GHC.Types.Error

Messages

data Messages e

A collection of messages emitted by GHC during error reporting. A diagnostic message is typically a warning or an error. See Note [Messages].

INVARIANT: All the messages in this collection must be relevant, i.e. their Severity should not be SevIgnore. The smart constructor mkMessages will filter out any message which Severity is SevIgnore.

Instances

Functor Messages

Defined in GHC.Types.Error

Methods

fmap :: (a -> b) -> Messages a -> Messages b

(<$) :: a -> Messages b -> Messages a

Foldable Messages

Defined in GHC.Types.Error

Methods

fold :: Monoid m => Messages m -> m

foldMap :: Monoid m => (a -> m) -> Messages a -> m

foldMap' :: Monoid m => (a -> m) -> Messages a -> m

foldr :: (a -> b -> b) -> b -> Messages a -> b

foldr' :: (a -> b -> b) -> b -> Messages a -> b

foldl :: (b -> a -> b) -> b -> Messages a -> b

foldl' :: (b -> a -> b) -> b -> Messages a -> b

foldr1 :: (a -> a -> a) -> Messages a -> a

foldl1 :: (a -> a -> a) -> Messages a -> a

toList :: Messages a -> [a]

null :: Messages a -> Bool

length :: Messages a -> Int

elem :: Eq a => a -> Messages a -> Bool

maximum :: Ord a => Messages a -> a

minimum :: Ord a => Messages a -> a

sum :: Num a => Messages a -> a

product :: Num a => Messages a -> a

Traversable Messages

Defined in GHC.Types.Error

Methods

traverse :: Applicative f => (a -> f b) -> Messages a -> f (Messages b)

sequenceA :: Applicative f => Messages (f a) -> f (Messages a)

mapM :: Monad m => (a -> m b) -> Messages a -> m (Messages b)

sequence :: Monad m => Messages (m a) -> m (Messages a)

Diagnostic e => ToJson (Messages e)

Defined in GHC.Types.Error

Methods

json :: Messages e -> JsonDoc

Diagnostic e => Outputable (Messages e)

Defined in GHC.Types.Error

Methods

ppr :: Messages e -> SDoc

Monoid (Messages e)

Defined in GHC.Types.Error

Methods

mempty :: Messages e

mappend :: Messages e -> Messages e -> Messages e

mconcat :: [Messages e] -> Messages e

Semigroup (Messages e)

Defined in GHC.Types.Error

Methods

(<>) :: Messages e -> Messages e -> Messages e

sconcat :: NonEmpty (Messages e) -> Messages e

stimes :: Integral b => b -> Messages e -> Messages e

mkMessages :: Bag (MsgEnvelope e) -> Messages e

getMessages :: Messages e -> Bag (MsgEnvelope e)

emptyMessages :: Messages e

isEmptyMessages :: Messages e -> Bool

singleMessage :: MsgEnvelope e -> Messages e

addMessage :: MsgEnvelope e -> Messages e -> Messages e

Adds a Message to the input collection of messages. See Note [Discarding Messages].

unionMessages :: Messages e -> Messages e -> Messages e

Joins two collections of messages together. See Note [Discarding Messages].

unionManyMessages :: Foldable f => f (Messages e) -> Messages e

Joins many Messagess together

filterMessages :: (MsgEnvelope e -> Bool) -> Messages e -> Messages e

data MsgEnvelope e

An envelope for GHC's facts about a running program, parameterised over the domain-specific (i.e. parsing, typecheck-renaming, etc) diagnostics.

To say things differently, GHC emits diagnostics about the running program, each of which is wrapped into a MsgEnvelope that carries specific information like where the error happened, etc. Finally, multiple MsgEnvelopes are aggregated into Messages that are returned to the user.

Constructors

MsgEnvelope

Fields

• errMsgSpan :: SrcSpan

  The SrcSpan is used for sorting errors into line-number order

• errMsgContext :: NamePprCtx
• errMsgDiagnostic :: e
• errMsgSeverity :: Severity
• errMsgReason :: ResolvedDiagnosticReason

  The actual reason caused this message

  See Note [Warnings controlled by multiple flags]

Instances

Functor MsgEnvelope

Defined in GHC.Types.Error

Methods

fmap :: (a -> b) -> MsgEnvelope a -> MsgEnvelope b

(<$) :: a -> MsgEnvelope b -> MsgEnvelope a

Foldable MsgEnvelope

Defined in GHC.Types.Error

Methods

fold :: Monoid m => MsgEnvelope m -> m

foldMap :: Monoid m => (a -> m) -> MsgEnvelope a -> m

foldMap' :: Monoid m => (a -> m) -> MsgEnvelope a -> m

foldr :: (a -> b -> b) -> b -> MsgEnvelope a -> b

foldr' :: (a -> b -> b) -> b -> MsgEnvelope a -> b

foldl :: (b -> a -> b) -> b -> MsgEnvelope a -> b

foldl' :: (b -> a -> b) -> b -> MsgEnvelope a -> b

foldr1 :: (a -> a -> a) -> MsgEnvelope a -> a

foldl1 :: (a -> a -> a) -> MsgEnvelope a -> a

toList :: MsgEnvelope a -> [a]

null :: MsgEnvelope a -> Bool

length :: MsgEnvelope a -> Int

elem :: Eq a => a -> MsgEnvelope a -> Bool

maximum :: Ord a => MsgEnvelope a -> a

minimum :: Ord a => MsgEnvelope a -> a

sum :: Num a => MsgEnvelope a -> a

product :: Num a => MsgEnvelope a -> a

Traversable MsgEnvelope

Defined in GHC.Types.Error

Methods

traverse :: Applicative f => (a -> f b) -> MsgEnvelope a -> f (MsgEnvelope b)

sequenceA :: Applicative f => MsgEnvelope (f a) -> f (MsgEnvelope a)

mapM :: Monad m => (a -> m b) -> MsgEnvelope a -> m (MsgEnvelope b)

sequence :: Monad m => MsgEnvelope (m a) -> m (MsgEnvelope a)

