Simply wraps an unknown Diagnostic message a. It can be used by plugins to provide custom diagnostic messages originated during typechecking/renaming.

Wrap an IfaceMessage to a TcRnMessage for when we attempt to load interface files during typechecking but encounter an error.

TcRnMessageWithInfo is a constructor which is used when extra information is needed to be provided in order to qualify a diagnostic and where it was originated (and why). It carries an extra UnitState which can be used to pretty-print some names and it wraps a TcRnMessageDetailed, which includes any extra context associated with this diagnostic.

TcRnWithHsDocContext annotates an error message with the context in which it originated.

TcRnSolverReport is the constructor used to report unsolved constraints after constraint solving, as well as other errors such as hole fit errors.

See the documentation of TcSolverReportMsg datatype for an overview of the different errors.

TcRnSolverDepthError is an error that occurs when the constraint solver exceeds the maximum recursion depth.

Example:

class C a where { meth :: a } instance Cls [a] => Cls a where { meth = head . meth }

t :: () t = meth

Test cases: T7788 T8550 T9554 T15316A T17267{∅,a,b,c,e} T17458 ContextStack1 T22924b TcCoercibleFail

TcRnRedundantConstraints is a warning that is emitted when a binding has a user-written type signature which contains superfluous constraints.

Example:

f :: (Eq a, Ord a) => a -> a -> a f x y = (x < y) || x == y -- `Eq a` is superfluous: the `Ord a` constraint suffices.

Test cases: T9939, T10632, T18036a, T20602, PluralS, T19296.

TcRnInaccessibleCode is a warning that is emitted when the RHS of a pattern match is inaccessible, because the constraint solver has detected a contradiction.

Example:

data B a where { MkTrue :: B True; MkFalse :: B False }

foo :: B False -> Bool foo MkFalse = False foo MkTrue = True -- Inaccessible: requires True ~ False

Test cases: T7293, T7294, T15558, T17646, T18572, T18610, tcfail167.

TcRnInaccessibleCoAxBranch is a warning that is emitted when a closed type family has a branch which is inaccessible due to a more general, prior branch.

Example: type family F a where F a = Int F Bool = Bool Test cases: T9085, T14066a, T9085, T6018, tc265,

A type which was expected to have a fixed runtime representation does not have a fixed runtime representation.

Example:

data D (a :: TYPE r) = MkD a

Test cases: T11724, T18534, RepPolyPatSynArg, RepPolyPatSynUnliftedNewtype, RepPolyPatSynRes, T20423

TcRnImplicitLift is a warning (controlled with -Wimplicit-lift) that occurs when a Template Haskell quote implicitly uses lift.

Example: warning1 :: Lift t => t -> Q Exp warning1 x = [| x |]

Test cases: th/T17804

TcRnUnusedPatternBinds is a warning (controlled with -Wunused-pattern-binds) that occurs if a pattern binding binds no variables at all, unless it is a lone wild-card pattern, or a banged pattern.

Example: Just _ = rhs3 -- Warning: unused pattern binding (_, _) = rhs4 -- Warning: unused pattern binding _ = rhs3 -- No warning: lone wild-card pattern !() = rhs4 -- No warning: banged pattern; behaves like seq

Test cases: rename/{T13646,T17c,T17e,T7085}

TcRnUnusedQuantifiedTypeVar is a warning that occurs if there are unused quantified type variables.

Examples: f :: forall a. Int -> Char

Test cases: renameshould_compileExplicitForAllRules1 renameshould_compileT5331

TcRnDodgyImports is a group of warnings (controlled with -Wdodgy-imports).

See DodgyImportsReason for the different warnings.

TcRnDodgyExports is a warning (controlled by -Wdodgy-exports) that occurs when an export of the form 'T(..)' for a type constructor T does not actually export anything beside T itself.

Example: module Foo ( T(..) -- Warning: T is a type synonym , A(..) -- Warning: A is a type family , C(..) -- Warning: C is a data family ) where

type T = Int type family A :: * -> * data family C :: * -> *

Test cases: warningsshould_compileDodgyExports01

TcRnMissingImportList is a warning (controlled by -Wmissing-import-lists) that occurs when an import declaration does not explicitly list all the names brought into scope.

Test cases: renameshould_compileT4489

When a module marked trustworthy or unsafe (using -XTrustworthy or -XUnsafe) is compiled with a plugin, the TcRnUnsafeDueToPlugin warning (controlled by -Wunsafe) is used as the reason the module was inferred to be unsafe. This warning is not raised if the -fplugin-trustworthy flag is passed.

Test cases: plugins/T19926

TcRnModMissingRealSrcSpan is an error that occurs when compiling a module that lacks an associated RealSrcSpan.

Test cases: None

TcRnIdNotExportedFromModuleSig is an error pertaining to backpack that occurs when an identifier required by a signature is not exported by the module or signature that is being used as a substitution for that signature.

Example(s): None

Test cases: backpackshould_failbkpfail36

TcRnIdNotExportedFromLocalSig is an error pertaining to backpack that occurs when an identifier which is necessary for implementing a module signature is not exported from that signature.

Example(s): None

Test cases: backpackshould_failbkpfail30 backpackshould_failbkpfail31 backpackshould_failbkpfail34

TcRnShadowedName is a warning (controlled by -Wname-shadowing) that occurs whenever an inner-scope value has the same name as an outer-scope value, i.e. the inner value shadows the outer one. This can catch typographical errors that turn into hard-to-find bugs. The warning is suppressed for names beginning with an underscore.

Examples(s): f = ... let f = id in ... f ... -- NOT OK, f is shadowed f x = do { _ignore <- this; _ignore <- that; return (the other) } -- suppressed via underscore

Test cases: typecheckshould_compileT10971a renameshould_compilern039 renameshould_compilern064 renameshould_compileT1972 renameshould_failT2723 renameshould_compileT3262 driver/werror renameshould_failT22478d typecheckshould_failTyAppPat_ScopedTyVarConflict

TcRnInvalidWarningCategory is an error that occurs when a warning is declared with a category name that is not the special category "deprecations", and either does not begin with the prefix "x-" indicating a user-defined category, or contains characters not valid in category names. See Note [Warning categories] in GHC.Unit.Module.Warnings

Examples(s): module M {-# WARNING in "invalid" Oops #-} where

{-# WARNING in "x- spaces not allowed" foo Oops #-}

Test cases: warningsshould_failWarningCategoryInvalid

TcRnDuplicateWarningDecls is an error that occurs whenever a warning is declared twice.

Examples(s): {-# DEPRECATED foo "Don't use me" #-} {-# DEPRECATED foo "Don't use me" #-} foo :: Int foo = 2

Test cases: renameshould_failrnfail058

TcRnSimplifierTooManyIterations is an error that occurs whenever the constraint solver in the simplifier hits the iterations' limit.

Examples(s): None.

Test cases: None.

TcRnIllegalPatSynDecl is an error that occurs whenever there is an illegal pattern synonym declaration.

Examples(s):

varWithLocalPatSyn x = case x of P -> () where pattern P = () -- not valid, it can't be local, it must be defined at top-level.

Test cases: patsynshould_faillocal

TcRnLinearPatSyn is an error that occurs whenever a pattern synonym signature uses a field that is not unrestricted.

Example(s): None

Test cases: linearshould_failLinearPatSyn2

TcRnEmptyRecordUpdate is an error that occurs whenever a record is updated without specifying any field.

Examples(s):

$(deriveJSON defaultOptions{} ''Bad) -- not ok, no fields selected for update of defaultOptions

Test cases: th/T12788

TcRnIllegalFieldPunning is an error that occurs whenever field punning is used without the NamedFieldPuns extension enabled.

Examples(s):

data Foo = Foo { a :: Int }

foo :: Foo -> Int foo Foo{a} = a -- Not ok, punning used without extension.

Test cases: parsershould_failRecordDotSyntaxFail12

TcRnIllegalWildcardsInRecord is an error that occurs whenever wildcards (..) are used in a record without the relevant extension being enabled.

Examples(s):

data Foo = Foo { a :: Int }

foo :: Foo -> Int foo Foo{..} = a -- Not ok, wildcards used without extension.

Test cases: parsershould_failRecordWildCardsFail

TcRnIllegalWildcardInType is an error that occurs when a wildcard appears in a type in a location in which wildcards aren't allowed.

