Add NoUnusedVariables rule

elm.json

@@ -7,13 +7,15 @@
     "exposed-modules": [
         "Lint",
         "Lint.Rule",
-        "Lint.Rule.NoDebug"
+        "Lint.Rule.NoDebug",
+        "Lint.Rule.NoUnusedVariables"
     ],
     "elm-version": "0.19.0 <= v < 0.20.0",
     "dependencies": {
         "elm/core": "1.0.0 <= v < 2.0.0",
         "elm/html": "1.0.0 <= v < 2.0.0",
         "elm/regex": "1.0.0 <= v < 2.0.0",
+        "mgold/elm-nonempty-list": "4.0.0 <= v < 5.0.0",
         "stil4m/elm-syntax": "7.0.2 <= v < 8.0.0"
     },
     "test-dependencies": {

example/Main.elm

@@ -9,6 +9,7 @@ import Html.Events exposing (onInput)
 import Lint exposing (Rule, Severity(..), lintSource)
 import Lint.Error exposing (Error)
 import Lint.Rule.NoDebug
+import Lint.Rule.NoUnusedVariables
 import Result exposing (Result)
 
 
@@ -19,6 +20,7 @@ type Msg
 config : List ( Severity, Rule )
 config =
     [ ( Critical, Lint.Rule.NoDebug.rule )
+    , ( Critical, Lint.Rule.NoUnusedVariables.rule )
 
     -- , ( Critical, Lint.Rule.DefaultPatternPosition.rule { position = Lint.Rule.DefaultPatternPosition.Last } )
     -- , ( Critical, Lint.Rule.NoConstantCondition.rule )
@@ -27,7 +29,6 @@ config =
     -- , ( Critical, Lint.Rule.NoImportingEverything.rule { exceptions = [ "Html" ] } )
     -- , ( Critical, Lint.Rule.NoNestedLet.rule )
     -- , ( Critical, Lint.Rule.NoUnannotatedFunction.rule )
-    -- , ( Critical, Lint.Rule.NoUnusedVariables.rule )
     -- , ( Critical, Lint.Rule.NoUselessIf.rule )
     -- , ( Critical, Lint.Rule.NoUselessPatternMatching.rule )
     -- , ( Warning, Lint.Rule.NoWarningComments.rule )

example/elm.json

@@ -10,11 +10,13 @@
             "elm/browser": "1.0.1",
             "elm/core": "1.0.0",
             "elm/html": "1.0.0",
+            "mgold/elm-nonempty-list": "4.0.0",
             "stil4m/elm-syntax": "7.0.2"
         },
         "indirect": {
             "elm/json": "1.0.0",
             "elm/parser": "1.1.0",
+            "elm/random": "1.0.0",
             "elm/time": "1.0.0",
             "elm/url": "1.0.0",
             "elm/virtual-dom": "1.0.2",

src/Lint.elm

@@ -51,7 +51,7 @@ import Elm.Syntax.Expression exposing (Expression)
 import Elm.Syntax.File exposing (File)
 import Elm.Syntax.Node exposing (Node)
 import Lint.Error exposing (Error)
-import Lint.NodeToVisitor exposing (declarationsIntoVisitors, expressionToVisitors)
+import Lint.NodeToVisitor exposing (createVisitorsForFile, expressionToVisitors)
 import Lint.Rule exposing (Direction, Implementation, Visitor, initialContext)
 
 
@@ -127,8 +127,7 @@ parseSource source =
 -}
 lint : File -> Implementation context -> List Error
 lint file rule =
-    file.declarations
-        |> declarationsIntoVisitors
+    createVisitorsForFile file
         |> lintWithVisitors rule
 
 

src/Lint/NodeToVisitor.elm

@@ -1,10 +1,14 @@
-module Lint.NodeToVisitor exposing (declarationsIntoVisitors, expressionToVisitors)
+module Lint.NodeToVisitor exposing (createVisitorsForFile, expressionToVisitors)
 
 import Elm.Syntax.Declaration exposing (Declaration(..))
 import Elm.Syntax.Expression exposing (Expression(..), Function, FunctionImplementation, LetDeclaration(..))
+import Elm.Syntax.File exposing (File)
+import Elm.Syntax.Import exposing (Import)
 import Elm.Syntax.Infix exposing (InfixDirection(..))
+import Elm.Syntax.Module exposing (Module)
 import Elm.Syntax.Node exposing (Node, value)
-import Lint.Rule exposing (Direction(..), Visitor, evaluateExpression, finalEvaluation)
+import Elm.Syntax.TypeAnnotation exposing (TypeAnnotation(..))
+import Lint.Rule exposing (Direction(..), Visitor, evaluateDeclaration, evaluateExpression, evaluateImport, evaluateModuleDefinition, evaluateTypeAnnotation, finalEvaluation)
 
 
 createExitAndEnterWithChildren : (Direction -> nodeType -> Visitor context) -> nodeType -> List (Visitor context) -> List (Visitor context)
@@ -21,11 +25,31 @@ moduleVisitor rule context =
     finalEvaluation rule context
 
