Add the ability to ignore weeds

src/Weeder.hs

@@ -22,6 +22,7 @@ module Weeder
 
     -- * Declarations
   , Declaration(..)
+  , declarationMatchesRegularExpression
   )
    where
 
@@ -65,7 +66,7 @@ import HieTypes
   , NodeInfo( NodeInfo, nodeIdentifiers, nodeAnnotations )
   , Scope( ModuleScope )
   )
-import Module ( Module, moduleStableString )
+import Module ( Module, moduleName, moduleNameString, moduleStableString )
 import Name ( Name, nameModule_maybe, nameOccName )
 import OccName
   ( OccName
@@ -84,6 +85,9 @@ import Control.Lens ( (%=) )
 -- mtl
 import Control.Monad.State.Class ( MonadState )
 
+-- regex-tdfa
+import Text.Regex.TDFA ( (=~) )
+
 -- transformers
 import Control.Monad.Trans.Maybe ( runMaybeT )
 
@@ -119,6 +123,11 @@ declarationStableName Declaration { declModule, declOccName } =
     intercalate "$" [ namespace, moduleStableString declModule, "$", occNameString declOccName ]
 
 
+declarationMatchesRegularExpression :: Declaration -> String -> Bool
+declarationMatchesRegularExpression d p =
+  ( moduleNameString ( moduleName ( declModule d ) ) <> "." <> occNameString ( declOccName d ) ) =~ p
+
+
 -- | All information maintained by 'analyseHieFile'.
 data Analysis =
   Analysis

src/Weeder/Config.hs

@@ -22,6 +22,10 @@ data Config = Config
     -- ^ If True, consider all declarations in a type class as part of the root
     -- set. Weeder is currently unable to identify whether or not a type class
     -- instance is used - enabling this option can prevent false positives.
+  , ignore :: Set String
+    -- ^ Any weeds matching these regular expressions will not be reported. This
+    -- is different from 'rootPatterns', which causes the weed to become a root,
+    -- while this option is purely about filtering the reporting output.
   }
 
 
@@ -31,7 +35,8 @@ data Config = Config
 config :: Dhall.Decoder Config
 config =
   Dhall.record do
-    rootPatterns <- Set.fromList <$> Dhall.field "roots" ( Dhall.list Dhall.string )
+    rootPatterns   <- Set.fromList <$> Dhall.field "roots" ( Dhall.list Dhall.string )
     typeClassRoots <- Dhall.field "type-class-roots" Dhall.bool
+    ignore         <- Set.fromList <$> Dhall.field "ignore" ( Dhall.list Dhall.string )
 
     return Config{..}

src/Weeder/Main.hs

@@ -46,9 +46,6 @@ import OccName ( occNameString )
 import SrcLoc ( realSrcSpanStart, srcLocCol, srcLocLine )
 import UniqSupply ( mkSplitUniqSupply )
 
--- regex-tdfa
-import Text.Regex.TDFA ( (=~) )
-
 -- optparse-applicative
 import Options.Applicative
 
@@ -94,7 +91,7 @@ main = do
 -- This will recursively find all @.hie@ files in the current directory, perform
 -- analysis, and report all unused definitions according to the 'Config'.
 mainWithConfig :: [FilePath] -> Config -> IO ()
-mainWithConfig hieDirectories Config{ rootPatterns, typeClassRoots } = do
+mainWithConfig hieDirectories Config{ rootPatterns, typeClassRoots, ignore } = do
   hieFilePaths <-
     concat <$>
       traverse getHieFilesIn
@@ -116,11 +113,7 @@ mainWithConfig hieDirectories Config{ rootPatterns, typeClassRoots } = do
   let
     roots =
       Set.filter
-        ( \d ->
-            any
-              ( ( moduleNameString ( moduleName ( declModule d ) ) <> "." <> occNameString ( declOccName d ) ) =~ )
-              rootPatterns
-        )
+        ( \d -> any ( declarationMatchesRegularExpression d ) rootPatterns )
         ( allDeclarations analysis )
 
     reachableSet =
@@ -142,6 +135,8 @@ mainWithConfig hieDirectories Config{ rootPatterns, typeClassRoots } = do
               spans <- Map.lookup d ( declarationSites analysis )
               guard $ not $ null spans
 
+              guard $ all (not . declarationMatchesRegularExpression d) ignore
+
               let snippets = do
                     srcSpan <- Set.toList spans