Examples:

Type synonyms:

type T = _

Class declarations and instances:

class C _ instance C _

Standalone kind signatures:

type D :: _ data D

Test cases: ExtraConstraintsWildcardInTypeSplice2 ExtraConstraintsWildcardInTypeSpliceUsed ExtraConstraintsWildcardNotLast ExtraConstraintsWildcardTwice NestedExtraConstraintsWildcard NestedNamedExtraConstraintsWildcard PartialClassMethodSignature PartialClassMethodSignature2 T12039 T13324_fail1 UnnamedConstraintWildcard1 UnnamedConstraintWildcard2 WildcardInADT1 WildcardInADT2 WildcardInADT3 WildcardInADTContext1 WildcardInDefault WildcardInDefaultSignature WildcardInDeriving WildcardInForeignExport WildcardInForeignImport WildcardInGADT1 WildcardInGADT2 WildcardInInstanceHead WildcardInInstanceSig WildcardInNewtype WildcardInPatSynSig WildcardInStandaloneDeriving WildcardInTypeFamilyInstanceRHS WildcardInTypeSynonymRHS saks_fail003 T15433a

TcRnIllegalNamedWildcardInTypeArgument is an error that occurs when a named wildcard is used in a required type argument.

Example:

vfun :: forall (a :: k) -> () x = vfun _nwc -- ^^^^ -- named wildcards not allowed in type arguments

Test cases: T23738_fail_wild

TcRnDuplicateFieldName is an error that occurs whenever there are duplicate field names in a single record.

Examples(s):

data R = MkR { x :: Int, x :: Bool } f r = r { x = 3, x = 4 }

Test cases: T21959.

TcRnIllegalViewPattern is an error that occurs whenever the ViewPatterns syntax is used but the ViewPatterns language extension is not enabled.

Examples(s): data Foo = Foo { a :: Int }

foo :: Foo -> Int foo (a -> l) = l -- not OK, the ViewPattern extension is not enabled.

Test cases: parsershould_failViewPatternsFail

TcRnCharLiteralOutOfRange is an error that occurs whenever a character is out of range.

Examples(s): None

Test cases: None

TcRnNegativeNumTypeLiteral is an error that occurs whenever a type-level number literal is negative.

type Neg = -1

Test cases: th/T8412 typecheckshould_failT8306

TcRnIllegalWildcardsInConstructor is an error that occurs whenever the record wildcards '..' are used inside a constructor without labeled fields.

Examples(s): None

Test cases: renameshould_failT9815.hs renameshould_failT9815b.hs renameshould_failT9815ghci.hs renameshould_failT9815bghci.hs

TcRnIgnoringAnnotations is a warning that occurs when the source code contains annotation pragmas but the platform in use does not support an external interpreter such as GHCi and therefore the annotations are ignored.

Example(s): None

Test cases: None

TcRnAnnotationInSafeHaskell is an error that occurs if annotation pragmas are used in conjunction with Safe Haskell.

Example(s): None

Test cases: annotationsshould_failT10826

TcRnInvalidTypeApplication is an error that occurs when a visible type application is used with an expression that does not accept "specified" type arguments.

Example(s): foo :: forall {a}. a -> a foo x = x bar :: () bar = let x = foo @Int 42 in ()

Test cases: overloadedrecfldsshould_failoverloadedlabelsfail03 typecheckshould_failExplicitSpecificity1 typecheckshould_failExplicitSpecificity10 typecheckshould_failExplicitSpecificity2 typecheckshould_failT17173 typecheckshould_failVtaFail

TcRnTagToEnumMissingValArg is an error that occurs when the 'tagToEnum#' function is not applied to a single value argument.

Example(s): tagToEnum# 1 2

Test cases: None

TcRnTagToEnumUnspecifiedResTy is an error that occurs when the 'tagToEnum#' function is not given a concrete result type.

Example(s): foo :: forall a. a foo = tagToEnum# 0#

Test cases: typecheckshould_failtcfail164

TcRnTagToEnumResTyNotAnEnum is an error that occurs when the 'tagToEnum#' function is given a result type that is not an enumeration type.

Example(s): foo :: Int -- not an enumeration TyCon foo = tagToEnum# 0#

Test cases: typecheckshould_failtcfail164

TcRnTagToEnumResTyTypeData is an error that occurs when the 'tagToEnum#' function is given a result type that is headed by a type data type, as the data constructors of a type data do not exist at the term level.

Example(s): type data Letter = A | B | C

foo :: Letter foo = tagToEnum# 0#

Test cases: type-datashould_failTDTagToEnum.hs

TcRnArrowIfThenElsePredDependsOnResultTy is an error that occurs when the predicate type of an ifThenElse expression in arrow notation depends on the type of the result.

Example(s): None

Test cases: None

TcRnIllegalHsBootOrSigDecl is an error that occurs when an hs-boot file contains declarations that are not allowed, such as bindings.

Examples:

• - A.hs-boot f :: Int -> Int f x = 2 * x -- binding not allowed
• - B.hs-boot type family F a where { F Int = Bool }
• - type family equations not allowed
• - C.hsig bar :: Int -> Int {-# RULES forall x. bar x = x #-} -- RULES not allowed

Test cases:

• bindings: T19781
• class instance body: none
• type family instance: HsBootFam
• splice: none
• foreign declaration: none
• default declaration: none
• RULEs: none

TcRnBootMismatch is a family of errors that occur when there is a mismatch between the hs-boot and hs files.

Examples:

• - A.hs-boot foo :: Int -> Bool data D = MkD
• - A.hs foo :: Int -> Char foo = chr

data D = MkD Int

Test cases:

• missing export: bkpcabal06, bkpfail{01,05,09,16,35}, rnfail{047,055}
• missing definition: none
• missing instance: T14075
• mismatch in exports: bkpfail{03,19}
• conflicting definitions: bkpcabal02, bkpfail{04,06,07,10,12,133,14,15,17,22,23,25,26,27,41,42,45,47,50,52,53,54}, T19244{a,b}, T23344, ClosedFam3, rnfail055

TcRnRecursivePatternSynonym is an error that occurs when a pattern synonym is defined in terms of itself, either directly or indirectly.

Example(s): pattern A = B pattern B = A

Test cases: patsynshould_failT16900

TcRnPartialTypeSigTyVarMismatch is an error that occurs when a partial type signature attempts to unify two different types.

Example(s): f :: a -> b -> _ f x y = [x, y]

Test cases: partial-sigsshould_failT14449

TcRnPartialTypeSigBadQuantifier is an error that occurs when a type variable being quantified over in the partial type signature of a function gets unified with a type that is free in that function's context.

Example(s): foo :: Num a => a -> a foo xxx = g xxx where g :: forall b. Num b => _ -> b g y = xxx + y

Test cases: partial-sigshould_failT14479

TcRnMissingSignature is a warning that occurs when a top-level binding or a pattern synonym does not have a type signature.

Controlled by the flags: -Wmissing-signatures -Wmissing-exported-signatures -Wmissing-pattern-synonym-signatures -Wmissing-exported-pattern-synonym-signatures -Wmissing-kind-signatures -Wmissing-poly-kind-signatures

Test cases: T11077 (top-level bindings) T12484 (pattern synonyms) T19564 (kind signatures)

TcRnPolymorphicBinderMissingSig is a warning controlled by -Wmissing-local-signatures that occurs when a local polymorphic binding lacks a type signature.

Example(s): id a = a

Test cases: warningsshould_compileT12574

TcRnOverloadedSig is an error that occurs when a binding group conflicts with the monomorphism restriction.

Example(s): data T a = T a mono = ... where x :: Applicative f => f a T x = ...

Test cases: typecheckshould_compileT11339

TcRnTupleConstraintInst is an error that occurs whenever an instance for a tuple constraint is specified.

Examples(s): class C m a class D m a f :: (forall a. Eq a => (C m a, D m a)) => m a f = undefined

Test cases: quantified-constraints/T15334

TcRnUserTypeError is an error that occurs due to a user's custom type error, which can be triggered by adding a TypeError constraint in a type signature or typeclass instance.

Examples(s): f :: TypeError (Text "This is a type error") f = undefined

Test cases: typecheckshould_failCustomTypeErrors02 typecheckshould_failCustomTypeErrors03

TcRnConstraintInKind is an error that occurs whenever a constraint is specified in a kind.

Examples(s): data Q :: Eq a => Type where {}

Test cases: dependentshould_failT13895 polykinds/T16263 saksshould_failsaks_fail004 typecheckshould_failT16059a typecheckshould_failT18714

TcRnUnboxedTupleTypeFuncArg is an error that occurs whenever an unboxed tuple or unboxed sum type is specified as a function argument, when the appropriate extension (`-XUnboxedTuples` or `-XUnboxedSums`) isn't enabled.

Examples(s): -- T15073.hs import T15073a newtype Foo a = MkFoo a deriving P

• - T15073a.hs class P a where p :: a -> (# a #)

Test cases: derivingshould_failT15073.hs derivingshould_failT15073a.hs typecheckshould_failT16059d

TcRnLinearFuncInKind is an error that occurs whenever a linear function is specified in a kind.