 
+moduleDefinitionVisitor : Node Module -> Visitor context
+moduleDefinitionVisitor node rule context =
+    evaluateModuleDefinition rule context node
+
+
+importVisitor : Node Import -> Visitor context
+importVisitor node rule context =
+    evaluateImport rule context node
+
+
 expressionVisitor : Direction -> Node Expression -> Visitor context
 expressionVisitor direction node rule context =
     evaluateExpression rule context direction node
 
 
+declarationVisitor : Direction -> Node Declaration -> Visitor context
+declarationVisitor direction node rule context =
+    evaluateDeclaration rule context direction node
+
+
+typeAnnotationVisitor : Direction -> Node TypeAnnotation -> Visitor context
+typeAnnotationVisitor direction node rule context =
+    evaluateTypeAnnotation rule context direction node
+
+
 functionToExpression : Function -> Node Expression
 functionToExpression { documentation, signature, declaration } =
     let
@@ -71,6 +95,9 @@ expressionToVisitors node =
                 ParenthesizedExpression expr ->
                     [ expr ]
 
+                Operator name ->
+                    []
+
                 OperatorApplication operator direction left right ->
                     case direction of
                         Left ->
@@ -109,6 +136,9 @@ expressionToVisitors node =
                     expressions
 
                 -- TODO Implement the rest
+                PrefixOperator name ->
+                    []
+
                 _ ->
                     []
 
@@ -118,24 +148,58 @@ expressionToVisitors node =
     createExitAndEnterWithChildren expressionVisitor node childrenVisitors
 
 
-declarationToVisitors : Declaration -> List (Visitor context)
-declarationToVisitors declaration =
+typeAnnotationToVisitor : Node TypeAnnotation -> List (Visitor context)
+typeAnnotationToVisitor node =
     let
         childrenVisitors =
-            case declaration of
+            case value node of
+                GenericType _ ->
+                    []
+
+                _ ->
+                    []
+    in
+    createExitAndEnterWithChildren typeAnnotationVisitor node childrenVisitors
+
+
+declarationToVisitors : Node Declaration -> List (Visitor context)
+declarationToVisitors node =
+    let
+        childrenVisitors =
+            case value node of
                 FunctionDeclaration function ->
                     functionToExpression function |> expressionToVisitors
 
                 -- TODO Implement the rest
+                CustomTypeDeclaration { constructors } ->
+                    constructors
+                        |> List.concatMap (value >> .arguments)
+                        |> List.concatMap typeAnnotationToVisitor
+
                 _ ->
                     []
     in
-    -- createExitAndEnterWithChildren statementVisitor declaration childrenVisitors
-    childrenVisitors
+    createExitAndEnterWithChildren declarationVisitor node childrenVisitors
 
 
 declarationsIntoVisitors : List (Node Declaration) -> List (Visitor context)
 declarationsIntoVisitors declarations =
-    declarations
-        |> List.concatMap (value >> declarationToVisitors)
-        |> (\allVisitors -> List.append allVisitors [ moduleVisitor ])
+    List.concatMap declarationToVisitors declarations
+
+
+importsIntoVisitors : List (Node Import) -> List (Visitor context)
+importsIntoVisitors imports =
+    List.map importVisitor imports
+
+
+moduleDefinitionIntoVisitor : Node Module -> Visitor context
+moduleDefinitionIntoVisitor moduleNode =
+    moduleDefinitionVisitor moduleNode
+
+
+createVisitorsForFile : File -> List (Visitor context)
+createVisitorsForFile file =
+    [ moduleDefinitionIntoVisitor file.moduleDefinition ]
+        ++ importsIntoVisitors file.imports
+        ++ declarationsIntoVisitors file.declarations
+        ++ [ moduleVisitor ]

src/Lint/Rule.elm

@@ -2,7 +2,7 @@ module Lint.Rule exposing
     ( Direction(..)
     , Implementation, createRule
     , Visitor, LintResult
-    , evaluateExpression, finalEvaluation, initialContext
+    , evaluateDeclaration, evaluateExpression, evaluateImport, evaluateModuleDefinition, evaluateTypeAnnotation, finalEvaluation, initialContext
     )
 
 {-| This module contains functions that are used for writing rules.
@@ -24,9 +24,13 @@ module Lint.Rule exposing
 
