    {-# LANGUAGE GADTs, ViewPatterns #-}

    -- | The @FamInst@ type: family instance heads
    module GHC.Tc.Instance.Family (
            FamInstEnvs, tcGetFamInstEnvs,
            checkFamInstConsistency, tcExtendLocalFamInstEnv,
            tcLookupDataFamInst, tcLookupDataFamInst_maybe,
            tcInstNewTyCon_maybe, tcTopNormaliseNewTypeTF_maybe,

            -- * Injectivity
            reportInjectivityErrors, reportConflictingInjectivityErrs
        ) where

    import GHC.Prelude

    import GHC.Driver.DynFlags
    import GHC.Driver.Env

    import GHC.Core.FamInstEnv
    import GHC.Core.Coercion
    import GHC.Core.TyCon
    import GHC.Core.Coercion.Axiom
    import GHC.Core.DataCon ( dataConName )
    import GHC.Core.TyCo.Rep
    import GHC.Core.TyCo.FVs

    import GHC.Iface.Load

    import GHC.Tc.Errors.Types
    import GHC.Tc.Types.Evidence
    import GHC.Tc.Utils.Monad
    import GHC.Tc.Utils.TcType

    import GHC.Unit.External
    import GHC.Unit.Module
    import GHC.Unit.Module.ModIface
    import GHC.Unit.Module.ModDetails
    import GHC.Unit.Module.Deps
    import GHC.Unit.Home.ModInfo

    import GHC.Types.SrcLoc as SrcLoc
    import GHC.Types.Name.Reader
    import GHC.Types.Name
    import GHC.Types.Var.Set

    import GHC.Utils.Outputable
    import GHC.Utils.Misc
    import GHC.Utils.Panic
    import GHC.Utils.FV

    import GHC.Data.Bag( Bag, unionBags, unitBag )
    import GHC.Data.Maybe

    import Control.Monad
    import Data.List.NonEmpty ( NonEmpty(..) )
    import qualified Data.List.NonEmpty as NE
    import Data.Function ( on )

    import qualified GHC.LanguageExtensions  as LangExt
    import GHC.Unit.Env (unitEnv_hpts)
    import Data.List (sortOn)

    {- Note [The type family instance consistency story]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    To preserve type safety we must ensure that for any given module, all
    the type family instances used either in that module or in any module
    it directly or indirectly imports are consistent. For example, consider

      module F where
        type family F a

      module A where
        import F( F )
        type instance F Int = Bool
        f :: F Int -> Bool
        f x = x

      module B where
        import F( F )
        type instance F Int = Char
        g :: Char -> F Int
        g x = x

      module Bad where
        import A( f )
        import B( g )
        bad :: Char -> Int
        bad c = f (g c)

    Even though module Bad never mentions the type family F at all, by
    combining the functions f and g that were type checked in contradictory
    type family instance environments, the function bad is able to coerce
    from one type to another. So when we type check Bad we must verify that
    the type family instances defined in module A are consistent with those
    defined in module B.

    How do we ensure that we maintain the necessary consistency?

    * Call a module which defines at least one type family instance a
      "family instance module". This flag `mi_finsts` is recorded in the
      interface file.

    * For every module we calculate the set of all of its direct and
      indirect dependencies that are family instance modules. This list
      `dep_finsts` is also recorded in the interface file so we can compute
      this list for a module from the lists for its direct dependencies.

    * When type checking a module M we check consistency of all the type
      family instances that are either provided by its `dep_finsts` or
      defined in the module M itself. This is a pairwise check, i.e., for
      every pair of instances we must check that they are consistent.

      - For family instances coming from `dep_finsts`, this is checked in
        checkFamInstConsistency, called from tcRnImports. See Note
        [Checking family instance consistency] for details on this check
        (and in particular how we avoid having to do all these checks for
        every module we compile).

      - That leaves checking the family instances defined in M itself
        against instances defined in either M or its `dep_finsts`. This is
        checked in `tcExtendLocalFamInstEnv'.

    There are four subtle points in this scheme which have not been
    addressed yet.

    * We have checked consistency of the family instances *defined* by M
      or its imports, but this is not by definition the same thing as the
      family instances *used* by M or its imports.  Specifically, we need to
      ensure when we use a type family instance while compiling M that this
      instance was really defined from either M or one of its imports,
      rather than being an instance that we happened to know about from
      reading an interface file in the course of compiling an unrelated
      module. Otherwise, we'll end up with no record of the fact that M
      depends on this family instance and type safety will be compromised.
      See #13102.

    * It can also happen that M uses a function defined in another module
      which is not transitively imported by M. Examples include the
      desugaring of various overloaded constructs, and references inserted
      by Template Haskell splices. If that function's definition makes use
      of type family instances which are not checked against those visible
      from M, type safety can again be compromised. See #13251.

    * When a module C imports a boot module B.hs-boot, we check that C's
      type family instances are compatible with those visible from
      B.hs-boot. However, C will eventually be linked against a different
      module B.hs, which might define additional type family instances which
      are inconsistent with C's. This can also lead to loss of type safety.
      See #9562.

    * The call to checkFamConsistency for imported functions occurs very
      early (in tcRnImports) and that causes problems if the imported
      instances use type declared in the module being compiled.
      See Note [Loading your own hi-boot file] in GHC.Iface.Load.
    -}

    {-
    ************************************************************************
    *                                                                      *
            Optimised overlap checking for family instances
    *                                                                      *
    ************************************************************************

    Note [Checking family instance consistency]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    For any two family instance modules that we import directly or indirectly, we
    check whether the instances in the two modules are consistent, *unless* we can
    be certain that the instances of the two modules have already been checked for
    consistency during the compilation of modules that we import.

    Why do we need to check?  Consider
       module X1 where                module X2 where
        data T1                         data T2
        type instance F T1 b = Int      type instance F a T2 = Char
        f1 :: F T1 a -> Int             f2 :: Char -> F a T2
        f1 x = x                        f2 x = x

    Now if we import both X1 and X2 we could make (f2 . f1) :: Int -> Char.
    Notice that neither instance is an orphan.

    How do we know which pairs of modules have already been checked? For each
    module M we directly import, we look up the family instance modules that M
    imports (directly or indirectly), say F1, ..., FN. For any two modules
    among M, F1, ..., FN, we know that the family instances defined in those
    two modules are consistent--because we checked that when we compiled M.

    For every other pair of family instance modules we import (directly or
    indirectly), we check that they are consistent now. (So that we can be
    certain that the modules in our `GHC.Driver.Env.dep_finsts' are consistent.)

    Note [Checking family instance optimization]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    As explained in Note [Checking family instance consistency]
    we need to ensure that every pair of transitive imports that define type family
    instances is consistent.

    Let's define df(A) = transitive imports of A that define type family instances
    + A, if A defines type family instances

    Then for every direct import A, df(A) is already consistent.

    Let's name the current module M.

    We want to make sure that df(M) is consistent.
    df(M) = df(D_1) U df(D_2) U ... U df(D_i) where D_1 .. D_i are direct imports.

    We perform the check iteratively, maintaining a set of consistent modules 'C'
    and trying to add df(D_i) to it.

    The key part is how to ensure that the union C U df(D_i) is consistent.

    Let's consider two modules: A and B from C U df(D_i).
    There are nine possible ways to choose A and B from C U df(D_i):

                 | A in C only      | A in C and B in df(D_i) | A in df(D_i) only
    --------------------------------------------------------------------------------
    B in C only  | Already checked  | Already checked         | Needs to be checked
                 | when checking C  | when checking C         |
    --------------------------------------------------------------------------------
    B in C and   | Already checked  | Already checked         | Already checked when
    B in df(D_i) | when checking C  | when checking C         | checking df(D_i)
    --------------------------------------------------------------------------------
    B in df(D_i) | Needs to be      | Already checked         | Already checked when
    only         | checked          | when checking df(D_i)   | checking df(D_i)

    That means to ensure that C U df(D_i) is consistent we need to check every
    module from C - df(D_i) against every module from df(D_i) - C and
    every module from df(D_i) - C against every module from C - df(D_i).
    But since the checks are symmetric it suffices to pick A from C - df(D_i)
    and B from df(D_i) - C.

    In other words these are the modules we need to check:
      [ (m1, m2) | m1 <- C, m1 not in df(D_i)
                 , m2 <- df(D_i), m2 not in C ]

    One final thing to note here is that if there's lot of overlap between
    subsequent df(D_i)'s then we expect those set differences to be small.
    That situation should be pretty common in practice, there's usually
    a set of utility modules that every module imports directly or indirectly.

    This is basically the idea from #13092, comment:14.

    Note [Order of type family consistency checks]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    Consider a module M which imports modules A, B and C, all defining (open) type
    family instances.

    We can waste a lot of work in type family consistency checking depending on the
    order in which the modules are processed.

    Suppose for example that C imports A and B. When we compiled C, we will have
    checked A and B for consistency against eachother. This means that, when
    processing the imports of M to check type family instance consistency:

    * if C is processed first, then A and B will not need to be checked for
      consistency against eachother again,
    * if we process A and B before C,then the
      consistency checks between A and B will be performed again. This is wasted
      work, as we already performed them for C.

    This can make a significant difference. Keeping the nomenclature of the above
    example for illustration, we have observed situations in practice in which the
    compilation time of M goes from 1 second (the "processing A and B first" case)
    down to 80 milliseconds (the "processing C first" case).

