Add UseMutationWhenValueIsMutable code fix

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

@@ -0,0 +1,73 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+namespace Microsoft.VisualStudio.FSharp.Editor
+
+open System.Composition
+open System.Threading
+open System.Threading.Tasks
+
+open Microsoft.CodeAnalysis.Text
+open Microsoft.CodeAnalysis.CodeFixes
+
+open FSharp.Compiler.SourceCodeServices
+open FSharp.Compiler.Range
+
+[<ExportCodeFixProvider(FSharpConstants.FSharpLanguageName, Name = "UseMutationWhenValueIsMutable"); Shared>]
+type internal FSharpUseMutationWhenValueIsMutableFixProvider
+    [<ImportingConstructor>]
+    (
+        checkerProvider: FSharpCheckerProvider, 
+        projectInfoManager: FSharpProjectOptionsManager
+    ) =
+    inherit CodeFixProvider()
+
+    static let userOpName = "UseMutationWhenValueIsMutable"
+
+    let fixableDiagnosticIds = set ["FS0020"]
+
+    override _.FixableDiagnosticIds = Seq.toImmutableArray fixableDiagnosticIds
+
+    override _.RegisterCodeFixesAsync context : Task =
+        asyncMaybe {
+            let diagnostics =
+                context.Diagnostics
+                |> Seq.filter (fun x -> fixableDiagnosticIds |> Set.contains x.Id)
+                |> Seq.toImmutableArray
+
+            let document = context.Document
+            do! Option.guard (not(isSignatureFile document.FilePath))
+            let position = context.Span.Start
+            let checker = checkerProvider.Checker
+            let! parsingOptions, projectOptions = projectInfoManager.TryGetOptionsForEditingDocumentOrProject(document, CancellationToken.None, userOpName)
+            let! sourceText = document.GetTextAsync () |> liftTaskAsync
+            let defines = CompilerEnvironment.GetCompilationDefinesForEditing parsingOptions
+            let textLine = sourceText.Lines.GetLineFromPosition position
+            let textLinePos = sourceText.Lines.GetLinePosition position
+            let fcsTextLineNumber = Line.fromZ textLinePos.Line
+            let! _, _, checkFileResults = checker.ParseAndCheckDocument (document, projectOptions, sourceText=sourceText, userOpName=userOpName)
+            let! lexerSymbol = Tokenizer.getSymbolAtPosition (document.Id, sourceText, position, document.FilePath, defines, SymbolLookupKind.Greedy, false, false)
+            let! symbolUse = checkFileResults.GetSymbolUseAtLocation(fcsTextLineNumber, lexerSymbol.Ident.idRange.EndColumn, textLine.ToString(), lexerSymbol.FullIsland)
+
+            match symbolUse.Symbol with
+            | :? FSharpMemberOrFunctionOrValue as mfv when mfv.IsValue && mfv.IsMutable ->
+                let title = SR.UseMutationWhenValueIsMutable()
+                let! symbolSpan = RoslynHelpers.TryFSharpRangeToTextSpan(sourceText, symbolUse.RangeAlternate)
+                let mutable pos = symbolSpan.End
+                let mutable ch = sourceText.GetSubText(pos).ToString()
+
+                // We're looking for the possibly erroneous '='
+                while pos <= context.Span.Length && ch <> "=" do
+                    pos <- pos + 1
+                    ch <- sourceText.GetSubText(pos).ToString()
+
+                let codeFix =
+                    CodeFixHelpers.createTextChangeCodeFix(
+                        title,
+                        context,
+                        (fun () -> asyncMaybe.Return [| TextChange(TextSpan(pos + 1, 1), "<-") |]))
+
+                context.RegisterCodeFix(codeFix, diagnostics)
+            | _ -> ()
+        }
+        |> Async.Ignore
+        |> RoslynHelpers.StartAsyncUnitAsTask(context.CancellationToken)  

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

@@ -89,6 +89,7 @@
     <Compile Include="Commands\FsiCommandService.fs" />
     <Compile Include="Commands\XmlDocCommandService.fs" />
     <Compile Include="CodeFix\CodeFixHelpers.fs" />
+    <Compile Include="CodeFix\UseMutationWhenValueIsMutable.fs" />
     <Compile Include="CodeFix\MakeDeclarationMutable.fs" />
     <Compile Include="CodeFix\ChangeToUpcast.fs" />
     <Compile Include="CodeFix\AddMissingEqualsToTypeDefinition.fs" />

