Add details to the message of every rule

This will make it easier to have helpful explanations and suggestions
like the Elm compiler does

src/Lint.elm

@@ -27,6 +27,7 @@ type alias LintError =
     { file : Maybe String
     , ruleName : String
     , message : String
+    , details : List String
     , range : Range
     }
 
@@ -113,6 +114,7 @@ errorToRuleError file rule error =
     { file = file
     , ruleName = Rule.name rule
     , message = Rule.errorMessage error
+    , details = Rule.errorDetails error
     , range = Rule.errorRange error
     }
 

src/Lint/Rule.elm

@@ -3,7 +3,7 @@ module Lint.Rule exposing
     , newSchema, fromSchema
     , withSimpleModuleDefinitionVisitor, withSimpleImportVisitor, withSimpleDeclarationVisitor, withSimpleExpressionVisitor
     , withInitialContext, withModuleDefinitionVisitor, withImportVisitor, Direction(..), withDeclarationVisitor, withExpressionVisitor, withFinalEvaluation
-    , Error, error, errorMessage, errorRange
+    , Error, error, errorMessage, errorDetails, errorRange
     , name, analyzer
     )
 
@@ -127,7 +127,7 @@ implementing the rule you wish to create.
 
 ## Errors
 
-@docs Error, error, errorMessage, errorRange
+@docs Error, error, errorMessage, errorDetails, errorRange
 
 
 # ACCESS
@@ -933,6 +933,7 @@ name of the rule that emitted it and the file name.
 type Error
     = Error
         { message : String
+        , details : List String
         , range : Range
         }
 
@@ -944,13 +945,18 @@ In most cases, you can get it using [`Node.range`](https://package.elm-lang.org/
 
     error : Node a -> Error
     error node =
-        Rule.error "Remove the use of `Debug` before shipping to production" (Node.range node)
+        Rule.error
+            { message = "Remove the use of `Debug` before shipping to production"
+            , details = "The `Debug` module is useful when developing, but is not meant to be shipped to production or published in a package. I suggest removing it's use before committing and attempting to push to production."
+            }
+            (Node.range node)
 
 -}
-error : String -> Range -> Error
-error message range =
+error : { message : String, details : List String } -> Range -> Error
+error { message, details } range =
     Error
         { message = message
+        , details = details
         , range = range
         }
 
@@ -962,6 +968,13 @@ errorMessage (Error err) =
     err.message
 
 
+{-| Get the error details of an [`Error`](#Error).
+-}
+errorDetails : Error -> List String
+errorDetails (Error err) =
+    err.details
+
+
 {-| Get the [`Range`](https://package.elm-lang.org/packages/stil4m/elm-syntax/7.1.0/Elm-Syntax-Range)
 of an [`Error`](#Error).
 -}

src/Lint/Rule/NoDebug.elm

@@ -69,7 +69,11 @@ rule =
 
 error : Node a -> Error
 error node =
-    Rule.error "Remove the use of `Debug` before shipping to production" (Node.range node)
+    Rule.error
+        { message = "Remove the use of `Debug` before shipping to production"
+        , details = [ "The `Debug` module is useful when developing, but is not meant to be shipped to production or published in a package. I suggest removing it's use before committing and attempting to push to production." ]
+        }
+        (Node.range node)
 
 
 importVisitor : Node Import -> List Error

src/Lint/Rule/NoExtraBooleanComparison.elm

@@ -67,10 +67,12 @@ rule =
         |> Rule.fromSchema
 
 
-error : Node a -> String -> Error
-error node comparedValue =
+error : Node a -> String -> String -> Error
+error node operator comparedValue =
     Rule.error
-        ("Unnecessary comparison with `" ++ comparedValue ++ "`")
+        { message = "Unnecessary comparison with `" ++ comparedValue ++ "`"
+        , details = [ "You can simplify this expression by removing the `" ++ operator ++ "` operator and the value `" ++ comparedValue ++ "`." ]
+        }
         (Node.range node)
 
 
@@ -80,7 +82,7 @@ expressionVisitor node =
         Expression.OperatorApplication operator _ left right ->
             if isEqualityOperator operator then
                 List.filterMap isTrueOrFalse [ left, right ]
-                    |> List.map (error node)
+                    |> List.map (error node operator)
 
             else
                 []

src/Lint/Rule/NoImportingEverything.elm

@@ -70,7 +70,14 @@ rule config =
 
 error : Range -> String -> Error
 error range name =
-    Rule.error ("Do not expose everything from " ++ name) range
+    Rule.error
+        { message = "Do not expose everything from " ++ name
+        , details =
+            [ "Exposing `(..)` from a module means making all it's exposed functions and types available in the file's namespace. This makes it hard to tell which module a function or type comes from."
+            , "A preferred pattern is to import functions by name (`import Html exposing (div, span)`) or to use qualified imports (`import Html`, then `Html.div`). If the module name is too long, you can give an alias to the imported module (`import Html.Attributes as Attr`)."
+            ]
+        }
+        range
 
 
 importVisitor : Configuration -> Node Import -> List Error

src/Lint/Rule/NoUnusedTypeConstructors.elm

@@ -101,7 +101,9 @@ initialContext =
 error : Node String -> Error
 error node =
     Rule.error
-        ("Type constructor `" ++ Node.value node ++ "` is not used.")
+        { message = "Type constructor `" ++ Node.value node ++ "` is not used."
+        , details = [ "Since it is not being used, I recommend removing it. It should make the code clearer to read for other people." ]
+        }
         (Node.range node)
 
