Language.Haskell.HLint

This module provides a way to apply HLint hints. If you want to just run hlint in-process and collect the results see hlint.

If you want to approximate the hlint experience with a more structured API try:

(flags, classify, hint) <- autoSettings
Right m <- parseModuleEx flags "MyFile.hs" Nothing
print $ applyHints classify hint [m]

Generate hints

hlint :: [String] -> IO [Idea]

This function takes a list of command line arguments, and returns the given hints. To see a list of arguments type hlint --help at the console. This function writes to the stdout/stderr streams, unless --quiet is specified.

As an example:

do hints <- hlint ["src", "--ignore=Use map","--quiet"]
   when (length hints > 3) $ error "Too many hints!"

Warning: The flags provided by HLint are relatively stable, but do not have the same API stability guarantees as the rest of the strongly-typed API. Do not run this function on your server with untrusted input.

applyHints :: [Classify] -> Hint -> [ModuleEx] -> [Idea]

Given a way of classifying results, and a Hint, apply to a set of modules generating a list of Ideas. The Idea values will be ordered within a file.

Given a set of modules, it may be faster to pass each to applyHints in a singleton list. When given multiple modules at once this function attempts to find hints between modules, which is slower and often pointless (by default HLint passes modules singularly, using --cross to pass all modules together).

Idea data type

data Idea

An idea suggest by a Hint.

Constructors

Idea

Fields

• ideaModule :: [String]

  The modules the idea is for, usually a singleton.

• ideaDecl :: [String]

  The declarations the idea is for, usually a singleton, typically the function name, but may be a type name.

• ideaSeverity :: Severity

  The severity of the idea, e.g. Warning.

• ideaHint :: String

  The name of the hint that generated the idea, e.g. "Use reverse".

• ideaSpan :: SrcSpan

  The source code the idea relates to.

• ideaFrom :: String

  The contents of the source code the idea relates to.

• ideaTo :: Maybe String

  The suggested replacement, or Nothing for no replacement (e.g. on parse errors).

• ideaNote :: [Note]

  Notes about the effect of applying the replacement.

• ideaRefactoring :: [Refactoring SrcSpan]

  How to perform this idea

Instances

Show Idea

Defined in Idea

Methods

showsPrec :: Int -> Idea -> ShowS

show :: Idea -> String

showList :: [Idea] -> ShowS

Eq Idea

Defined in Idea

Methods

(==) :: Idea -> Idea -> Bool

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

data Severity

How severe an issue is.

Constructors

Ignore

The issue has been explicitly ignored and will usually be hidden (pass --show on the command line to see ignored ideas).

Suggestion

Suggestions are things that some people may consider improvements, but some may not.

Warning

Warnings are suggestions that are nearly always a good idea to apply.

Error

Available as a setting for the user. Only parse errors have this setting by default.

Instances

ToJSON Severity

Defined in Config.Type

Methods

toJSON :: Severity -> Value

toEncoding :: Severity -> Encoding

toJSONList :: [Severity] -> Value

toEncodingList :: [Severity] -> Encoding

omitField :: Severity -> Bool

Data Severity

Defined in Config.Type

Methods

gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Severity -> c Severity

gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c Severity

toConstr :: Severity -> Constr

dataTypeOf :: Severity -> DataType

dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c Severity)

dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c Severity)

gmapT :: (forall b. Data b => b -> b) -> Severity -> Severity

gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Severity -> r

gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Severity -> r

gmapQ :: (forall d. Data d => d -> u) -> Severity -> [u]

gmapQi :: Int -> (forall d. Data d => d -> u) -> Severity -> u

gmapM :: Monad m => (forall d. Data d => d -> m d) -> Severity -> m Severity

gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Severity -> m Severity

gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Severity -> m Severity

Bounded Severity

Defined in Config.Type

Methods

minBound :: Severity

maxBound :: Severity

Enum Severity

Defined in Config.Type

Methods

succ :: Severity -> Severity

pred :: Severity -> Severity

toEnum :: Int -> Severity

fromEnum :: Severity -> Int

enumFrom :: Severity -> [Severity]

enumFromThen :: Severity -> Severity -> [Severity]

enumFromTo :: Severity -> Severity -> [Severity]

enumFromThenTo :: Severity -> Severity -> Severity -> [Severity]

