might be able to be used in a deriving clause if -XDeriveAnyClass
is willing to support it. The canDeriveAnyClass function checks if this is the
case.
-}

hasStockDeriving
  :: Class -> Maybe (SrcSpan
                     -> TyCon
                     -> [Type]
                     -> TcM (LHsBinds GhcPs, BagDerivStuff, [Name]))
hasStockDeriving :: Class
-> Maybe
     (SrcSpan
      -> TyCon -> [Type] -> TcM (LHsBinds GhcPs, BagDerivStuff, [Name]))
hasStockDeriving Class
clas
  = Assoc
  Unique
  (SrcSpan
   -> TyCon -> [Type] -> TcM (LHsBinds GhcPs, BagDerivStuff, [Name]))
-> Unique
-> Maybe
     (SrcSpan
      -> TyCon -> [Type] -> TcM (LHsBinds GhcPs, BagDerivStuff, [Name]))
forall a b. Eq a => Assoc a b -> a -> Maybe b
assocMaybe Assoc
  Unique
  (SrcSpan
   -> TyCon -> [Type] -> TcM (LHsBinds GhcPs, BagDerivStuff, [Name]))
gen_list (Class -> Unique
forall a. Uniquable a => a -> Unique
getUnique Class
clas)
  where
    gen_list
      :: [(Unique, SrcSpan
                   -> TyCon
                   -> [Type]
                   -> TcM (LHsBinds GhcPs, BagDerivStuff, [Name]))]
    gen_list :: Assoc
  Unique
  (SrcSpan
   -> TyCon -> [Type] -> TcM (LHsBinds GhcPs, BagDerivStuff, [Name]))
gen_list = [ (Unique
eqClassKey,          (SrcSpan
 -> TyCon
 -> IOEnv (Env TcGblEnv TcLclEnv) (LHsBinds GhcPs, BagDerivStuff))
-> SrcSpan
-> TyCon
-> [Type]
-> TcM (LHsBinds GhcPs, BagDerivStuff, [Name])
forall {m :: * -> *} {t} {t} {a} {b} {p} {a}.
Monad m =>
(t -> t -> m (a, b)) -> t -> t -> p -> m (a, b, [a])
simpleM SrcSpan
-> TyCon
-> IOEnv (Env TcGblEnv TcLclEnv) (LHsBinds GhcPs, BagDerivStuff)
gen_Eq_binds)
               , (Unique
ordClassKey,         (SrcSpan
 -> TyCon
 -> IOEnv (Env TcGblEnv TcLclEnv) (LHsBinds GhcPs, BagDerivStuff))
-> SrcSpan
-> TyCon
-> [Type]
-> TcM (LHsBinds GhcPs, BagDerivStuff, [Name])
forall {m :: * -> *} {t} {t} {a} {b} {p} {a}.
Monad m =>
(t -> t -> m (a, b)) -> t -> t -> p -> m (a, b, [a])
simpleM SrcSpan
-> TyCon
-> IOEnv (Env TcGblEnv TcLclEnv) (LHsBinds GhcPs, BagDerivStuff)
gen_Ord_binds)
               , (Unique
enumClassKey,        (SrcSpan
 -> TyCon
 -> IOEnv (Env TcGblEnv TcLclEnv) (LHsBinds GhcPs, BagDerivStuff))
-> SrcSpan
-> TyCon
-> [Type]
-> TcM (LHsBinds GhcPs, BagDerivStuff, [Name])
forall {m :: * -> *} {t} {t} {a} {b} {p} {a}.
Monad m =>
(t -> t -> m (a, b)) -> t -> t -> p -> m (a, b, [a])
simpleM SrcSpan
-> TyCon
-> IOEnv (Env TcGblEnv TcLclEnv) (LHsBinds GhcPs, BagDerivStuff)
gen_Enum_binds)
               , (Unique
boundedClassKey,     (SrcSpan -> TyCon -> (LHsBinds GhcPs, BagDerivStuff))
-> SrcSpan
-> TyCon
-> [Type]
-> TcM (LHsBinds GhcPs, BagDerivStuff, [Name])
forall {m :: * -> *} {t} {t} {a} {b} {p} {a}.
Monad m =>
(t -> t -> (a, b)) -> t -> t -> p -> m (a, b, [a])
simple SrcSpan -> TyCon -> (LHsBinds GhcPs, BagDerivStuff)
gen_Bounded_binds)
               , (Unique
ixClassKey,          (SrcSpan
 -> TyCon
 -> IOEnv (Env TcGblEnv TcLclEnv) (LHsBinds GhcPs, BagDerivStuff))
-> SrcSpan
-> TyCon
-> [Type]
-> TcM (LHsBinds GhcPs, BagDerivStuff, [Name])
forall {m :: * -> *} {t} {t} {a} {b} {p} {a}.
Monad m =>
(t -> t -> m (a, b)) -> t -> t -> p -> m (a, b, [a])
simpleM SrcSpan
-> TyCon
-> IOEnv (Env TcGblEnv TcLclEnv) (LHsBinds GhcPs, BagDerivStuff)
gen_Ix_binds)
               , (Unique
showClassKey,        ((Name -> Fixity)
 -> SrcSpan -> TyCon -> (LHsBinds GhcPs, BagDerivStuff))
-> SrcSpan
-> TyCon
-> [Type]
-> TcM (LHsBinds GhcPs, BagDerivStuff, [Name])
forall {t} {a} {b} {p}.
((Name -> Fixity) -> t -> TyCon -> (a, b))
-> t -> TyCon -> p -> IOEnv (Env TcGblEnv TcLclEnv) (a, b, [Name])
read_or_show (Name -> Fixity)
-> SrcSpan -> TyCon -> (LHsBinds GhcPs, BagDerivStuff)
gen_Show_binds)
               , (Unique
readClassKey,        ((Name -> Fixity)
 -> SrcSpan -> TyCon -> (LHsBinds GhcPs, BagDerivStuff))
-> SrcSpan
-> TyCon
-> [Type]
-> TcM (LHsBinds GhcPs, BagDerivStuff, [Name])
forall {t} {a} {b} {p}.
((Name -> Fixity) -> t -> TyCon -> (a, b))
-> t -> TyCon -> p -> IOEnv (Env TcGblEnv TcLclEnv) (a, b, [Name])
read_or_show (Name -> Fixity)
-> SrcSpan -> TyCon -> (LHsBinds GhcPs, BagDerivStuff)
gen_Read_binds)
               , (Unique
dataClassKey,        (SrcSpan
 -> TyCon
 -> IOEnv (Env TcGblEnv TcLclEnv) (LHsBinds GhcPs, BagDerivStuff))
-> SrcSpan
-> TyCon
-> [Type]
-> TcM (LHsBinds GhcPs, BagDerivStuff, [Name])
forall {m :: * -> *} {t} {t} {a} {b} {p} {a}.
Monad m =>
(t -> t -> m (a, b)) -> t -> t -> p -> m (a, b, [a])
simpleM SrcSpan
-> TyCon
-> IOEnv (Env TcGblEnv TcLclEnv) (LHsBinds GhcPs, BagDerivStuff)
gen_Data_binds)
               , (Unique
functorClassKey,     (SrcSpan -> TyCon -> (LHsBinds GhcPs, BagDerivStuff))
-> SrcSpan
-> TyCon
-> [Type]
-> TcM (LHsBinds GhcPs, BagDerivStuff, [Name])
forall {m :: * -> *} {t} {t} {a} {b} {p} {a}.
Monad m =>
(t -> t -> (a, b)) -> t -> t -> p -> m (a, b, [a])
simple SrcSpan -> TyCon -> (LHsBinds GhcPs, BagDerivStuff)
gen_Functor_binds)
               , (Unique
foldableClassKey,    (SrcSpan -> TyCon -> (LHsBinds GhcPs, BagDerivStuff))
-> SrcSpan
-> TyCon
-> [Type]
-> TcM (LHsBinds GhcPs, BagDerivStuff, [Name])
forall {m :: * -> *} {t} {t} {a} {b} {p} {a}.
Monad m =>
(t -> t -> (a, b)) -> t -> t -> p -> m (a, b, [a])
simple SrcSpan -> TyCon -> (LHsBinds GhcPs, BagDerivStuff)
gen_Foldable_binds)
               , (Unique
traversableClassKey, (SrcSpan -> TyCon -> (LHsBinds GhcPs, BagDerivStuff))
-> SrcSpan
-> TyCon
-> [Type]
-> TcM (LHsBinds GhcPs, BagDerivStuff, [Name])
forall {m :: * -> *} {t} {t} {a} {b} {p} {a}.
Monad m =>
(t -> t -> (a, b)) -> t -> t -> p -> m (a, b, [a])
simple SrcSpan -> TyCon -> (LHsBinds GhcPs, BagDerivStuff)
gen_Traversable_binds)
               , (Unique
liftClassKey,        (SrcSpan -> TyCon -> (LHsBinds GhcPs, BagDerivStuff))
-> SrcSpan
-> TyCon
-> [Type]
-> TcM (LHsBinds GhcPs, BagDerivStuff, [Name])
forall {m :: * -> *} {t} {t} {a} {b} {p} {a}.
Monad m =>
(t -> t -> (a, b)) -> t -> t -> p -> m (a, b, [a])
simple SrcSpan -> TyCon -> (LHsBinds GhcPs, BagDerivStuff)
gen_Lift_binds)
               , (Unique
genClassKey,         (TyCon
 -> [Type]
 -> IOEnv (Env TcGblEnv TcLclEnv) (LHsBinds GhcPs, FamInst))
-> SrcSpan
-> TyCon
-> [Type]
-> TcM (LHsBinds GhcPs, BagDerivStuff, [Name])
forall {m :: * -> *} {t} {a} {p}.
Monad m =>
(TyCon -> t -> m (a, FamInst))
-> p -> TyCon -> t -> m (a, BagDerivStuff, [Name])
generic (GenericKind
-> TyCon
-> [Type]
-> IOEnv (Env TcGblEnv TcLclEnv) (LHsBinds GhcPs, FamInst)
gen_Generic_binds GenericKind
Gen0))
               , (Unique
gen1ClassKey,        (TyCon
 -> [Type]
 -> IOEnv (Env TcGblEnv TcLclEnv) (LHsBinds GhcPs, FamInst))
-> SrcSpan
-> TyCon
-> [Type]
-> TcM (LHsBinds GhcPs, BagDerivStuff, [Name])
forall {m :: * -> *} {t} {a} {p}.
Monad m =>
(TyCon -> t -> m (a, FamInst))
-> p -> TyCon -> t -> m (a, BagDerivStuff, [Name])
generic (GenericKind
-> TyCon
-> [Type]
-> IOEnv (Env TcGblEnv TcLclEnv) (LHsBinds GhcPs, FamInst)
gen_Generic_binds GenericKind
Gen1)) ]