Diagnostic e => ToJson (MsgEnvelope e)

Defined in GHC.Types.Error

Methods

json :: MsgEnvelope e -> JsonDoc

Show (MsgEnvelope DiagnosticMessage)

Defined in GHC.Types.Error

Methods

showsPrec :: Int -> MsgEnvelope DiagnosticMessage -> ShowS

show :: MsgEnvelope DiagnosticMessage -> String

showList :: [MsgEnvelope DiagnosticMessage] -> ShowS

Classifying Messages

data MessageClass

The class for a diagnostic message. The main purpose is to classify a message within GHC, to distinguish it from a debug/dump message vs a proper diagnostic, for which we include a DiagnosticReason.

Constructors

MCOutput

MCFatal

MCInteractive

MCDump

Log message intended for compiler developers No file/line/column stuff

MCInfo

Log messages intended for end users. No file/line/column stuff.

MCDiagnostic Severity ResolvedDiagnosticReason (Maybe DiagnosticCode)

Diagnostics from the compiler. This constructor is very powerful as it allows the construction of a MessageClass with a completely arbitrary permutation of Severity and DiagnosticReason. As such, users are encouraged to use the mkMCDiagnostic smart constructor instead. Use this constructor directly only if you need to construct and manipulate diagnostic messages directly, for example inside Error. In all the other circumstances, especially when emitting compiler diagnostics, use the smart constructor.

The Maybe DiagnosticCode field carries a code (if available) for this diagnostic. If you are creating a message not tied to any error-message type, then use Nothing. In the long run, this really should always have a DiagnosticCode. See Note [Diagnostic codes].

Instances

ToJson MessageClass

Defined in GHC.Types.Error

Methods

json :: MessageClass -> JsonDoc

data Severity

Used to describe warnings and errors o The message has a file/line/column heading, plus "warning:" or "error:", added by mkLocMessage o With SevIgnore the message is suppressed o Output is intended for end users

Constructors

SevIgnore

Ignore this message, for example in case of suppression of warnings users don't want to see. See Note [Suppressing Messages]

SevWarning

SevError

Instances

ToJson Severity

Defined in GHC.Types.Error

Methods

json :: Severity -> JsonDoc

Outputable Severity

Defined in GHC.Types.Error

Methods

ppr :: Severity -> SDoc

Show Severity

Defined in GHC.Types.Error

Methods

showsPrec :: Int -> Severity -> ShowS

show :: Severity -> String

showList :: [Severity] -> ShowS

Eq Severity

Defined in GHC.Types.Error

Methods

(==) :: Severity -> Severity -> Bool

(/=) :: Severity -> Severity -> Bool

Ord Severity

Defined in GHC.Types.Error

Methods

compare :: Severity -> Severity -> Ordering

(<) :: Severity -> Severity -> Bool

(<=) :: Severity -> Severity -> Bool

(>) :: Severity -> Severity -> Bool

(>=) :: Severity -> Severity -> Bool

max :: Severity -> Severity -> Severity

min :: Severity -> Severity -> Severity

class HasDefaultDiagnosticOpts (DiagnosticOpts a) => Diagnostic a where

A class identifying a diagnostic. Dictionary.com defines a diagnostic as:

"a message output by a computer diagnosing an error in a computer program, computer system, or component device".

A Diagnostic carries the actual description of the message (which, in GHC's case, it can be an error or a warning) and the reason why such message was generated in the first place.

Associated Types

type DiagnosticOpts a

Type of configuration options for the diagnostic.

Methods

diagnosticMessage :: DiagnosticOpts a -> a -> DecoratedSDoc

Extract the error message text from a Diagnostic.

diagnosticReason :: a -> DiagnosticReason

Extract the reason for this diagnostic. For warnings, a DiagnosticReason includes the warning flag.

diagnosticHints :: a -> [GhcHint]

Extract any hints a user might use to repair their code to avoid this diagnostic.

diagnosticCode :: a -> Maybe DiagnosticCode

Get the DiagnosticCode associated with this Diagnostic. This can return Nothing for at least two reasons:

1. The message might be from a plugin that does not supply codes.
2. The message might not yet have been assigned a code. See the Diagnostic instance for DiagnosticMessage.

Ideally, case (2) would not happen, but because some errors in GHC still use the old system of just writing the error message in-place (instead of using a dedicated error type and constructor), we do not have error codes for all errors. #18516 tracks our progress toward this goal.