 -}
 
+import Elm.Syntax.Declaration exposing (Declaration)
 import Elm.Syntax.Expression exposing (Expression)
 import Elm.Syntax.File exposing (File)
+import Elm.Syntax.Import exposing (Import)
+import Elm.Syntax.Module exposing (Module)
 import Elm.Syntax.Node exposing (Node)
+import Elm.Syntax.TypeAnnotation exposing (TypeAnnotation)
 import Lint.Error exposing (Error)
 
 
@@ -85,7 +89,11 @@ type Implementation context
 
 
 type alias Visitors context =
-    { visitExpression : context -> Direction -> Node Expression -> ( List Error, context )
+    { visitModuleDefinition : context -> Node Module -> ( List Error, context )
+    , visitImport : context -> Node Import -> ( List Error, context )
+    , visitExpression : context -> Direction -> Node Expression -> ( List Error, context )
+    , visitDeclaration : context -> Direction -> Node Declaration -> ( List Error, context )
+    , visitTypeAnnotation : context -> Direction -> Node TypeAnnotation -> ( List Error, context )
     , visitEnd : context -> ( List Error, context )
     }
 
@@ -96,7 +104,11 @@ createRule initContext createVisitors =
         { initContext = initContext
         , visitors =
             createVisitors
-                { visitExpression = \ctx direction node -> ( [], ctx )
+                { visitModuleDefinition = \ctx node -> ( [], ctx )
+                , visitImport = \ctx node -> ( [], ctx )
+                , visitExpression = \ctx direction node -> ( [], ctx )
+                , visitDeclaration = \ctx direction node -> ( [], ctx )
+                , visitTypeAnnotation = \ctx direction node -> ( [], ctx )
                 , visitEnd = \ctx -> ( [], ctx )
                 }
         }
@@ -107,11 +119,31 @@ initialContext (Implementation { initContext }) =
     initContext
 
 
+evaluateModuleDefinition : Implementation context -> context -> Node Module -> ( List Error, context )
+evaluateModuleDefinition (Implementation { visitors }) =
+    visitors.visitModuleDefinition
+
+
+evaluateImport : Implementation context -> context -> Node Import -> ( List Error, context )
+evaluateImport (Implementation { visitors }) =
+    visitors.visitImport
+
+
 evaluateExpression : Implementation context -> context -> Direction -> Node Expression -> ( List Error, context )
 evaluateExpression (Implementation { visitors }) =
     visitors.visitExpression
 
 
+evaluateDeclaration : Implementation context -> context -> Direction -> Node Declaration -> ( List Error, context )
+evaluateDeclaration (Implementation { visitors }) =
+    visitors.visitDeclaration
+
+
+evaluateTypeAnnotation : Implementation context -> context -> Direction -> Node TypeAnnotation -> ( List Error, context )
+evaluateTypeAnnotation (Implementation { visitors }) =
+    visitors.visitTypeAnnotation
+
+
 finalEvaluation : Implementation context -> context -> ( List Error, context )
 finalEvaluation (Implementation { visitors }) =
     visitors.visitEnd