 

src/Lint/Rule/NoUnusedVariables.elm

@@ -106,7 +106,9 @@ emptyScope =
 error : VariableType -> Range -> String -> Error
 error variableType range_ name =
     Rule.error
-        (variableTypeToString variableType ++ " `" ++ name ++ "` is not used" ++ variableTypeWarning variableType)
+        { message = variableTypeToString variableType ++ " `" ++ name ++ "` is not used" ++ variableTypeWarning variableType
+        , details = [ "Since it is not being used, I recommend removing it. It should make the code clearer to read for other people." ]
+        }
         range_
 
 

src/Lint/Test.elm

@@ -141,7 +141,16 @@ run rule sourceCode =
                 { getCodeAtLocation = getCodeAtLocationInSourceCode sourceCode
                 , checkIfLocationIsAmbiguous = checkIfLocationIsAmbiguousInSourceCode sourceCode
                 }
-                (List.map (\error_ -> Rule.error error_.message error_.range) errors)
+                (List.map
+                    (\error_ ->
+                        Rule.error
+                            { message = error_.message
+                            , details = error_.details
+                            }
+                            error_.range
+                    )
+                    errors
+                )
 
         Err _ ->
             ParseFailure

tests/ErrorMessageTest.elm

@@ -60,8 +60,16 @@ didNotExpectErrorsTest =
             let
                 errors : List Error
                 errors =
-                    [ Rule.error "Some error" dummyRange
-                    , Rule.error "Some other error" dummyRange
+                    [ Rule.error
+                        { message = "Some error"
+                        , details = [ "Some details" ]
+                        }
+                        dummyRange
+                    , Rule.error
+                        { message = "Some other error"
+                        , details = [ "Some other details" ]
+                        }
+                        dummyRange
                     ]
             in
             ErrorMessage.didNotExpectErrors errors
@@ -90,7 +98,11 @@ messageMismatchTest =
 
                 error : Error
                 error =
-                    Rule.error "Some error message" dummyRange
+                    Rule.error
+                        { message = "Some error"
+                        , details = [ "Some details" ]
+                        }
+                        dummyRange
             in
             ErrorMessage.messageMismatch expectedError error
                 |> expectMessageEqual """
@@ -102,7 +114,7 @@ I was looking for the error with the following message:
 
 but I found the following error message:
 
-  `Some error message`"""
+  `Some error`"""
 
 
 underMismatchTest : Test
@@ -113,7 +125,11 @@ underMismatchTest =
                 let
                     error : Error
                     error =
-                        Rule.error "Some error" dummyRange
+                        Rule.error
+                            { message = "Some error"
+                            , details = [ "Some details" ]
+                            }
+                            dummyRange
                 in
                 ErrorMessage.underMismatch
                     error
@@ -142,7 +158,11 @@ calling `Rule.error`"""
                 let
                     error : Error
                     error =
-                        Rule.error "Some other error" dummyRange
+                        Rule.error
+                            { message = "Some other error"
+                            , details = [ "Some other details" ]
+                            }
+                            dummyRange
                 in
                 ErrorMessage.underMismatch
                     error
@@ -185,7 +205,9 @@ wrongLocationTest =
                     error : Error
                     error =
                         Rule.error
-                            "Some error"
+                            { message = "Some error"
+                            , details = [ "Some details" ]
+                            }
                             { start = { row = 3, column = 1 }, end = { row = 3, column = 5 } }
                 in
                 ErrorMessage.wrongLocation
@@ -219,7 +241,9 @@ but I found it at:
                     error : Error
                     error =
                         Rule.error
-                            "Some other error"
+                            { message = "Some other error"
+                            , details = [ "Some other details" ]
+                            }
                             { start = { row = 4, column = 1 }, end = { row = 5, column = 3 } }
                 in
                 ErrorMessage.wrongLocation
@@ -288,7 +312,9 @@ tooManyErrorsTest =
                     extraErrors : List Rule.Error
                     extraErrors =
                         [ Rule.error
-                            "Remove the use of `Debug` before shipping to production"
+                            { message = "Remove the use of `Debug` before shipping to production"
+                            , details = [ "Some details about Debug" ]
+                            }
                             { start = { row = 2, column = 1 }, end = { row = 2, column = 5 } }
                         ]
                 in
@@ -307,10 +333,14 @@ I found 1 error too many:
                     extraErrors : List Rule.Error
                     extraErrors =
                         [ Rule.error
-                            "Remove the use of `Debug` before shipping to production"
+                            { message = "Remove the use of `Debug` before shipping to production"
+                            , details = [ "Some details about Debug" ]
+                            }
                             { start = { row = 2, column = 1 }, end = { row = 2, column = 5 } }
                         , Rule.error
-                            "Remove the use of `Debug` before shipping to production"
+                            { message = "Remove the use of `Debug` before shipping to production"
+                            , details = [ "Some details about Debug" ]
+                            }
                             { start = { row = 3, column = 1 }, end = { row = 3, column = 5 } }
                         ]
                 in
@@ -345,7 +375,9 @@ locationIsAmbiguousInSourceCodeTest =
                     error : Error
                     error =
                         Rule.error
-                            "Some error"
+                            { message = "Some error"
+                            , details = [ "Some details" ]
+                            }
                             { start = { row = 3, column = 1 }, end = { row = 3, column = 5 } }
                 in
                 ErrorMessage.locationIsAmbiguousInSourceCode
@@ -387,7 +419,9 @@ Tip: I found them at:
                     error : Error
                     error =
                         Rule.error
-                            "Some other error"
+                            { message = "Some other error"
+                            , details = [ "Some other details" ]
+                            }
                             { start = { row = 3, column = 1 }, end = { row = 4, column = 3 } }
                 in
                 ErrorMessage.locationIsAmbiguousInSourceCode