    Clearly we should engineer that C is checked before B and A, but by what scheme?

    A simple one is to observe that if a module M is in the transitive closure of X
    then the size of the consistent family set of M is less than or equal to size
    of the consistent family set of X.

    Therefore, by sorting the imports by the size of the consistent family set and
    processing the largest first, we make sure to process modules in topological
    order.

    For a particular project, without this change we did 40 million checks and with
    this change we did 22.9 million checks. This is significant as before this change
    type family consistency checks accounted for 26% of total type checker allocations which
    was reduced to 15%.

    See tickets #25554 for discussion about this exact issue and #25555 for
    why we still do redundant checks.

    -}

    -- We don't need to check the current module, this is done in
    -- tcExtendLocalFamInstEnv.
    -- See Note [The type family instance consistency story].
    checkFamInstConsistency :: [Module] -> TcM ()
    checkFamInstConsistency :: [Module] -> TcM ()
    checkFamInstConsistency [Module]
    directlyImpMods
      = do { (eps, hug) <- TcRnIf TcGblEnv TcLclEnv (ExternalPackageState, HomeUnitGraph)
    forall gbl lcl.
    TcRnIf gbl lcl (ExternalPackageState, HomeUnitGraph)
    getEpsAndHug
           ; traceTc "checkFamInstConsistency" (ppr directlyImpMods)
           ; let { -- Fetch the iface of a given module.  Must succeed as
                   -- all directly imported modules must already have been loaded.
                   modIface Module
    mod =
                     case HomeUnitGraph -> PackageIfaceTable -> Module -> Maybe ModIface
    lookupIfaceByModule HomeUnitGraph
    hug (ExternalPackageState -> PackageIfaceTable
    eps_PIT ExternalPackageState
    eps) Module
    mod of
                       Maybe ModIface
    Nothing    -> String -> SDoc -> ModIface
    forall a. String -> SDoc -> a
    panicDoc String
    "FamInst.checkFamInstConsistency"
                                              (Module -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Module
    mod SDoc -> SDoc -> SDoc
    forall doc. IsDoc doc => doc -> doc -> doc
    $$ HomeUnitGraph -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr HomeUnitGraph
    hug)
                       Just ModIface
    iface -> ModIface
    iface

                   -- Which family instance modules were checked for consistency
                   -- when we compiled `mod`?
                   -- Itself (if a family instance module) and its dep_finsts.
                   -- This is df(D_i) from
                   -- Note [Checking family instance optimization]
                 ; modConsistent :: Module -> [Module]
                 ; modConsistent Module
    mod =
                     if ModIfaceBackend -> WhetherHasFamInst
    mi_finsts (ModIface -> IfaceBackendExts 'ModIfaceFinal
    forall (phase :: ModIfacePhase).
    ModIface_ phase -> IfaceBackendExts phase
    mi_final_exts (Module -> ModIface
    modIface Module
    mod)) then Module
    modModule -> [Module] -> [Module]
    forall a. a -> [a] -> [a]
    :[Module]
    deps else [Module]
    deps
                     where
                     deps :: [Module]
    deps = Dependencies -> [Module]
    dep_finsts (Dependencies -> [Module])
    -> (Module -> Dependencies) -> Module -> [Module]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . ModIface -> Dependencies
    forall (phase :: ModIfacePhase). ModIface_ phase -> Dependencies
    mi_deps (ModIface -> Dependencies)
    -> (Module -> ModIface) -> Module -> Dependencies
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . Module -> ModIface
    modIface (Module -> [Module]) -> Module -> [Module]
    forall a b. (a -> b) -> a -> b
    $ Module
    mod

                 ; debug_consistent_set = (Module -> (Module, Int)) -> [Module] -> [(Module, Int)]
    forall a b. (a -> b) -> [a] -> [b]
    map (\Module
    x -> (Module
    x, [Module] -> Int
    forall a. [a] -> Int
    forall (t :: * -> *) a. Foldable t => t a -> Int
    length (Module -> [Module]
    modConsistent Module
    x))) [Module]
    directlyImpMods

                 -- Sorting the list by size has the effect of performing a topological sort.
                 -- See Note [Order of type family consistency checks]
                 ; init_consistent_set = [Module] -> [Module]
    forall a. [a] -> [a]
    reverse ((Module -> Int) -> [Module] -> [Module]
    forall b a. Ord b => (a -> b) -> [a] -> [a]
    sortOn ([Module] -> Int
    forall a. [a] -> Int
    forall (t :: * -> *) a. Foldable t => t a -> Int
    length ([Module] -> Int) -> (Module -> [Module]) -> Module -> Int
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . Module -> [Module]
    modConsistent) [Module]
    directlyImpMods)

                 ; hmiModule     = ModIface -> Module
    forall (phase :: ModIfacePhase). ModIface_ phase -> Module
    mi_module (ModIface -> Module)
    -> (HomeModInfo -> ModIface) -> HomeModInfo -> Module
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . HomeModInfo -> ModIface
    hm_iface
                 ; hmiFamInstEnv = FamInstEnv -> [FamInst] -> FamInstEnv
    extendFamInstEnvList FamInstEnv
    emptyFamInstEnv
                                   ([FamInst] -> FamInstEnv)
    -> (HomeModInfo -> [FamInst]) -> HomeModInfo -> FamInstEnv
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . ModDetails -> [FamInst]
    md_fam_insts (ModDetails -> [FamInst])
    -> (HomeModInfo -> ModDetails) -> HomeModInfo -> [FamInst]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . HomeModInfo -> ModDetails
    hm_details
                 ; hpt_fam_insts = [(Module, FamInstEnv)] -> ModuleEnv FamInstEnv
    forall a. [(Module, a)] -> ModuleEnv a
    mkModuleEnv [ (HomeModInfo -> Module
    hmiModule HomeModInfo
    hmi, HomeModInfo -> FamInstEnv
    hmiFamInstEnv HomeModInfo
    hmi)
                                               | HomePackageTable
    hpt <- HomeUnitGraph -> [HomePackageTable]
    unitEnv_hpts HomeUnitGraph
    hug
                                               , HomeModInfo
    hmi <- HomePackageTable -> [HomeModInfo]
    eltsHpt HomePackageTable
    hpt ]