Instances

Diagnostic DriverMessage

Defined in GHC.Driver.Errors.Ppr

Associated Types

type DiagnosticOpts DriverMessage

Defined in GHC.Driver.Errors.Ppr

type DiagnosticOpts DriverMessage = DriverMessageOpts

Methods

diagnosticMessage :: DiagnosticOpts DriverMessage -> DriverMessage -> DecoratedSDoc

diagnosticReason :: DriverMessage -> DiagnosticReason

diagnosticHints :: DriverMessage -> [GhcHint]

diagnosticCode :: DriverMessage -> Maybe DiagnosticCode

Diagnostic GhcMessage

Defined in GHC.Driver.Errors.Ppr

Associated Types

type DiagnosticOpts GhcMessage

Defined in GHC.Driver.Errors.Ppr

type DiagnosticOpts GhcMessage = GhcMessageOpts

Methods

diagnosticMessage :: DiagnosticOpts GhcMessage -> GhcMessage -> DecoratedSDoc

diagnosticReason :: GhcMessage -> DiagnosticReason

diagnosticHints :: GhcMessage -> [GhcHint]

diagnosticCode :: GhcMessage -> Maybe DiagnosticCode

Diagnostic DsMessage

Defined in GHC.HsToCore.Errors.Ppr

Associated Types

type DiagnosticOpts DsMessage

Defined in GHC.HsToCore.Errors.Ppr

type DiagnosticOpts DsMessage = NoDiagnosticOpts

Methods

diagnosticMessage :: DiagnosticOpts DsMessage -> DsMessage -> DecoratedSDoc

diagnosticReason :: DsMessage -> DiagnosticReason

diagnosticHints :: DsMessage -> [GhcHint]

diagnosticCode :: DsMessage -> Maybe DiagnosticCode

Diagnostic IfaceMessage

Defined in GHC.Iface.Errors.Ppr

Associated Types

type DiagnosticOpts IfaceMessage

Defined in GHC.Iface.Errors.Ppr

type DiagnosticOpts IfaceMessage = IfaceMessageOpts

Methods

diagnosticMessage :: DiagnosticOpts IfaceMessage -> IfaceMessage -> DecoratedSDoc

diagnosticReason :: IfaceMessage -> DiagnosticReason

diagnosticHints :: IfaceMessage -> [GhcHint]

diagnosticCode :: IfaceMessage -> Maybe DiagnosticCode

Diagnostic PsMessage

Defined in GHC.Parser.Errors.Ppr

Associated Types

type DiagnosticOpts PsMessage

Defined in GHC.Parser.Errors.Ppr

type DiagnosticOpts PsMessage = NoDiagnosticOpts

Methods

diagnosticMessage :: DiagnosticOpts PsMessage -> PsMessage -> DecoratedSDoc

diagnosticReason :: PsMessage -> DiagnosticReason

diagnosticHints :: PsMessage -> [GhcHint]

diagnosticCode :: PsMessage -> Maybe DiagnosticCode

Diagnostic TcRnMessage

Defined in GHC.Tc.Errors.Ppr

Associated Types

type DiagnosticOpts TcRnMessage

Defined in GHC.Tc.Errors.Ppr

type DiagnosticOpts TcRnMessage = TcRnMessageOpts

Methods

diagnosticMessage :: DiagnosticOpts TcRnMessage -> TcRnMessage -> DecoratedSDoc

diagnosticReason :: TcRnMessage -> DiagnosticReason

diagnosticHints :: TcRnMessage -> [GhcHint]

diagnosticCode :: TcRnMessage -> Maybe DiagnosticCode

Diagnostic DiagnosticMessage

Defined in GHC.Types.Error

Associated Types

type DiagnosticOpts DiagnosticMessage

Defined in GHC.Types.Error

type DiagnosticOpts DiagnosticMessage = NoDiagnosticOpts

Methods

diagnosticMessage :: DiagnosticOpts DiagnosticMessage -> DiagnosticMessage -> DecoratedSDoc

diagnosticReason :: DiagnosticMessage -> DiagnosticReason

diagnosticHints :: DiagnosticMessage -> [GhcHint]

diagnosticCode :: DiagnosticMessage -> Maybe DiagnosticCode

HasDefaultDiagnosticOpts opts => Diagnostic (UnknownDiagnostic opts)

Defined in GHC.Types.Error

Associated Types

type DiagnosticOpts (UnknownDiagnostic opts)

Defined in GHC.Types.Error

type DiagnosticOpts (UnknownDiagnostic opts) = opts

Methods

diagnosticMessage :: DiagnosticOpts (UnknownDiagnostic opts) -> UnknownDiagnostic opts -> DecoratedSDoc

diagnosticReason :: UnknownDiagnostic opts -> DiagnosticReason

diagnosticHints :: UnknownDiagnostic opts -> [GhcHint]

diagnosticCode :: UnknownDiagnostic opts -> Maybe DiagnosticCode

data UnknownDiagnostic opts where

An existential wrapper around an unknown diagnostic.

Constructors

UnknownDiagnostic :: forall a opts. (Diagnostic a, Typeable a) => (opts -> DiagnosticOpts a) -> a -> UnknownDiagnostic opts

Instances

HasDefaultDiagnosticOpts opts => Diagnostic (UnknownDiagnostic opts)

Defined in GHC.Types.Error

Associated Types

type DiagnosticOpts (UnknownDiagnostic opts)

Defined in GHC.Types.Error

type DiagnosticOpts (UnknownDiagnostic opts) = opts

Methods

diagnosticMessage :: DiagnosticOpts (UnknownDiagnostic opts) -> UnknownDiagnostic opts -> DecoratedSDoc

diagnosticReason :: UnknownDiagnostic opts -> DiagnosticReason

diagnosticHints :: UnknownDiagnostic opts -> [GhcHint]

diagnosticCode :: UnknownDiagnostic opts -> Maybe DiagnosticCode

type DiagnosticOpts (UnknownDiagnostic opts)

