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

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)

Functor Messages

Defined in GHC.Types.Error

Methods

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

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

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

Diagnostic e => Outputable (Messages e)

Defined in GHC.Types.Error

Methods

ppr :: Messages e -> SDoc

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

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

Instances

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)

Functor MsgEnvelope

Defined in GHC.Types.Error

Methods

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

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

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 DiagnosticReason (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

Show Severity

Defined in GHC.Types.Error

Methods

showsPrec :: Int -> Severity -> ShowS

show :: Severity -> String

showList :: [Severity] -> ShowS

ToJson Severity

Defined in GHC.Types.Error

Methods

json :: Severity -> JsonDoc

Outputable Severity

Defined in GHC.Types.Error

Methods

ppr :: Severity -> SDoc

Eq Severity

Defined in GHC.Types.Error

Methods

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

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

class 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

defaultDiagnosticOpts :: DiagnosticOpts a

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

Methods

defaultDiagnosticOpts :: DiagnosticOpts DriverMessage

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

Methods

defaultDiagnosticOpts :: DiagnosticOpts GhcMessage

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

Methods

defaultDiagnosticOpts :: DiagnosticOpts DsMessage

diagnosticMessage :: DiagnosticOpts DsMessage -> DsMessage -> DecoratedSDoc

diagnosticReason :: DsMessage -> DiagnosticReason

diagnosticHints :: DsMessage -> [GhcHint]

diagnosticCode :: DsMessage -> Maybe DiagnosticCode

Diagnostic PsMessage

Defined in GHC.Parser.Errors.Ppr

Associated Types

type DiagnosticOpts PsMessage

Methods

defaultDiagnosticOpts :: DiagnosticOpts PsMessage

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

Methods

defaultDiagnosticOpts :: DiagnosticOpts TcRnMessage

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

Methods

defaultDiagnosticOpts :: DiagnosticOpts DiagnosticMessage

diagnosticMessage :: DiagnosticOpts DiagnosticMessage -> DiagnosticMessage -> DecoratedSDoc

diagnosticReason :: DiagnosticMessage -> DiagnosticReason

diagnosticHints :: DiagnosticMessage -> [GhcHint]

diagnosticCode :: DiagnosticMessage -> Maybe DiagnosticCode

Diagnostic UnknownDiagnostic

Defined in GHC.Types.Error

Associated Types

type DiagnosticOpts UnknownDiagnostic

Methods

defaultDiagnosticOpts :: DiagnosticOpts UnknownDiagnostic

diagnosticMessage :: DiagnosticOpts UnknownDiagnostic -> UnknownDiagnostic -> DecoratedSDoc

diagnosticReason :: UnknownDiagnostic -> DiagnosticReason

diagnosticHints :: UnknownDiagnostic -> [GhcHint]

diagnosticCode :: UnknownDiagnostic -> Maybe DiagnosticCode

data UnknownDiagnostic where

An existential wrapper around an unknown diagnostic.

Constructors

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

Instances

Diagnostic UnknownDiagnostic

Defined in GHC.Types.Error

Associated Types

type DiagnosticOpts UnknownDiagnostic

Methods

defaultDiagnosticOpts :: DiagnosticOpts UnknownDiagnostic

diagnosticMessage :: DiagnosticOpts UnknownDiagnostic -> UnknownDiagnostic -> DecoratedSDoc

diagnosticReason :: UnknownDiagnostic -> DiagnosticReason

diagnosticHints :: UnknownDiagnostic -> [GhcHint]

diagnosticCode :: UnknownDiagnostic -> Maybe DiagnosticCode

type DiagnosticOpts UnknownDiagnostic

Defined in GHC.Types.Error

type DiagnosticOpts UnknownDiagnostic = NoDiagnosticOpts

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 intepret 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

Methods

defaultDiagnosticOpts :: DiagnosticOpts DiagnosticMessage

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.

WarningWithFlag !WarningFlag

Warning was enabled with the flag.

ErrorWithoutFlag

Born as an error.

Instances

Show DiagnosticReason

Defined in GHC.Types.Error

Methods

showsPrec :: Int -> DiagnosticReason -> ShowS

show :: DiagnosticReason -> String

showList :: [DiagnosticReason] -> ShowS

Outputable DiagnosticReason

Defined in GHC.Types.Error

Methods

ppr :: DiagnosticReason -> SDoc

Eq DiagnosticReason

Defined in GHC.Types.Error

Methods

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

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

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

data NoDiagnosticOpts

Constructors

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

forall a.(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:

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

SuggestTypeSignatureForm

Suggests that a type signature should have form variable :: type in order to be accepted by GHC.

Triggered by: PsErrInvalidTypeSignature Test case(s): parsershould_failT3811

SuggestFixOrphanInstance

Suggests to move an orphan instance or to newtype-wrap it.

Triggered by: TcRnOrphanInstance Test cases(s): warningsshould_compileT9178 typecheckshould_compileT4912

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

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

SuggestRenameForall

Suggests to use an identifier other than forall Triggered by: TcRnForallIdentifier

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 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, ...

SuggestImportingDataCon

Suggest importing a data constructor to bring it into scope Triggered by: TcRnTypeCannotBeMarshaled

Test cases: ccfail004

SuggestPlacePragmaInHeader

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

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

IsString SDoc

Defined in GHC.Utils.Outputable

Methods

fromString :: String -> SDoc

IsDoc SDoc

Defined in GHC.Utils.Outputable

Associated Types

type Line SDoc = (r :: Type)

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

Outputable SDoc

Defined in GHC.Utils.Outputable

Methods

ppr :: SDoc -> 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

Outputable DiagnosticCode

Defined in GHC.Types.Error

Methods

ppr :: DiagnosticCode -> SDoc