                 }

           ; traceTc "init_consistent_set" (ppr debug_consistent_set)
           ; checkMany hpt_fam_insts modConsistent init_consistent_set
           }
      where
        -- See Note [Checking family instance optimization]
        checkMany
          :: ModuleEnv FamInstEnv   -- home package family instances
          -> (Module -> [Module])   -- given A, modules checked when A was checked
          -> [Module]               -- modules to process
          -> TcM ()
        checkMany :: ModuleEnv FamInstEnv -> (Module -> [Module]) -> [Module] -> TcM ()
    checkMany ModuleEnv FamInstEnv
    hpt_fam_insts Module -> [Module]
    modConsistent [Module]
    mods = [Module] -> ModuleSet -> [Module] -> TcM ()
    go [] ModuleSet
    emptyModuleSet [Module]
    mods
          where
          go :: [Module] -- list of consistent modules
             -> ModuleSet -- set of consistent modules, same elements as the
                          -- list above
             -> [Module] -- modules to process
             -> TcM ()
          go :: [Module] -> ModuleSet -> [Module] -> TcM ()
    go [Module]
    _ ModuleSet
    _ [] = () -> TcM ()
    forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()
          go [Module]
    consistent ModuleSet
    consistent_set (Module
    mod:[Module]
    mods) = do
            String -> SDoc -> TcM ()
    traceTc String
    "checkManySize" ([SDoc] -> SDoc
    forall doc. IsDoc doc => [doc] -> doc
    vcat [String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "mod:" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Module -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Module
    mod
                                          , String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "m1:" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Int -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr ([Module] -> Int
    forall a. [a] -> Int
    forall (t :: * -> *) a. Foldable t => t a -> Int
    length [Module]
    to_check_from_mod)
                                          , String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "m2:" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Int -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr ([Module] -> Int
    forall a. [a] -> Int
    forall (t :: * -> *) a. Foldable t => t a -> Int
    length ([Module]
    to_check_from_consistent))
                                          , String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "product:" SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> Int -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr ([Module] -> Int
    forall a. [a] -> Int
    forall (t :: * -> *) a. Foldable t => t a -> Int
    length [Module]
    to_check_from_mod Int -> Int -> Int
    forall a. Num a => a -> a -> a
    * [Module] -> Int
    forall a. [a] -> Int
    forall (t :: * -> *) a. Foldable t => t a -> Int
    length [Module]
    to_check_from_consistent)
                                          ])
            [TcM ()] -> TcM ()
    forall (t :: * -> *) (m :: * -> *) a.
    (Foldable t, Monad m) =>
    t (m a) -> m ()
    sequence_
              [ ModuleEnv FamInstEnv -> Module -> Module -> TcM ()
    check ModuleEnv FamInstEnv
    hpt_fam_insts Module
    m1 Module
    m2
              | Module
    m1 <- [Module]
    to_check_from_mod
                -- loop over toCheckFromMod first, it's usually smaller,
                -- it may even be empty
              , Module
    m2 <- [Module]
    to_check_from_consistent
              ]
            [Module] -> ModuleSet -> [Module] -> TcM ()
    go [Module]
    consistent' ModuleSet
    consistent_set' [Module]
    mods
            where
            mod_deps_consistent :: [Module]
    mod_deps_consistent =  Module -> [Module]
    modConsistent Module
    mod
            mod_deps_consistent_set :: ModuleSet
    mod_deps_consistent_set = [Module] -> ModuleSet
    mkModuleSet [Module]
    mod_deps_consistent
            consistent' :: [Module]
    consistent' = [Module]
    to_check_from_mod [Module] -> [Module] -> [Module]
    forall a. [a] -> [a] -> [a]
    ++ [Module]
    consistent
            consistent_set' :: ModuleSet
    consistent_set' =
              ModuleSet -> [Module] -> ModuleSet
    extendModuleSetList ModuleSet
    consistent_set [Module]
    to_check_from_mod
            to_check_from_consistent :: [Module]
    to_check_from_consistent =
              (Module -> WhetherHasFamInst) -> [Module] -> [Module]
    forall a. (a -> WhetherHasFamInst) -> [a] -> [a]
    filterOut (Module -> ModuleSet -> WhetherHasFamInst
    `elemModuleSet` ModuleSet
    mod_deps_consistent_set) [Module]
    consistent
            to_check_from_mod :: [Module]
    to_check_from_mod =
              (Module -> WhetherHasFamInst) -> [Module] -> [Module]
    forall a. (a -> WhetherHasFamInst) -> [a] -> [a]
    filterOut (Module -> ModuleSet -> WhetherHasFamInst
    `elemModuleSet` ModuleSet
    consistent_set) [Module]
    mod_deps_consistent
            -- Why don't we just minusModuleSet here?
            -- We could, but doing so means one of two things:
            --
            --   1. When looping over the cartesian product we convert
            --   a set into a non-deterministically ordered list. Which
            --   happens to be fine for interface file determinism
            --   in this case, today, because the order only
            --   determines the order of deferred checks. But such
            --   invariants are hard to keep.
            --
            --   2. When looping over the cartesian product we convert
            --   a set into a deterministically ordered list - this
            --   adds some additional cost of sorting for every
            --   direct import.
            --
            --   That also explains why we need to keep both 'consistent'
            --   and 'consistentSet'.
            --
            --   See also Note [ModuleEnv performance and determinism].
        check :: ModuleEnv FamInstEnv -> Module -> Module -> TcM ()
    check ModuleEnv FamInstEnv
    hpt_fam_insts Module
    m1 Module
    m2
          = do { env1' <- ModuleEnv FamInstEnv -> Module -> TcM FamInstEnv
    getFamInsts ModuleEnv FamInstEnv
    hpt_fam_insts Module
    m1
               ; env2' <- getFamInsts hpt_fam_insts m2
               -- We're checking each element of env1 against env2.
               -- The cost of that is dominated by the size of env1, because
               -- for each instance in env1 we look it up in the type family
               -- environment env2, and lookup is cheap.
               -- The code below ensures that env1 is the smaller environment.
               ; let sizeE1 = FamInstEnv -> Int
    famInstEnvSize FamInstEnv
    env1'
                     sizeE2 = FamInstEnv -> Int
    famInstEnvSize FamInstEnv
    env2'
                     (env1, env2) = if sizeE1 < sizeE2 then (env1', env2')
                                                       else (env2', env1')

               ; let check_now = FamInstEnv -> [FamInst]
    famInstEnvElts FamInstEnv
    env1
               ; mapM_ (checkForConflicts (emptyFamInstEnv, env2))           check_now
               ; mapM_ (checkForInjectivityConflicts (emptyFamInstEnv,env2)) check_now
     }

    getFamInsts :: ModuleEnv FamInstEnv -> Module -> TcM FamInstEnv
    getFamInsts :: ModuleEnv FamInstEnv -> Module -> TcM FamInstEnv
    getFamInsts ModuleEnv FamInstEnv
    hpt_fam_insts Module
    mod
      | Just FamInstEnv
    env <- ModuleEnv FamInstEnv -> Module -> Maybe FamInstEnv
    forall a. ModuleEnv a -> Module -> Maybe a
    lookupModuleEnv ModuleEnv FamInstEnv
    hpt_fam_insts Module
    mod = FamInstEnv -> TcM FamInstEnv
    forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
    forall (m :: * -> *) a. Monad m => a -> m a
    return FamInstEnv
    env
      | WhetherHasFamInst
    otherwise = do { _ <- IfG ModIface -> TcRn ModIface
    forall a. IfG a -> TcRn a
    initIfaceTcRn (SDoc -> Module -> IfG ModIface
    forall lcl. SDoc -> Module -> IfM lcl ModIface
    loadSysInterface SDoc
    doc Module
    mod)
                       ; eps <- getEps
                       ; return (expectJust "checkFamInstConsistency" $
                                 lookupModuleEnv (eps_mod_fam_inst_env eps) mod) }
      where
        doc :: SDoc
    doc = Module -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr Module
    mod SDoc -> SDoc -> SDoc
    forall doc. IsLine doc => doc -> doc -> doc
    <+> String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "is a family-instance module"

    {-
    ************************************************************************
    *                                                                      *
            Lookup
    *                                                                      *
    ************************************************************************

    -}

    -- | If @co :: T ts ~ rep_ty@ then:
    --
    -- > instNewTyCon_maybe T ts = Just (rep_ty, co)
    --
    -- Checks for a newtype, and for being saturated
    -- Just like Coercion.instNewTyCon_maybe, but returns a TcCoercion
    tcInstNewTyCon_maybe :: TyCon -> [TcType] -> Maybe (TcType, TcCoercion)
    tcInstNewTyCon_maybe :: TyCon -> [TcType] -> Maybe (TcType, TcCoercion)
    tcInstNewTyCon_maybe = TyCon -> [TcType] -> Maybe (TcType, TcCoercion)
    instNewTyCon_maybe

    -- | Like 'tcLookupDataFamInst_maybe', but returns the arguments back if
    -- there is no data family to unwrap.
    -- Returns a Representational coercion
    tcLookupDataFamInst :: FamInstEnvs -> TyCon -> [TcType]
                        -> (TyCon, [TcType], Coercion)
    tcLookupDataFamInst :: (FamInstEnv, FamInstEnv)
    -> TyCon -> [TcType] -> (TyCon, [TcType], TcCoercion)
    tcLookupDataFamInst (FamInstEnv, FamInstEnv)
    fam_inst_envs TyCon
    tc [TcType]
    tc_args
      | Just (TyCon
    rep_tc, [TcType]
    rep_args, TcCoercion
    co)
          <- (FamInstEnv, FamInstEnv)
    -> TyCon -> [TcType] -> Maybe (TyCon, [TcType], TcCoercion)
    tcLookupDataFamInst_maybe (FamInstEnv, FamInstEnv)
    fam_inst_envs TyCon
    tc [TcType]
    tc_args
      = (TyCon
    rep_tc, [TcType]
    rep_args, TcCoercion
    co)
      | WhetherHasFamInst
    otherwise
      = (TyCon
    tc, [TcType]
    tc_args, TcType -> TcCoercion
    mkRepReflCo (TyCon -> [TcType] -> TcType
    mkTyConApp TyCon
    tc [TcType]
    tc_args))

    tcLookupDataFamInst_maybe :: FamInstEnvs -> TyCon -> [TcType]
                              -> Maybe (TyCon, [TcType], Coercion)
    -- ^ Converts a data family type (eg F [a]) to its representation type (eg FList a)
    -- and returns a coercion between the two: co :: F [a] ~R FList a.
    tcLookupDataFamInst_maybe :: (FamInstEnv, FamInstEnv)
    -> TyCon -> [TcType] -> Maybe (TyCon, [TcType], TcCoercion)
    tcLookupDataFamInst_maybe (FamInstEnv, FamInstEnv)
    fam_inst_envs TyCon
    tc [TcType]
    tc_args
      | TyCon -> WhetherHasFamInst
    isDataFamilyTyCon TyCon
    tc
      , FamInstMatch
    match : [FamInstMatch]
    _ <- (FamInstEnv, FamInstEnv) -> TyCon -> [TcType] -> [FamInstMatch]
    lookupFamInstEnv (FamInstEnv, FamInstEnv)
    fam_inst_envs TyCon
    tc [TcType]
    tc_args
      , FamInstMatch { fim_instance :: FamInstMatch -> FamInst
    fim_instance = rep_fam :: FamInst
    rep_fam@(FamInst { fi_axiom :: FamInst -> CoAxiom Unbranched
    fi_axiom = CoAxiom Unbranched
    ax
                                                       , fi_cvs :: FamInst -> [CoVar]
    fi_cvs   = [CoVar]
    cvs })
                     , fim_tys :: FamInstMatch -> [TcType]
    fim_tys      = [TcType]
    rep_args
                     , fim_cos :: FamInstMatch -> [TcCoercion]
    fim_cos      = [TcCoercion]
    rep_cos } <- FamInstMatch
    match
      , let rep_tc :: TyCon
    rep_tc = FamInst -> TyCon
    dataFamInstRepTyCon FamInst
    rep_fam
            co :: TcCoercion
    co     = Role
    -> CoAxiom Unbranched -> [TcType] -> [TcCoercion] -> TcCoercion
    mkUnbranchedAxInstCo Role
    Representational CoAxiom Unbranched
    ax [TcType]
    rep_args
                                          ([CoVar] -> [TcCoercion]
    mkCoVarCos [CoVar]
    cvs)
      = WhetherHasFamInst
    -> Maybe (TyCon, [TcType], TcCoercion)
    -> Maybe (TyCon, [TcType], TcCoercion)
    forall a. HasCallStack => WhetherHasFamInst -> a -> a
    assert ([TcCoercion] -> WhetherHasFamInst
    forall a. [a] -> WhetherHasFamInst
    forall (t :: * -> *) a. Foldable t => t a -> WhetherHasFamInst
    null [TcCoercion]
    rep_cos) (Maybe (TyCon, [TcType], TcCoercion)
     -> Maybe (TyCon, [TcType], TcCoercion))
    -> Maybe (TyCon, [TcType], TcCoercion)
    -> Maybe (TyCon, [TcType], TcCoercion)
    forall a b. (a -> b) -> a -> b
    $ -- See Note [Constrained family instances] in ??? (renamed?)
        (TyCon, [TcType], TcCoercion)
    -> Maybe (TyCon, [TcType], TcCoercion)
    forall a. a -> Maybe a
    Just (TyCon
    rep_tc, [TcType]
    rep_args, TcCoercion
    co)

      | WhetherHasFamInst
    otherwise
      = Maybe (TyCon, [TcType], TcCoercion)
    forall a. Maybe a
    Nothing