src/Lint/Rule/NoUnusedVariables.elm

@@ -0,0 +1,512 @@
+module Lint.Rule.NoUnusedVariables exposing (rule)
+
+{-|
+
+@docs rule
+
+
+# Fail
+
+    a n =
+        n + 1
+
+    b =
+        a 2
+
+
+# Success
+
+    a n =
+        n + 1
+
+-}
+
+import Dict exposing (Dict)
+import Elm.Syntax.Declaration exposing (Declaration(..))
+import Elm.Syntax.Exposing exposing (Exposing(..), TopLevelExpose(..))
+import Elm.Syntax.Expression exposing (Expression(..), Function, LetDeclaration(..))
+import Elm.Syntax.Import exposing (Import)
+import Elm.Syntax.Module as Module exposing (Module(..))
+import Elm.Syntax.Node exposing (Node, range, value)
+import Elm.Syntax.Range exposing (Range)
+import Elm.Syntax.TypeAnnotation exposing (TypeAnnotation(..))
+import Lint exposing (Rule, lint)
+import Lint.Error exposing (Error)
+import Lint.Rule exposing (Direction(..), Implementation, createRule)
+import List.Nonempty as Nonempty exposing (Nonempty)
+import Set exposing (Set)
+
+
+type alias Scope =
+    { declared : Dict String Range
+    , used : Set String
+    }
+
+
+type alias Context =
+    { scopes : Nonempty Scope
+    , exposesEverything : Bool
+    }
+
+
+emptyScope : Scope
+emptyScope =
+    Scope Dict.empty Set.empty
+
+
+{-| Reports variables that are declared but never used.
+
+    rules =
+        [ NoUnusedVariables.rule
+        ]
+
+-}
+rule : Rule
+rule input =
+    lint input implementation
+
+
+implementation : Implementation Context
+implementation =
+    createRule
+        (Context (Nonempty.fromElement emptyScope) False)
+        (\v ->
+            { v
+                | visitModuleDefinition = visitModuleDefinition
+                , visitImport = visitImport
+                , visitDeclaration = visitDeclaration
+                , visitExpression = visitExpression
+                , visitEnd = visitEnd
+            }
+        )
+
+
+visitModuleDefinition : Context -> Node Module -> ( List Error, Context )
+visitModuleDefinition ctx moduleNode =
+    case Module.exposingList (value moduleNode) of
+        All _ ->
+            ( [], { ctx | exposesEverything = True } )
+
+        Explicit list ->
+            let
+                names =
+                    List.filterMap
+                        (\node ->
+                            case value node of
+                                FunctionExpose name ->
+                                    Just name
+
+                                TypeOrAliasExpose name ->
+                                    Just name
+
+                                TypeExpose { name } ->
+                                    Just name
+
+                                InfixExpose name ->
+                                    -- Just name
+                                    Nothing
+                        )
+                        list
+            in
+            ( [], markAllAsUsed names ctx )
+
+
+visitImport : Context -> Node Import -> ( List Error, Context )
+visitImport ctx node =
+    let
+        newContext =
+            value node
+                |> .exposingList
+                |> Maybe.map (value >> collectFromExposing)
+                |> Maybe.withDefault []
+                |> List.foldl (\( range, name ) context -> register range name context) ctx
+    in
+    ( [], newContext )
+
+
+collectFromExposing : Exposing -> List ( Range, String )
+collectFromExposing exposing_ =
+    case exposing_ of
+        All _ ->
+            []
+
+        Explicit list ->
+            List.filterMap
+                (\node ->
+                    case value node of
+                        FunctionExpose name ->
+                            Just ( range node, name )
+
+                        InfixExpose name ->
+                            Just ( range node, name )
+
+                        _ ->
+                            Nothing
+                )
+                list
+
+
+markAllAsUsed : List String -> Context -> Context
+markAllAsUsed names ctx =
+    List.foldl markAsUsed ctx names
+
+
+error : Range -> String -> Error
+error range_ name =
+    Error "NoUnusedVariables" ("Variable `" ++ name ++ "` is not used") range_
+
+
+visitDeclaration : Context -> Direction -> Node Declaration -> ( List Error, Context )
+visitDeclaration ctx direction node =
+    case ( direction, value node ) of
+        ( Enter, FunctionDeclaration function ) ->
+            let
+                declaration =
+                    value function.declaration
+
+                namesUsedInSignature =
+                    function.signature
+                        |> Maybe.map (value >> .typeAnnotation >> collectNamesFromTypeAnnotation)
+                        |> Maybe.withDefault []
+
+                newContext =
+                    ctx
+                        |> register (range declaration.name) (value declaration.name)
+                        |> markAllAsUsed namesUsedInSignature
+            in
+            ( [], newContext )
+
+        ( Enter, CustomTypeDeclaration { name } ) ->
+            ( [], register (range name) (value name) ctx )
