Add a codefix that suggests replacements for unknown identifiers

src/fsharp/ErrorResolutionHints.fs

@@ -9,18 +9,17 @@ let minStringLengthForThreshold = 3
 
 let thresholdForSuggestions = 0.7
 
-/// Filters predictions based on edit distance to an unknown identifier.
+/// Filters predictions based on edit distance to the given unknown identifier.
 let FilterPredictions (unknownIdent:string) (predictionsF:ErrorLogger.Suggestions) =    
     let unknownIdent = unknownIdent.ToUpperInvariant()
     let useThreshold = unknownIdent.Length >= minStringLengthForThreshold
     predictionsF()
     |> Seq.choose (fun p -> 
         let similarity = Internal.Utilities.EditDistance.JaroWinklerDistance unknownIdent (p.ToUpperInvariant())
-        if not useThreshold || similarity >= thresholdForSuggestions then
+        if not useThreshold || similarity >= thresholdForSuggestions || p.Contains unknownIdent then
             Some(similarity,p)
         else
-            None
-        )
+            None)
     |> Seq.sortByDescending fst
     |> Seq.mapi (fun i x -> i,x) 
     |> Seq.takeWhile (fun (i,_) -> i < maxSuggestions) 
@@ -31,19 +30,17 @@ let FormatPredictions errorStyle normalizeF (predictions: (float * string) list)
     match predictions with
     | [] -> System.String.Empty
     | _ ->
+        " " + FSComp.SR.undefinedNameSuggestionsIntro() + 
         match errorStyle with
         | ErrorLogger.ErrorStyle.VSErrors ->
             let predictionText =
                 predictions 
                 |> List.map (snd >> normalizeF)
                 |> String.concat ", "
 
-            " " + FSComp.SR.undefinedNameRecordLabelDetails() + " " + predictionText
+            " " + predictionText
         | _ ->
-            let predictionText =
-                predictions 
-                |> List.map (snd >> normalizeF)
-                |> Seq.map (sprintf "%s   %s" System.Environment.NewLine) 
-                |> String.concat ""
-
-            System.Environment.NewLine + FSComp.SR.undefinedNameRecordLabelDetails() + predictionText
+            predictions
+            |> List.map (snd >> normalizeF) 
+            |> List.map (sprintf "%s   %s" System.Environment.NewLine)
+            |> String.concat ""

src/fsharp/FSComp.txt

@@ -12,9 +12,10 @@ undefinedNameType,"The type '%s' is not defined."
 undefinedNameTypeIn,"The type '%s' is not defined in '%s'."
 undefinedNameRecordLabelOrNamespace,"The record label or namespace '%s' is not defined."
 undefinedNameRecordLabel,"The record label '%s' is not defined."
-undefinedNameRecordLabelDetails,"Maybe you want one of the following:"
+undefinedNameSuggestionsIntro,"Maybe you want one of the following:"
 undefinedNameTypeParameter,"The type parameter '%s is not defined."
 undefinedNamePatternDiscriminator,"The pattern discriminator '%s' is not defined."
+replaceWithSuggestion,"Replace with '%s'"
 missingElseBranch,"The 'if' expression is missing an 'else' branch. The 'then' branch has type '%s'. Because 'if' is an expression, and not a statement, add an 'else' branch which returns a value of the same type."
 elseBranchHasWrongType,"All branches of an 'if' expression must return the same type. This expression was expected to have type '%s' but here has type '%s'."
 commaInsteadOfSemicolonInRecord,"A ';' is used to separate field values in records. Consider replacing ',' with ';'."

tests/fsharp/core/load-script/out.stderr.bsl

@@ -1,6 +1,4 @@
 
-usesfsi.fsx(2,1): error FS0039: The namespace or module 'fsi' is not defined.
-
-Maybe you want one of the following:
+usesfsi.fsx(2,1): error FS0039: The namespace or module 'fsi' is not defined. Maybe you want one of the following:
 