    simple :: (t -> t -> (a, b)) -> t -> t -> p -> m (a, b, [a])
simple t -> t -> (a, b)
gen_fn t
loc t
tc p
_
      = let (a
binds, b
deriv_stuff) = t -> t -> (a, b)
gen_fn t
loc t
tc
        in (a, b, [a]) -> m (a, b, [a])
forall (m :: * -> *) a. Monad m => a -> m a
return (a
binds, b
deriv_stuff, [])

    -- Like `simple`, but monadic. The only monadic thing that these functions
    -- do is allocate new Uniques, which are used for generating the names of
    -- auxiliary bindings.
    -- See Note [Auxiliary binders] in GHC.Tc.Deriv.Generate.
    simpleM :: (t -> t -> m (a, b)) -> t -> t -> p -> m (a, b, [a])
simpleM t -> t -> m (a, b)
gen_fn t
loc t
tc p
_
      = do { (a
binds, b
deriv_stuff) <- t -> t -> m (a, b)
gen_fn t
loc t
tc
           ; (a, b, [a]) -> m (a, b, [a])
forall (m :: * -> *) a. Monad m => a -> m a
return (a
binds, b
deriv_stuff, []) }

    read_or_show :: ((Name -> Fixity) -> t -> TyCon -> (a, b))
-> t -> TyCon -> p -> IOEnv (Env TcGblEnv TcLclEnv) (a, b, [Name])
read_or_show (Name -> Fixity) -> t -> TyCon -> (a, b)
gen_fn t
loc TyCon
tc p
_
      = do { Name -> Fixity
fix_env <- TyCon -> TcM (Name -> Fixity)
getDataConFixityFun TyCon
tc
           ; let (a
binds, b
deriv_stuff) = (Name -> Fixity) -> t -> TyCon -> (a, b)
gen_fn Name -> Fixity
fix_env t
loc TyCon
tc
                 field_names :: [Name]
field_names          = TyCon -> [Name]
all_field_names TyCon
tc
           ; (a, b, [Name]) -> IOEnv (Env TcGblEnv TcLclEnv) (a, b, [Name])
forall (m :: * -> *) a. Monad m => a -> m a
return (a
binds, b
deriv_stuff, [Name]
field_names) }

    generic :: (TyCon -> t -> m (a, FamInst))
-> p -> TyCon -> t -> m (a, BagDerivStuff, [Name])
generic TyCon -> t -> m (a, FamInst)
gen_fn p
_ TyCon
tc t
inst_tys
      = do { (a
binds, FamInst
faminst) <- TyCon -> t -> m (a, FamInst)
gen_fn TyCon
tc t
inst_tys
           ; let field_names :: [Name]
field_names = TyCon -> [Name]
all_field_names TyCon
tc
           ; (a, BagDerivStuff, [Name]) -> m (a, BagDerivStuff, [Name])
forall (m :: * -> *) a. Monad m => a -> m a
return (a
binds, DerivStuff -> BagDerivStuff
forall a. a -> Bag a
unitBag (FamInst -> DerivStuff
DerivFamInst FamInst
faminst), [Name]
field_names) }

    -- See Note [Deriving and unused record selectors]
    all_field_names :: TyCon -> [Name]
all_field_names = (FieldLbl Name -> Name) -> [FieldLbl Name] -> [Name]
forall a b. (a -> b) -> [a] -> [b]
map FieldLbl Name -> Name
forall a. FieldLbl a -> a
flSelector ([FieldLbl Name] -> [Name])
-> (TyCon -> [FieldLbl Name]) -> TyCon -> [Name]
forall b c a. (b -> c) -> (a -> b) -> a -> c
. (DataCon -> [FieldLbl Name]) -> [DataCon] -> [FieldLbl Name]
forall (t :: * -> *) a b. Foldable t => (a -> [b]) -> t a -> [b]
concatMap DataCon -> [FieldLbl Name]
dataConFieldLabels
                                     ([DataCon] -> [FieldLbl Name])
-> (TyCon -> [DataCon]) -> TyCon -> [FieldLbl Name]
forall b c a. (b -> c) -> (a -> b) -> a -> c
. TyCon -> [DataCon]
tyConDataCons

{-
Note [Deriving and unused record selectors]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider this (see #13919):

  module Main (main) where

  data Foo = MkFoo {bar :: String} deriving Show

  main :: IO ()
  main = print (Foo "hello")

Strictly speaking, the record selector `bar` is unused in this module, since
neither `main` nor the derived `Show` instance for `Foo` mention `bar`.
However, the behavior of `main` is affected by the presence of `bar`, since
it will print different output depending on whether `MkFoo` is defined using
record selectors or not. Therefore, we do not to issue a
"Defined but not used: ‘bar’" warning for this module, since removing `bar`
changes the program's behavior. This is the reason behind the [Name] part of
the return type of `hasStockDeriving`—it tracks all of the record selector
`Name`s for which -Wunused-binds should be suppressed.