Examples(s): data A :: * %1 -> *

Test cases: linearshould_failLinearKind linearshould_failLinearKind2 linearshould_failLinearKind3

TcRnForAllEscapeError is an error that occurs whenever a quantified type's kind mentions quantified type variable.

Examples(s): type T :: TYPE (BoxedRep l) data T = MkT

Test cases: unlifted-datatypesshould_failUnlDataNullaryPoly

TcRnVDQInTermType is an error that occurs whenever a visible dependent quantification is specified in the type of a term.

Examples(s): a = (undefined :: forall k -> k -> Type) @Int

Test cases: dependentshould_failT15859 dependentshould_failT16326_Fail1 dependentshould_failT16326_Fail2 dependentshould_failT16326_Fail3 dependentshould_failT16326_Fail4 dependentshould_failT16326_Fail5 dependentshould_failT16326_Fail6 dependentshould_failT16326_Fail7 dependentshould_failT16326_Fail8 dependentshould_failT16326_Fail9 dependentshould_failT16326_Fail10 dependentshould_failT16326_Fail11 dependentshould_failT16326_Fail12 dependentshould_failT17687 dependentshould_failT18271

TcRnBadQuantPredHead is an error that occurs whenever a quantified predicate lacks a class or type variable head.

Examples(s): class (forall a. A t a => A t [a]) => B t where type A t a :: Constraint

Test cases: quantified-constraints/T16474

TcRnIllegalTupleConstraint is an error that occurs whenever an illegal tuple constraint is specified.

Examples(s): g :: ((Show a, Num a), Eq a) => a -> a g = undefined

Test cases: typecheckshould_failtcfail209a

TcRnNonTypeVarArgInConstraint is an error that occurs whenever a non type-variable argument is specified in a constraint.

Examples(s): data T instance Eq Int => Eq T

Test cases: ghciscriptsT13202 ghciscriptsT13202a polykinds/T12055a typecheckshould_failT10351 typecheckshould_failT19187 typecheckshould_failT6022 typecheckshould_failT8883

TcRnIllegalImplicitParam is an error that occurs whenever an illegal implicit parameter is specified.

Examples(s): type Bla = ?x::Int data T = T instance Bla => Eq T

Test cases: polykinds/T11466 typecheckshould_failT8912 typecheckshould_failtcfail041 typecheckshould_failtcfail211 typecheckshould_failtcrun045

TcRnIllegalConstraintSynonymOfKind is an error that occurs whenever an illegal constraint synonym of kind is specified.

Examples(s): type Showish = Show f :: (Showish a) => a -> a f = undefined

Test cases: typecheckshould_failtcfail209

TcRnOversaturatedVisibleKindArg is an error that occurs whenever an illegal oversaturated visible kind argument is specified.

Examples(s): type family F2 :: forall (a :: Type). Type where F2 @a = Maybe a

Test cases: typecheckshould_failT15793 typecheckshould_failT16255

TcRnForAllRankErr is an error that occurs whenever an illegal ranked type is specified.

Examples(s): foo :: (a,b) -> (a~b => t) -> (a,b) foo p x = p

Test cases: - ghcishould_runT15806 - indexed-typesshould_failSimpleFail15 - typecheckshould_failT11355 - typecheckshould_failT12083a - typecheckshould_failT12083b - typecheckshould_failT16059c - typecheckshould_failT16059e - typecheckshould_failT17213 - typecheckshould_failT18939_Fail - typecheckshould_failT2538 - typecheckshould_failT5957 - typecheckshould_failT7019 - typecheckshould_failT7019a - typecheckshould_failT7809 - typecheckshould_failT9196 - typecheckshould_failtcfail127 - typecheckshould_failtcfail184 - typecheckshould_failtcfail196 - typecheckshould_failtcfail197

TcRnSimplifiableConstraint is a warning triggered by the occurrence of a simplifiable constraint in a context, when MonoLocalBinds is not enabled.

Examples(s): simplifiableEq :: Eq (a, a) => a -> a -> Bool simplifiableEq = undefined

Test cases: - indexed-typesshould_compileT15322 - partial-sigsshould_compileSomethingShowable - typecheckshould_compileT13526

TcRnArityMismatch is an error that occurs when a type constructor is supplied with fewer arguments than required.

Examples(s): f Left = undefined

Test cases: - backpackshould_failbkpfail25.bkp - ghcishould_failT16013 - ghcishould_failT16287 - indexed-typesshould_failBadSock - indexed-typesshould_failT9433 - module/mod60 - ndexed-typesshould_failT2157 - parsershould_failParserNoBinaryLiterals2 - parsershould_failParserNoBinaryLiterals3 - patsynshould_failT12819 - polykinds/T10516 - typecheckshould_failT12124 - typecheckshould_failT15954 - typecheckshould_failT16874 - typecheckshould_failtcfail100 - typecheckshould_failtcfail101 - typecheckshould_failtcfail107 - typecheckshould_failtcfail129 - typecheckshould_failtcfail187

TcRnIllegalClassInstance is a collection of diagnostics that arise from an invalid class or family instance declaration.

See IllegalInstanceReason.

TcRnMonomorphicBindings is a warning (controlled by -Wmonomorphism-restriction) that arises when the monomorphism restriction applies to the given bindings.

Examples(s): {-# OPTIONS_GHC -Wmonomorphism-restriction #-}

bar = 10

foo :: Int foo = bar

main :: IO () main = print foo

The example above emits the warning (for bar), because without monomorphism restriction the inferred type for bar is 'bar :: Num p => p'. This warning tells us that if we were to enable '-XMonomorphismRestriction' we would make bar less polymorphic, as its type would become 'bar :: Int', so GHC warns us about that.

Test cases: typecheckshould_compileT13785

TcRnOrphanInstance is a warning (controlled by -Worphans) that arises when a typeclass instance or family instance is an "orphan", i.e. if it appears in a module in which neither the class/family nor the type being instanced are declared in the same module.

Examples(s): None

Test cases: warningsshould_compileT9178 typecheckshould_compileT4912

TcRnFunDepConflict is an error that occurs when there are functional dependencies conflicts between instance declarations.

Examples(s): None

Test cases: typecheckshould_failT2307 typecheckshould_failtcfail096 typecheckshould_failtcfail202

TcRnDupInstanceDecls is an error that occurs when there are duplicate instance declarations.

Examples(s): class Foo a where foo :: a -> Int

instance Foo Int where foo = id

instance Foo Int where foo = const 42

Test cases: cabalT12733T12733 typecheckshould_failtcfail035 typecheckshould_failtcfail023 backpackshould_failbkpfail18 typecheckshould_failTcNullaryTCFail typecheckshould_failtcfail036 typecheckshould_failtcfail073 module/mod51 module/mod52 module/mod44

TcRnConflictingFamInstDecls is an error that occurs when there are conflicting family instance declarations.

Examples(s): None.

Test cases: indexed-typesshould_failExplicitForAllFams4b indexed-typesshould_failNoGood indexed-typesshould_failOver indexed-typesshould_failOverDirectThisMod indexed-typesshould_failOverIndirectThisMod indexed-typesshould_failSimpleFail11a indexed-typesshould_failSimpleFail11b indexed-typesshould_failSimpleFail11c indexed-typesshould_failSimpleFail11d indexed-typesshould_failSimpleFail2a indexed-typesshould_failSimpleFail2b indexed-typesshould_failT13092/T13092 indexed-typesshould_failT13092c/T13092c indexed-typesshould_failT14179 indexed-typesshould_failT2334A indexed-typesshould_failT2677 indexed-typesshould_failT3330b indexed-typesshould_failT4246 indexed-typesshould_failT7102a indexed-typesshould_failT9371 polykinds/T7524 typecheckshould_failUnliftedNewtypesOverlap

TcRnFamInstNotInjective is a collection of errors that arise from a type family equation violating the injectivity annotation.

See InjectivityErrReason.

TcRnBangOnUnliftedType is a warning (controlled by -Wredundant-strictness-flags) that occurs when a strictness annotation is applied to an unlifted type.

Example(s): data T = MkT !Int# -- Strictness flag has no effect on unlifted types

Test cases: typecheckshould_compileT20187a typecheckshould_compileT20187b

TcRnLazyBangOnUnliftedType is a warning (controlled by -Wredundant-strictness-flags) that occurs when a lazy annotation is applied to an unlifted type.

Example(s): data T = MkT ~Int# -- Lazy flag has no effect on unlifted types

Test cases: typecheckshould_compileT21951a typecheckshould_compileT21951b

TcRnMultipleDefaultDeclarations is an error that occurs when a module has more than one default declaration for the same class.