    -- | 'tcTopNormaliseNewTypeTF_maybe' gets rid of top-level newtypes,
    -- potentially looking through newtype /instances/ and type synonyms.
    --
    -- It is only used by the type inference engine (specifically, when
    -- solving representational equality), and hence it is careful to unwrap
    -- only if the relevant data constructor is in scope.  That's why
    -- it gets a GlobalRdrEnv argument.
    --
    -- It is careful not to unwrap data/newtype instances nor synonyms
    -- if it can't continue unwrapping.  Such care is necessary for proper
    -- error messages.
    --
    -- It does not look through type families.
    -- It does not normalise arguments to a tycon.
    --
    -- If the result is Just ((gres, co), rep_ty), then
    --    co : ty ~R rep_ty
    --    gres are the GREs for the data constructors that
    --                          had to be in scope
    tcTopNormaliseNewTypeTF_maybe :: FamInstEnvs
                                  -> GlobalRdrEnv
                                  -> Type
                                  -> Maybe ((Bag GlobalRdrElt, TcCoercion), Type)
    tcTopNormaliseNewTypeTF_maybe :: (FamInstEnv, FamInstEnv)
    -> GlobalRdrEnv
    -> TcType
    -> Maybe ((Bag (GlobalRdrEltX GREInfo), TcCoercion), TcType)
    tcTopNormaliseNewTypeTF_maybe (FamInstEnv, FamInstEnv)
    faminsts GlobalRdrEnv
    rdr_env TcType
    ty
    -- cf. FamInstEnv.topNormaliseType_maybe and Coercion.topNormaliseNewType_maybe
      = NormaliseStepper (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    -> ((Bag (GlobalRdrEltX GREInfo), TcCoercion)
        -> (Bag (GlobalRdrEltX GREInfo), TcCoercion)
        -> (Bag (GlobalRdrEltX GREInfo), TcCoercion))
    -> TcType
    -> Maybe ((Bag (GlobalRdrEltX GREInfo), TcCoercion), TcType)
    forall ev.
    NormaliseStepper ev
    -> (ev -> ev -> ev) -> TcType -> Maybe (ev, TcType)
    topNormaliseTypeX NormaliseStepper (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    stepper (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    -> (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    -> (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    plus TcType
    ty
      where
        plus :: (Bag GlobalRdrElt, TcCoercion) -> (Bag GlobalRdrElt, TcCoercion)
             -> (Bag GlobalRdrElt, TcCoercion)
        plus :: (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    -> (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    -> (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    plus (Bag (GlobalRdrEltX GREInfo)
    gres1, TcCoercion
    co1) (Bag (GlobalRdrEltX GREInfo)
    gres2, TcCoercion
    co2) = ( Bag (GlobalRdrEltX GREInfo)
    gres1 Bag (GlobalRdrEltX GREInfo)
    -> Bag (GlobalRdrEltX GREInfo) -> Bag (GlobalRdrEltX GREInfo)
    forall a. Bag a -> Bag a -> Bag a
    `unionBags` Bag (GlobalRdrEltX GREInfo)
    gres2
                                         , TcCoercion
    co1 TcCoercion -> TcCoercion -> TcCoercion
    `mkTransCo` TcCoercion
    co2 )

        stepper :: NormaliseStepper (Bag GlobalRdrElt, TcCoercion)
        stepper :: NormaliseStepper (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    stepper = NormaliseStepper (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    unwrap_newtype NormaliseStepper (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    -> NormaliseStepper (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    -> NormaliseStepper (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    forall ev.
    NormaliseStepper ev -> NormaliseStepper ev -> NormaliseStepper ev
    `composeSteppers` NormaliseStepper (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    unwrap_newtype_instance

        -- For newtype instances we take a double step or nothing, so that
        -- we don't return the representation type of the newtype instance,
        -- which would lead to terrible error messages
        unwrap_newtype_instance :: NormaliseStepper (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    unwrap_newtype_instance RecTcChecker
    rec_nts TyCon
    tc [TcType]
    tys
          | Just (TyCon
    tc', [TcType]
    tys', TcCoercion
    co) <- (FamInstEnv, FamInstEnv)
    -> TyCon -> [TcType] -> Maybe (TyCon, [TcType], TcCoercion)
    tcLookupDataFamInst_maybe (FamInstEnv, FamInstEnv)
    faminsts TyCon
    tc [TcType]
    tys
          = (TcCoercion -> TcCoercion)
    -> (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    -> (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    forall a b.
    (a -> b)
    -> (Bag (GlobalRdrEltX GREInfo), a)
    -> (Bag (GlobalRdrEltX GREInfo), b)
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    fmap (TcCoercion -> TcCoercion -> TcCoercion
    mkTransCo TcCoercion
    co) ((Bag (GlobalRdrEltX GREInfo), TcCoercion)
     -> (Bag (GlobalRdrEltX GREInfo), TcCoercion))
    -> NormaliseStepResult (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    -> NormaliseStepResult (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    <$> NormaliseStepper (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    unwrap_newtype RecTcChecker
    rec_nts TyCon
    tc' [TcType]
    tys'
          | WhetherHasFamInst
    otherwise = NormaliseStepResult (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    forall ev. NormaliseStepResult ev
    NS_Done

        unwrap_newtype :: NormaliseStepper (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    unwrap_newtype RecTcChecker
    rec_nts TyCon
    tc [TcType]
    tys
          | Just DataCon
    con <- TyCon -> Maybe DataCon
    newTyConDataCon_maybe TyCon
    tc
          , Just GlobalRdrEltX GREInfo
    gre <- GlobalRdrEnv -> Name -> Maybe (GlobalRdrEltX GREInfo)
    forall info.
    Outputable info =>
    GlobalRdrEnvX info -> Name -> Maybe (GlobalRdrEltX info)
    lookupGRE_Name GlobalRdrEnv
    rdr_env (DataCon -> Name
    dataConName DataCon
    con)
               -- This is where we check that the
               -- data constructor is in scope
          = (,) (GlobalRdrEltX GREInfo -> Bag (GlobalRdrEltX GREInfo)
    forall a. a -> Bag a
    unitBag GlobalRdrEltX GREInfo
    gre) (TcCoercion -> (Bag (GlobalRdrEltX GREInfo), TcCoercion))
    -> NormaliseStepResult TcCoercion
    -> NormaliseStepResult (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    <$> NormaliseStepper TcCoercion
    unwrapNewTypeStepper RecTcChecker
    rec_nts TyCon
    tc [TcType]
    tys

          | WhetherHasFamInst
    otherwise
          = NormaliseStepResult (Bag (GlobalRdrEltX GREInfo), TcCoercion)
    forall ev. NormaliseStepResult ev
    NS_Done

    {-
    ************************************************************************
    *                                                                      *
            Extending the family instance environment
    *                                                                      *
    ************************************************************************
    -}

    -- Add new locally-defined family instances, checking consistency with
    -- previous locally-defined family instances as well as all instances
    -- available from imported modules. This requires loading all of our
    -- imports that define family instances (if we haven't loaded them already).
    tcExtendLocalFamInstEnv :: [FamInst] -> TcM a -> TcM a

    -- If we weren't actually given any instances to add, then we don't want
    -- to go to the bother of loading family instance module dependencies.
    tcExtendLocalFamInstEnv :: forall a. [FamInst] -> TcM a -> TcM a
    tcExtendLocalFamInstEnv [] TcM a
    thing_inside = TcM a
    thing_inside

    -- Otherwise proceed...
    tcExtendLocalFamInstEnv [FamInst]
    fam_insts TcM a
    thing_inside
     = do { -- Load family-instance modules "below" this module, so that
            -- allLocalFamInst can check for consistency with them
            -- See Note [The type family instance consistency story]
            [FamInst] -> TcM ()
    loadDependentFamInstModules [FamInst]
    fam_insts

            -- Now add the instances one by one
          ; env <- TcRnIf TcGblEnv TcLclEnv TcGblEnv
    forall gbl lcl. TcRnIf gbl lcl gbl
    getGblEnv
          ; (inst_env', fam_insts') <- foldlM addLocalFamInst
                                           (tcg_fam_inst_env env, tcg_fam_insts env)
                                           fam_insts