+
+        ( Enter, AliasDeclaration { name } ) ->
+            ( [], register (range name) (value name) ctx )
+
+        _ ->
+            ( [], ctx )
+
+
+collectNamesFromTypeAnnotation : Node TypeAnnotation -> List String
+collectNamesFromTypeAnnotation node =
+    case value node of
+        FunctionTypeAnnotation a b ->
+            collectNamesFromTypeAnnotation a ++ collectNamesFromTypeAnnotation b
+
+        Typed nameNode params ->
+            let
+                name =
+                    nameNode
+                        |> value
+                        |> Tuple.second
+            in
+            name :: List.concatMap collectNamesFromTypeAnnotation params
+
+        Record list ->
+            list
+                |> List.map (value >> Tuple.second)
+                |> List.concatMap collectNamesFromTypeAnnotation
+
+        GenericRecord name list ->
+            list
+                |> value
+                |> List.map (value >> Tuple.second)
+                |> List.concatMap collectNamesFromTypeAnnotation
+
+        _ ->
+            []
+
+
+register : Range -> String -> Context -> Context
+register range name ctx =
+    let
+        scopes =
+            mapNonemptyHead
+                (\scope ->
+                    { scope | declared = Dict.insert name range scope.declared }
+                )
+                ctx.scopes
+    in
+    { ctx | scopes = scopes }
+
+
+markAsUsed : String -> Context -> Context
+markAsUsed name ctx =
+    let
+        scopes =
+            mapNonemptyHead
+                (\scope ->
+                    { scope | used = Set.insert name scope.used }
+                )
+                ctx.scopes
+    in
+    { ctx | scopes = scopes }
+
+
+visitExpression : Context -> Direction -> Node Expression -> ( List Error, Context )
+visitExpression ctx direction node =
+    case ( direction, value node ) of
+        ( Enter, FunctionOrValue [] name ) ->
+            ( [], markAsUsed name ctx )
+
+        ( Enter, OperatorApplication name _ _ _ ) ->
+            ( [], markAsUsed name ctx )
+
+        ( Enter, PrefixOperator name ) ->
+            ( [], markAsUsed name ctx )
+
+        ( Enter, LetExpression { declarations } ) ->
+            let
+                newContext =
+                    List.foldl
+                        (\declaration context ->
+                            case value declaration of
+                                LetFunction function ->
+                                    registerFunction function context
+
+                                LetDestructuring pattern _ ->
+                                    context
+                        )
+                        { ctx | scopes = Nonempty.cons emptyScope ctx.scopes }
+                        declarations
+            in
+            ( [], newContext )
+
+        ( Exit, LetExpression _ ) ->
+            let
+                ( errors, remainingUsed ) =
+                    makeReport (Nonempty.head ctx.scopes)
+
+                ctxWithPoppedScope =
+                    { ctx | scopes = Nonempty.pop ctx.scopes }
+            in
+            ( errors
+            , markAllAsUsed remainingUsed ctxWithPoppedScope
+            )
+
+        _ ->
+            ( [], ctx )
+
+
+registerFunction : Function -> Context -> Context
+registerFunction function ctx =
+    let
+        declaration =
+            value function.declaration
+    in
+    register (range declaration.name) (value declaration.name) ctx
+
+
+visitEnd : Context -> ( List Error, Context )
+visitEnd ctx =
+    let
+        errors =
+            if ctx.exposesEverything then
+                []
+
+            else
+                ctx.scopes
+                    |> Nonempty.head
+                    |> makeReport
+                    |> Tuple.first
+    in
+    ( errors, ctx )
+
+
+makeReport : Scope -> ( List Error, List String )
+makeReport { declared, used } =
+    let
+        nonUsedVars =
+            Set.diff used (Set.fromList <| Dict.keys declared)
+                |> Set.toList
+
+        errors =
+            Dict.filter (\key _ -> not <| Set.member key used) declared
+                |> Dict.toList
+                |> List.map (\( key, node ) -> error node key)
+    in
+    ( errors, nonUsedVars )
+
+
+
+-- ( Enter, Variable names ) ->
+--     case names of
+--         [ name ] ->
+--             ( [], { ctx | scopes = addUsedToStack ctx.scopes [ name ] } )
+--
+--         _ ->
+--             ( [], ctx )
+--
+-- ( Enter, LetExpression declarations ) ->
+--     let
+--         variables =
+--             List.map Tuple.first declarations
+--                 |> List.filterMap variableName
+--                 |> List.concat
+--                 |> Set.fromList
+--
+--         newScope =
+--             Scope variables Set.empty
+--     in
+--     ( [], { ctx | scopes = newScope :: ctx.scopes } )
+--
+-- ( Exit, LetExpression _ ) ->
+--     let
+--         ( errors, variablesUsedButNotFromThisScope ) =
+--             ctx.scopes
+--                 |> List.head