Example: default (Integer, Int) -- implicitly applies to Num default (Double, Float) -- 2nd default declaration not allowed

Text cases: module/mod58

TcRnWarnClashingDefaultImports is a warning that occurs when a module imports more than one default declaration for the same class, and they are not all subsumed by one of them nor by a local `default` declaration.

See Note [Named default declarations] in GHC.Tc.Gen.Default

Test cases: default/Import07.hs

TcRnBadDefaultType is an error that occurs when a type used in a default declaration does not have an instance for any of the applicable classes.

Example(s): data Foo default (Foo)

Test cases: typecheckshould_failT11974b

TcRnPatSynBundledWithNonDataCon is an error that occurs when a module's export list bundles a pattern synonym with a type that is not a proper `data` or `newtype` construction.

Example(s): module Foo (MyClass(.., P)) where pattern P = Nothing class MyClass a where foo :: a -> Int

Test cases: patsynshould_failexport-class

TcRnPatSynBundledWithWrongType is an error that occurs when the export list of a module has a pattern synonym bundled with a type that does not match the type of the pattern synonym.

Example(s): module Foo (R(P,x)) where data Q = Q Int data R = R pattern P{x} = Q x

Text cases: patsynshould_failexport-ps-rec-sel patsynshould_failexport-type-synonym patsynshould_failexport-type

TcRnDupeModuleExport is a warning controlled by -Wduplicate-exports that occurs when a module appears more than once in an export list.

Example(s): module Foo (module Bar, module Bar) import Bar

Text cases: None

TcRnExportedModNotImported is an error that occurs when an export list contains a module that is not imported.

Example(s): None

Text cases: module/mod135 module/mod8 renameshould_failrnfail028 backpackshould_failbkpfail48

TcRnNullExportedModule is a warning controlled by -Wdodgy-exports that occurs when an export list contains a module that has no exports.

Example(s): module Foo (module Bar) where import Bar ()

Test cases: None

TcRnMissingExportList is a warning controlled by -Wmissing-export-lists that occurs when a module does not have an explicit export list.

Example(s): None

Test cases: typecheckshould_failMissingExportList03

TcRnExportHiddenComponents is an error that occurs when an export contains constructor or class methods that are not visible.

Example(s): None

Test cases: None

TcRnExportHiddenDefault is an error that occurs when an export contains a class default (with language extension NamedDefaults) that is not visible.

Example(s): None

Test cases: default/fail06.hs

TcRnDuplicateExport is a warning (controlled by -Wduplicate-exports) that occurs when an identifier appears in an export list more than once.

Example(s): None

Test cases: module/MultiExport module/mod128 module/mod14 module/mod5 overloadedrecfldsshould_failDuplicateExports patsynshould_compileT11959

TcRnExportedParentChildMismatch is an error that occurs when an export is bundled with a parent that it does not belong to

Example(s): module Foo (T(a)) where data T a = True

Test cases: module/T11970 module/T11970B module/mod17 module/mod3 overloadedrecfldsshould_failNoParent

TcRnConflictingExports is an error that occurs when different identifiers that have the same name are being exported by a module.

Example(s): module Foo (Bar.f, module Baz) where import qualified Bar (f) import Baz (f)

Test cases: module/mod131 module/mod142 module/mod143 module/mod144 module/mod145 module/mod146 module/mod150 module/mod155 overloadedrecfldsshould_failT14953 overloadedrecfldsshould_failoverloadedrecfldsfail10 renameshould_failrnfail029 renameshould_failrnfail040 typecheckshould_failT16453E2 typecheckshould_failtcfail025 typecheckshould_failtcfail026

TcRnDuplicateFieldExport is an error that occurs when a module exports multiple record fields with the same name, without enabling DuplicateRecordFields.

Example:

module M1 where data D1 = MkD1 { foo :: Int } module M2 where data D2 = MkD2 { foo :: Int } module M ( D1(..), D2(..) ) where import module M1 import module M2

Test case: overloadedrecfldsshould_failoverloadedrecfldsfail10

TcRnAmbiguousRecordUpdate is a warning, controlled by -Wambiguous-fields, which occurs when a user relies on the type-directed disambiguation mechanism to disambiguate a record update. This will not be supported by -XDuplicateRecordFields in future releases.

Example(s):

data Person = MkPerson { personId :: Int, name :: String } data Address = MkAddress { personId :: Int, address :: String } bad1 x = x { personId = 4 } :: Person -- ambiguous bad2 (x :: Person) = x { personId = 4 } -- ambiguous good x = (x :: Person) { personId = 4 } -- not ambiguous

Test cases: overloadedrecfldsshould_failoverloadedrecfldsfail06

TcRnMissingFields is a warning controlled by -Wmissing-fields occurring when the intialisation of a record is missing one or more (lazy) fields.

Example(s): data Rec = Rec { a :: Int, b :: String, c :: Bool } x = Rec { a = 1, b = "two" } -- missing field c

Test cases: deSugarshould_compileT13870 deSugarshould_compileds041 patsynshould_compileT11283 renameshould_compileT5334 renameshould_compileT12229 renameshould_compileT5892a warningsshould_failWerrorFail2

TcRnFieldUpdateInvalidType is an error occurring when an updated field's type mentions something that is outside the universally quantified variables of the data constructor, such as an existentially quantified type.

Example(s): data X = forall a. MkX { f :: a } x = (MkX ()) { f = False }

Test cases: patsynshould_failrecords-exquant typecheckshould_failT3323

TcRnMissingStrictFields is an error occurring when a record field marked as strict is omitted when constructing said record.

Example(s): data R = R { strictField :: !Bool, nonStrict :: Int } x = R { nonStrict = 1 }

Test cases: typecheckshould_failT18869 typecheckshould_failtcfail085 typecheckshould_failtcfail112

TcRnAmbiguousFieldInUpdate is an error that occurs when a field in a record update clashes with another field or top-level function of the same name, and the user hasn't enabled -XDisambiguateRecordFields.

Example:

{-# LANGUAGE NoFieldSelectors #-} {-# LANGUAGE NoDisambiguateRecordFields #-} module M where

data A = MkA { fld :: Int }

fld :: Bool fld = False

f r = r { fld = 3 }

TcRnBadRecordUpdate is an error when a regular (non-overloaded) record update cannot be pinned down to any one parent.

The problem with the record update is stored in the BadRecordUpdateReason field.

Example(s):

data R1 = R1 { x :: Int } data R2 = R2 { x :: Int } update r = r { x = 1 } -- ambiguous

data R1 = R1 { x :: Int, y :: Int } data R2 = R2 { y :: Int, z :: Int } update r = r { x = 1, y = 2, z = 3 } -- no parent has all the fields

Test cases: overloadedrecfldsshould_failoverloadedrecfldsfail01 overloadedrecfldsshould_failoverloadedrecfldsfail01 overloadedrecfldsshould_failoverloadedrecfldsfail14

TcRnStaticFormNotClosed is an error pertaining to terms that are marked static using the -XStaticPointers extension but which are not closed terms.

Example(s): f x = static x

Test cases: renameshould_failRnStaticPointersFail01 renameshould_failRnStaticPointersFail03

TcRnUselessTypeable is a warning (controlled by -Wderiving-typeable) that occurs when trying to derive an instance of the Typeable class. Deriving Typeable is no longer necessary (hence the "useless") as all types automatically derive Typeable in modern GHC versions.

Example(s): None.

Test cases: warningsshould_compileDerivingTypeable

TcRnDerivingDefaults is a warning (controlled by -Wderiving-defaults) that occurs when both DeriveAnyClass and GeneralizedNewtypeDeriving are enabled, and therefore GHC defaults to DeriveAnyClass, which might not be what the user wants.

Example(s): None.

Test cases: typecheckshould_compileT15839a derivingshould_compileT16179

TcRnNonUnaryTypeclassConstraint is an error that occurs when GHC encounters a non-unary constraint when trying to derive a typeclass.

Example(s): class A deriving instance A data B deriving A -- We cannot derive A, is not unary (i.e. 'class A a').