Generic Severity

Defined in Config.Type

Associated Types

type Rep Severity :: Type -> Type

Methods

from :: Severity -> Rep Severity x

to :: Rep Severity x -> Severity

Read Severity

Defined in Config.Type

Methods

readsPrec :: Int -> ReadS Severity

readList :: ReadS [Severity]

readPrec :: ReadPrec Severity

readListPrec :: ReadPrec [Severity]

Show Severity

Defined in Config.Type

Methods

showsPrec :: Int -> Severity -> ShowS

show :: Severity -> String

showList :: [Severity] -> ShowS

Eq Severity

Defined in Config.Type

Methods

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

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

Ord Severity

Defined in Config.Type

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

type Rep Severity

Defined in Config.Type

type Rep Severity = D1 ('MetaData "Severity" "Config.Type" "hlint-3.8-3om2fwq1HzU5EOBAoGKHAk" 'False) ((C1 ('MetaCons "Ignore" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons "Suggestion" 'PrefixI 'False) (U1 :: Type -> Type)) :+: (C1 ('MetaCons "Warning" 'PrefixI 'False) (U1 :: Type -> Type) :+: C1 ('MetaCons "Error" 'PrefixI 'False) (U1 :: Type -> Type)))

data Note

A note describing the impact of the replacement.

Constructors

IncreasesLaziness

The replacement is increases laziness, for example replacing reverse (reverse x) with x makes the code lazier.

DecreasesLaziness

The replacement is decreases laziness, for example replacing (fst x, snd x) with x makes the code stricter.

RemovesError String

The replacement removes errors, for example replacing foldr1 (+) with sum removes an error on [], and might contain the text "on []".

ValidInstance String String

The replacement assumes standard type class lemmas, a hint with the note ValidInstance "Eq" "x" might only be valid if the x variable has a reflexive Eq instance.

RequiresExtension String

The replacement requires this extension to be available.

Note String

An arbitrary note.

Instances

Show Note

Defined in Config.Type

Methods

showsPrec :: Int -> Note -> ShowS

show :: Note -> String

showList :: [Note] -> ShowS

Eq Note

Defined in Config.Type

Methods

(==) :: Note -> Note -> Bool

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

Ord Note

Defined in Config.Type

Methods

compare :: Note -> Note -> Ordering

(<) :: Note -> Note -> Bool

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

(>) :: Note -> Note -> Bool

(>=) :: Note -> Note -> Bool

max :: Note -> Note -> Note

min :: Note -> Note -> Note

unpackSrcSpan :: SrcSpan -> Maybe (FilePath, (Int, Int), (Int, Int))

Unpack a SrcSpan value. Useful to allow using the Idea information without adding a dependency on ghc or ghc-lib-parser. Unpacking gives:

(filename, (startLine, startCol), (endLine, endCol))

Following the GHC API, end column is the column after the end of the error. Lines and columns are 1-based. Returns Nothing if there is no helpful location information.

showIdeaANSI :: Idea -> String

Show an Idea with ANSI color codes to give syntax coloring to the Haskell code.

Settings

data Classify

How to classify an Idea. If any matching field is "" then it matches everything.

Constructors

Classify

Fields

• classifySeverity :: Severity

  Severity to set the Idea to.

• classifyHint :: String

  Match on Idea field ideaHint.

• classifyModule :: String

  Match on Idea field ideaModule.

• classifyDecl :: String

  Match on Idea field ideaDecl.

Instances

Show Classify

Defined in Config.Type

Methods

showsPrec :: Int -> Classify -> ShowS

show :: Classify -> String

showList :: [Classify] -> ShowS

getHLintDataDir :: IO FilePath

Get the Cabal configured data directory of HLint.

autoSettings :: IO (ParseFlags, [Classify], Hint)

The function produces a tuple containing ParseFlags (for parseModuleEx), and Classify and Hint for applyHints. It approximates the normal HLint configuration steps, roughly:

1. Use findSettings with readSettingsFile to find and load the HLint settings files.
1. Use parseFlagsAddFixities and resolveHints to transform the outputs of findSettings.