Currently, the only three stock derived classes that require this are Read,
Show, and Generic, as their derived code all depend on the record selectors
of the derived data type's constructors.

See also Note [Newtype deriving and unused constructors] in GHC.Tc.Deriv for
another example of a similar trick.
-}

getDataConFixityFun :: TyCon -> TcM (Name -> Fixity)
-- If the TyCon is locally defined, we want the local fixity env;
-- but if it is imported (which happens for standalone deriving)
-- we need to get the fixity env from the interface file
-- c.f. GHC.Rename.Env.lookupFixity, and #9830
getDataConFixityFun :: TyCon -> TcM (Name -> Fixity)
getDataConFixityFun TyCon
tc
  = do { Module
this_mod <- IOEnv (Env TcGblEnv TcLclEnv) Module
forall (m :: * -> *). HasModule m => m Module
getModule
       ; if Module -> Name -> Bool
nameIsLocalOrFrom Module
this_mod Name
name
         then do { FixityEnv
fix_env <- TcRn FixityEnv
getFixityEnv
                 ; (Name -> Fixity) -> TcM (Name -> Fixity)
forall (m :: * -> *) a. Monad m => a -> m a
return (FixityEnv -> Name -> Fixity
lookupFixity FixityEnv
fix_env) }
         else do { ModIface
iface <- SDoc -> Name -> TcRn ModIface
loadInterfaceForName SDoc
doc Name
name
                            -- Should already be loaded!
                 ; (Name -> Fixity) -> TcM (Name -> Fixity)
forall (m :: * -> *) a. Monad m => a -> m a
return (ModIface -> OccName -> Fixity
mi_fix ModIface
iface (OccName -> Fixity) -> (Name -> OccName) -> Name -> Fixity
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Name -> OccName
nameOccName) } }
  where
    name :: Name
name = TyCon -> Name
tyConName TyCon
tc
    doc :: SDoc
doc = String -> SDoc
text String
"Data con fixities for" SDoc -> SDoc -> SDoc
<+> Name -> SDoc
forall a. Outputable a => a -> SDoc
ppr Name
name

------------------------------------------------------------------
-- Check side conditions that dis-allow derivability for the originative
-- deriving strategies (stock and anyclass).
-- See Note [Deriving strategies] in GHC.Tc.Deriv for an explanation of what
-- "originative" means.
--
-- This is *apart* from the coerce-based strategies, newtype and via.
--
-- Here we get the representation tycon in case of family instances as it has
-- the data constructors - but we need to be careful to fall back to the
-- family tycon (with indexes) in error messages.

checkOriginativeSideConditions
  :: DynFlags -> DerivContext -> Class -> [TcType]
  -> TyCon -> TyCon
  -> OriginativeDerivStatus
checkOriginativeSideConditions :: DynFlags
-> DerivContext
-> Class
-> [Type]
-> TyCon
-> TyCon
-> OriginativeDerivStatus
checkOriginativeSideConditions DynFlags
dflags DerivContext
deriv_ctxt Class
cls [Type]
cls_tys TyCon
tc TyCon
rep_tc
    -- First, check if stock deriving is possible...
  | Just Condition
cond <- DerivContext -> Class -> Maybe Condition
stockSideConditions DerivContext
deriv_ctxt Class
cls
  = case (Condition
cond DynFlags
dflags TyCon
tc TyCon
rep_tc) of
        NotValid SDoc
err -> SDoc -> OriginativeDerivStatus
StockClassError SDoc
err  -- Class-specific error
        Validity
IsValid  | [Type] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null (TyCon -> [Type] -> [Type]
filterOutInvisibleTypes (Class -> TyCon
classTyCon Class
cls) [Type]
cls_tys)
                   -- All stock derivable classes are unary in the sense that
                   -- there should be not types in cls_tys (i.e., no type args
                   -- other than last). Note that cls_types can contain
                   -- invisible types as well (e.g., for Generic1, which is
                   -- poly-kinded), so make sure those are not counted.
                 , Just SrcSpan
-> TyCon -> [Type] -> TcM (LHsBinds GhcPs, BagDerivStuff, [Name])
gen_fn <- Class
-> Maybe
     (SrcSpan
      -> TyCon -> [Type] -> TcM (LHsBinds GhcPs, BagDerivStuff, [Name]))
hasStockDeriving Class
cls
                   -> (SrcSpan
 -> TyCon -> [Type] -> TcM (LHsBinds GhcPs, BagDerivStuff, [Name]))
-> OriginativeDerivStatus
CanDeriveStock SrcSpan
-> TyCon -> [Type] -> TcM (LHsBinds GhcPs, BagDerivStuff, [Name])
gen_fn
                 | Bool
otherwise -> SDoc -> OriginativeDerivStatus
StockClassError (Class -> [Type] -> SDoc
classArgsErr Class
cls [Type]
cls_tys)
                   -- e.g. deriving( Eq s )

    -- ...if not, try falling back on DeriveAnyClass.
  | NotValid SDoc
err <- DynFlags -> Validity
canDeriveAnyClass DynFlags
dflags
  = SDoc -> OriginativeDerivStatus
NonDerivableClass SDoc
err  -- Neither anyclass nor stock work

  | Bool
otherwise
  = OriginativeDerivStatus
CanDeriveAnyClass   -- DeriveAnyClass should work

classArgsErr :: Class -> [Type] -> SDoc
classArgsErr :: Class -> [Type] -> SDoc
classArgsErr Class
cls [Type]
cls_tys = SDoc -> SDoc
quotes (Type -> SDoc
forall a. Outputable a => a -> SDoc
ppr (Class -> [Type] -> Type
mkClassPred Class
cls [Type]
cls_tys)) SDoc -> SDoc -> SDoc
<+> String -> SDoc
text String
"is not a class"