Test cases: derivingshould_failT7959 derivingshould_faildrvfail005 derivingshould_faildrvfail009 derivingshould_faildrvfail006

TcRnPartialTypeSignatures is a warning (controlled by -Wpartial-type-signatures) that occurs when a wildcard '_' is found in place of a type in a signature or a type class derivation

Example(s): foo :: _ -> Int foo = ...

deriving instance _ => Eq (Foo a)

Test cases: dependentshould_compileT11241 dependentshould_compileT15076 dependentshould_compileT14880-2 typecheckshould_compileT17024 typecheckshould_compileT10072 partial-sigsshould_failTidyClash2 partial-sigsshould_failDefaulting1MROff partial-sigsshould_failWildcardsInPatternAndExprSig partial-sigsshould_failT10615 partial-sigsshould_failT14584a partial-sigsshould_failTidyClash partial-sigsshould_failT11122 partial-sigsshould_failT14584 partial-sigsshould_failT10045 partial-sigsshould_failPartialTypeSignaturesDisabled partial-sigsshould_failT10999 partial-sigsshould_failExtraConstraintsWildcardInExpressionSignature partial-sigsshould_failExtraConstraintsWildcardInPatternSplice partial-sigsshould_failWildcardInstantiations partial-sigsshould_runT15415 partial-sigsshould_compileT10463 partial-sigsshould_compileT15039a partial-sigsshould_compileT16728b partial-sigsshould_compileT15039c partial-sigsshould_compileT10438 partial-sigsshould_compileSplicesUsed partial-sigsshould_compileT18008 partial-sigsshould_compileExprSigLocal partial-sigsshould_compileT11339a partial-sigsshould_compileT11670 partial-sigsshould_compileWarningWildcardInstantiations partial-sigsshould_compileT16728 partial-sigsshould_compileT12033 partial-sigsshould_compileT15039b partial-sigsshould_compileT10403 partial-sigsshould_compileT11192 partial-sigsshould_compileT16728a partial-sigsshould_compileTypedSplice partial-sigsshould_compileT15039d partial-sigsshould_compileT11016 partial-sigsshould_compileT13324_compile2 linearshould_failLinearPartialSig polykinds/T14265 polykinds/T14172

TcRnCannotDeriveInstance is an error that occurs every time a typeclass instance can't be derived. The DeriveInstanceErrReason will contain the specific reason this error arose.

Example(s): None.

Test cases: genericsT10604T10604_no_PolyKinds derivingshould_faildrvfail009 derivingshould_faildrvfail-functor2 derivingshould_failT10598_fail3 derivingshould_failderiving-via-fail2 derivingshould_failderiving-via-fail derivingshould_failT16181

TcRnLazyGADTPattern is an error that occurs when a user writes a nested GADT pattern match inside a lazy (~) pattern.

Test case: gadt/lazypat

TcRnArrowProcGADTPattern is an error that occurs when a user writes a GADT pattern inside arrow proc notation.

Test case: arrowsshould_failarrowfail004.

TcRnCapturedTermName is a warning (controlled by -Wterm-variable-capture) that occurs when an implicitly quantified type variable's name is already used for a term. Example: a = 10 f :: a -> a

Test cases: T22513a T22513b T22513c T22513d T22513e T22513f T22513g T22513h T22513i

TcRnTypeEqualityOutOfScope is a warning (controlled by -Wtype-equality-out-of-scope) that occurs when the type equality (a ~ b) is not in scope.

Test case: warningsshould_compileT18862b

TcRnTypeEqualityRequiresOperators is a warning (controlled by -Wtype-equality-requires-operators) that occurs when the type equality (a ~ b) is used without the TypeOperators extension.

Example: {-# LANGUAGE NoTypeOperators #-} f :: (a ~ b) => a -> b

Test case: T18862a

TcRnIllegalTypeOperator is an error that occurs when a type operator is used without the TypeOperators extension.

Example: {-# LANGUAGE NoTypeOperators #-} f :: Vec a n -> Vec a m -> Vec a (n + m)

Test case: T12811

TcRnIllegalTypeOperatorDecl is an error that occurs when a type or class operator is declared without the TypeOperators extension.

See Note [Type and class operator definitions]

Example: {-# LANGUAGE Haskell2010 #-} {-# LANGUAGE MultiParamTypeClasses #-}

module T3265 where

data a :+: b = Left a | Right b

class a :*: b where {}

Test cases: T3265, tcfail173

TcRnGADTMonoLocalBinds is a warning controlled by -Wgadt-mono-local-binds that occurs when pattern matching on a GADT when -XMonoLocalBinds is off.

Example(s): None

Test cases: T20485, T20485a

The TcRnNotInScope constructor is used for various not-in-scope errors. See NotInScopeError for more details.

TcRnTermNameInType is an error that occurs when a term-level identifier is used in a type.

Example:

import qualified Prelude

bad :: Prelude.fst (Bool, Float) bad = False

Test cases: T21605{c,d}

TcRnUntickedPromotedThing is a warning (controlled with -Wunticked-promoted-constructors) that is triggered by an unticked occurrence of a promoted data constructor.

Examples:

data A = MkA type family F (a :: A) where { F MkA = Bool }

type B = [ Int, Bool ]

Test cases: T9778, T19984.

TcRnIllegalBuiltinSyntax is an error that occurs when built-in syntax appears in an unexpected location, e.g. as a data constructor or in a fixity declaration.

Examples:

infixl 5 :

data P = (,)

Test cases: rnfail042, T14907b, T15124, T15233.

TcRnWarnDefaulting is a warning (controlled by -Wtype-defaults) that is triggered whenever a Wanted typeclass constraint is solving through the defaulting of a type variable.

Example:

one = show 1 -- We get Wanteds Show a0, Num a0, and default a0 to Integer.

Test cases: none (which are really specific to defaulting), but see e.g. tcfail204.

TcRnIncorrectNameSpace is an error that occurs when a Name is used in the incorrect NameSpace, e.g. a type constructor or class used in a term, or a term variable used in a type.

Example:

list2 = $( conE ''(:) appE litE (IntegerL 5) appE conE '[] ) -- ^^^^^ -- should use a single quotation tick, i.e. '(:)

Test cases: T20884.

TcRnForeignImportPrimExtNotSet is an error occurring when a foreign import is declared using the prim calling convention without having turned on the -XGHCForeignImportPrim extension.

Example(s): foreign import prim "foo" foo :: ByteArray# -> (# Int#, Int# #)

Test cases: ffishould_failT20116

TcRnForeignImportPrimSafeAnn is an error declaring that the safe/unsafe annotation should not be used with prim foreign imports.

Example(s): foreign import prim unsafe "my_primop_cmm" :: ...

Test cases: None

TcRnForeignFunctionImportAsValue is an error explaining that foreign value imports cannot have function types.

Example(s): foreign import capi "math.h value sqrt" f :: CInt -> CInt

Test cases: ffishould_failcapi_value_function

TcRnFunPtrImportWithoutAmpersand is a warning controlled by -Wdodgy-foreign-imports that informs the user of a possible missing & in the declaration of a foreign import with a FunPtr return type.

Example(s): foreign import ccall "f" f :: FunPtr (Int -> IO ())

Test cases: ffishould_compileT1357

TcRnIllegalForeignDeclBackend is an error occurring when a foreign import declaration is not compatible with the code generation backend being used.

Example(s): None

Test cases: None

TcRnUnsupportedCallConv informs the user that the calling convention specified for a foreign export declaration is not compatible with the target platform. It is a warning controlled by -Wunsupported-calling-conventions in the case of stdcall but is otherwise considered an error.

Example(s): None

Test cases: None

TcRnIllegalForeignType is an error for when a type appears in a foreign function signature that is not compatible with the FFI.

Example(s): None

Test cases: ffishould_failT3066 ffishould_failccfail004 ffishould_failT10461 ffishould_failT7506 ffishould_failT5664 safeHaskellghcip6 safeHaskellsafeLanguageSafeLang08 ffishould_failT16702 linearshould_failLinearFFI ffishould_failT7243

TcRnInvalidCIdentifier indicates a C identifier that is not valid.

Example(s): foreign import prim safe "not valid" cmm_test2 :: Int# -> Int#

Test cases: th/T10638

TcRnExpectedValueId is an error occurring when something that is not a value identifier is used where one is expected.

Example(s): none

Test cases: none

TcRnRecSelectorEscapedTyVar is an error indicating that a record field selector containing an existential type variable is used as a function rather than in a pattern match.

Example(s): data Rec = forall a. Rec { field :: a } field (Rec True)

Test cases: patsynshould_failrecords-exquant typecheckshould_failT3176

TcRnPatSynNotBidirectional is an error for when a non-bidirectional pattern synonym is used as a constructor.

Example(s): pattern Five :: Int pattern Five <- 5 five = Five

Test cases: patsynshould_failrecords-no-uni-update patsynshould_failrecords-no-uni-update2

TcRnIllegalDerivingItem is an error for when something other than a type class appears in a deriving statement.

Example(s): data X = X deriving Int

Test cases: derivingshould_failT5922

TcRnIllegalDefaultClass is an error for when something other than a type class appears in a default declaration after the keyword.

