path: root/compiler/GHC/Types/Hint.hs

{-# LANGUAGE ExistentialQuantification #-}

module GHC.Types.Hint (
    GhcHint(..)
  , AvailableBindings(..)
  , InstantiationSuggestion(..)
  , LanguageExtensionHint(..)
  , suggestExtension
  , suggestExtensionWithInfo
  , suggestExtensions
  , suggestExtensionsWithInfo
  , suggestAnyExtension
  , suggestAnyExtensionWithInfo
  ) where

import GHC.Prelude

import qualified Data.List.NonEmpty as NE

import GHC.Utils.Outputable
import qualified GHC.LanguageExtensions as LangExt
import Data.Typeable
import GHC.Unit.Module (ModuleName, Module)
import GHC.Hs.Extension (GhcTc)
import GHC.Core.Coercion
import GHC.Types.Name (Name)
import GHC.Types.Basic (Activation, RuleName)
import GHC.Parser.Errors.Basic
import {-# SOURCE #-} Language.Haskell.Syntax.Expr
  -- This {-# SOURCE #-} import should be removable once
  -- 'Language.Haskell.Syntax.Bind' no longer depends on 'GHC.Tc.Types.Evidence'.

-- | The bindings we have available in scope when
-- suggesting an explicit type signature.
data AvailableBindings
  = NamedBindings  (NE.NonEmpty Name)
  | UnnamedBinding
  -- ^ An unknown binding (i.e. too complicated to turn into a 'Name')

data LanguageExtensionHint
  = -- | Suggest to enable the input extension. 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.
     SuggestSingleExtension !SDoc !LangExt.Extension
    -- | Suggest to enable the input extensions. The list
    -- is to be intended as /disjuctive/ 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.
  | SuggestAnyExtension !SDoc [LangExt.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.
  | SuggestExtensions !SDoc [LangExt.Extension]

-- | Suggests a single extension without extra user info.
suggestExtension :: LangExt.Extension -> GhcHint
suggestExtension ext = SuggestExtension (SuggestSingleExtension empty ext)

-- | Like 'suggestExtension' but allows supplying extra info for the user.
suggestExtensionWithInfo :: SDoc -> LangExt.Extension -> GhcHint
suggestExtensionWithInfo extraInfo ext = SuggestExtension (SuggestSingleExtension extraInfo ext)

-- | Suggests to enable /every/ extension in the list.
suggestExtensions :: [LangExt.Extension] -> GhcHint
suggestExtensions exts = SuggestExtension (SuggestExtensions empty exts)

-- | Like 'suggestExtensions' but allows supplying extra info for the user.
suggestExtensionsWithInfo :: SDoc -> [LangExt.Extension] -> GhcHint
suggestExtensionsWithInfo extraInfo exts = SuggestExtension (SuggestExtensions extraInfo exts)

-- | Suggests to enable /any/ extension in the list.
suggestAnyExtension :: [LangExt.Extension] -> GhcHint
suggestAnyExtension exts = SuggestExtension (SuggestAnyExtension empty exts)

-- | Like 'suggestAnyExtension' but allows supplying extra info for the user.
suggestAnyExtensionWithInfo :: SDoc -> [LangExt.Extension] -> GhcHint
suggestAnyExtensionWithInfo extraInfo exts = SuggestExtension (SuggestAnyExtension extraInfo exts)

-- | A type for hints emitted by GHC.
-- A /hint/ suggests a possible way to deal with a particular warning or error.
data GhcHint
  =
    {-| 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.
    -}
    forall a. (Outputable a, Typeable a) => UnknownHint a
    {-| 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): parser/should_fail/T12429, parser/should_fail/T8501c,
                      parser/should_fail/T18251e, ... (and many more)

    -}
  | SuggestExtension !LanguageExtensionHint
    {-| Suggests that a monadic code block is probably missing a \"do\" keyword.

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

        Test case(s): parser/should_fail/T8501a, parser/should_fail/readFail007,
                      parser/should_fail/InfixAppPatErr, parser/should_fail/T984
    -}
  | SuggestMissingDo
    {-| Suggests that a \"let\" expression is needed in a \"do\" block.

       Test cases: None (that explicitly test this particular hint is emitted).
    -}
  | SuggestLetInDo
    {-| Suggests to add an \".hsig\" signature file to the Cabal manifest.

      Triggered by: 'GHC.Driver.Errors.Types.DriverUnexpectedSignature', if Cabal
                    is being used.

      Example: See comment of 'DriverUnexpectedSignature'.

      Test case(s): driver/T12955

    -}
  | SuggestAddSignatureCabalFile !ModuleName
    {-| Suggests to explicitly list the instantiations for the signatures in
        the GHC invocation command.

      Triggered by: 'GHC.Driver.Errors.Types.DriverUnexpectedSignature', if Cabal
                    is /not/ being used.

      Example: See comment of 'DriverUnexpectedSignature'.