Defined in GHC.Types.Error

type DiagnosticOpts (UnknownDiagnostic opts) = opts

mkSimpleUnknownDiagnostic :: (Diagnostic a, Typeable a, DiagnosticOpts a ~ NoDiagnosticOpts) => a -> UnknownDiagnostic b

Make a "simple" unknown diagnostic which doesn't have any configuration options.

mkUnknownDiagnostic :: (Typeable a, Diagnostic a) => a -> UnknownDiagnostic (DiagnosticOpts a)

Make an unknown diagnostic which uses the same options as the context it will be embedded into.

embedUnknownDiagnostic :: (Diagnostic a, Typeable a) => (opts -> DiagnosticOpts a) -> a -> UnknownDiagnostic opts

Embed a more complicated diagnostic which requires a potentially different options type.

data DiagnosticMessage

A generic Diagnostic message, without any further classification or provenance: By looking at a DiagnosticMessage we don't know neither where it was generated nor how to interpret its payload (as it's just a structured document). All we can do is to print it out and look at its DiagnosticReason.

Constructors

DiagnosticMessage

Fields

• diagMessage :: !DecoratedSDoc
• diagReason :: !DiagnosticReason
• diagHints :: [GhcHint]

Instances

Diagnostic DiagnosticMessage

Defined in GHC.Types.Error

Associated Types

type DiagnosticOpts DiagnosticMessage

Defined in GHC.Types.Error

type DiagnosticOpts DiagnosticMessage = NoDiagnosticOpts

Methods

diagnosticMessage :: DiagnosticOpts DiagnosticMessage -> DiagnosticMessage -> DecoratedSDoc

diagnosticReason :: DiagnosticMessage -> DiagnosticReason

diagnosticHints :: DiagnosticMessage -> [GhcHint]

diagnosticCode :: DiagnosticMessage -> Maybe DiagnosticCode

Show (MsgEnvelope DiagnosticMessage)

Defined in GHC.Types.Error

Methods

showsPrec :: Int -> MsgEnvelope DiagnosticMessage -> ShowS

show :: MsgEnvelope DiagnosticMessage -> String

showList :: [MsgEnvelope DiagnosticMessage] -> ShowS

type DiagnosticOpts DiagnosticMessage

Defined in GHC.Types.Error

type DiagnosticOpts DiagnosticMessage = NoDiagnosticOpts

data DiagnosticReason

The reason why a Diagnostic was emitted in the first place. Diagnostic messages are born within GHC with a very precise reason, which can be completely statically-computed (i.e. this is an error or a warning no matter what), or influenced by the specific state of the DynFlags at the moment of the creation of a new Diagnostic. For example, a parsing error is always going to be an error, whereas a 'WarningWithoutFlag Opt_WarnUnusedImports' might turn into an error due to '-Werror' or '-Werror=warn-unused-imports'. Interpreting a DiagnosticReason together with its associated Severity gives us the full picture.

Constructors

WarningWithoutFlag

Born as a warning.

WarningWithFlags !(NonEmpty WarningFlag)

Warning was enabled with the flag.

WarningWithCategory !WarningCategory

Warning was enabled with a custom category.

ErrorWithoutFlag

Born as an error.

Bundled Patterns

pattern WarningWithFlag :: WarningFlag -> DiagnosticReason

The single warning case DiagnosticReason is very common.

Instances

Outputable DiagnosticReason

Defined in GHC.Types.Error

Methods

ppr :: DiagnosticReason -> SDoc

Show DiagnosticReason

Defined in GHC.Types.Error

Methods

showsPrec :: Int -> DiagnosticReason -> ShowS

show :: DiagnosticReason -> String

showList :: [DiagnosticReason] -> ShowS

Eq DiagnosticReason

Defined in GHC.Types.Error

Methods

(==) :: DiagnosticReason -> DiagnosticReason -> Bool

(/=) :: DiagnosticReason -> DiagnosticReason -> Bool

newtype ResolvedDiagnosticReason

Like a DiagnosticReason, but resolved against a specific set of DynFlags to work out which warning flag actually enabled this warning.

Constructors

ResolvedDiagnosticReason

Fields

• resolvedDiagnosticReason :: DiagnosticReason

Instances

Outputable ResolvedDiagnosticReason

Defined in GHC.Types.Error

Methods

ppr :: ResolvedDiagnosticReason -> SDoc

data DiagnosticHint

A generic Hint message, to be used with DiagnosticMessage.

Constructors

DiagnosticHint !SDoc

Instances

Outputable DiagnosticHint

Defined in GHC.Types.Error

Methods

ppr :: DiagnosticHint -> SDoc

mkPlainDiagnostic :: DiagnosticReason -> [GhcHint] -> SDoc -> DiagnosticMessage

mkPlainError :: [GhcHint] -> SDoc -> DiagnosticMessage

Create an error DiagnosticMessage holding just a single SDoc

mkDecoratedDiagnostic :: DiagnosticReason -> [GhcHint] -> [SDoc] -> DiagnosticMessage