Example(s): default Integer (Int)

Test cases: default/fail01

TcRnIllegalNamedDefault is an error for specifying an explicit default class name without -XNamedDefaults.

Example(s): default Num (Integer)

Test cases: default/fail02

TcRnUnexpectedAnnotation indicates the erroroneous use of an annotation such as strictness, laziness, or unpacking.

Example(s): data T = T { t :: Maybe {-# UNPACK #-} Int } data C = C { f :: !IntMap Int }

Test cases: parsershould_failunpack_inside_type typecheckshould_failT7210 renameshould_failT22478b

TcRnIllegalRecordSyntax is an error indicating an illegal use of record syntax.

Example(s): data T = T Int { field :: Int }

Test cases: renameshould_failT7943 renameshould_failT9077 renameshould_failT22478b

TcRnInvalidVisibleKindArgument is an error for a kind application on a target type that cannot accept it.

Example(s): bad :: Int Type bad = 1 type Foo :: forall a {b}. a -> b -> b type Foo x y = y type Bar = Foo Bool @Int True 42

Test cases: indexed-typesshould_failT16356_Fail3 typecheckshould_failExplicitSpecificity7 typecheckshould_failT12045b typecheckshould_failT12045c typecheckshould_failT15592a typecheckshould_failT15816

TcRnTooManyBinders is an error for a type constructor that is declared with more arguments then its kind specifies.

Example(s): type T :: Type -> (Type -> Type) -> Type data T a (b :: Type -> Type) x1 (x2 :: Type -> Type)

Test cases: saksshould_failsaks_fail008

TcRnDifferentNamesForTyVar is an error that indicates different names being used for the same type variable.

Example(s): data SameKind :: k -> k -> * data Q (a :: k1) (b :: k2) c = MkQ (SameKind a b)

Test cases: polykinds/T11203 polykinds/T11821a saksshould_failT20916 typecheckshould_failT17566b typecheckshould_failT17566c

TcRnDisconnectedTyVar is an error for a data declaration that has a kind signature, where the implicitly-bound type type variables can't be matched up unambiguously with the ones from the signature. See Note [Disconnected type variables] in GHC.Tc.Gen.HsType.

Test cases: T24083

TcRnInvalidReturnKind is an error for a data declaration that has a kind signature with an invalid result kind.

Example(s): data family Foo :: Constraint

Test cases: typecheckshould_failT14048b typecheckshould_failUnliftedNewtypesConstraintFamily typecheckshould_failT12729 typecheckshould_failT15883 typecheckshould_failT16829a typecheckshould_failT16829b typecheckshould_failUnliftedNewtypesNotEnabled typecheckshould_failtcfail079

TcRnUnexpectedKindVar is an error that occurs when the user tries to use kind variables without -XPolyKinds.

Example: f :: forall k a. Proxy (a :: k)

Test cases: polykinds/BadKindVar polykinds/T14710 saksshould_failT16722

TcRnIllegalKind is used for a various illegal kinds errors including

Example: type T :: forall k. Type -- without emabled -XPolyKinds

Test cases: polykinds/T16762b

TcRnClassKindNotConstraint is an error for a type class that has a kind that is not equivalent to Constraint.

Example(s): type C :: Type -> Type class C a

Test cases: saksshould_failT16826

TcRnUnpromotableThing is an error that occurs when the user attempts to use the promoted version of something which is not promotable.

Example(s): data T :: T -> * data X a where MkX :: Show a => a -> X a foo :: Proxy ('MkX 'True) foo = Proxy

Test cases: dependentshould_failPromotedClass dependentshould_failT14845_fail1 dependentshould_failT14845_fail2 dependentshould_failT15215 dependentshould_failT13780c dependentshould_failT15245 polykinds/T5716 polykinds/T5716a polykinds/T6129 polykinds/T7433 patsynshould_failT11265 patsynshould_failT9161-1 patsynshould_failT9161-2 dependentshould_failSelfDep polykinds/PolyKinds06 polykinds/PolyKinds07 polykinds/T13625 polykinds/T15116 polykinds/T15116a saksshould_failT16727a saksshould_failT16727b renameshould_failT12686 renameshould_failT16635a renameshould_failT16635b renameshould_failT16635c

TcRnIllegalTermLevelUse is an error that occurs when the user attempts to use a type-level entity at the term-level.

Examples: f x = Int -- illegal use of a type constructor g (Proxy :: Proxy a) = a -- illegal use of a type variable

Note that the namespace cannot be used to determine if a name refers to a type-level entity:

{-# LANGUAGE RequiredTypeArguments #-} bad :: forall (a :: k) -> k bad t = t

The name t is assigned the varName namespace but stands for a type variable that cannot be used at the term level.

Test cases: T18740a, T18740b, T23739_fail_ret, T23739_fail_case

TcRnMatchesHaveDiffNumArgs is an error occurring when something has matches that have different numbers of arguments

Example(s): foo x = True foo x y = False

Test cases: renameshould_failrnfail045 typecheckshould_failT20768_fail

TcRnUnexpectedPatSigType is an error occurring when there is a type signature in a pattern without -XScopedTypeVariables extension

Examples: f (a :: Bool) = ...

Test case: renameshould_failT11663

TcRnIllegalKindSignature is an error occurring when there is a kind signature without -XKindSignatures extension

Examples: data Foo (a :: Nat) = ....

Test case: parsershould_failreadFail036

TcRnDataKindsError is an error occurring when there is an illegal type or kind, probably required -XDataKinds and is used without the enabled extension.

This error can occur in both the renamer and the typechecker. The field of type Either (HsType GhcPs) Type reflects this: this field will contain a Left value if the error occurred in the renamer, and this field will contain a Right value if the error occurred in the typechecker.

Examples:

type Foo = [Nat, Char]

type Bar = [Int, String]

Test cases: linearshould_failT18888 parsershould_failreadFail001 polykinds/T7151 polykinds/T7433 renameshould_failT13568 renameshould_failT22478e th/TH_Promoted1Tuple typecheckshould_compiletcfail094 typecheckshould_compileT22141a typecheckshould_compileT22141b typecheckshould_compileT22141c typecheckshould_compileT22141d typecheckshould_compileT22141e typecheckshould_compileT22141f typecheckshould_compileT22141g typecheckshould_failT20873c typecheckshould_failT20873d

TcRnCannotBindScopedTyVarInPatSig is an error stating that scoped type variables cannot be used in pattern bindings.

Example(s): let (x :: a) = 5

Test cases: typecheckshould_compiletc141

TcRnCannotBindTyVarsInPatBind is an error for when type variables are introduced in a pattern binding

Example(s): Just @a x = Just True

Test cases: typecheckshould_failTyAppPat_PatternBinding typecheckshould_failTyAppPat_PatternBindingExistential

TcRnTooManyTyArgsInConPattern is an error occurring when a constructor pattern has more than the expected number of type arguments

Example(s): f (Just Int Bool x) = x

Test cases: typecheckshould_failTyAppPat_TooMany typecheckshould_failT20443b

TcRnMultipleInlinePragmas is a warning signifying that multiple inline pragmas reference the same definition.

Example(s): {-# INLINE foo #-} {-# INLINE foo #-} foo :: Bool -> Bool foo = id

Test cases: none

TcRnUnexpectedPragmas is a warning that occurs when unexpected pragmas appear in the source.

Example(s):

Test cases: none

TcRnNonOverloadedSpecialisePragma is a warning for a specialise pragma being placed on a definition that is not overloaded.

Example(s): {-# SPECIALISE foo :: Bool -> Bool #-} foo :: Bool -> Bool foo = id

Test cases: simplCoreshould_compileT8537 typecheckshould_compileT10504

TcRnSpecialiseNotVisible is a warning that occurs when the subject of a SPECIALISE pragma has a definition that is not visible from the current module.

Example(s): none

Test cases: none

TcRnPragmaWarning is a warning that can happen when usage of something is warned or deprecated by pragma.

Test cases: DeprU T5281 T5867 rn050 rn066 (here is a warning, not deprecation) T3303 ExportWarnings1 ExportWarnings2 ExportWarnings3 ExportWarnings4 ExportWarnings5 ExportWarnings6 InstanceWarnings

TcRnDifferentExportWarnings is an error that occurs when the warning messages for exports of a name differ between several export items.

Test case: DifferentExportWarnings

TcRnIncompleteExportWarnings is a warning (controlled by -Wincomplete-export-warnings) that occurs when some of the exports of a name do not have an export warning and some do

Test case: ExportWarnings6

TcRnIllegalHsigDefaultMethods is an error that occurs when a binding for a class default method is provided in a Backpack signature file.

