Main types

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

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.

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 the TcSolverReportMsg datatype for an overview of the different errors.

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.

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}

TcRnDodgyImports is a warning (controlled with -Wdodgy-imports) that occurs when a datatype T is imported with all constructors, i.e. 'T(..)', but has been exported abstractly, i.e. T.

Test cases: renameshould_compileT7167

TcRnDodgyExports is a warning (controlled by -Wdodgy-exports) that occurs when a datatype T is exported with all constructors, i.e. 'T(..)', but is it just a type synonym or a type/data family.

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 occurrs 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

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

Examples(s): None.

Test cases: None.

TcRnDuplicateWarningDecls 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

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

Examples(s): None.

Test cases: None.

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

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

Examples(s): None

Test cases: None

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

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

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

Example(s): None

Test cases: None

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

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

TcRnAbstractClassInst is an error that occurs whenever an instance of an abstract class is specified.

Examples(s): -- A.hs-boot module A where class C a

• - B.hs module B where import {-# SOURCE #-} A instance C Int where
• - A.hs module A where import B class C a where f :: a
• - Main.hs import A main = print (f :: Int)

Test cases: typecheckshould_failT13068

TcRnNoClassInstHead is an error that occurs whenever an instance head is not headed by a class.

Examples(s): instance c

Test cases: typecheckrenameT5513 typecheckrenameT16385

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

TcRnIllegalClassInst is an error that occurs whenever a class instance is specified for a non-class.

Examples(s): type C1 a = (Show (a -> Bool)) instance C1 Int where

Test cases: polykinds/T13267

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

TcRnBadAssociatedType is an error that occurs whenever a class doesn't have an associated type.

Examples(s): $(do d <- instanceD (cxt []) (conT ''Eq appT conT ''Foo) [tySynInstD $ tySynEqn Nothing (conT ''Rep appT conT ''Foo) (conT ''Maybe)] return [d]) ======> instance Eq Foo where type Rep Foo = Maybe

Test cases: th/T12387a

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

TcRnMonomorphicBindings is a warning (controlled by -Wmonomorphism-restriction) that arise 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 -Wwarn-orphans) that arises when a typeclass instance is an "orphan", i.e. if it appears in a module in which neither the class 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

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

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

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

Text cases: module/mod58

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

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

TcRnAmbiguousField is a warning controlled by -Wambiguous-fields occurring when a record update's type cannot be precisely determined. 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

TcRnNoConstructorHasAllFields is an error that occurs when a record update has fields that no single constructor encompasses.

Example(s): data Foo = A { x :: Bool } | B { y :: Int } foo = (A False) { x = True, y = 5 }

Test cases: overloadedrecfldsshould_failoverloadedrecfldsfail08 patsynshould_failmixed-pat-syn-record-sels typecheckshould_failT7989

TcRnSpecialClassInst is an error that occurs when a user attempts to define an instance for a built-in typeclass such as Coercible, Typeable, or KnownNat, outside of a signature file.

Test cases: derivingshould_failT9687 derivingshould_failT14916 polykinds/T8132 typecheckshould_failTcCoercibleFail2 typecheckshould_failT12837 typecheckshould_failT14390

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.

TcRnForallIdentifier is a warning (controlled with -Wforall-identifier) that occurs when a definition uses forall as an identifier.

Example: forall x = () g forall = ()

Test cases: T20609 T20609a T20609b T20609c T20609d

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: T18862b

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

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.

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:

f x = Int

Test cases: T18740a, T20884.

Data constructor fields must have a fixed runtime representation.

Tests: T11734, T18534.

Pattern synonym signature arguments must have a fixed runtime representation.

Test: RepPolyPatSynArg.

Pattern synonym signature scrutinee must have a fixed runtime representation.

Test: RepPolyPatSynRes.

The shadowed name is local to the module

The shadowed name is global, typically imported from elsewhere.

The typeclass instance is not well-kinded.

The instance type | We cannot derive instances in boot files

We cannot use GND on non-newtype types

We cannot derive instances of nullary classes

Last arg must be newtype or data application

The given PredType is not a class.

The given (representation of the) TyCon has no data constructors.

GHC simply doesn't how to how derive the input Class for the given Type.

The given TyCon must be an enumeration. See Note [Enumeration types] in GHC.Core.TyCon

The given TyCon must have precisely one constructor.

The given data type must have some parameters.

The given data type must not have a class context.

We couldn't derive an instance for a particular data constructor for a variety of reasons.

We couldn't derive a Generic instance for the given type for a variety of reasons

We couldn't derive an instance either because the type was not an enum type or because it did have more than one constructor.

The given DataCon must be truly polymorphic in the last argument of the data type.

The given DataCon must not use the type variable in a function argument"

The given DataCon must not contain function types

The given DataCon must use the type variable only as the last argument of a data type

The given DataCon is a GADT so we cannot directly derive an istance for it.

The given DataCon has existentials type vars in its type.

The given DataCon has constraints in its type.