Create a DiagnosticMessage from a list of bulleted SDocs and a DiagnosticReason

mkDecoratedError :: [GhcHint] -> [SDoc] -> DiagnosticMessage

Create an error DiagnosticMessage from a list of bulleted SDocs

pprDiagnostic :: Diagnostic e => e -> SDoc

class HasDefaultDiagnosticOpts opts where

Methods

defaultOpts :: opts

Instances

HasDefaultDiagnosticOpts DriverMessageOpts

Defined in GHC.Driver.Errors.Ppr

Methods

defaultOpts :: DriverMessageOpts

HasDefaultDiagnosticOpts GhcMessageOpts

Defined in GHC.Driver.Errors.Ppr

Methods

defaultOpts :: GhcMessageOpts

HasDefaultDiagnosticOpts IfaceMessageOpts

Defined in GHC.Iface.Errors.Ppr

Methods

defaultOpts :: IfaceMessageOpts

HasDefaultDiagnosticOpts TcRnMessageOpts

Defined in GHC.Tc.Errors.Ppr

Methods

defaultOpts :: TcRnMessageOpts

HasDefaultDiagnosticOpts NoDiagnosticOpts

Defined in GHC.Types.Error

Methods

defaultOpts :: NoDiagnosticOpts

defaultDiagnosticOpts :: HasDefaultDiagnosticOpts (DiagnosticOpts opts) => DiagnosticOpts opts

data NoDiagnosticOpts

Constructors

NoDiagnosticOpts

Instances

HasDefaultDiagnosticOpts NoDiagnosticOpts

Defined in GHC.Types.Error

Methods

defaultOpts :: NoDiagnosticOpts

Hints and refactoring actions

data GhcHint

A type for hints emitted by GHC. A hint suggests a possible way to deal with a particular warning or error.

Constructors

(Outputable a, Typeable a) => UnknownHint a

An "unknown" hint. This type constructor allows arbitrary -- hints to be embedded. The typical use case would be GHC plugins -- willing to emit hints alongside their custom diagnostics.

SuggestExtension !LanguageExtensionHint

Suggests adding a particular language extension. GHC will do its best trying to guess when the user is using the syntax of a particular language extension without having the relevant extension enabled.

Example: If the user uses the keyword "mdo" (and we are in a monadic block), but the relevant extension is not enabled, GHC will emit a 'SuggestExtension RecursiveDo'.

Test case(s): parsershould_failT12429, parsershould_failT8501c, parsershould_failT18251e, ... (and many more)

SuggestCorrectPragmaName ![String]

Suggests possible corrections of a misspelled pragma. Its argument represents all applicable suggestions.

Example: {-# LNGUAGE BangPatterns #-}

Test case(s): parsershould_compileT21589

SuggestMissingDo

Suggests that a monadic code block is probably missing a "do" keyword.

Example: main = putStrLn "hello" putStrLn "world"

Test case(s): parsershould_failT8501a, parsershould_failreadFail007, parsershould_failInfixAppPatErr, parsershould_failT984

SuggestLetInDo

Suggests that a "let" expression is needed in a "do" block.

Test cases: None (that explicitly test this particular hint is emitted).

SuggestAddSignatureCabalFile !ModuleName

Suggests to add an ".hsig" signature file to the Cabal manifest.

Triggered by: DriverUnexpectedSignature, if Cabal is being used.

Example: See comment of DriverUnexpectedSignature.

Test case(s): driver/T12955

SuggestSignatureInstantiations !ModuleName [InstantiationSuggestion]

Suggests to explicitly list the instantiations for the signatures in the GHC invocation command.

Triggered by: DriverUnexpectedSignature, if Cabal is not being used.

Example: See comment of DriverUnexpectedSignature.

Test case(s): driver/T12955

SuggestUseSpaces

Suggests to use spaces instead of tabs.

Triggered by: PsWarnTab.

Examples: None Test Case(s): None

SuggestUseWhitespaceAfter !OperatorWhitespaceSymbol

Suggests adding a whitespace after the given symbol.

Examples: None Test Case(s): parsershould_compileT18834a.hs

SuggestUseWhitespaceAround !String !OperatorWhitespaceOccurrence

Suggests adding a whitespace around the given operator symbol, as it might be repurposed as special syntax by a future language extension. The second parameter is how such operator occurred, if in a prefix, suffix or tight infix position.

Triggered by: PsWarnOperatorWhitespace.

Example: h a b = a+b -- not OK, no spaces around +.

Test Case(s): parsershould_compileT18834b.hs

SuggestParentheses

Suggests wrapping an expression in parentheses

Examples: None Test Case(s): None

SuggestIncreaseMaxPmCheckModels

Suggests to increase the -fmax-pmcheck-models limit for the pattern match checker.

Triggered by: DsMaxPmCheckModelsReached

Test case(s): pmcheckshould_compileTooManyDeltas pmcheckshould_compileTooManyDeltas pmcheckshould_compileT11822

SuggestAddTypeSignatures AvailableBindings

Suggests adding a type signature, typically to resolve ambiguity or help GHC inferring types.

SuggestBindToWildcard !(LHsExpr GhcTc)

Suggests to explicitly discard the result of a monadic action by binding the result to the '_' wilcard.

Example: main = do _ <- getCurrentTime

SuggestAddInlineOrNoInlinePragma !Var !Activation

SuggestAddPhaseToCompetingRule !RuleName

SuggestAddToHSigExportList !Name !(Maybe Module)

Suggests adding an identifier to the export list of a signature.

SuggestIncreaseSimplifierIterations

Suggests increasing the limit for the number of iterations in the simplifier.

SuggestUseTypeFromDataKind (Maybe RdrName)

Suggests to explicitly import Type from the Kind module, because using "*" to mean Type relies on the StarIsType extension, which will become deprecated in the future.