+--                 |> makeReport
+--
+--         newScopes =
+--             List.drop 1 ctx.scopes
+--     in
+--     ( errors, { ctx | scopes = addUsedToStack newScopes (Set.toList variablesUsedButNotFromThisScope) } )
+-- addUsedToStack : List Scope -> List String -> List Scope
+-- addUsedToStack scopes variables =
+--     let
+--         lastScope =
+--             case List.head scopes of
+--                 Nothing ->
+--                     Debug.log "Unexpected Empty scope stack" emptyScope
+--
+--                 Just scope ->
+--                     { scope | used = Set.union scope.used (Set.fromList variables) }
+--     in
+--     lastScope :: List.drop 1 scopes
+--
+--
+-- addFoundToStack : List Scope -> List String -> List Scope
+-- addFoundToStack scopes variables =
+--     let
+--         lastScope =
+--             case List.head scopes of
+--                 Nothing ->
+--                     Debug.log "Unexpected Empty scope stack" emptyScope
+--
+--                 Just scope ->
+--                     { scope | declared = Set.union scope.declared (Set.fromList variables) }
+--     in
+--     lastScope :: List.drop 1 scopes
+-- makeReport : Maybe Scope -> ( List Error, Set String )
+-- makeReport maybeScope =
+--     case maybeScope of
+--         Nothing ->
+--             Debug.log "Unexpected Empty scope stack" ( [], Set.empty )
+--
+--         Just scope ->
+--             let
+--                 notUsed =
+--                     Set.diff scope.declared scope.used
+--
+--                 variablesUsedButNotFromThisScope =
+--                     Set.diff scope.used scope.declared
+--
+--                 errors =
+--                     Set.diff scope.declared scope.used
+--                         |> Set.toList
+--                         |> List.sort
+--                         |> List.map error
+--             in
+--             ( errors, variablesUsedButNotFromThisScope )
+--
+-- variableName : Expression -> Maybe (List String)
+-- variableName expr =
+--     case expr of
+--         Variable names ->
+--             Just names
+--
+--         Application var _ ->
+--             variableName var
+--
+--         _ ->
+--             Nothing
+--
+--
+-- getExported : ExportSet -> Set String
+-- getExported exportType =
+--     case exportType of
+--         -- Ignore as this case is handled by `exposesEverything`
+--         AllExport ->
+--             Set.empty
+--
+--         SubsetExport exports ->
+--             List.map getExported exports
+--                 |> List.foldl Set.union Set.empty
+--
+--         FunctionExport name ->
+--             Set.singleton name
+--
+--         TypeExport name _ ->
+--             Set.singleton name
+--
+--
+-- addExposedVariables : Context -> Ast.Statement.ExportSet -> Context
+-- addExposedVariables ctx exportType =
+--     { ctx
+--         | scopes =
+--             getExported exportType
+--                 |> Set.toList
+--                 |> addUsedToStack ctx.scopes
+--     }
+--
+--
+-- statementFn : Context -> Direction Statement -> ( List Error, Context )
+-- statementFn ctx node =
+--     case node of
+--         Enter (FunctionDeclaration name args body) ->
+--             ( [], { ctx | scopes = addFoundToStack ctx.scopes [ name ] } )
+--
+--         Enter (ModuleDeclaration names AllExport) ->
+--             ( [], { ctx | exposesEverything = True } )
+--
+--         Enter (PortModuleDeclaration names AllExport) ->
+--             ( [], { ctx | exposesEverything = True } )
+--
+--         Enter (ImportStatement module_ alias_ (Just (SubsetExport imported))) ->
+--             let
+--                 variables =
+--                     List.foldl
+--                         (\var res ->
+--                             case var of
+--                                 FunctionExport name ->
+--                                     name :: res
+--
+--                                 _ ->
+--                                     res
+--                         )
+--                         []
+--                         imported
+--             in
+--             ( [], { ctx | scopes = addFoundToStack ctx.scopes variables } )
+--
+--         Enter (ModuleDeclaration names exportType) ->
+--             ( [], addExposedVariables ctx exportType )
+--
+--         Enter (PortModuleDeclaration names exportType) ->
+--             ( [], addExposedVariables ctx exportType )
+--
+--         _ ->
+--             ( [], ctx )
+--
+--
+-- moduleEndFn : Context -> ( List Error, Context )
+-- moduleEndFn ctx =
+--     let
+--         ( errors, _ ) =
+--             if ctx.exposesEverything then
+--                 ( [], Set.empty )
+--
+--             else
+--                 ctx.scopes
+--                     |> List.head
+--                     |> makeReport
+--     in
+--     ( errors, ctx )
+
+
+mapNonemptyHead : (a -> a) -> Nonempty a -> Nonempty a
+mapNonemptyHead fn nonempty =
+    let
+        newHead =
+            fn (Nonempty.head nonempty)
+    in
+    Nonempty.replaceHead newHead nonempty