The given DataCon has a higher-rank type.

The type must not have some datatype context.

The data constructor must not have exotic unlifted or polymorphic arguments.

The data constructor must be a vanilla constructor.

The type must have some type parameters. check (d) from Note [Requirements for deriving Generic and Rep] in GHC.Tc.Deriv.Generics.

The data constructor must not have existential arguments.

The derivation applies a type to an argument involving the last parameter but the applied type is not of kind * -> *.

The associated type family of the class

The associated type family of the class

whether -XCUSKs is enabled

Wrap a message with additional information.

Prefer using the mkTcReportWithInfo smart constructor

Quantified variables appear out of dependency order.

Example:

forall (a :: k) k. ...

Test cases: BadTelescope2, T16418, T16247, T16726, T18451.

We came across a custom type error and we have decided to report it.

Example:

type family F a where F a = TypeError (Text "error")

err :: F () err = ()

Test cases: CustomTypeErrors0{1,2,3,4,5}, T12104.

We want to report an out of scope variable or a typed hole. See HoleError.

A type equality between a type variable and a polytype.

Test cases: T12427a, T2846b, T10194, ...

Couldn't unify two types or kinds.

Example:

3 + 3# -- can't match a lifted type with an unlifted type

Test cases: T1396, T8263, ...

A type has an unexpected kind.

Test cases: T2994, T7609, ...

A mismatch between two types, which arose from a type equality.

Test cases: T1470, tcfail212.

A violation of the representation-polymorphism invariants.

See FixedRuntimeRepErrorInfo and FixedRuntimeRepContext for more information.

A skolem type variable escapes its scope.

Example:

data Ex where { MkEx :: a -> MkEx } foo (MkEx x) = x

Test cases: TypeSkolEscape, T11142.

Trying to unify an untouchable variable, e.g. a variable from an outer scope.

Test case: Simple14

An equality between two types is blocked on a kind equality beteen their kinds.

Test cases: none.

Something was not applied to sufficiently many arguments.

Example:

instance Eq Maybe where {..}

Test case: T11563.

Trying to use an unbound implicit parameter.

Example:

foo :: Int foo = ?param

Test case: tcfail130.

Couldn't solve some Wanted constraints using the Givens. This is the most commonly used constructor, used for generic "No instance for ..." and "Could not deduce ... from" messages.

A constraint couldn't be solved because it contains ambiguous type variables.

Example:

class C a b where f :: (a,b)

x = fst f

Test case: T4921.

Could not solve a constraint; there were several unifying candidate instances but no matching instances. This is used to report as much useful information as possible about why we couldn't choose any instance, e.g. because of ambiguous type variables.

Could not solve a constraint using available instances because the instances overlap.

Test cases: tcfail118, tcfail121, tcfail218.

Could not solve a constraint from instances because instances declared in a Safe module cannot overlap instances from other modules (with -XSafeHaskell).

Test cases: SH_Overlap{1,2,5,6,7,11}.

Some type variables remained ambiguous: print them to the user.

Specify some information about a type variable, e.g. its SkolemInfo.

Remind the user that a particular type family is not injective.

Explain why we couldn't coerce between two types. See CoercibleMsg.

Display the expected and actual types.

Display the expected and actual types, after expanding type synonyms.

Explain how a kind equality originated.

Add some information to disambiguate errors in which two Names would otherwise appear to be identical.

See Note [Disambiguating (X ~ X) errors].

Report some type variables that might be participating in an occurs-check failure.

A run-of-the-mill "not in scope" error.

An exact Name was not in scope.

This usually indicates a problem with a Template Haskell splice.

Test cases: T5971, T18263.

always at least 2 elements

Couldn't find a top-level binding.

Happens when specifying an annotation for something that is not in scope.

Test cases: annfail01, annfail02, annfail11.

A class doesnt have a method with this name, or, a class doesn't have an associated type with this name, or, a record doesn't have a record field with this name.

Couldn't find a module with the requested name.

The imported modules don't export what we're looking for.

Report an out-of-scope data constructor or variable masquerading as an expression hole.

See Note [Insoluble holes] in GHC.Tc.Types.Constraint. See NotInScopeError for other not-in-scope errors.

Test cases: T9177a.

Report a typed hole, or wildcard, with additional information.

Not knowing the role of a type constructor prevents us from concluding that two types are representationally equal.

Example:

foo :: Applicative m => m (Sum Int) foo = coerce (pure $ 1 :: Int)

We don't know what role m has, so we can't coerce `m Int` to `m (Sum Int)`.

Test cases: T8984, TcCoercibleFail.

The fact that a TyCon is abstract prevents us from decomposing a TyConApp and deducing that two types are representationally equal.

Test cases: none.

We can't unwrap a newtype whose constructor is not in scope.

Example:

import Data.Ord (Down) -- NB: not importing the constructor foo :: Int -> Down Int foo = coerce

Test cases: TcCoercibleFail.

C, Asm, or LLVM

C, Asm, LLVM, or interpreted