Triggered by: PsWarnStarIsType Example: None Test case(s): wcompat-warnings/WCompatWarningsOn.hs

SuggestQualifiedAfterModuleName

Suggests placing the qualified keyword after the module name.

Triggered by: PsWarnImportPreQualified Example: None Test case(s): module/mod184.hs

SuggestThQuotationSyntax

Suggests using TemplateHaskell quotation syntax.

Triggered by: PsErrEmptyDoubleQuotes only if TemplateHaskell is enabled. Example: None Test case(s): parsershould_failT13450TH.hs

SuggestRoles [Role]

Suggests alternative roles in case we found an illegal one.

Triggered by: PsErrIllegalRoleName Example: None Test case(s): rolesshould_failRoles7.hs

SuggestQualifyStarOperator

Suggests qualifying the * operator in modules where StarIsType is enabled.

Triggered by: PsWarnStarBinder Test case(s): warningsshould_compileStarBinder.hs

SuggestTypeSignatureRemoveQualifier

Suggests that for a type signature 'M.x :: ...' the qualifier should be omitted in order to be accepted by GHC.

Triggered by: PsErrInvalidTypeSignature Test case(s): module/mod98

SuggestFixOrphanInst

Suggests to move an orphan instance (for a typeclass or a type or data family), or to newtype-wrap it.

Triggered by: TcRnOrphanInstance Test cases(s): warningsshould_compileT9178 typecheckshould_compileT4912 indexed-typesshould_compileT22717_fam_orph

Fields

• isFamilyInstance :: Maybe FamFlavor

  Whether this is a family instance (of the given FamFlavor), or a class instance (Nothing).

SuggestAddStandaloneDerivation

Suggests to use a standalone deriving declaration when GHC can't derive a typeclass instance in a trivial way.

Triggered by: DerivBadErrConstructor Test cases(s): typecheckshould_failtcfail086

SuggestAddStandaloneKindSignature Name

Suggests to add a standalone kind signature when GHC can't perform kind inference.

Triggered by: TcRnInvisBndrWithoutSig Test case(s): typecheckshould_failT22560_fail_d

SuggestFillInWildcardConstraint

Suggests the user to fill in the wildcard constraint to disambiguate which constraint that is.

Example: deriving instance _ => Eq (Foo f a)

Triggered by: DerivBadErrConstructor Test cases(s): partial-sigsshould_failT13324_fail2

SuggestAppropriateTHTick NameSpace

Suggests to use the appropriate Template Haskell tick: a single tick for a term-level NameSpace, or a double tick for a type-level NameSpace.

Triggered by: TcRnIncorrectNameSpace.

SuggestDumpSlices

Suggests enabling -ddump-splices to help debug an issue when a Name is not in scope or is used in multiple different namespaces (e.g. both as a data constructor and a type constructor).

Concomitant with NoExactName or SameName errors, see e.g. "GHC.Rename.Env.lookupExactOcc_either". Test cases: T5971, T7241, T13937.

SuggestAddTick UntickedPromotedThing

Suggests adding a tick to refer to something which has been promoted to the type level, e.g. a data constructor.

Test cases: T9778, T19984.

SuggestMoveToDeclarationSite

Something is split off from its corresponding declaration. For example, a datatype is given a role declaration in a different module.

Test cases: T495, T8485, T2713, T5533.

Fields

• SDoc

  fixity declaration, role annotation, type signature, ...

• RdrName

  the RdrName for the declaration site

SuggestSimilarNames RdrName (NonEmpty SimilarName)

Suggest a similar name that the user might have meant, e.g. suggest traverse when the user has written travrese.

Test case: mod73.

RemindFieldSelectorSuppressed

Remind the user that the field selector has been suppressed because of -XNoFieldSelectors.

Test cases: NFSSuppressed, records-nofieldselectors.

Fields

• suppressed_selector :: RdrName
• suppressed_parents :: [Name]

ImportSuggestion OccName ImportSuggestion

Suggest importing from a module, removing a hiding clause, or explain to the user that we couldn't find a module with the given ModuleName.

Test cases: mod28, mod36, mod87, mod114, ...

SuggestPlacePragmaInHeader

Found a pragma in the body of a module, suggest placing it in the header.

SuggestPatternMatchingSyntax

Suggest using pattern matching syntax for a non-bidirectional pattern synonym

Test cases: patsynshould_failrecord-exquant typecheckshould_failT3176

SuggestSpecialiseVisibilityHints Name

Suggest tips for making a definition visible for the purpose of writing a SPECIALISE pragma for it in a different module.

Test cases: none

SuggestRenameTypeVariable

Suggest renaming implicitly quantified type variable in case it captures a term's name.

SuggestExplicitBidiPatSyn Name (LPat GhcRn) [LIdP GhcRn]

SuggestSafeHaskell

Suggest enabling one of the SafeHaskell modes Safe, Unsafe or Trustworthy.

SuggestRemoveRecordWildcard

Suggest removing a record wildcard from a pattern when it doesn't bind anything useful.

SuggestMoveNonCanonicalDefinition

Suggest moving a method implementation to a different instance to its superclass that defines the canonical version of the method.

Fields

• Name

  move the implementation from this method

• Name

  ... to this method

• String

  Documentation URL

SuggestIncreaseReductionDepth

Suggest to increase the solver maximum reduction depth

SuggestRemoveNonCanonicalDefinition

Suggest removing a method implementation when a superclass defines the canonical version of that method.