tests/NoDebugTest.elm

@@ -5,7 +5,7 @@ import Lint exposing (Rule)
 import Lint.Error exposing (Error)
 import Lint.Rule exposing (LintResult)
 import Lint.Rule.NoDebug exposing (rule)
-import Test exposing (Test, describe, only, test)
+import Test exposing (Test, describe, test)
 import TestUtil exposing (expectErrors, ruleTester)
 
 

tests/NoUnusedVariablesTest.elm

@@ -0,0 +1,288 @@
+module NoUnusedVariablesTest exposing (all)
+
+import Elm.Syntax.Range exposing (Location, Range)
+import Lint exposing (Rule)
+import Lint.Error exposing (Error)
+import Lint.Rule exposing (LintResult)
+import Lint.Rule.NoUnusedVariables exposing (rule)
+import Test exposing (Test, describe, test)
+import TestUtil exposing (expectErrors, ruleTester)
+
+
+testRule : String -> LintResult
+testRule =
+    ruleTester rule
+
+
+error : String -> Range -> Error
+error =
+    Error "NoUnusedVariables"
+
+
+location : Int -> Int -> Int -> Range
+location row columnStart columnEnd =
+    { start = { row = row, column = columnStart }
+    , end = { row = row, column = columnEnd }
+    }
+
+
+tests : List Test
+tests =
+    [ test "should not report exposed top-level variables" <|
+        \() ->
+            testRule """module A exposing (a)
+a = 1"""
+                |> expectErrors []
+    , test "should not report used top-level variables" <|
+        \() ->
+            testRule """module A exposing (b)
+a n = 1
+b = a 1"""
+                |> expectErrors []
+    , test "should report unused top-level variables" <|
+        \() ->
+            testRule """module A exposing (b)
+a = 1"""
+                |> expectErrors [ error "Variable `a` is not used" (location 2 1 2) ]
+    , test "should report unused top-level variables even if they are annotated" <|
+        \() ->
+            testRule """module A exposing (b)
+a: Int
+a = 1"""
+                |> expectErrors [ error "Variable `a` is not used" (location 3 1 2) ]
+    , test "should not report unused top-level variables if everything is exposed" <|
+        \() ->
+            testRule """module A exposing (..)
+a n = 1
+b = a 1"""
+                |> expectErrors []
+    , test "should not report unused top-level variables that are exposed by name" <|
+        \() ->
+            testRule """module A exposing (a, b)
+a = 1
+b = 2"""
+                |> expectErrors []
+    , test "should not report unused top-level variables that are exposed by name, but report others" <|
+        \() ->
+            testRule """module A exposing (a, b)
+a = 1
+b = 2
+c = 3"""
+                |> expectErrors [ error "Variable `c` is not used" (location 4 1 2) ]
+    , test "should not report unused top-level variables if everything is exposed (port module)" <|
+        \() ->
+            testRule """port module A exposing (..)
+a n = 1
+b = a 1"""
+                |> expectErrors []
+    , test "should not report unused top-level variables that are exposed by name (port module)" <|
+        \() ->
+            testRule """port module A exposing (a, b)
+a = 1
+b = 2"""
+                |> expectErrors []
+    , test "should not report unused top-level variables that are exposed by name, but report others (port module)" <|
+        \() ->
+            testRule """port module A exposing (a, b)
+a = 1
+b = 2
+c = 3"""
+                |> expectErrors [ error "Variable `c` is not used" (location 4 1 2) ]
+    , test "should report unused variables from let declarations" <|
+        \() ->
+            testRule """module A exposing (a)
+a = let b = 1
+    in 2"""
+                |> expectErrors [ error "Variable `b` is not used" (location 2 9 10) ]
+    , test "should report unused variables from let even if they are exposed by name" <|
+        \() ->
+            testRule """module A exposing (a, b)
+a = let b = 1
+    in 2"""
+                |> expectErrors [ error "Variable `b` is not used" (location 2 9 10) ]
+    , test "should report unused functions from let even if they are exposed by name" <|
+        \() ->
+            testRule """module A exposing (a)
+a = let b param = 1
+    in 2"""
+                |> expectErrors [ error "Variable `b` is not used" (location 2 9 10) ]
+    , test "should report unused variables from let even if everything is exposed" <|
+        \() ->
+            testRule """module A exposing (..)
+a = let b = 1
+    in 2"""
+                |> expectErrors [ error "Variable `b` is not used" (location 2 9 10) ]
+    , test "should not report top-level variables used inside a let expression" <|
+        \() ->
+            testRule """module A exposing (a)
+b = 1
+a = let c = 1
+    in b + c"""
+                |> expectErrors []
+    , test "should not report top-level variables used inside let declarations" <|
+        \() ->
+            testRule """module A exposing (a)
+b = 1
+a = let c = b
+    in c"""
+                |> expectErrors []
+    , test "should not report top-level variables used in nested lets" <|
+        \() ->
+            testRule """module A exposing (a)
+b = 1
+a = let
+      c = b
+      d = let
+            e = 1
+          in
+            b + c + e
+    in
+      d"""
+                |> expectErrors []
+    , test "should not report variables from let declarations that are used in the expression" <|
+        \() ->
+            testRule """module A exposing (a)
+a = let c = 1
+    in c"""
+                |> expectErrors []