          ; let env' = TcGblEnv
    env { tcg_fam_insts    = fam_insts'
                           , tcg_fam_inst_env = inst_env' }
          ; setGblEnv env' thing_inside
          }

    loadDependentFamInstModules :: [FamInst] -> TcM ()
    -- Load family-instance modules "below" this module, so that
    -- allLocalFamInst can check for consistency with them
    -- See Note [The type family instance consistency story]
    loadDependentFamInstModules :: [FamInst] -> TcM ()
    loadDependentFamInstModules [FamInst]
    fam_insts
     = do { env <- TcRnIf TcGblEnv TcLclEnv TcGblEnv
    forall gbl lcl. TcRnIf gbl lcl gbl
    getGblEnv
          ; let this_mod = TcGblEnv -> Module
    tcg_mod TcGblEnv
    env
                imports  = TcGblEnv -> ImportAvails
    tcg_imports TcGblEnv
    env

                want_module Module
    mod  -- See Note [Home package family instances]
                  | Module
    mod Module -> Module -> WhetherHasFamInst
    forall a. Eq a => a -> a -> WhetherHasFamInst
    == Module
    this_mod = WhetherHasFamInst
    False
                  | WhetherHasFamInst
    home_fams_only  = Module -> Unit
    forall unit. GenModule unit -> unit
    moduleUnit Module
    mod Unit -> Unit -> WhetherHasFamInst
    forall a. Eq a => a -> a -> WhetherHasFamInst
    == Module -> Unit
    forall unit. GenModule unit -> unit
    moduleUnit Module
    this_mod
                  | WhetherHasFamInst
    otherwise       = WhetherHasFamInst
    True
                home_fams_only = (FamInst -> WhetherHasFamInst) -> [FamInst] -> WhetherHasFamInst
    forall (t :: * -> *) a.
    Foldable t =>
    (a -> WhetherHasFamInst) -> t a -> WhetherHasFamInst
    all (Module -> Name -> WhetherHasFamInst
    nameIsHomePackage Module
    this_mod (Name -> WhetherHasFamInst)
    -> (FamInst -> Name) -> FamInst -> WhetherHasFamInst
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . FamInst -> Name
    fi_fam) [FamInst]
    fam_insts

          ; loadModuleInterfaces (text "Loading family-instance modules") $
            filter want_module (imp_finsts imports) }

    {- Note [Home package family instances]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Optimization: If we're only defining type family instances
    for type families *defined in the home package*, then we
    only have to load interface files that belong to the home
    package. The reason is that there's no recursion between
    packages, so modules in other packages can't possibly define
    instances for our type families.

    (Within the home package, we could import a module M that
    imports us via an hs-boot file, and thereby defines an
    instance of a type family defined in this module. So we can't
    apply the same logic to avoid reading any interface files at
    all, when we define an instances for type family defined in
    the current module.
    -}

    -- Check that the proposed new instance is OK,
    -- and then add it to the home inst env
    -- This must be lazy in the fam_inst arguments, see Note [Lazy axiom match]
    -- in GHC.Core.FamInstEnv
    addLocalFamInst :: (FamInstEnv,[FamInst])
                    -> FamInst
                    -> TcM (FamInstEnv, [FamInst])
    addLocalFamInst :: (FamInstEnv, [FamInst])
    -> FamInst -> IOEnv (Env TcGblEnv TcLclEnv) (FamInstEnv, [FamInst])
    addLocalFamInst (FamInstEnv
    home_fie, [FamInst]
    my_fis) FamInst
    fam_inst
            -- home_fie includes home package and this module
            -- my_fies is just the ones from this module
      = do { String -> SDoc -> TcM ()
    traceTc String
    "addLocalFamInst" (FamInst -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr FamInst
    fam_inst)

               -- Unlike the case of class instances, don't override existing
               -- instances in GHCi; it's unsound. See #7102.

           ; mod <- IOEnv (Env TcGblEnv TcLclEnv) Module
    forall (m :: * -> *). HasModule m => m Module
    getModule
           ; traceTc "alfi" (ppr mod)

               -- Fetch imported instances, so that we report
               -- overlaps correctly.
               -- Really we ought to only check consistency with
               -- those instances which are transitively imported
               -- by the current module, rather than every instance
               -- we've ever seen. Fixing this is part of #13102.
           ; eps <- getEps
           ; let inst_envs = (ExternalPackageState -> FamInstEnv
    eps_fam_inst_env ExternalPackageState
    eps, FamInstEnv
    home_fie)
                 home_fie' = FamInstEnv -> FamInst -> FamInstEnv
    extendFamInstEnv FamInstEnv
    home_fie FamInst
    fam_inst

               -- Check for conflicting instance decls and injectivity violations
           ; ((), no_errs) <- askNoErrs $
             do { checkForConflicts            inst_envs fam_inst
                ; checkForInjectivityConflicts inst_envs fam_inst
                ; checkInjectiveEquation       fam_inst
                }

           ; if no_errs then
                return (home_fie', fam_inst : my_fis)
             else
                return (home_fie,  my_fis) }

    {-
    ************************************************************************
    *                                                                      *
            Checking an instance against conflicts with an instance env
    *                                                                      *
    ************************************************************************

    Check whether a single family instance conflicts with those in two instance
    environments (one for the EPS and one for the HPT).
    -}

    -- | Checks to make sure no two family instances overlap.
    checkForConflicts :: FamInstEnvs -> FamInst -> TcM ()
    checkForConflicts :: (FamInstEnv, FamInstEnv) -> FamInst -> TcM ()
    checkForConflicts (FamInstEnv, FamInstEnv)
    inst_envs FamInst
    fam_inst
      = do { let conflicts :: [FamInst]
    conflicts = (FamInstEnv, FamInstEnv) -> FamInst -> [FamInst]
    lookupFamInstEnvConflicts (FamInstEnv, FamInstEnv)
    inst_envs FamInst
    fam_inst
           ; String -> SDoc -> TcM ()
    traceTc String
    "checkForConflicts" (SDoc -> TcM ()) -> SDoc -> TcM ()
    forall a b. (a -> b) -> a -> b
    $
             [SDoc] -> SDoc
    forall doc. IsDoc doc => [doc] -> doc
    vcat [ [FamInst] -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr [FamInst]
    conflicts
                  , FamInst -> SDoc
    forall a. Outputable a => a -> SDoc
    ppr FamInst
    fam_inst
                  -- , ppr inst_envs
             ]
           ; FamInst -> [FamInst] -> TcM ()
    reportConflictInstErr FamInst
    fam_inst [FamInst]
    conflicts }

    checkForInjectivityConflicts :: FamInstEnvs -> FamInst -> TcM ()
      -- see Note [Verifying injectivity annotation] in GHC.Core.FamInstEnv, check 1B1.
    checkForInjectivityConflicts :: (FamInstEnv, FamInstEnv) -> FamInst -> TcM ()
    checkForInjectivityConflicts (FamInstEnv, FamInstEnv)
    instEnvs FamInst
    famInst
        | TyCon -> WhetherHasFamInst
    isTypeFamilyTyCon TyCon
    tycon   -- as opposed to data family tycon
        , Injective [WhetherHasFamInst]
    inj <- TyCon -> Injectivity
    tyConInjectivityInfo TyCon
    tycon
        = let conflicts :: [CoAxBranch]
    conflicts = [WhetherHasFamInst]
    -> (FamInstEnv, FamInstEnv) -> FamInst -> [CoAxBranch]
    lookupFamInstEnvInjectivityConflicts [WhetherHasFamInst]
    inj (FamInstEnv, FamInstEnv)
    instEnvs FamInst
    famInst in
          TyCon -> [CoAxBranch] -> CoAxBranch -> TcM ()
    reportConflictingInjectivityErrs TyCon
    tycon [CoAxBranch]
    conflicts (CoAxiom Unbranched -> CoAxBranch
    coAxiomSingleBranch (FamInst -> CoAxiom Unbranched
    fi_axiom FamInst
    famInst))

        | WhetherHasFamInst
    otherwise
        = () -> TcM ()
    forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()

        where tycon :: TyCon
    tycon = FamInst -> TyCon
    famInstTyCon FamInst
    famInst

    -- | Check whether a new open type family equation can be added without
    -- violating injectivity annotation supplied by the user. Returns True when
    -- this is possible and False if adding this equation would violate injectivity
    -- annotation. This looks only at the one equation; it does not look for
    -- interaction between equations. Use checkForInjectivityConflicts for that.
    -- Does checks (2)-(4) of Note [Verifying injectivity annotation] in "GHC.Core.FamInstEnv".
    checkInjectiveEquation :: FamInst -> TcM ()
    checkInjectiveEquation :: FamInst -> TcM ()
    checkInjectiveEquation FamInst
    famInst
        | TyCon -> WhetherHasFamInst
    isTypeFamilyTyCon TyCon
    tycon
        -- type family is injective in at least one argument
        , Injective [WhetherHasFamInst]
    inj <- TyCon -> Injectivity
    tyConInjectivityInfo TyCon
    tycon = do
        { dflags <- IOEnv (Env TcGblEnv TcLclEnv) DynFlags
    forall (m :: * -> *). HasDynFlags m => m DynFlags
    getDynFlags
        ; let axiom = CoAxiom Unbranched -> CoAxBranch
    coAxiomSingleBranch CoAxiom Unbranched
    fi_ax
              -- see Note [Verifying injectivity annotation] in GHC.Core.FamInstEnv
        ; reportInjectivityErrors dflags fi_ax axiom inj
        }