If you want to do anything custom (e.g. using a different data directory, storing intermediate outputs, loading hints from a database) you are expected to copy and paste this function, then change it to your needs.

argsSettings :: [String] -> IO (ParseFlags, [Classify], Hint)

A version of autoSettings which respects some of the arguments supported by HLint. If arguments unrecognised by HLint are used it will result in an error. Arguments which have no representation in the return type are silently ignored.

findSettings :: (String -> IO (FilePath, Maybe String)) -> Maybe String -> IO ([FixityInfo], [Classify], Hint)

Given a function to load a module (typically readSettingsFile), and a module to start from (defaults to hlint.yaml) find the information from all settings files.

readSettingsFile :: Maybe FilePath -> String -> IO (FilePath, Maybe String)

Given a directory (or Nothing to imply getHLintDataDir), and a module name (e.g. HLint.Default), find the settings file associated with it, returning the name of the file, and (optionally) the contents.

This function looks for all settings files starting with HLint. in the directory argument, and all other files relative to the current directory.

Hints

data Hint

Functions to generate hints, combined using the Monoid instance.

Instances

Monoid Hint

Defined in Hint.Type

Methods

mempty :: Hint

mappend :: Hint -> Hint -> Hint

mconcat :: [Hint] -> Hint

Semigroup Hint

Defined in Hint.Type

Methods

(<>) :: Hint -> Hint -> Hint

sconcat :: NonEmpty Hint -> Hint

stimes :: Integral b => b -> Hint -> Hint

Modules

data ModuleEx

Result of parseModuleEx, representing a parsed module.

parseModuleEx :: ParseFlags -> FilePath -> Maybe String -> IO (Either ParseError ModuleEx)

Parse a Haskell module. Applies the C pre processor, and uses best-guess fixity resolution if there are ambiguities. The filename - is treated as stdin. Requires some flags (often defaultParseFlags), the filename, and optionally the contents of that file.

Note that certain programs, e.g. main = do successfully parse with GHC, but then fail with an error in the renamer. These programs will return a successful parse.

createModuleEx :: Located (HsModule GhcPs) -> ModuleEx

Create a ModuleEx from a GHC module. It is assumed the incoming parsed module has not been adjusted to account for operator fixities (it uses the HLint default fixities).

createModuleExWithFixities :: [(String, Fixity)] -> Located (HsModule GhcPs) -> ModuleEx

data ParseError

A parse error.

Constructors

ParseError

Fields

• parseErrorLocation :: SrcSpan

  Location of the error.

• parseErrorMessage :: String

  Message about the cause of the error.

• parseErrorContents :: String

  Snippet of several lines (typically 5) including a > character pointing at the faulty line.

Parse flags

defaultParseFlags :: ParseFlags

Default value for ParseFlags.

data ParseFlags

Created with defaultParseFlags, used by parseModuleEx.

Constructors

ParseFlags

Fields

• cppFlags :: CppFlags

  How the file is preprocessed (defaults to NoCpp).

• baseLanguage :: Maybe Language

  Base language (e.g. Haskell98, Haskell2010), defaults to Nothing.

• enabledExtensions :: [Extension]

  List of extensions enabled for parsing, defaults to many non-conflicting extensions.

• disabledExtensions :: [Extension]

  List of extensions disabled for parsing, usually empty.

• fixities :: [FixityInfo]

  List of fixities to be aware of, defaults to those defined in base.

data CppFlags

What C pre processor should be used.

Constructors

CppSimple

Lines prefixed with # are stripped.

Cpphs CpphsOptions

The cpphs library is used.

type FixityInfo = (String, Associativity, Int)

A Fixity definition, comprising the name the fixity applies to, the direction and the precedence. As an example, a source file containing:

infixr 3 `foo`

would create ("foo", RightAssociative, 3).

parseFlagsAddFixities :: [FixityInfo] -> ParseFlags -> ParseFlags

Given some fixities, add them to the existing fixities in ParseFlags.