-- Side conditions (whether the datatype must have at least one constructor,
-- required language extensions, etc.) for using GHC's stock deriving
-- mechanism on certain classes (as opposed to classes that require
-- GeneralizedNewtypeDeriving or DeriveAnyClass). Returns Nothing for a
-- class for which stock deriving isn't possible.
stockSideConditions :: DerivContext -> Class -> Maybe Condition
stockSideConditions :: DerivContext -> Class -> Maybe Condition
stockSideConditions DerivContext
deriv_ctxt Class
cls
  | Unique
cls_key Unique -> Unique -> Bool
forall a. Eq a => a -> a -> Bool
== Unique
eqClassKey          = Condition -> Maybe Condition
forall a. a -> Maybe a
Just (Condition
cond_std Condition -> Condition -> Condition
`andCond` Class -> Condition
cond_args Class
cls)
  | Unique
cls_key Unique -> Unique -> Bool
forall a. Eq a => a -> a -> Bool
== Unique
ordClassKey         = Condition -> Maybe Condition
forall a. a -> Maybe a
Just (Condition
cond_std Condition -> Condition -> Condition
`andCond` Class -> Condition
cond_args Class
cls)
  | Unique
cls_key Unique -> Unique -> Bool
forall a. Eq a => a -> a -> Bool
== Unique
showClassKey        = Condition -> Maybe Condition
forall a. a -> Maybe a
Just (Condition
cond_std Condition -> Condition -> Condition
`andCond` Class -> Condition
cond_args Class
cls)
  | Unique
cls_key Unique -> Unique -> Bool
forall a. Eq a => a -> a -> Bool
== Unique
readClassKey        = Condition -> Maybe Condition
forall a. a -> Maybe a
Just (Condition
cond_std Condition -> Condition -> Condition
`andCond` Class -> Condition
cond_args Class
cls)
  | Unique
cls_key Unique -> Unique -> Bool
forall a. Eq a => a -> a -> Bool
== Unique
enumClassKey        = Condition -> Maybe Condition
forall a. a -> Maybe a
Just (Condition
cond_std Condition -> Condition -> Condition
`andCond` Condition
cond_isEnumeration)
  | Unique
cls_key Unique -> Unique -> Bool
forall a. Eq a => a -> a -> Bool
== Unique
ixClassKey          = Condition -> Maybe Condition
forall a. a -> Maybe a
Just (Condition
cond_std Condition -> Condition -> Condition
`andCond` Class -> Condition
cond_enumOrProduct Class
cls)
  | Unique
cls_key Unique -> Unique -> Bool
forall a. Eq a => a -> a -> Bool
== Unique
boundedClassKey     = Condition -> Maybe Condition
forall a. a -> Maybe a
Just (Condition
cond_std Condition -> Condition -> Condition
`andCond` Class -> Condition
cond_enumOrProduct Class
cls)
  | Unique
cls_key Unique -> Unique -> Bool
forall a. Eq a => a -> a -> Bool
== Unique
dataClassKey        = Condition -> Maybe Condition
forall a. a -> Maybe a
Just (Extension -> Condition
checkFlag Extension
LangExt.DeriveDataTypeable Condition -> Condition -> Condition
`andCond`
                                           Condition
cond_vanilla Condition -> Condition -> Condition
`andCond`
                                           Class -> Condition
cond_args Class
cls)
  | Unique
cls_key Unique -> Unique -> Bool
forall a. Eq a => a -> a -> Bool
== Unique
functorClassKey     = Condition -> Maybe Condition
forall a. a -> Maybe a
Just (Extension -> Condition
checkFlag Extension
LangExt.DeriveFunctor Condition -> Condition -> Condition
`andCond`
                                           Condition
cond_vanilla Condition -> Condition -> Condition
`andCond`
                                           Bool -> Bool -> Condition
cond_functorOK Bool
True Bool
False)
  | Unique
cls_key Unique -> Unique -> Bool
forall a. Eq a => a -> a -> Bool
== Unique
foldableClassKey    = Condition -> Maybe Condition
forall a. a -> Maybe a
Just (Extension -> Condition
checkFlag Extension
LangExt.DeriveFoldable Condition -> Condition -> Condition
`andCond`
                                           Condition
cond_vanilla Condition -> Condition -> Condition
`andCond`
                                           Bool -> Bool -> Condition
cond_functorOK Bool
False Bool
True)
                                           -- Functor/Fold/Trav works ok
                                           -- for rank-n types
  | Unique
cls_key Unique -> Unique -> Bool
forall a. Eq a => a -> a -> Bool
== Unique
traversableClassKey = Condition -> Maybe Condition
forall a. a -> Maybe a
Just (Extension -> Condition
checkFlag Extension
LangExt.DeriveTraversable Condition -> Condition -> Condition
`andCond`
                                           Condition
cond_vanilla Condition -> Condition -> Condition
`andCond`
                                           Bool -> Bool -> Condition
cond_functorOK Bool
False Bool
False)
  | Unique
cls_key Unique -> Unique -> Bool
forall a. Eq a => a -> a -> Bool
== Unique
genClassKey         = Condition -> Maybe Condition
forall a. a -> Maybe a
Just (Extension -> Condition
checkFlag Extension
LangExt.DeriveGeneric Condition -> Condition -> Condition
`andCond`
                                           Condition
cond_vanilla Condition -> Condition -> Condition
`andCond`
                                           Condition
cond_RepresentableOk)
  | Unique
cls_key Unique -> Unique -> Bool
forall a. Eq a => a -> a -> Bool
== Unique
gen1ClassKey        = Condition -> Maybe Condition
forall a. a -> Maybe a
Just (Extension -> Condition
checkFlag Extension
LangExt.DeriveGeneric Condition -> Condition -> Condition
`andCond`
                                           Condition
cond_vanilla Condition -> Condition -> Condition
`andCond`
                                           Condition
cond_Representable1Ok)
  | Unique
cls_key Unique -> Unique -> Bool
forall a. Eq a => a -> a -> Bool
== Unique
liftClassKey        = Condition -> Maybe Condition
forall a. a -> Maybe a
Just (Extension -> Condition
checkFlag Extension
LangExt.DeriveLift Condition -> Condition -> Condition
`andCond`
                                           Condition
cond_vanilla Condition -> Condition -> Condition
`andCond`
                                           Class -> Condition
cond_args Class
cls)
  | Bool
otherwise                      = Maybe Condition
forall a. Maybe a
Nothing
  where
    cls_key :: Unique
cls_key = Class -> Unique
forall a. Uniquable a => a -> Unique
getUnique Class
cls
    cond_std :: Condition
cond_std     = DerivContext -> Bool -> Condition
cond_stdOK DerivContext
deriv_ctxt Bool
False
      -- Vanilla data constructors, at least one, and monotype arguments
    cond_vanilla :: Condition
cond_vanilla = DerivContext -> Bool -> Condition
cond_stdOK DerivContext
deriv_ctxt Bool
True
      -- Vanilla data constructors but allow no data cons or polytype arguments

canDeriveAnyClass :: DynFlags -> Validity
-- IsValid: we can (try to) derive it via an empty instance declaration
-- NotValid s:  we can't, reason s
canDeriveAnyClass :: DynFlags -> Validity
canDeriveAnyClass DynFlags
dflags
  | Bool -> Bool
not (Extension -> DynFlags -> Bool
xopt Extension
LangExt.DeriveAnyClass DynFlags
dflags)
  = SDoc -> Validity
NotValid (String -> SDoc
text String
"Try enabling DeriveAnyClass")
  | Bool
otherwise
  = Validity
IsValid   -- OK!

type Condition
   = DynFlags

  -> TyCon    -- ^ The data type's 'TyCon'. For data families, this is the
              -- family 'TyCon'.

  -> TyCon    -- ^ For data families, this is the representation 'TyCon'.
              -- Otherwise, this is the same as the other 'TyCon' argument.

