Add a codefix that suggests replacements for unknown identifiers

src/fsharp/ErrorResolutionHints.fs

@@ -9,7 +9,7 @@ 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
@@ -38,12 +38,12 @@ let FormatPredictions errorStyle normalizeF (predictions: (float * string) list)
                 |> List.map (snd >> normalizeF)
                 |> String.concat ", "
 
-            " " + FSComp.SR.undefinedNameRecordLabelDetails() + " " + predictionText
+            " " + FSComp.SR.undefinedNameSuggestionsIntro() + " " + 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
+            System.Environment.NewLine + FSComp.SR.undefinedNameSuggestionsIntro() + predictionText

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 ';'."

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"]
+    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() |> Async.AwaitTask
+                    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 |> List.contains x.Id)
+            |> Seq.iter (fun x ->
+                let message = x.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 = [| x |].ToImmutableArray()
+
+                    for suggestion in suggestions do
+                        let codefix = 
+                            createCodeFix(
+                                FSComp.SR.replaceWithSuggestion suggestion, 
+                                context, 
+                                TextChange(TextSpan(context.Span.Start, context.Span.End), 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>