Fields

• Name

  method with non-canonical implementation

• Name

  possible other method to use as the RHS instead

• String

  Documentation URL

SuggestEtaReduceAbsDataTySyn TyCon

Suggest eta-reducing a type synonym used in the implementation of abstract data.

RemindRecordMissingField FastString Type Type

Remind the user that there is no field of a type and name in the record, constructors are in the usual order $x$, $r$, $a$

SuggestBindTyVarOnLhs RdrName

Suggest binding the type variable on the LHS of the type declaration

SuggestAnonymousWildcard

Suggest using an anonymous wildcard instead of a named wildcard

SuggestExplicitQuantification RdrName

Suggest explicitly quantifying a type variable instead of relying on implicit quantification

SuggestBindTyVarExplicitly Name

Suggest binding explicitly; e.g data T @k (a :: F k) = ....

Instances

Outputable GhcHint

Defined in GHC.Types.Hint.Ppr

Methods

ppr :: GhcHint -> SDoc

data AvailableBindings

The bindings we have available in scope when suggesting an explicit type signature.

Constructors

NamedBindings (NonEmpty Name)

UnnamedBinding

An unknown binding (i.e. too complicated to turn into a Name)

data LanguageExtensionHint

Constructors

SuggestSingleExtension !SDoc !Extension

Suggest to enable the input extension. This is the hint that GHC emits if this is not a "known" fix, i.e. this is GHC giving its best guess on what extension might be necessary to make a certain program compile. For example, GHC might suggests to enable BlockArguments when the user simply formatted incorrectly the input program, so GHC here is trying to be as helpful as possible. If the input SDoc is not empty, it will contain some extra information about the why the extension is required, but it's totally irrelevant/redundant for IDEs and other tools.

SuggestAnyExtension !SDoc [Extension]

Suggest to enable the input extensions. The list is to be intended as disjunctive i.e. the user is suggested to enable any of the extensions listed. If the input SDoc is not empty, it will contain some extra information about the why the extensions are required, but it's totally irrelevant/redundant for IDEs and other tools.

SuggestExtensions !SDoc [Extension]

Suggest to enable the input extensions. The list is to be intended as conjunctive i.e. the user is suggested to enable all the extensions listed. If the input SDoc is not empty, it will contain some extra information about the why the extensions are required, but it's totally irrelevant/redundant for IDEs and other tools.

SuggestExtensionInOrderTo !SDoc !Extension

Suggest to enable the input extension in order to fix a certain problem. This is the suggestion that GHC emits when is more-or-less clear "what's going on". For example, if both DeriveAnyClass and GeneralizedNewtypeDeriving are turned on, the right thing to do is to enabled DerivingStrategies, so in contrast to SuggestSingleExtension GHC will be a bit more "imperative" (i.e. "Use X Y Z in order to ... "). If the input SDoc is not empty, it will contain some extra information about the why the extensions are required, but it's totally irrelevant/redundant for IDEs and other tools.

suggestExtension :: Extension -> GhcHint

Suggests a single extension without extra user info.

suggestExtensionWithInfo :: SDoc -> Extension -> GhcHint

Like suggestExtension but allows supplying extra info for the user.

suggestExtensions :: [Extension] -> GhcHint

Suggests to enable every extension in the list.

suggestExtensionsWithInfo :: SDoc -> [Extension] -> GhcHint

Like suggestExtensions but allows supplying extra info for the user.

suggestAnyExtension :: [Extension] -> GhcHint

Suggests to enable any extension in the list.

suggestAnyExtensionWithInfo :: SDoc -> [Extension] -> GhcHint

Like suggestAnyExtension but allows supplying extra info for the user.

useExtensionInOrderTo :: SDoc -> Extension -> GhcHint

noHints :: [GhcHint]

Helper function to use when no hints can be provided. Currently this function can be used to construct plain DiagnosticMessage and add hints to them, but once #18516 will be fully executed, the main usage of this function would be in the implementation of the diagnosticHints typeclass method, to report the fact that a particular Diagnostic has no hints.

Rendering Messages

data SDoc

Represents a pretty-printable document.

To display an SDoc, use printSDoc, printSDocLn, bufLeftRenderSDoc, or renderWithContext. Avoid calling runSDoc directly as it breaks the abstraction layer.