  -> Validity -- ^ 'IsValid' if deriving an instance for this 'TyCon' is
              -- possible. Otherwise, it's @'NotValid' err@, where @err@
              -- explains what went wrong.

orCond :: Condition -> Condition -> Condition
orCond :: Condition -> Condition -> Condition
orCond Condition
c1 Condition
c2 DynFlags
dflags TyCon
tc TyCon
rep_tc
  = case (Condition
c1 DynFlags
dflags TyCon
tc TyCon
rep_tc, Condition
c2 DynFlags
dflags TyCon
tc TyCon
rep_tc) of
     (Validity
IsValid,    Validity
_)          -> Validity
IsValid    -- c1 succeeds
     (Validity
_,          Validity
IsValid)    -> Validity
IsValid    -- c21 succeeds
     (NotValid SDoc
x, NotValid SDoc
y) -> SDoc -> Validity
NotValid (SDoc
x SDoc -> SDoc -> SDoc
$$ String -> SDoc
text String
"  or" SDoc -> SDoc -> SDoc
$$ SDoc
y)
                                            -- Both fail

andCond :: Condition -> Condition -> Condition
andCond :: Condition -> Condition -> Condition
andCond Condition
c1 Condition
c2 DynFlags
dflags TyCon
tc TyCon
rep_tc
  = Condition
c1 DynFlags
dflags TyCon
tc TyCon
rep_tc Validity -> Validity -> Validity
`andValid` Condition
c2 DynFlags
dflags TyCon
tc TyCon
rep_tc

-- | Some common validity checks shared among stock derivable classes. One
-- check that absolutely must hold is that if an instance @C (T a)@ is being
-- derived, then @T@ must be a tycon for a data type or a newtype. The
-- remaining checks are only performed if using a @deriving@ clause (i.e.,
-- they're ignored if using @StandaloneDeriving@):
--
-- 1. The data type must have at least one constructor (this check is ignored
--    if using @EmptyDataDeriving@).
--
-- 2. The data type cannot have any GADT constructors.
--
-- 3. The data type cannot have any constructors with existentially quantified
--    type variables.
--
-- 4. The data type cannot have a context (e.g., @data Foo a = Eq a => MkFoo@).
--
-- 5. The data type cannot have fields with higher-rank types.
cond_stdOK
  :: DerivContext -- ^ 'SupplyContext' if this is standalone deriving with a
                  -- user-supplied context, 'InferContext' if not.
                  -- If it is the former, we relax some of the validity checks
                  -- we would otherwise perform (i.e., "just go for it").

  -> Bool         -- ^ 'True' <=> allow higher rank arguments and empty data
                  -- types (with no data constructors) even in the absence of
                  -- the -XEmptyDataDeriving extension.

  -> Condition
cond_stdOK :: DerivContext -> Bool -> Condition
cond_stdOK DerivContext
deriv_ctxt Bool
permissive DynFlags
dflags TyCon
tc TyCon
rep_tc
  = Validity
valid_ADT Validity -> Validity -> Validity
`andValid` Validity
valid_misc
  where
    valid_ADT, valid_misc :: Validity
    valid_ADT :: Validity
valid_ADT
      | TyCon -> Bool
isAlgTyCon TyCon
tc Bool -> Bool -> Bool
|| TyCon -> Bool
isDataFamilyTyCon TyCon
tc
      = Validity
IsValid
      | Bool
otherwise
        -- Complain about functions, primitive types, and other tycons that
        -- stock deriving can't handle.
      = SDoc -> Validity
NotValid (SDoc -> Validity) -> SDoc -> Validity
forall a b. (a -> b) -> a -> b
$ String -> SDoc
text String
"The last argument of the instance must be a"
               SDoc -> SDoc -> SDoc
<+> String -> SDoc
text String
"data or newtype application"

    valid_misc :: Validity
valid_misc
      = case DerivContext
deriv_ctxt of
         SupplyContext [Type]
_ -> Validity
IsValid
                -- Don't check these conservative conditions for
                -- standalone deriving; just generate the code
                -- and let the typechecker handle the result
         InferContext Maybe SrcSpan
wildcard
           | [DataCon] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [DataCon]
data_cons -- 1.
           , Bool -> Bool
not Bool
permissive
           -> Extension -> Condition
checkFlag Extension
LangExt.EmptyDataDeriving DynFlags
dflags TyCon
tc TyCon
rep_tc Validity -> Validity -> Validity
`orValid`
              SDoc -> Validity
NotValid (TyCon -> SDoc
no_cons_why TyCon
rep_tc SDoc -> SDoc -> SDoc
$$ SDoc
empty_data_suggestion)
           | Bool -> Bool
not ([SDoc] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [SDoc]
con_whys)
           -> SDoc -> Validity
NotValid ([SDoc] -> SDoc
vcat [SDoc]
con_whys SDoc -> SDoc -> SDoc
$$ Maybe SrcSpan -> SDoc
forall {a}. Maybe a -> SDoc
possible_fix_suggestion Maybe SrcSpan
wildcard)
           | Bool
otherwise
           -> Validity
IsValid

    empty_data_suggestion :: SDoc
empty_data_suggestion =
      String -> SDoc
text String
"Use EmptyDataDeriving to enable deriving for empty data types"
    possible_fix_suggestion :: Maybe a -> SDoc
possible_fix_suggestion Maybe a
wildcard
      = case Maybe a
wildcard of
          Just a
_ ->
            String -> SDoc
text String
"Possible fix: fill in the wildcard constraint yourself"
          Maybe a
Nothing ->
            String -> SDoc
text String
"Possible fix: use a standalone deriving declaration instead"
    data_cons :: [DataCon]
data_cons  = TyCon -> [DataCon]
tyConDataCons TyCon
rep_tc
    con_whys :: [SDoc]
con_whys   = [Validity] -> [SDoc]
getInvalids ((DataCon -> Validity) -> [DataCon] -> [Validity]
forall a b. (a -> b) -> [a] -> [b]
map DataCon -> Validity
check_con [DataCon]
data_cons)

    check_con :: DataCon -> Validity
    check_con :: DataCon -> Validity
check_con DataCon
con
      | Bool -> Bool
not ([EqSpec] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [EqSpec]
eq_spec) -- 2.
      = String -> Validity
bad String
"is a GADT"
      | Bool -> Bool
not ([TyVar] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [TyVar]
ex_tvs) -- 3.
      = String -> Validity
bad String
"has existential type variables in its type"
      | Bool -> Bool
not ([Type] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [Type]
theta) -- 4.
      = String -> Validity
bad String
"has constraints in its type"
      | Bool -> Bool
not (Bool
permissive Bool -> Bool -> Bool
|| (Type -> Bool) -> [Type] -> Bool
forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
all Type -> Bool
isTauTy ((Scaled Type -> Type) -> [Scaled Type] -> [Type]
forall a b. (a -> b) -> [a] -> [b]
map Scaled Type -> Type
forall a. Scaled a -> a
scaledThing ([Scaled Type] -> [Type]) -> [Scaled Type] -> [Type]
forall a b. (a -> b) -> a -> b
$ DataCon -> [Scaled Type]
dataConOrigArgTys DataCon
con)) -- 5.
      = String -> Validity
bad String
"has a higher-rank type"
      | Bool
otherwise
      = Validity
IsValid
      where
        ([TyVar]
_, [TyVar]
ex_tvs, [EqSpec]
eq_spec, [Type]
theta, [Scaled Type]
_, Type
_) = DataCon
-> ([TyVar], [TyVar], [EqSpec], [Type], [Scaled Type], Type)
dataConFullSig DataCon
con
        bad :: String -> Validity
bad String
msg = SDoc -> Validity
NotValid (DataCon -> SDoc -> SDoc
badCon DataCon
con (String -> SDoc
text String
msg))