+    , test "should not report unused function parameters" <|
+        \() ->
+            testRule """module A exposing (a)
+a n = 1"""
+                |> expectErrors []
+    , test "should report unused imported functions" <|
+        \() ->
+            testRule """module A exposing (b)
+import Foo exposing (a)"""
+                |> expectErrors [ error "Variable `a` is not used" (location 2 22 23) ]
+    , test "should report unused imported functions (multiple imports)" <|
+        \() ->
+            testRule """module A exposing (d)
+import Foo exposing (C, a, b)"""
+                |> expectErrors
+                    [ error "Variable `a` is not used" (location 2 25 26)
+                    , error "Variable `b` is not used" (location 2 28 29)
+                    ]
+
+    -- Needs to be improved, every case should create a new scope stack
+    -- Right now, every parameter is considered used, which is not great
+    , test "should not report unused pattern matching parameters" <|
+        \() ->
+            testRule """module A exposing (a)
+a = case thing of
+    Foo b c -> []"""
+                |> expectErrors []
+
+    -- Should B and C be reported if they are not used? Probably.
+    , test "should report unused custom type declarations" <|
+        \() ->
+            testRule """module A exposing (a)
+type A = B | C"""
+                |> expectErrors [ error "Variable `A` is not used" (location 2 6 7) ]
+    , test "should report unused type aliases declarations" <|
+        \() ->
+            testRule """module A exposing (a)
+type alias A = { a : B }"""
+                |> expectErrors [ error "Variable `A` is not used" (location 2 12 13) ]
+    , test "should not report type used in a signature" <|
+        \() ->
+            testRule """module A exposing (a)
+type alias A = { a : B }
+a : A
+a = {a = 1}"""
+                |> expectErrors []
+    , test "should not report type used in a signature with multiple arguments" <|
+        \() ->
+            testRule """module A exposing (a)
+type alias A = { a : B }
+a : String -> A
+a str = {a = str}"""
+                |> expectErrors []
+    , test "should not report type used in a signature with parameterized types (as generic type)" <|
+        \() ->
+            testRule """module A exposing (a)
+type alias A = { a : B }
+a : A B
+a = []"""
+                |> expectErrors []
+    , test "should not report type used in a signature with parameterized types (as parameter)" <|
+        \() ->
+            testRule """module A exposing (a)
+type alias A = { a : B }
+a : List A
+a = []"""
+                |> expectErrors []
+    , test "should not report type used in a signature with a record" <|
+        \() ->
+            testRule """module A exposing (a)
+type alias A = { a : B }
+a : { c: A }
+a str = {c = str}"""
+                |> expectErrors []
+    , test "should not report type used in a signature with a generic record" <|
+        \() ->
+            testRule """module A exposing (a)
+type alias A = { a : B }
+a : { r | c: A }
+a str = {c = str}"""
+                |> expectErrors []
+    , test "should not report type if it's exposed" <|
+        \() ->
+            testRule """module A exposing (A)
+type A a = B a"""
+                |> expectErrors []
+    , test "should not report custom type if it's exposed with its sub-types" <|
+        \() ->
+            testRule """module A exposing (A(..))
+type A = B | C | D"""
+                |> expectErrors []
+    , test "should report unused variable even if it's present in a generic type" <|
+        \() ->
+            testRule """module A exposing (A)
+a = 1
+type A a = B a"""
+                |> expectErrors [ error "Variable `a` is not used" (location 2 1 2) ]
+    , test "should report unused variable even if it's present in a generic record type" <|
+        \() ->
+            testRule """module A exposing (a)
+r = 1
+a : { r | c: A }
+a str = {c = str}"""
+                |> expectErrors [ error "Variable `r` is not used" (location 2 1 2) ]
+    , test "should report unused operator import" <|
+        \() ->
+            testRule """module A exposing (a)
+import Parser exposing ((</>))"""
+                |> expectErrors [ error "Variable `</>` is not used" (location 2 25 30) ]
+    , test "should not report used operator (infix)" <|
+        \() ->
+            testRule """module A exposing (a)
+import Parser exposing ((</>))
+a = 1 </> 2"""
+                |> expectErrors []
+    , test "should not report used operator (prefix)" <|
+        \() ->
+            testRule """module A exposing (a)
+import Parser exposing ((</>))
+a = (</>) 2"""
+                |> expectErrors []
+
+    -- ##################################################################################################
+    -- , test "should report unused opaque types" <|
+    --     \() ->
+    --         testRule """module A exposing (a)
+    -- type A = A Int"""
+    --             |> expectErrors [ error "Variable `A` is not used" (location 2 6 7) ]
+    -- , test "should not report used opaque types" <|
+    --     \() ->
+    --         testRule """module A exposing (a)
+    -- type A = A Int
+    -- a : A
+    -- a = 1"""
+    --             |> expectErrors [ error "Variable `A` is not used" (location 2 6 7) ]
+    ]
+
+
+all : Test
+all =
+    describe "NoUnusedVariables" tests