    FSharp

tests/fsharp/typecheck/sigs/neg06.bsl

@@ -1,5 +1,5 @@
 
-neg06.fs(3,40,3,45): typecheck error FS0039: The field, constructor or member 'Ascii' is not defined. Maybe you want one of the following: ASCII
+neg06.fs(3,40,3,45): typecheck error FS0039: The field, constructor or member 'Ascii' is not defined. Maybe you want one of the following: ASCII, get_ASCII
 
 neg06.fs(12,6,12,31): typecheck error FS0942: Struct types are always sealed
 

vsintegration/src/FSharp.Editor/CodeFix/ReplaceWithSuggestion.fs

@@ -0,0 +1,55 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+namespace rec Microsoft.VisualStudio.FSharp.Editor
+
+open System
+open System.Composition
+open System.Collections.Immutable
+open System.Threading
+open System.Threading.Tasks
+
+open Microsoft.CodeAnalysis
+open Microsoft.CodeAnalysis.Text
+open Microsoft.CodeAnalysis.CodeFixes
+open Microsoft.CodeAnalysis.CodeActions
+
+[<ExportCodeFixProvider(FSharpCommonConstants.FSharpLanguageName, Name = "ReplaceWithSuggestion"); Shared>]
+type internal FSharpReplaceWithSuggestionCodeFixProvider() =
+    inherit CodeFixProvider()
+    let fixableDiagnosticIds = ["FS0039"; "FS1129"; "FS0495"] |> Set.ofList
+    let maybeString = FSComp.SR.undefinedNameSuggestionsIntro()
+
+    let createCodeFix (title: string, context: CodeFixContext, textChange: TextChange) =
+        CodeAction.Create(
+            title,
+            (fun (cancellationToken: CancellationToken) ->
+                async {
+                    let! sourceText = context.Document.GetTextAsync()
+                    return context.Document.WithText(sourceText.WithChanges(textChange))
+                } |> CommonRoslynHelpers.StartAsyncAsTask(cancellationToken)),
+            title)
+
+    override __.FixableDiagnosticIds = fixableDiagnosticIds.ToImmutableArray()
+
+    override __.RegisterCodeFixesAsync context : Task =
+        async { 
+            context.Diagnostics 
+            |> Seq.filter (fun x -> fixableDiagnosticIds |> Set.contains x.Id)
+            |> Seq.iter (fun diagnostic ->
+                let message = diagnostic.GetMessage()
+                let splitted = message.Split([|maybeString|], StringSplitOptions.None)
+                if splitted.Length > 1 then
+                    let suggestions = 
+                        splitted.[1].Split([|' '; '\r'; '\n'|], StringSplitOptions.RemoveEmptyEntries) 
+                        |> Array.map (fun s -> s.Trim())
+
+                    let diagnostics = [| diagnostic |].ToImmutableArray()
+
+                    for suggestion in suggestions do
+                        let codefix = 
+                            createCodeFix(
+                                FSComp.SR.replaceWithSuggestion suggestion, 
+                                context,
+                                TextChange(context.Span, suggestion))
+                        context.RegisterCodeFix(codefix, diagnostics))
+        } |> CommonRoslynHelpers.StartAsyncUnitAsTask(context.CancellationToken)

vsintegration/src/FSharp.Editor/FSharp.Editor.fsproj

@@ -62,6 +62,7 @@
     <Compile Include="Commands\FsiCommandService.fs" />
     <Compile Include="CodeFix\AddNewKeywordToDisposableConstructorInvocation.fs" />
     <Compile Include="CodeFix\AddOpenCodeFixProvider.fs" />
+    <Compile Include="CodeFix\ReplaceWithSuggestion.fs" />
     <Compile Include="CodeFix\PrefixUnusedValueWithUnderscore.fs" />
   </ItemGroup>
   <ItemGroup>

vsintegration/tests/unittests/DocumentDiagnosticAnalyzerTests.fs

@@ -231,7 +231,7 @@ let x: float = 1.2(*start*).(*end*)3
 let gDateTime (arr: (*start*)DateTime(*end*)[]) =
     arr.[0]
             """,
-            expectedMessage = "The type 'DateTime' is not defined.\r\nMaybe you want one of the following:\r\n   nativeint\r\n   DelegateEvent")
+            expectedMessage = "The type 'DateTime' is not defined. Maybe you want one of the following:\r\n   nativeint\r\n   DelegateEvent")
 
     [<Test>]
     member public this.Error_CyclicalDeclarationDoesNotCrash() =