no_cons_why :: TyCon -> SDoc
no_cons_why :: TyCon -> SDoc
no_cons_why TyCon
rep_tc = SDoc -> SDoc
quotes (TyCon -> SDoc
pprSourceTyCon TyCon
rep_tc) SDoc -> SDoc -> SDoc
<+>
                     String -> SDoc
text String
"must have at least one data constructor"

cond_RepresentableOk :: Condition
cond_RepresentableOk :: Condition
cond_RepresentableOk DynFlags
_ TyCon
_ TyCon
rep_tc = TyCon -> Validity
canDoGenerics TyCon
rep_tc

cond_Representable1Ok :: Condition
cond_Representable1Ok :: Condition
cond_Representable1Ok DynFlags
_ TyCon
_ TyCon
rep_tc = TyCon -> Validity
canDoGenerics1 TyCon
rep_tc

cond_enumOrProduct :: Class -> Condition
cond_enumOrProduct :: Class -> Condition
cond_enumOrProduct Class
cls = Condition
cond_isEnumeration Condition -> Condition -> Condition
`orCond`
                         (Condition
cond_isProduct Condition -> Condition -> Condition
`andCond` Class -> Condition
cond_args Class
cls)

cond_args :: Class -> Condition
-- ^ For some classes (eg 'Eq', 'Ord') we allow unlifted arg types
-- by generating specialised code.  For others (eg 'Data') we don't.
-- For even others (eg 'Lift'), unlifted types aren't even a special
-- consideration!
cond_args :: Class -> Condition
cond_args Class
cls DynFlags
_ TyCon
_ TyCon
rep_tc
  = case [Type]
bad_args of
      []     -> Validity
IsValid
      (Type
ty:[Type]
_) -> SDoc -> Validity
NotValid (SDoc -> Int -> SDoc -> SDoc
hang (String -> SDoc
text String
"Don't know how to derive" SDoc -> SDoc -> SDoc
<+> SDoc -> SDoc
quotes (Class -> SDoc
forall a. Outputable a => a -> SDoc
ppr Class
cls))
                             Int
2 (String -> SDoc
text String
"for type" SDoc -> SDoc -> SDoc
<+> SDoc -> SDoc
quotes (Type -> SDoc
forall a. Outputable a => a -> SDoc
ppr Type
ty)))
  where
    bad_args :: [Type]
bad_args = [ Type
arg_ty | DataCon
con <- TyCon -> [DataCon]
tyConDataCons TyCon
rep_tc
                        , Scaled Type
_ Type
arg_ty <- DataCon -> [Scaled Type]
dataConOrigArgTys DataCon
con
                        , HasDebugCallStack => Type -> Maybe Bool
Type -> Maybe Bool
isLiftedType_maybe Type
arg_ty Maybe Bool -> Maybe Bool -> Bool
forall a. Eq a => a -> a -> Bool
/= Bool -> Maybe Bool
forall a. a -> Maybe a
Just Bool
True
                        , Bool -> Bool
not (Type -> Bool
ok_ty Type
arg_ty) ]

    cls_key :: Unique
cls_key = Class -> Unique
classKey Class
cls
    ok_ty :: Type -> Bool
ok_ty Type
arg_ty
     | Unique
cls_key Unique -> Unique -> Bool
forall a. Eq a => a -> a -> Bool
== Unique
eqClassKey   = Type
-> [(Type, (RdrName, RdrName, RdrName, RdrName, RdrName))] -> Bool
forall a. Type -> [(Type, a)] -> Bool
check_in Type
arg_ty [(Type, (RdrName, RdrName, RdrName, RdrName, RdrName))]
ordOpTbl
     | Unique
cls_key Unique -> Unique -> Bool
forall a. Eq a => a -> a -> Bool
== Unique
ordClassKey  = Type
-> [(Type, (RdrName, RdrName, RdrName, RdrName, RdrName))] -> Bool
forall a. Type -> [(Type, a)] -> Bool
check_in Type
arg_ty [(Type, (RdrName, RdrName, RdrName, RdrName, RdrName))]
ordOpTbl
     | Unique
cls_key Unique -> Unique -> Bool
forall a. Eq a => a -> a -> Bool
== Unique
showClassKey = Type -> [(Type, LHsExpr GhcPs -> LHsExpr GhcPs)] -> Bool
forall a. Type -> [(Type, a)] -> Bool
check_in Type
arg_ty [(Type, LHsExpr GhcPs -> LHsExpr GhcPs)]
boxConTbl
     | Unique
cls_key Unique -> Unique -> Bool
forall a. Eq a => a -> a -> Bool
== Unique
liftClassKey = Bool
True     -- Lift is levity-polymorphic
     | Bool
otherwise               = Bool
False    -- Read, Ix etc

    check_in :: Type -> [(Type,a)] -> Bool
    check_in :: forall a. Type -> [(Type, a)] -> Bool
check_in Type
arg_ty [(Type, a)]
tbl = ((Type, a) -> Bool) -> [(Type, a)] -> Bool
forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
any (Type -> Type -> Bool
eqType Type
arg_ty (Type -> Bool) -> ((Type, a) -> Type) -> (Type, a) -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. (Type, a) -> Type
forall a b. (a, b) -> a
fst) [(Type, a)]
tbl


cond_isEnumeration :: Condition
cond_isEnumeration :: Condition
cond_isEnumeration DynFlags
_ TyCon
_ TyCon
rep_tc
  | TyCon -> Bool
isEnumerationTyCon TyCon
rep_tc = Validity
IsValid
  | Bool
otherwise                 = SDoc -> Validity
NotValid SDoc
why
  where
    why :: SDoc
why = [SDoc] -> SDoc
sep [ SDoc -> SDoc
quotes (TyCon -> SDoc
pprSourceTyCon TyCon
rep_tc) SDoc -> SDoc -> SDoc
<+>
                  String -> SDoc
text String
"must be an enumeration type"
              , String -> SDoc
text String
"(an enumeration consists of one or more nullary, non-GADT constructors)" ]
                  -- See Note [Enumeration types] in GHC.Core.TyCon

cond_isProduct :: Condition
cond_isProduct :: Condition
cond_isProduct DynFlags
_ TyCon
_ TyCon
rep_tc
  | TyCon -> Bool
isProductTyCon TyCon
rep_tc = Validity
IsValid
  | Bool
otherwise             = SDoc -> Validity
NotValid SDoc
why
  where
    why :: SDoc
why = SDoc -> SDoc
quotes (TyCon -> SDoc
pprSourceTyCon TyCon
rep_tc) SDoc -> SDoc -> SDoc
<+>
          String -> SDoc
text String
"must have precisely one constructor"