        -- if there was no injectivity annotation or tycon does not represent a
        -- type family we report no conflicts
        | WhetherHasFamInst
    otherwise
        = () -> TcM ()
    forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()

        where tycon :: TyCon
    tycon = FamInst -> TyCon
    famInstTyCon FamInst
    famInst
              fi_ax :: CoAxiom Unbranched
    fi_ax = FamInst -> CoAxiom Unbranched
    fi_axiom FamInst
    famInst

    -- | Report a list of injectivity errors together with their source locations.
    -- Looks only at one equation; does not look for conflicts *among* equations.
    reportInjectivityErrors
       :: DynFlags
       -> CoAxiom br   -- ^ Type family for which we generate errors
       -> CoAxBranch   -- ^ Currently checked equation (represented by axiom)
       -> [Bool]       -- ^ Injectivity annotation
       -> TcM ()
    reportInjectivityErrors :: forall (br :: BranchFlag).
    DynFlags
    -> CoAxiom br -> CoAxBranch -> [WhetherHasFamInst] -> TcM ()
    reportInjectivityErrors DynFlags
    dflags CoAxiom br
    fi_ax CoAxBranch
    axiom [WhetherHasFamInst]
    inj
      = WhetherHasFamInst -> SDoc -> TcM () -> TcM ()
    forall a. HasCallStack => WhetherHasFamInst -> SDoc -> a -> a
    assertPpr ((WhetherHasFamInst -> WhetherHasFamInst)
    -> [WhetherHasFamInst] -> WhetherHasFamInst
    forall (t :: * -> *) a.
    Foldable t =>
    (a -> WhetherHasFamInst) -> t a -> WhetherHasFamInst
    any WhetherHasFamInst -> WhetherHasFamInst
    forall a. a -> a
    id [WhetherHasFamInst]
    inj) (String -> SDoc
    forall doc. IsLine doc => String -> doc
    text String
    "No injective type variables") (TcM () -> TcM ()) -> TcM () -> TcM ()
    forall a b. (a -> b) -> a -> b
    $
        do let lhs :: [TcType]
    lhs             = CoAxBranch -> [TcType]
    coAxBranchLHS CoAxBranch
    axiom
               rhs :: TcType
    rhs             = CoAxBranch -> TcType
    coAxBranchRHS CoAxBranch
    axiom
               fam_tc :: TyCon
    fam_tc          = CoAxiom br -> TyCon
    forall (br :: BranchFlag). CoAxiom br -> TyCon
    coAxiomTyCon CoAxiom br
    fi_ax
               (TyVarSet
    unused_inj_tvs, HasKinds
    unused_vis, SuggestUndecidableInstances
    undec_inst_flag)
                               = DynFlags
    -> TyCon
    -> [TcType]
    -> TcType
    -> (TyVarSet, HasKinds, SuggestUndecidableInstances)
    unusedInjTvsInRHS DynFlags
    dflags TyCon
    fam_tc [TcType]
    lhs TcType
    rhs
               inj_tvs_unused :: WhetherHasFamInst
    inj_tvs_unused  = WhetherHasFamInst -> WhetherHasFamInst
    not (WhetherHasFamInst -> WhetherHasFamInst)
    -> WhetherHasFamInst -> WhetherHasFamInst
    forall a b. (a -> b) -> a -> b
    $ TyVarSet -> WhetherHasFamInst
    isEmptyVarSet TyVarSet
    unused_inj_tvs
               tf_headed :: WhetherHasFamInst
    tf_headed       = TcType -> WhetherHasFamInst
    isTFHeaded TcType
    rhs
               bare_variables :: [TcType]
    bare_variables  = [TcType] -> TcType -> [TcType]
    bareTvInRHSViolated [TcType]
    lhs TcType
    rhs
               wrong_bare_rhs :: WhetherHasFamInst
    wrong_bare_rhs  = WhetherHasFamInst -> WhetherHasFamInst
    not (WhetherHasFamInst -> WhetherHasFamInst)
    -> WhetherHasFamInst -> WhetherHasFamInst
    forall a b. (a -> b) -> a -> b
    $ [TcType] -> WhetherHasFamInst
    forall a. [a] -> WhetherHasFamInst
    forall (t :: * -> *) a. Foldable t => t a -> WhetherHasFamInst
    null [TcType]
    bare_variables

           WhetherHasFamInst -> TcM () -> TcM ()
    forall (f :: * -> *).
    Applicative f =>
    WhetherHasFamInst -> f () -> f ()
    when WhetherHasFamInst
    inj_tvs_unused (TcM () -> TcM ()) -> TcM () -> TcM ()
    forall a b. (a -> b) -> a -> b
    $ TyCon
    -> TyVarSet
    -> HasKinds
    -> SuggestUndecidableInstances
    -> CoAxBranch
    -> TcM ()
    reportUnusedInjectiveVarsErr TyCon
    fam_tc TyVarSet
    unused_inj_tvs
                                                              HasKinds
    unused_vis SuggestUndecidableInstances
    undec_inst_flag CoAxBranch
    axiom
           WhetherHasFamInst -> TcM () -> TcM ()
    forall (f :: * -> *).
    Applicative f =>
    WhetherHasFamInst -> f () -> f ()
    when WhetherHasFamInst
    tf_headed      (TcM () -> TcM ()) -> TcM () -> TcM ()
    forall a b. (a -> b) -> a -> b
    $ TyCon -> CoAxBranch -> TcM ()
    reportTfHeadedErr            TyCon
    fam_tc CoAxBranch
    axiom
           WhetherHasFamInst -> TcM () -> TcM ()
    forall (f :: * -> *).
    Applicative f =>
    WhetherHasFamInst -> f () -> f ()
    when WhetherHasFamInst
    wrong_bare_rhs (TcM () -> TcM ()) -> TcM () -> TcM ()
    forall a b. (a -> b) -> a -> b
    $ TyCon -> [TcType] -> CoAxBranch -> TcM ()
    reportBareVariableInRHSErr   TyCon
    fam_tc [TcType]
    bare_variables CoAxBranch
    axiom

    -- | Is type headed by a type family application?
    isTFHeaded :: Type -> Bool
    -- See Note [Verifying injectivity annotation], case 3.
    isTFHeaded :: TcType -> WhetherHasFamInst
    isTFHeaded TcType
    ty | Just TcType
    ty' <- TcType -> Maybe TcType
    coreView TcType
    ty
                  = TcType -> WhetherHasFamInst
    isTFHeaded TcType
    ty'
    isTFHeaded TcType
    ty | (TyConApp TyCon
    tc [TcType]
    args) <- TcType
    ty
                  , TyCon -> WhetherHasFamInst
    isTypeFamilyTyCon TyCon
    tc
                  = [TcType]
    args [TcType] -> Int -> WhetherHasFamInst
    forall a. [a] -> Int -> WhetherHasFamInst
    `lengthIs` TyCon -> Int
    tyConArity TyCon
    tc
    isTFHeaded TcType
    _  = WhetherHasFamInst
    False

    -- | If a RHS is a bare type variable return a set of LHS patterns that are not
    -- bare type variables.
    bareTvInRHSViolated :: [Type] -> Type -> [Type]
    -- See Note [Verifying injectivity annotation], case 2.
    bareTvInRHSViolated :: [TcType] -> TcType -> [TcType]
    bareTvInRHSViolated [TcType]
    pats TcType
    rhs | TcType -> WhetherHasFamInst
    isTyVarTy TcType
    rhs
       = (TcType -> WhetherHasFamInst) -> [TcType] -> [TcType]
    forall a. (a -> WhetherHasFamInst) -> [a] -> [a]
    filter (WhetherHasFamInst -> WhetherHasFamInst
    not (WhetherHasFamInst -> WhetherHasFamInst)
    -> (TcType -> WhetherHasFamInst) -> TcType -> WhetherHasFamInst
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . TcType -> WhetherHasFamInst
    isTyVarTy) [TcType]
    pats
    bareTvInRHSViolated [TcType]
    _ TcType
    _ = []

    ------------------------------------------------------------------
    -- Checking for the coverage condition for injective type families
    ------------------------------------------------------------------

    {-
    Note [Coverage condition for injective type families]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The Injective Type Families paper describes how we can tell whether
    or not a type family equation upholds the injectivity condition.
    Briefly, consider the following:

      type family F a b = r | r -> a      -- NB: b is not injective

      type instance F ty1 ty2 = ty3

    We need to make sure that all variables mentioned in ty1 are mentioned in ty3
    -- that's how we know that knowing ty3 determines ty1. But they can't be
    mentioned just anywhere in ty3: they must be in *injective* positions in ty3.
    For example:

      type instance F a Int = Maybe (G a)

    This is no good, if G is not injective. However, if G is indeed injective,
    then this would appear to meet our needs. There is a trap here, though: while
    knowing G a does indeed determine a, trying to compute a from G a might not
    terminate. This is precisely the same problem that we have with functional
    dependencies and their liberal coverage condition. Here is the test case:

      type family G a = r | r -> a
      type instance G [a] = [G a]
      [W] G alpha ~ [alpha]

    We see that the equation given applies, because G alpha equals a list. So we
    learn that alpha must be [beta] for some beta. We then have

      [W] G [beta] ~ [[beta]]

    This can reduce to

      [W] [G beta] ~ [[beta]]

    which then decomposes to

      [W] G beta ~ [beta]

    right where we started. The equation G [a] = [G a] thus is dangerous: while
    it does not violate the injectivity assumption, it might throw us into a loop,
    with a particularly dastardly Wanted.