      Test case(s): driver/T12955
    -}
  | SuggestSignatureInstantiations !ModuleName [InstantiationSuggestion]
    {-| Suggests to use spaces instead of tabs.

        Triggered by: 'GHC.Parser.Errors.Types.PsWarnTab'.

        Examples: None
        Test Case(s): None
    -}
  | SuggestUseSpaces
    {-| Suggests adding a whitespace after the given symbol.

        Examples: None
        Test Case(s): parser/should_compile/T18834a.hs
    -}
  | SuggestUseWhitespaceAfter !OperatorWhitespaceSymbol
    {-| 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: 'GHC.Parser.Errors.Types.PsWarnOperatorWhitespace'.

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

        Test Case(s): parser/should_compile/T18834b.hs
    -}
  | SuggestUseWhitespaceAround !String !OperatorWhitespaceOccurrence
    {-| Suggests wrapping an expression in parentheses

        Examples: None
        Test Case(s): None
    -}
  | SuggestParentheses
    {-| Suggests to increase the -fmax-pmcheck-models limit for the pattern match checker.

      Triggered by: 'GHC.HsToCore.Errors.Types.DsMaxPmCheckModelsReached'

      Test case(s): pmcheck/should_compile/TooManyDeltas
                    pmcheck/should_compile/TooManyDeltas
                    pmcheck/should_compile/T11822
    -}
  | SuggestIncreaseMaxPmCheckModels
    {-| Suggests adding a type signature, typically to resolve ambiguity or help GHC inferring types.

    -}
  | SuggestAddTypeSignatures AvailableBindings
    {-| Suggests to explicitly discard the result of a monadic action by binding the result to
        the '_' wilcard.

        Example:
           main = do
             _ <- getCurrentTime

    -}
  | SuggestBindToWildcard !(LHsExpr GhcTc)

  | SuggestAddInlineOrNoInlinePragma !Var !Activation

  | SuggestAddPhaseToCompetingRule !RuleName
    {-| Suggests adding an identifier to the export list of a signature.
    -}
  | SuggestAddToHSigExportList !Name !(Maybe Module)
    {-| Suggests increasing the limit for the number of iterations in the simplifier.

    -}
  | SuggestIncreaseSimplifierIterations
    {-| Suggests to explicitly import 'Type' from the 'Data.Kind' module, because
        using "*" to mean 'Data.Kind.Type' relies on the StarIsType extension, which
        will become deprecated in the future.

        Triggered by: 'GHC.Parser.Errors.Types.PsWarnStarIsType'
        Example: None
        Test case(s): wcompat-warnings/WCompatWarningsOn.hs

    -}
  | SuggestUseTypeFromDataKind

    {-| Suggests placing the 'qualified' keyword /after/ the module name.

        Triggered by: 'GHC.Parser.Errors.Types.PsWarnImportPreQualified'
        Example: None
        Test case(s): module/mod184.hs

    -}
  | SuggestQualifiedAfterModuleName

    {-| Suggests using TemplateHaskell quotation syntax.

        Triggered by: 'GHC.Parser.Errors.Types.PsErrEmptyDoubleQuotes' only if TemplateHaskell
                      is enabled.
        Example: None
        Test case(s): parser/should_fail/T13450TH.hs

    -}
  | SuggestThQuotationSyntax

    {-| Suggests alternative roles in case we found an illegal one.

        Triggered by: 'GHC.Parser.Errors.Types.PsErrIllegalRoleName'
        Example: None
        Test case(s): roles/should_fail/Roles7.hs

    -}
  | SuggestRoles [Role]

    {-| Suggests qualifying the '*' operator in modules where StarIsType is enabled.

        Triggered by: 'GHC.Parser.Errors.Types.PsWarnStarBinder'
        Test case(s): warnings/should_compile/StarBinder.hs
    -}
  | SuggestQualifyStarOperator

    {-| Suggests that a type signature should have form <variable> :: <type>
        in order to be accepted by GHC.

        Triggered by: 'GHC.Parser.Errors.Types.PsErrInvalidTypeSignature'
        Test case(s): parser/should_fail/T3811
    -}
  | SuggestTypeSignatureForm

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

        Triggered by: 'GHC.Tc.Errors.Types.TcRnOrphanInstance'
        Test cases(s): warnings/should_compile/T9178
                       typecheck/should_compile/T4912
    -}
  | SuggestFixOrphanInstance

-- | An 'InstantiationSuggestion' for a '.hsig' file. This is generated
-- by GHC in case of a 'DriverUnexpectedSignature' and suggests a way
-- to instantiate a particular signature, where the first argument is
-- the signature name and the second is the module where the signature
-- was defined.
-- Example:
--
-- src/MyStr.hsig:2:11: error:
--     Unexpected signature: ‘MyStr’
--     (Try passing -instantiated-with="MyStr=<MyStr>"
--      replacing <MyStr> as necessary.)
data InstantiationSuggestion = InstantiationSuggestion !ModuleName !Module