cond_functorOK :: Bool -> Bool -> Condition
-- OK for Functor/Foldable/Traversable class
-- Currently: (a) at least one argument
--            (b) don't use argument contravariantly
--            (c) don't use argument in the wrong place, e.g. data T a = T (X a a)
--            (d) optionally: don't use function types
--            (e) no "stupid context" on data type
cond_functorOK :: Bool -> Bool -> Condition
cond_functorOK Bool
allowFunctions Bool
allowExQuantifiedLastTyVar DynFlags
_ TyCon
_ TyCon
rep_tc
  | [TyVar] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [TyVar]
tc_tvs
  = SDoc -> Validity
NotValid (String -> SDoc
text String
"Data type" SDoc -> SDoc -> SDoc
<+> SDoc -> SDoc
quotes (TyCon -> SDoc
forall a. Outputable a => a -> SDoc
ppr TyCon
rep_tc)
              SDoc -> SDoc -> SDoc
<+> String -> SDoc
text String
"must have some type parameters")

  | Bool -> Bool
not ([Type] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
null [Type]
bad_stupid_theta)
  = SDoc -> Validity
NotValid (String -> SDoc
text String
"Data type" SDoc -> SDoc -> SDoc
<+> SDoc -> SDoc
quotes (TyCon -> SDoc
forall a. Outputable a => a -> SDoc
ppr TyCon
rep_tc)
              SDoc -> SDoc -> SDoc
<+> String -> SDoc
text String
"must not have a class context:" SDoc -> SDoc -> SDoc
<+> [Type] -> SDoc
pprTheta [Type]
bad_stupid_theta)

  | Bool
otherwise
  = [Validity] -> Validity
allValid ((DataCon -> Validity) -> [DataCon] -> [Validity]
forall a b. (a -> b) -> [a] -> [b]
map DataCon -> Validity
check_con [DataCon]
data_cons)
  where
    tc_tvs :: [TyVar]
tc_tvs            = TyCon -> [TyVar]
tyConTyVars TyCon
rep_tc
    last_tv :: TyVar
last_tv           = [TyVar] -> TyVar
forall a. [a] -> a
last [TyVar]
tc_tvs
    bad_stupid_theta :: [Type]
bad_stupid_theta  = (Type -> Bool) -> [Type] -> [Type]
forall a. (a -> Bool) -> [a] -> [a]
filter Type -> Bool
is_bad (TyCon -> [Type]
tyConStupidTheta TyCon
rep_tc)
    is_bad :: Type -> Bool
is_bad Type
pred       = TyVar
last_tv TyVar -> VarSet -> Bool
`elemVarSet` Type -> VarSet
exactTyCoVarsOfType Type
pred
      -- See Note [Check that the type variable is truly universal]

    data_cons :: [DataCon]
data_cons = TyCon -> [DataCon]
tyConDataCons TyCon
rep_tc
    check_con :: DataCon -> Validity
check_con DataCon
con = [Validity] -> Validity
allValid (DataCon -> Validity
check_universal DataCon
con Validity -> [Validity] -> [Validity]
forall a. a -> [a] -> [a]
: FFoldType Validity -> DataCon -> [Validity]
forall a. FFoldType a -> DataCon -> [a]
foldDataConArgs (DataCon -> FFoldType Validity
ft_check DataCon
con) DataCon
con)

    check_universal :: DataCon -> Validity
    check_universal :: DataCon -> Validity
check_universal DataCon
con
      | Bool
allowExQuantifiedLastTyVar
      = Validity
IsValid -- See Note [DeriveFoldable with ExistentialQuantification]
                -- in GHC.Tc.Deriv.Functor
      | Just TyVar
tv <- Type -> Maybe TyVar
getTyVar_maybe ([Type] -> Type
forall a. [a] -> a
last (Type -> [Type]
tyConAppArgs (DataCon -> Type
dataConOrigResTy DataCon
con)))
      , TyVar
tv TyVar -> [TyVar] -> Bool
forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
`elem` DataCon -> [TyVar]
dataConUnivTyVars DataCon
con
      , Bool -> Bool
not (TyVar
tv TyVar -> VarSet -> Bool
`elemVarSet` [Type] -> VarSet
exactTyCoVarsOfTypes (DataCon -> [Type]
dataConTheta DataCon
con))
      = Validity
IsValid   -- See Note [Check that the type variable is truly universal]
      | Bool
otherwise
      = SDoc -> Validity
NotValid (DataCon -> SDoc -> SDoc
badCon DataCon
con SDoc
existential)

    ft_check :: DataCon -> FFoldType Validity
    ft_check :: DataCon -> FFoldType Validity
ft_check DataCon
con = FT :: forall a.
a
-> a
-> a
-> (a -> a -> a)
-> (TyCon -> [a] -> a)
-> (Type -> Type -> a -> a)
-> a
-> (TyVar -> a -> a)
-> FFoldType a
FT { ft_triv :: Validity
ft_triv = Validity
IsValid, ft_var :: Validity
ft_var = Validity
IsValid
                      , ft_co_var :: Validity
ft_co_var = SDoc -> Validity
NotValid (DataCon -> SDoc -> SDoc
badCon DataCon
con SDoc
covariant)
                      , ft_fun :: Validity -> Validity -> Validity
ft_fun = \Validity
x Validity
y -> if Bool
allowFunctions then Validity
x Validity -> Validity -> Validity
`andValid` Validity
y
                                                           else SDoc -> Validity
NotValid (DataCon -> SDoc -> SDoc
badCon DataCon
con SDoc
functions)
                      , ft_tup :: TyCon -> [Validity] -> Validity
ft_tup = \TyCon
_ [Validity]
xs  -> [Validity] -> Validity
allValid [Validity]
xs
                      , ft_ty_app :: Type -> Type -> Validity -> Validity
ft_ty_app = \Type
_ Type
_ Validity
x -> Validity
x
                      , ft_bad_app :: Validity
ft_bad_app = SDoc -> Validity
NotValid (DataCon -> SDoc -> SDoc
badCon DataCon
con SDoc
wrong_arg)
                      , ft_forall :: TyVar -> Validity -> Validity
ft_forall = \TyVar
_ Validity
x   -> Validity
x }

    existential :: SDoc
existential = String -> SDoc
text String
"must be truly polymorphic in the last argument of the data type"
    covariant :: SDoc
covariant   = String -> SDoc
text String
"must not use the type variable in a function argument"
    functions :: SDoc
functions   = String -> SDoc
text String
"must not contain function types"
    wrong_arg :: SDoc
wrong_arg   = String -> SDoc
text String
"must use the type variable only as the last argument of a data type"

checkFlag :: LangExt.Extension -> Condition
checkFlag :: Extension -> Condition
checkFlag Extension
flag DynFlags
dflags TyCon
_ TyCon
_
  | Extension -> DynFlags -> Bool
xopt Extension
flag DynFlags
dflags = Validity
IsValid
  | Bool
otherwise        = SDoc -> Validity
NotValid SDoc
why
  where
    why :: SDoc
why = String -> SDoc
text String
"You need " SDoc -> SDoc -> SDoc
<> String -> SDoc
text String
flag_str
          SDoc -> SDoc -> SDoc
<+> String -> SDoc
text String
"to derive an instance for this class"
    flag_str :: String
flag_str = case [ FlagSpec Extension -> String
forall flag. FlagSpec flag -> String
flagSpecName FlagSpec Extension
f | FlagSpec Extension
f <- [FlagSpec Extension]
xFlags , FlagSpec Extension -> Extension
forall flag. FlagSpec flag -> flag
flagSpecFlag FlagSpec Extension
f Extension -> Extension -> Bool
forall a. Eq a => a -> a -> Bool
== Extension
flag ] of
                 [String
s]   -> String
s
                 [String]
other -> String -> SDoc -> String
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"checkFlag" ([String] -> SDoc
forall a. Outputable a => a -> SDoc
ppr [String]
other)