    We thus do what functional dependencies do: require -XUndecidableInstances to
    accept this.

    Checking the coverage condition is not terribly hard, but we also want to produce
    a nice error message. A nice error message has at least two properties:

    1. If any of the variables involved are invisible or are used in an invisible context,
    we want to print invisible arguments (as -fprint-explicit-kinds does).

    2. If we fail to accept the equation because we're worried about non-termination,
    we want to suggest UndecidableInstances.

    To gather the right information, we can talk about the *usage* of a variable. Every
    variable is used either visibly or invisibly, and it is either not used at all,
    in a context where acceptance requires UndecidableInstances, or in a context that
    does not require UndecidableInstances. If a variable is used both visibly and
    invisibly, then we want to remember the fact that it was used invisibly: printing
    out invisibles will be helpful for the user to understand what is going on.
    If a variable is used where we need -XUndecidableInstances and where we don't,
    we can similarly just remember the latter.

    We thus define Visibility and NeedsUndecInstFlag below. These enumerations are
    *ordered*, and we used their Ord instances. We then define VarUsage, which is just a pair
    of a Visibility and a NeedsUndecInstFlag. (The visibility is irrelevant when a
    variable is NotPresent, but this extra slack in the representation causes no
    harm.) We finally define VarUsages as a mapping from variables to VarUsage.
    Its Monoid instance combines two maps, using the Semigroup instance of VarUsage
    to combine elements that are represented in both maps. In this way, we can
    compositionally analyze types (and portions thereof).

    To do the injectivity check:

    1. We build VarUsages that represent the LHS (rather, the portion of the LHS
    that is flagged as injective); each usage on the LHS is NotPresent, because we
    have not yet looked at the RHS.

    2. We also build a VarUsage for the RHS, done by injTyVarUsages.

    3. We then combine these maps. Now, every variable in the injective components of the LHS
    will be mapped to its correct usage (either NotPresent or perhaps needing
    -XUndecidableInstances in order to be seen as injective).

    4. We look up each var used in an injective argument on the LHS in
    the map, making a list of tvs that should be determined by the RHS
    but aren't.

    5. We then return the set of bad variables, whether any of the bad
    ones were used invisibly, and whether any bad ones need -XUndecidableInstances.
    If -XUndecidableInstances is enabled, than a var that needs the flag
    won't be bad, so it won't appear in this list.

    6. We use all this information to produce a nice error message, (a) switching
    on -fprint-explicit-kinds if appropriate and (b) telling the user about
    -XUndecidableInstances if appropriate.

    -}

    -- | Return the set of type variables that a type family equation is
    -- expected to be injective in but is not. Suppose we have @type family
    -- F a b = r | r -> a@. Then any variables that appear free in the first
    -- argument to F in an equation must be fixed by that equation's RHS.
    -- This function returns all such variables that are not indeed fixed.
    -- It also returns whether any of these variables appear invisibly
    -- and whether -XUndecidableInstances would help.
    -- See Note [Coverage condition for injective type families].
    unusedInjTvsInRHS :: DynFlags
                      -> TyCon  -- type family
                      -> [Type] -- LHS arguments
                      -> Type   -- the RHS
                      -> ( TyVarSet
                         , HasKinds                     -- YesHasKinds <=> one or more variable is used invisibly
                         , SuggestUndecidableInstances) -- YesSuggestUndecidableInstaces <=> suggest -XUndecidableInstances
    -- See Note [Verifying injectivity annotation] in GHC.Core.FamInstEnv.
    -- This function implements check (4) described there, further
    -- described in Note [Coverage condition for injective type families].
    -- In theory (and modulo the -XUndecidableInstances wrinkle),
    -- instead of implementing this whole check in this way, we could
    -- attempt to unify equation with itself.  We would reject exactly the same
    -- equations but this method gives us more precise error messages by returning
    -- precise names of variables that are not mentioned in the RHS.
    unusedInjTvsInRHS :: DynFlags
    -> TyCon
    -> [TcType]
    -> TcType
    -> (TyVarSet, HasKinds, SuggestUndecidableInstances)
    unusedInjTvsInRHS DynFlags
    dflags tycon :: TyCon
    tycon@(TyCon -> Injectivity
    tyConInjectivityInfo -> Injective [WhetherHasFamInst]
    inj_list) [TcType]
    lhs TcType
    rhs =
      -- Note [Coverage condition for injective type families], step 5
      (TyVarSet
    bad_vars, WhetherHasFamInst -> HasKinds
    hasKinds WhetherHasFamInst
    any_invisible, WhetherHasFamInst -> SuggestUndecidableInstances
    suggestUndecidableInstances WhetherHasFamInst
    suggest_undec)
        where
          undec_inst :: WhetherHasFamInst
    undec_inst = Extension -> DynFlags -> WhetherHasFamInst
    xopt Extension
    LangExt.UndecidableInstances DynFlags
    dflags

          inj_lhs :: [TcType]
    inj_lhs = [WhetherHasFamInst] -> [TcType] -> [TcType]
    forall a. [WhetherHasFamInst] -> [a] -> [a]
    filterByList [WhetherHasFamInst]
    inj_list [TcType]
    lhs
          lhs_vars :: TyVarSet
    lhs_vars = [TcType] -> TyVarSet
    tyCoVarsOfTypes [TcType]
    inj_lhs

          rhs_inj_vars :: TyVarSet
    rhs_inj_vars = FV -> TyVarSet
    fvVarSet (FV -> TyVarSet) -> FV -> TyVarSet
    forall a b. (a -> b) -> a -> b
    $ WhetherHasFamInst -> TcType -> FV
    injectiveVarsOfType WhetherHasFamInst
    undec_inst TcType
    rhs

          bad_vars :: TyVarSet
    bad_vars = TyVarSet
    lhs_vars TyVarSet -> TyVarSet -> TyVarSet
    `minusVarSet` TyVarSet
    rhs_inj_vars

          any_bad :: WhetherHasFamInst
    any_bad = WhetherHasFamInst -> WhetherHasFamInst
    not (WhetherHasFamInst -> WhetherHasFamInst)
    -> WhetherHasFamInst -> WhetherHasFamInst
    forall a b. (a -> b) -> a -> b
    $ TyVarSet -> WhetherHasFamInst
    isEmptyVarSet TyVarSet
    bad_vars

          invis_vars :: TyVarSet
    invis_vars = FV -> TyVarSet
    fvVarSet (FV -> TyVarSet) -> FV -> TyVarSet
    forall a b. (a -> b) -> a -> b
    $ [TcType] -> FV
    invisibleVarsOfTypes [TyCon -> [TcType] -> TcType
    mkTyConApp TyCon
    tycon [TcType]
    lhs, TcType
    rhs]

          any_invisible :: WhetherHasFamInst
    any_invisible = WhetherHasFamInst
    any_bad WhetherHasFamInst -> WhetherHasFamInst -> WhetherHasFamInst
    && (TyVarSet
    bad_vars TyVarSet -> TyVarSet -> WhetherHasFamInst
    `intersectsVarSet` TyVarSet
    invis_vars)
          suggest_undec :: WhetherHasFamInst
    suggest_undec = WhetherHasFamInst
    any_bad WhetherHasFamInst -> WhetherHasFamInst -> WhetherHasFamInst
    &&
                          WhetherHasFamInst -> WhetherHasFamInst
    not WhetherHasFamInst
    undec_inst WhetherHasFamInst -> WhetherHasFamInst -> WhetherHasFamInst
    &&
                          (TyVarSet
    lhs_vars TyVarSet -> TyVarSet -> WhetherHasFamInst
    `subVarSet` FV -> TyVarSet
    fvVarSet (WhetherHasFamInst -> TcType -> FV
    injectiveVarsOfType WhetherHasFamInst
    True TcType
    rhs))

    -- When the type family is not injective in any arguments
    unusedInjTvsInRHS DynFlags
    _ TyCon
    _ [TcType]
    _ TcType
    _ = (TyVarSet
    emptyVarSet, HasKinds
    NoHasKinds, SuggestUndecidableInstances
    NoSuggestUndecidableInstaces)

    ---------------------------------------
    -- Producing injectivity error messages
    ---------------------------------------

    -- | Report error message for a pair of equations violating an injectivity
    -- annotation. No error message if there are no branches.
    reportConflictingInjectivityErrs :: TyCon -> [CoAxBranch] -> CoAxBranch -> TcM ()
    reportConflictingInjectivityErrs :: TyCon -> [CoAxBranch] -> CoAxBranch -> TcM ()
    reportConflictingInjectivityErrs TyCon
    _ [] CoAxBranch
    _ = () -> TcM ()
    forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()
    reportConflictingInjectivityErrs TyCon
    fam_tc (CoAxBranch
    confEqn1:[CoAxBranch]
    _) CoAxBranch
    tyfamEqn
      = [(SrcSpan, TcRnMessage)] -> TcM ()
    addErrs [(TyCon -> NonEmpty CoAxBranch -> TcRnMessage)
    -> TyCon -> NonEmpty CoAxBranch -> (SrcSpan, TcRnMessage)
    buildInjectivityError (InjectivityErrReason -> TyCon -> NonEmpty CoAxBranch -> TcRnMessage
    TcRnFamInstNotInjective InjectivityErrReason
    InjErrRhsOverlap)
                                       TyCon
    fam_tc
                                       (CoAxBranch
    confEqn1 CoAxBranch -> [CoAxBranch] -> NonEmpty CoAxBranch
    forall a. a -> [a] -> NonEmpty a
    :| [CoAxBranch
    tyfamEqn])]