Instances

JsRender SDoc

Defined in GHC.JS.Ppr

Methods

(<+?>) :: SDoc -> SDoc -> SDoc

($$$) :: SDoc -> SDoc -> SDoc

jcat :: [SDoc] -> SDoc

jnest :: SDoc -> SDoc

addSemi :: SDoc -> SDoc

IsDoc SDoc

Defined in GHC.Utils.Outputable

Associated Types

type Line SDoc

Defined in GHC.Utils.Outputable

type Line SDoc = SDoc

Methods

line :: Line SDoc -> SDoc

($$) :: SDoc -> SDoc -> SDoc

lines_ :: [Line SDoc] -> SDoc

vcat :: [SDoc] -> SDoc

dualDoc :: SDoc -> HDoc -> SDoc

IsLine SDoc

Defined in GHC.Utils.Outputable

Methods

char :: Char -> SDoc

text :: String -> SDoc

ftext :: FastString -> SDoc

ztext :: FastZString -> SDoc

(<>) :: SDoc -> SDoc -> SDoc

(<+>) :: SDoc -> SDoc -> SDoc

sep :: [SDoc] -> SDoc

fsep :: [SDoc] -> SDoc

hcat :: [SDoc] -> SDoc

hsep :: [SDoc] -> SDoc

dualLine :: SDoc -> HLine -> SDoc

IsOutput SDoc

Defined in GHC.Utils.Outputable

Methods

empty :: SDoc

docWithContext :: (SDocContext -> SDoc) -> SDoc

docWithStyle :: SDoc -> (PprStyle -> SDoc) -> SDoc

Outputable SDoc

Defined in GHC.Utils.Outputable

Methods

ppr :: SDoc -> SDoc

IsString SDoc

Defined in GHC.Utils.Outputable

Methods

fromString :: String -> SDoc

OutputableP env SDoc

Defined in GHC.Utils.Outputable

Methods

pdoc :: env -> SDoc -> SDoc

type Line SDoc

Defined in GHC.Utils.Outputable

type Line SDoc = SDoc

data DecoratedSDoc

A DecoratedSDoc is isomorphic to a '[SDoc]' but it carries the invariant that the input '[SDoc]' needs to be rendered decorated into its final form, where the typical case would be adding bullets between each elements of the list. The type of decoration depends on the formatting function used, but in practice GHC uses the formatBulleted.

mkDecorated :: [SDoc] -> DecoratedSDoc

Creates a new DecoratedSDoc out of a list of SDoc.

mkSimpleDecorated :: SDoc -> DecoratedSDoc

Creates a new DecoratedSDoc out of a single SDoc

unionDecoratedSDoc :: DecoratedSDoc -> DecoratedSDoc -> DecoratedSDoc

Joins two DecoratedSDoc together. The resulting DecoratedSDoc will have a number of entries which is the sum of the lengths of the input.

mapDecoratedSDoc :: (SDoc -> SDoc) -> DecoratedSDoc -> DecoratedSDoc

Apply a transformation function to all elements of a DecoratedSDoc.

pprMessageBag :: Bag SDoc -> SDoc

mkLocMessage

Arguments

:: MessageClass

What kind of message?

-> SrcSpan

location

-> SDoc

message

-> SDoc

mkLocMessageWarningGroups

Arguments

:: Bool

Print warning groups (if applicable)?

-> MessageClass

What kind of message?

-> SrcSpan

location

-> SDoc

message

-> SDoc

Make an error message with location info, specifying whether to show warning groups (if applicable).

getCaretDiagnostic :: MessageClass -> SrcSpan -> IO SDoc

Queries

isIntrinsicErrorMessage :: Diagnostic e => MsgEnvelope e -> Bool

Returns True if this is, intrinsically, a failure. See Note [Intrinsic And Extrinsic Failures].

isExtrinsicErrorMessage :: MsgEnvelope e -> Bool

Returns True if the envelope contains a message that will stop compilation: either an intrinsic error or a fatal (-Werror) warning

isWarningMessage :: Diagnostic e => MsgEnvelope e -> Bool

getErrorMessages :: Diagnostic e => Messages e -> Bag (MsgEnvelope e)

getWarningMessages :: Diagnostic e => Messages e -> Bag (MsgEnvelope e)

partitionMessages :: Diagnostic e => Messages e -> (Messages e, Messages e)

Partitions the Messages and returns a tuple which first element are the warnings, and the second the errors.

errorsFound :: Diagnostic e => Messages e -> Bool

Are there any hard errors here? -Werror warnings are not detected. If you want to check for -Werror warnings, use errorsOrFatalWarningsFound.

errorsOrFatalWarningsFound :: Messages e -> Bool

Are there any errors or -Werror warnings here?

Diagnostic codes

data DiagnosticCode

A diagnostic code is a namespaced numeric identifier unique to the given diagnostic (error or warning).

All diagnostic codes defined within GHC are given the GHC namespace.

See Note [Diagnostic codes] in GHC.Types.Error.Codes.

Constructors

DiagnosticCode

Fields

• diagnosticCodeNameSpace :: String

  diagnostic code prefix (e.g. GHC)

• diagnosticCodeNumber :: Natural

  the actual diagnostic code

Instances

ToJson DiagnosticCode

Defined in GHC.Types.Error

Methods

json :: DiagnosticCode -> JsonDoc

Outputable DiagnosticCode

Defined in GHC.Types.Error

Methods

ppr :: DiagnosticCode -> SDoc

Show DiagnosticCode

Defined in GHC.Types.Error

Methods

showsPrec :: Int -> DiagnosticCode -> ShowS

show :: DiagnosticCode -> String

showList :: [DiagnosticCode] -> ShowS

Eq DiagnosticCode

Defined in GHC.Types.Error

Methods

(==) :: DiagnosticCode -> DiagnosticCode -> Bool

(/=) :: DiagnosticCode -> DiagnosticCode -> Bool

Ord DiagnosticCode

Defined in GHC.Types.Error

Methods

compare :: DiagnosticCode -> DiagnosticCode -> Ordering

(<) :: DiagnosticCode -> DiagnosticCode -> Bool

(<=) :: DiagnosticCode -> DiagnosticCode -> Bool

(>) :: DiagnosticCode -> DiagnosticCode -> Bool

(>=) :: DiagnosticCode -> DiagnosticCode -> Bool

max :: DiagnosticCode -> DiagnosticCode -> DiagnosticCode

min :: DiagnosticCode -> DiagnosticCode -> DiagnosticCode