std_class_via_coercible :: Class -> Bool
-- These standard classes can be derived for a newtype
-- using the coercible trick *even if no -XGeneralizedNewtypeDeriving
-- because giving so gives the same results as generating the boilerplate
std_class_via_coercible :: Class -> Bool
std_class_via_coercible Class
clas
  = Class -> Unique
classKey Class
clas Unique -> [Unique] -> Bool
forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
`elem` [Unique
eqClassKey, Unique
ordClassKey, Unique
ixClassKey, Unique
boundedClassKey]
        -- Not Read/Show because they respect the type
        -- Not Enum, because newtypes are never in Enum


non_coercible_class :: Class -> Bool
-- *Never* derive Read, Show, Typeable, Data, Generic, Generic1, Lift
-- by Coercible, even with -XGeneralizedNewtypeDeriving
-- Also, avoid Traversable, as the Coercible-derived instance and the "normal"-derived
-- instance behave differently if there's a non-lawful Applicative out there.
-- Besides, with roles, Coercible-deriving Traversable is ill-roled.
non_coercible_class :: Class -> Bool
non_coercible_class Class
cls
  = Class -> Unique
classKey Class
cls Unique -> [Unique] -> Bool
forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
`elem` ([ Unique
readClassKey, Unique
showClassKey, Unique
dataClassKey
                         , Unique
genClassKey, Unique
gen1ClassKey, Unique
typeableClassKey
                         , Unique
traversableClassKey, Unique
liftClassKey ])

badCon :: DataCon -> SDoc -> SDoc
badCon :: DataCon -> SDoc -> SDoc
badCon DataCon
con SDoc
msg = String -> SDoc
text String
"Constructor" SDoc -> SDoc -> SDoc
<+> SDoc -> SDoc
quotes (DataCon -> SDoc
forall a. Outputable a => a -> SDoc
ppr DataCon
con) SDoc -> SDoc -> SDoc
<+> SDoc
msg

------------------------------------------------------------------

newDerivClsInst :: ThetaType -> DerivSpec theta -> TcM ClsInst
newDerivClsInst :: forall theta. [Type] -> DerivSpec theta -> TcM ClsInst
newDerivClsInst [Type]
theta (DS { ds_name :: forall theta. DerivSpec theta -> Name
ds_name = Name
dfun_name, ds_overlap :: forall theta. DerivSpec theta -> Maybe OverlapMode
ds_overlap = Maybe OverlapMode
overlap_mode
                          , ds_tvs :: forall theta. DerivSpec theta -> [TyVar]
ds_tvs = [TyVar]
tvs, ds_cls :: forall theta. DerivSpec theta -> Class
ds_cls = Class
clas, ds_tys :: forall theta. DerivSpec theta -> [Type]
ds_tys = [Type]
tys })
  = Maybe OverlapMode
-> Name -> [TyVar] -> [Type] -> Class -> [Type] -> TcM ClsInst
newClsInst Maybe OverlapMode
overlap_mode Name
dfun_name [TyVar]
tvs [Type]
theta Class
clas [Type]
tys

extendLocalInstEnv :: [ClsInst] -> TcM a -> TcM a
-- Add new locally-defined instances; don't bother to check
-- for functional dependency errors -- that'll happen in GHC.Tc.TyCl.Instance
extendLocalInstEnv :: forall a. [ClsInst] -> TcM a -> TcM a
extendLocalInstEnv [ClsInst]
dfuns TcM a
thing_inside
 = do { TcGblEnv
env <- TcRnIf TcGblEnv TcLclEnv TcGblEnv
forall gbl lcl. TcRnIf gbl lcl gbl
getGblEnv
      ; let  inst_env' :: InstEnv
inst_env' = InstEnv -> [ClsInst] -> InstEnv
extendInstEnvList (TcGblEnv -> InstEnv
tcg_inst_env TcGblEnv
env) [ClsInst]
dfuns
             env' :: TcGblEnv
env'      = TcGblEnv
env { tcg_inst_env :: InstEnv
tcg_inst_env = InstEnv
inst_env' }
      ; TcGblEnv -> TcM a -> TcM a
forall gbl lcl a. gbl -> TcRnIf gbl lcl a -> TcRnIf gbl lcl a
setGblEnv TcGblEnv
env' TcM a
thing_inside }

{-
Note [Deriving any class]
~~~~~~~~~~~~~~~~~~~~~~~~~
Classic uses of a deriving clause, or a standalone-deriving declaration, are
for:
  * a stock class like Eq or Show, for which GHC knows how to generate
    the instance code
  * a newtype, via the mechanism enabled by GeneralizedNewtypeDeriving

The DeriveAnyClass extension adds a third way to derive instances, based on
empty instance declarations.

The canonical use case is in combination with GHC.Generics and default method
signatures. These allow us to have instance declarations being empty, but still
useful, e.g.

  data T a = ...blah..blah... deriving( Generic )
  instance C a => C (T a)  -- No 'where' clause

where C is some "random" user-defined class.

This boilerplate code can be replaced by the more compact

  data T a = ...blah..blah... deriving( Generic, C )

if DeriveAnyClass is enabled.

This is not restricted to Generics; any class can be derived, simply giving
rise to an empty instance.

See Note [Gathering and simplifying constraints for DeriveAnyClass] in
GHC.Tc.Deriv.Infer for an explanation hof how the instance context is inferred for
DeriveAnyClass.

Note [Check that the type variable is truly universal]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
For Functor and Traversable instances, we must check that the *last argument*
of the type constructor is used truly universally quantified.  Example

   data T a b where
     T1 :: a -> b -> T a b      -- Fine! Vanilla H-98
     T2 :: b -> c -> T a b      -- Fine! Existential c, but we can still map over 'b'
     T3 :: b -> T Int b         -- Fine! Constraint 'a', but 'b' is still polymorphic
     T4 :: Ord b => b -> T a b  -- No!  'b' is constrained
     T5 :: b -> T b b           -- No!  'b' is constrained
     T6 :: T a (b,b)            -- No!  'b' is constrained

Notice that only the first of these constructors is vanilla H-98. We only
need to take care about the last argument (b in this case).  See #8678.
Eg. for T1-T3 we can write

     fmap f (T1 a b) = T1 a (f b)
     fmap f (T2 b c) = T2 (f b) c
     fmap f (T3 x)   = T3 (f x)

We need not perform these checks for Foldable instances, however, since
functions in Foldable can only consume existentially quantified type variables,
rather than produce them (as is the case in Functor and Traversable functions.)
As a result, T can have a derived Foldable instance:

    foldr f z (T1 a b) = f b z
    foldr f z (T2 b c) = f b z
    foldr f z (T3 x)   = f x z
    foldr f z (T4 x)   = f x z
    foldr f z (T5 x)   = f x z
    foldr _ z T6       = z

See Note [DeriveFoldable with ExistentialQuantification] in GHC.Tc.Deriv.Functor.

For Functor and Traversable, we must take care not to let type synonyms
unfairly reject a type for not being truly universally quantified. An
example of this is:

    type C (a :: Constraint) b = a
    data T a b = C (Show a) b => MkT b

Here, the existential context (C (Show a) b) does technically mention the last
type variable b. But this is OK, because expanding the type synonym C would
give us the context (Show a), which doesn't mention b. Therefore, we must make
sure to expand type synonyms before performing this check. Not doing so led to
#13813.
-}