    -- | Report error message for equation with injective type variables unused in
    -- the RHS. Note [Coverage condition for injective type families], step 6
    reportUnusedInjectiveVarsErr :: TyCon
                                 -> TyVarSet
                                 -> HasKinds                    -- YesHasKinds <=> print invisible arguments
                                 -> SuggestUndecidableInstances -- YesSuggestUndecidableInstaces <=> suggest -XUndecidableInstances
                                 -> CoAxBranch
                                 -> TcM ()
    reportUnusedInjectiveVarsErr :: TyCon
    -> TyVarSet
    -> HasKinds
    -> SuggestUndecidableInstances
    -> CoAxBranch
    -> TcM ()
    reportUnusedInjectiveVarsErr TyCon
    fam_tc TyVarSet
    tvs HasKinds
    has_kinds SuggestUndecidableInstances
    undec_inst CoAxBranch
    tyfamEqn
      = let reason :: InjectivityErrReason
    reason     = TyVarSet
    -> HasKinds -> SuggestUndecidableInstances -> InjectivityErrReason
    InjErrCannotInferFromRhs TyVarSet
    tvs HasKinds
    has_kinds SuggestUndecidableInstances
    undec_inst
            (SrcSpan
    loc, TcRnMessage
    dia) = (TyCon -> NonEmpty CoAxBranch -> TcRnMessage)
    -> TyCon -> NonEmpty CoAxBranch -> (SrcSpan, TcRnMessage)
    buildInjectivityError (InjectivityErrReason -> TyCon -> NonEmpty CoAxBranch -> TcRnMessage
    TcRnFamInstNotInjective InjectivityErrReason
    reason) TyCon
    fam_tc (CoAxBranch
    tyfamEqn CoAxBranch -> [CoAxBranch] -> NonEmpty CoAxBranch
    forall a. a -> [a] -> NonEmpty a
    :| [])
        in SrcSpan -> TcRnMessage -> TcM ()
    addErrAt SrcSpan
    loc TcRnMessage
    dia

    -- | Report error message for equation that has a type family call at the top
    -- level of RHS
    reportTfHeadedErr :: TyCon -> CoAxBranch -> TcM ()
    reportTfHeadedErr :: TyCon -> CoAxBranch -> TcM ()
    reportTfHeadedErr TyCon
    fam_tc CoAxBranch
    branch
      = [(SrcSpan, TcRnMessage)] -> TcM ()
    addErrs [(TyCon -> NonEmpty CoAxBranch -> TcRnMessage)
    -> TyCon -> NonEmpty CoAxBranch -> (SrcSpan, TcRnMessage)
    buildInjectivityError (InjectivityErrReason -> TyCon -> NonEmpty CoAxBranch -> TcRnMessage
    TcRnFamInstNotInjective InjectivityErrReason
    InjErrRhsCannotBeATypeFam)
                                       TyCon
    fam_tc
                                       (CoAxBranch
    branch CoAxBranch -> [CoAxBranch] -> NonEmpty CoAxBranch
    forall a. a -> [a] -> NonEmpty a
    :| [])]

    -- | Report error message for equation that has a bare type variable in the RHS
    -- but LHS pattern is not a bare type variable.
    reportBareVariableInRHSErr :: TyCon -> [Type] -> CoAxBranch -> TcM ()
    reportBareVariableInRHSErr :: TyCon -> [TcType] -> CoAxBranch -> TcM ()
    reportBareVariableInRHSErr TyCon
    fam_tc [TcType]
    tys CoAxBranch
    branch
      = [(SrcSpan, TcRnMessage)] -> TcM ()
    addErrs [(TyCon -> NonEmpty CoAxBranch -> TcRnMessage)
    -> TyCon -> NonEmpty CoAxBranch -> (SrcSpan, TcRnMessage)
    buildInjectivityError (InjectivityErrReason -> TyCon -> NonEmpty CoAxBranch -> TcRnMessage
    TcRnFamInstNotInjective ([TcType] -> InjectivityErrReason
    InjErrRhsBareTyVar [TcType]
    tys))
                                       TyCon
    fam_tc
                                       (CoAxBranch
    branch CoAxBranch -> [CoAxBranch] -> NonEmpty CoAxBranch
    forall a. a -> [a] -> NonEmpty a
    :| [])]

    buildInjectivityError :: (TyCon -> NonEmpty CoAxBranch -> TcRnMessage)
                          -> TyCon
                          -> NonEmpty CoAxBranch
                          -> (SrcSpan, TcRnMessage)
    buildInjectivityError :: (TyCon -> NonEmpty CoAxBranch -> TcRnMessage)
    -> TyCon -> NonEmpty CoAxBranch -> (SrcSpan, TcRnMessage)
    buildInjectivityError TyCon -> NonEmpty CoAxBranch -> TcRnMessage
    mkErr TyCon
    fam_tc NonEmpty CoAxBranch
    branches
      = ( CoAxBranch -> SrcSpan
    coAxBranchSpan (NonEmpty CoAxBranch -> CoAxBranch
    forall a. NonEmpty a -> a
    NE.head NonEmpty CoAxBranch
    branches), TyCon -> NonEmpty CoAxBranch -> TcRnMessage
    mkErr TyCon
    fam_tc NonEmpty CoAxBranch
    branches )

    reportConflictInstErr :: FamInst -> [FamInst] -> TcRn ()
    reportConflictInstErr :: FamInst -> [FamInst] -> TcM ()
    reportConflictInstErr FamInst
    _ []
      = () -> TcM ()
    forall a. a -> IOEnv (Env TcGblEnv TcLclEnv) a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()  -- No conflicts
    reportConflictInstErr FamInst
    fam_inst (FamInst
    conf_inst : [FamInst]
    _) =
       -- The sortBy just arranges that instances are displayed in order
       -- of source location, which reduced wobbling in error messages,
       -- and is better for users
      let   sorted :: NonEmpty FamInst
    sorted  = (FamInst -> FamInst -> Ordering)
    -> NonEmpty FamInst -> NonEmpty FamInst
    forall a. (a -> a -> Ordering) -> NonEmpty a -> NonEmpty a
    NE.sortBy (SrcSpan -> SrcSpan -> Ordering
    SrcLoc.leftmost_smallest (SrcSpan -> SrcSpan -> Ordering)
    -> (FamInst -> SrcSpan) -> FamInst -> FamInst -> Ordering
    forall b c a. (b -> b -> c) -> (a -> b) -> a -> a -> c
    `on` FamInst -> SrcSpan
    getSpan) (FamInst
    fam_inst FamInst -> [FamInst] -> NonEmpty FamInst
    forall a. a -> [a] -> NonEmpty a
    NE.:| [FamInst
    conf_inst])
            fi1 :: FamInst
    fi1     = NonEmpty FamInst -> FamInst
    forall a. NonEmpty a -> a
    NE.head NonEmpty FamInst
    sorted
            span :: SrcSpan
    span    = CoAxBranch -> SrcSpan
    coAxBranchSpan (CoAxiom Unbranched -> CoAxBranch
    coAxiomSingleBranch (FamInst -> CoAxiom Unbranched
    famInstAxiom FamInst
    fi1))
            getSpan :: FamInst -> SrcSpan
    getSpan = CoAxiom Unbranched -> SrcSpan
    forall a. NamedThing a => a -> SrcSpan
    getSrcSpan (CoAxiom Unbranched -> SrcSpan)
    -> (FamInst -> CoAxiom Unbranched) -> FamInst -> SrcSpan
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . FamInst -> CoAxiom Unbranched
    famInstAxiom
      in SrcSpan -> TcM () -> TcM ()
    forall a. SrcSpan -> TcRn a -> TcRn a
    setSrcSpan SrcSpan
    span (TcM () -> TcM ()) -> TcM () -> TcM ()
    forall a b. (a -> b) -> a -> b
    $ TcRnMessage -> TcM ()
    addErr (TcRnMessage -> TcM ()) -> TcRnMessage -> TcM ()
    forall a b. (a -> b) -> a -> b
    $ NonEmpty FamInst -> TcRnMessage
    TcRnConflictingFamInstDecls NonEmpty FamInst
    sorted

    tcGetFamInstEnvs :: TcM FamInstEnvs
    -- Gets both the external-package inst-env
    -- and the home-pkg inst env (includes module being compiled)
    tcGetFamInstEnvs :: TcM (FamInstEnv, FamInstEnv)
    tcGetFamInstEnvs
      = do { eps <- TcRnIf TcGblEnv TcLclEnv ExternalPackageState
    forall gbl lcl. TcRnIf gbl lcl ExternalPackageState
    getEps; env <- getGblEnv
           ; return (eps_fam_inst_env eps, tcg_fam_inst_env env) }