Test case: bkpfail40

TcRnHsigFixityMismatch is an error indicating that the fixity decl in a Backpack signature file differs from the one in the source file for the same operator.

Test cases: bkpfail37, bkpfail38

TcRnHsigShapeMismatch is a group of errors related to mismatches between backpack signatures.

TcRnHsigMissingModuleExport is an error indicating that a module doesn't export a name exported by its signature.

Test cases: bkpfail01, bkpfail05, bkpfail09, bkpfail16, bkpfail35, bkpcabal06

TcRnBadGenericMethod This test ensures that if you provide a "more specific" type signatures for the default method, you must also provide a binding.

Example: {-# LANGUAGE DefaultSignatures #-}

class C a where meth :: a default meth :: Num a => a meth = 0

Test case: typecheckshould_failMissingDefaultMethodBinding.hs

TcRnWarningMinimalDefIncomplete is a warning that one must specify which methods must be implemented by all instances.

Example: class Cheater a where -- WARNING LINE cheater :: a {-# MINIMAL #-} -- warning!

Test case: warningsminimalWarnMinimal.hs:

TcRnIllegalQuasiQuotes is an error that occurs when a quasi-quote is used without the QuasiQuotes extension.

Example:

foo = [myQuoter|x y z|]

Test cases: none; the parser fails to parse this if QuasiQuotes is off.

TcRnTHError is a family of errors involving Template Haskell. See THError.

TcRnDefaultMethodForPragmaLacksBinding is an error that occurs when a default method pragma is missing an accompanying binding.

Test cases: typecheckshould_failT5084.hs typecheckshould_failT2354.hs

TcRnIgnoreSpecialisePragmaOnDefMethod is a warning that occurs when a specialise pragma is put on a default method.

Test cases: none

TcRnBadMethodErr is an error that happens when one attempts to provide a method in a class instance, when the class doesn't have a method by that name.

Test case: th/T12387

TcRnIllegalNewtype is an error that occurs when a newtype:

• Does not have exactly one field, or
• is non-linear, or
• is a GADT, or
• has a context in its constructor's type, or
• has existential type variables in its constructor's type, or
• has strictness annotations.

Test cases: gadt/T14719 indexed-typesshould_failT14033 indexed-typesshould_failT2334A linearshould_failLinearGADTNewtype parsershould_failreadFail008 polykinds/T11459 typecheckshould_failT15523 typecheckshould_failT15796 typecheckshould_failT17955 typecheckshould_failT18891a typecheckshould_failT21447 typecheckshould_failtcfail156

TcRnIllegalTypeData is an error that occurs when a type data declaration occurs without the TypeOperators extension.

See Note [Type data declarations]

Test case: type-datashould_failTDNoPragma

TcRnTypeDataForbids is an error that occurs when a type data declaration contains data declaration features that are forbidden in a type data declaration.

See Note [Type data declarations]

Test cases: type-datashould_failTDDeriving type-datashould_failTDRecordsGADT type-datashould_failTDRecordsH98 type-datashould_failTDStrictnessGADT type-datashould_failTDStrictnessH98

TcRnOrPatBindsVariables is an error that happens when an or-pattern binds term or type variables, e.g. (A @x; B y).

Test case: testsuiteteststypecheckshould_failOr3

TcRnUnsatisfiedMinimalDef is a warning that occurs when a class instance is missing methods that are required by the minimal definition.

Example: class C a where foo :: a -> a instance C () -- | foo needs to be defined here

Test cases: typecheckprog001typecheck.prog001 typecheckshould_compiletc126 typecheckshould_compileT7903 typecheckshould_compiletc116 typecheckshould_compiletc175 typecheckshould_compileHasKey typecheckshould_compiletc125 typecheckshould_compiletc078 typecheckshould_compiletc161 typecheckshould_failT5051 typecheckshould_compileT21583 backpackshould_compilebkp47 backpackshould_failbkpfail25 parsershould_compileT2245 parsershould_compileread014 indexed-typesshould_compileClass3 indexed-typesshould_compileSimple2 indexed-typesshould_failT7862 derivingshould_compilederiving-1935 derivingshould_compileT9968a derivingshould_compiledrv003 derivingshould_compileT4966 derivingshould_compileT14094 perfcompilerT15304 warningsminimalWarnMinimal simplCoreshould_compilesimpl020 deSugarshould_compileT14546d ghciscriptsT5820 ghciscriptsghci019

TcRnMisplacedInstSig is an error that happens when a method in a class instance is given a type signature, but the user has not enabled the InstanceSigs extension.

Test case: module/mod45

TcRnNoRebindableSyntaxRecordDot is an error triggered by an overloaded record update without RebindableSyntax enabled.

Example(s):

Test cases: parsershould_failRecordDotSyntaxFail5

TcRnNoFieldPunsRecordDot is an error triggered by the use of record field puns in an overloaded record update without enabling NamedFieldPuns.

Example(s): print $ a{ foo.bar.baz.quux }

Test cases: parsershould_failRecordDotSyntaxFail12

TcRnIllegalStaticExpression is an error thrown when user creates a static pointer via TemplateHaskell without enabling the StaticPointers extension.

Example(s):

Test cases: th/T14204

TcRnListComprehensionDuplicateBinding is an error triggered by duplicate let-bindings in a list comprehension.

Example(s): [ () | let a = 13 | let a = 17 ]

Test cases: typecheckshould_failtcfail092

TcRnEmptyStmtsGroup is an error triggered by an empty list of statements in a statement block. For more information, see EmptyStatementGroupErrReason

Example(s):

() | then ()

do

proc () -> do

Test cases: renameshould_failRnEmptyStatementGroup1

TcRnLastStmtNotExpr is an error caused by the last statement in a statement block not being an expression.

Example(s):

do x <- pure ()

do let x = 5

Test cases: renameshould_failT6060 parsershould_failT3811g parsershould_failreadFail028

TcRnUnexpectedStatementInContext is an error when a statement appears in an unexpected context (e.g. an arrow statement appears in a list comprehension).

Example(s):

Test cases: parsershould_failreadFail042 parsershould_failreadFail038 parsershould_failreadFail043

TcRnIllegalTupleSection is an error triggered by usage of a tuple section without enabling the TupleSections extension.

Example(s): (5,)

Test cases: renameshould_failrnfail056

TcRnIllegalImplicitParameterBindings is an error triggered by binding an implicit parameter in an mdo block.

Example(s): mdo { let { ?x = 5 }; () }

Test cases: renameshould_failRnImplicitBindInMdoNotation

TcRnSectionWithoutParentheses is an error triggered by attempting to use an operator section without parentheses.

Example(s): (head x, ())

Test cases: renameshould_failT2490 renameshould_failT5657

TcRnBindingOfExistingName is an error triggered by an attempt to rebind built-in syntax, punned list or tuple syntax, or a name quoted via Template Haskell.

Examples:

data [] data (->) $(pure [ValD (VarP 'succ) (NormalB (ConE 'True)) []])

Test cases: renameshould_failT14907b renameshould_failT22839 renameshould_failrnfail042 th/T13968

TcRnMultipleFixityDecls is an error triggered by multiple fixity declarations for the same operator.

Example(s):

infixr 6 $$ infixl 4 $$

Test cases: renameshould_failRnMultipleFixityFail

TcRnIllegalPatternSynonymDecl is an error thrown when a user defines a pattern synonyms without enabling the PatternSynonyms extension.

Example:

pattern O :: Int pattern O = 0

Test cases: renameshould_failRnPatternSynonymFail

TcRnIllegalClassBinding is an error triggered by a binding in a class or instance declaration of an illegal form.

Examples:

class ZeroOne a where zero :: a one :: a instance ZeroOne Int where (zero,one) = (0,1)

class C a where pattern P = ()

Test cases: module/mod48 patsynshould_failT9705-1 patsynshould_failT9705-2 typecheckshould_failtcfail021

TcRnOrphanCompletePragma is an error triggered by a {-# COMPLETE #-} pragma which does not mention any data constructors or pattern synonyms defined in the current module.

Test cases: patsynshould_failT13349

TcRnEmptyCase is an error thrown when a user uses a case expression with an empty list of alternatives without enabling the EmptyCase extension.

Example(s):

case () of

Test cases: renameshould_failRnEmptyCaseFail

TcRnNonStdGuards is a warning thrown when a user uses non-standard guards (e.g. patterns in guards) without enabling the PatternGuards extension. More realistically: the user has explicitly disabled PatternGuards, as it is enabled by default with `-XHaskell2010`.

Example(s):

f | 5 <- 2 + 3 = ...

Test cases: renameshould_compilern049

TcRnDuplicateSigDecl is an error triggered by two or more signatures for one entity.

Examples:

f :: Int -> Bool f :: Int -> Bool f _ = True

g x = x {-# INLINE g #-} {-# NOINLINE g #-}

pattern P = () {-# COMPLETE P #-} {-# COMPLETE P #-}

Test cases: module/mod68 parsershould_failOpaqueParseFail4 patsynshould_failT12165 renameshould_failrnfail048 renameshould_failT5589 renameshould_failT7338 renameshould_failT7338a

TcRnMisplacedSigDecl is an error triggered by the pragma application in the wrong context, like MINIMAL applied to a function or SPECIALIZE to an instance.

Example:

f x = x {-# MINIMAL f #-}

Test cases: renameshould_failT18138 warningsminimalWarnMinimalFail1

TcRnUnexpectedDefaultSig is an error thrown when a user uses default signatures without enabling the DefaultSignatures extension.

Example:

class C a where m :: a default m :: Num a => a m = 0

Test cases: renameshould_failRnDefaultSigFail

TcRnDuplicateMinimalSig is an error triggered by two or more minimal signatures for one type class.

Example:

class C where f :: () {-# MINIMAL f #-} {-# MINIMAL f #-}

Test cases: renameshould_failRnMultipleMinimalPragmaFail

TcRnIllegalInvisTyVarBndr is an error that occurs when invisible type variable binders in type declarations are used without enabling the TypeAbstractions extension.

Example: {-# LANGUAGE NoTypeAbstractions #-} -- extension disabled data T k (a :: k) (j :: Type) (b :: j) ^^ ^^^^^^^^^^^^

Test case: T22560_fail_ext

TcRnIllegalWildcardTyVarBndr is an error that occurs when a wildcard binder is used in a type declaration without enabling the TypeAbstractions extension.

Example: {-# LANGUAGE NoTypeAbstractions #-} -- extension disabled type Const a _ = a ^

Test case: T23501_fail_ext

TcRnInvalidInvisTyVarBndr is an error that occurs when an invisible type variable binder has no corresponding forall k. quantifier in the standalone kind signature.

Example: type P :: forall a -> Type data P @a = MkP

Test cases: T22560_fail_a T22560_fail_b

TcRnInvisBndrWithoutSig is an error triggered by attempting to use an invisible type variable binder in a type declaration without a standalone kind signature or a complete user-supplied kind.

Example: data T @k (a :: k) -- No CUSK, no SAKS

Test case: T22560_fail_d

TcRnDeprecatedInvisTyArgInConPat is a warning that triggers on type applications in constructor patterns when the user has not enabled '-XTypeAbstractions' but instead has enabled both '-XScopedTypeVariables' and '-XTypeApplications'.

This warning is a deprecation mechanism that is scheduled until GHC 9.12.

TcRnUnexpectedStandaloneDerivingDecl is an error thrown when a user uses standalone deriving without enabling the StandaloneDeriving extension.

Example:

deriving instance Eq Foo

Test cases: renameshould_failRnUnexpectedStandaloneDeriving

TcRnUnusedVariableInRuleDecl is an error triggered by forall'd variable in rewrite rule that does not appear on left-hand side

Example:

{-# RULES "rule" forall a. id = id #-}

Test cases: renameshould_failExplicitForAllRules2

TcRnUnexpectedStandaloneKindSig is an error thrown when a user uses standalone kind signature without enabling the StandaloneKindSignatures extension.

Example:

type D :: Type data D = D

Test cases: saksshould_failsaks_fail001

TcRnIllegalRuleLhs is an error triggered by malformed left-hand side of rewrite rule

Examples:

{-# RULES "test" forall x. f x = x #-}

{-# RULES "test" forall x. case x of = x #-}

Test cases: renameshould_failT15659

TcRnDuplicateRoleAnnot is an error triggered by two or more role annotations for one type

Example:

data D a type role D phantom type role D phantom

Test cases: rolesshould_failRoles8

TcRnDuplicateKindSig is an error triggered by two or more standalone kind signatures for one type

Example:

type D :: Type type D :: Type data D

Test cases: saksshould_failsaks_fail002

TcRnIllegalDerivStrategy is an error thrown when a user uses deriving strategy without enabling the DerivingStrategies extension or uses deriving via without enabling the DerivingVia extension.

Examples:

data T = T deriving stock Eq

data T = T deriving via Eq T

Test cases: derivingshould_failderiving-via-fail3 derivingshould_failT10598_fail4

TcRnIllegalMultipleDerivClauses is an error thrown when a user uses two or more deriving clauses without enabling the DerivingStrategies extension.

Example:

data T = T deriving Eq deriving Ord

Test cases: derivingshould_failT10598_fail5

TcRnNoDerivStratSpecified is a warning implied by -Wmissing-deriving-strategies and triggered by deriving without mentioning a strategy.

See TcRnNoDerivStratSpecifiedInfo cases for examples.

Test cases: derivingshould_compileT15798a derivingshould_compileT15798b derivingshould_compileT15798c derivingshould_compileT24955a derivingshould_compileT24955b derivingshould_compileT24955c

TcRnStupidThetaInGadt is an error triggered by data contexts in GADT-style data declaration

Example:

data (Eq a) => D a where MkD :: D Int

Test cases: renameshould_failRnStupidThetaInGadt

TcRnShadowedTyVarNameInFamResult is an error triggered by type variable in type family result that shadows type variable from left hand side

Example:

type family F a b c = b

Test cases: ghciscriptsT6018ghcirnfail renameshould_failT6018rnfail

TcRnIncorrectTyVarOnRhsOfInjCond is an error caused by a situation where the left-hand side of an injectivity condition of a type family is not a variable referring to the type family result. See Note [Renaming injectivity annotation] for more details.

Example:

type family F a = r | a -> a

Test cases: ghciscriptsT6018ghcirnfail renameshould_failT6018rnfail

TcRnUnknownTyVarsOnRhsOfInjCond is an error triggered by out-of-scope type variables on the right-hand side of a of an injectivity condition of a type family

Example:

type family F a = res | res -> b

Test cases: ghciscriptsT6018ghcirnfail renameshould_failT6018rnfail

TcRnLookupInstance groups several errors emitted when looking up class instances.

Test cases: none

TcRnBadlyStaged is an error that occurs when a TH binding is used in an invalid stage.

Test cases: T17820d

TcRnStageRestriction is an error that occurs when a top level splice refers to a local name.

Test cases: T17820, T21547, T5795, qq00[1-4], annfail0{3,4,6,9}

TcRnBadlyStagedWarn is a warning that occurs when a TH type binding is used in an invalid stage.

Controlled by flags: - Wbadly-staged-type

Test cases: T23829_timely T23829_tardy T23829_hasty

TcRnTyThingUsedWrong is an error that occurs when a thing is used where another thing was expected.

Test cases: none

TcRnCannotDefaultKindVar is an error that occurs when attempting to use unconstrained kind variables whose type isn't Type, without -XPolyKinds.

Test cases: T11334b

TcRnUninferrableTyVar is an error that occurs when metavariables in a type could not be defaulted.

Test cases: T17301, T17562, T17567, T17567StupidTheta, T15474, T21479

TcRnSkolemEscape is an error that occurs when type variables from an outer scope is used in a context where they should be locally scoped.

Test cases: T15076, T15076b, T14880-2, T15825, T14880, T15807, T16946, T14350, T14040A, T15795, T15795a, T14552

TcRnPatSynEscapedCoercion is an error indicating that a coercion escaped from a pattern synonym into a type. See Note [Coercions that escape] in GHC.Tc.TyCl.PatSyn

Test cases: T14507

TcRnPatSynExistentialInResult is an error indicating that the result type of a pattern synonym mentions an existential type variable.

Test cases: PatSynExistential

TcRnPatSynArityMismatch is an error indicating that the number of arguments in a pattern synonym's equation differs from the number of parameters in its signature.

Test cases: PatSynArity

TcRnPatSynInvalidRhs is an error group indicating that the pattern on the right hand side of a pattern synonym is invalid.

Test cases: unidir, T14112

TcRnZonkerMessage is collection of errors that occur when zonking, i.e. filling in metavariables with their final values.

See ZonkerMessage

TcRnTyFamDepsDisabled is an error indicating that a type family injectivity annotation was used without enabling the extension TypeFamilyDependencies.

Test cases: T11381

TcRnAbstractClosedTyFamDecl is an error indicating that an abstract closed type family was declared in a regular source file, while it is only allowed in hs-boot files.

Test cases: ClosedFam4

TcRnPartialFieldSelector is a warning indicating that a record field was not defined for all constructors of a data type.

Test cases: DRFPartialFields, T7169