vsintegration/src/FSharp.Editor/FSharp.Editor.resx

@@ -243,4 +243,7 @@
   <data name="ChangePrefixNegationToInfixSubtraction" xml:space="preserve">
     <value>Use subtraction instead of negation</value>
   </data>
+  <data name="UseMutationWhenValueIsMutable" xml:space="preserve">
+    <value>Use '&lt;-' to mutate value</value>
+  </data>
 </root>

vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.cs.xlf

@@ -192,6 +192,11 @@
         <target state="translated">Formátování</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseMutationWhenValueIsMutable">
+        <source>Use '&lt;-' to mutate value</source>
+        <target state="new">Use '&lt;-' to mutate value</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseUpcastKeyword">
         <source>Use 'upcast'</source>
         <target state="new">Use 'upcast'</target>

vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.de.xlf

@@ -192,6 +192,11 @@
         <target state="translated">Formatierung</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseMutationWhenValueIsMutable">
+        <source>Use '&lt;-' to mutate value</source>
+        <target state="new">Use '&lt;-' to mutate value</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseUpcastKeyword">
         <source>Use 'upcast'</source>
         <target state="new">Use 'upcast'</target>

vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.es.xlf

@@ -192,6 +192,11 @@
         <target state="translated">Formato</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseMutationWhenValueIsMutable">
+        <source>Use '&lt;-' to mutate value</source>
+        <target state="new">Use '&lt;-' to mutate value</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseUpcastKeyword">
         <source>Use 'upcast'</source>
         <target state="new">Use 'upcast'</target>

vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.fr.xlf

@@ -192,6 +192,11 @@
         <target state="translated">Mise en forme</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseMutationWhenValueIsMutable">
+        <source>Use '&lt;-' to mutate value</source>
+        <target state="new">Use '&lt;-' to mutate value</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseUpcastKeyword">
         <source>Use 'upcast'</source>
         <target state="new">Use 'upcast'</target>

vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.it.xlf

@@ -192,6 +192,11 @@
         <target state="translated">Formattazione</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseMutationWhenValueIsMutable">
+        <source>Use '&lt;-' to mutate value</source>
+        <target state="new">Use '&lt;-' to mutate value</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseUpcastKeyword">
         <source>Use 'upcast'</source>
         <target state="new">Use 'upcast'</target>

vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.ja.xlf

@@ -192,6 +192,11 @@
         <target state="translated">書式設定</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseMutationWhenValueIsMutable">
+        <source>Use '&lt;-' to mutate value</source>
+        <target state="new">Use '&lt;-' to mutate value</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseUpcastKeyword">
         <source>Use 'upcast'</source>
         <target state="new">Use 'upcast'</target>

vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.ko.xlf

@@ -192,6 +192,11 @@
         <target state="translated">서식</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseMutationWhenValueIsMutable">
+        <source>Use '&lt;-' to mutate value</source>
+        <target state="new">Use '&lt;-' to mutate value</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseUpcastKeyword">
         <source>Use 'upcast'</source>
         <target state="new">Use 'upcast'</target>

vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.pl.xlf

@@ -192,6 +192,11 @@
         <target state="translated">Formatowanie</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseMutationWhenValueIsMutable">
+        <source>Use '&lt;-' to mutate value</source>
+        <target state="new">Use '&lt;-' to mutate value</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseUpcastKeyword">
         <source>Use 'upcast'</source>
         <target state="new">Use 'upcast'</target>

vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.pt-BR.xlf

@@ -192,6 +192,11 @@
         <target state="translated">Formatação</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseMutationWhenValueIsMutable">
+        <source>Use '&lt;-' to mutate value</source>
+        <target state="new">Use '&lt;-' to mutate value</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseUpcastKeyword">
         <source>Use 'upcast'</source>
         <target state="new">Use 'upcast'</target>

vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.ru.xlf

@@ -192,6 +192,11 @@
         <target state="translated">Форматирование</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseMutationWhenValueIsMutable">
+        <source>Use '&lt;-' to mutate value</source>
+        <target state="new">Use '&lt;-' to mutate value</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseUpcastKeyword">
         <source>Use 'upcast'</source>
         <target state="new">Use 'upcast'</target>

vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.tr.xlf

@@ -192,6 +192,11 @@
         <target state="translated">Biçimlendirme</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseMutationWhenValueIsMutable">
+        <source>Use '&lt;-' to mutate value</source>
+        <target state="new">Use '&lt;-' to mutate value</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseUpcastKeyword">
         <source>Use 'upcast'</source>
         <target state="new">Use 'upcast'</target>

vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.zh-Hans.xlf

@@ -192,6 +192,11 @@
         <target state="translated">正在格式化</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseMutationWhenValueIsMutable">
+        <source>Use '&lt;-' to mutate value</source>
+        <target state="new">Use '&lt;-' to mutate value</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseUpcastKeyword">
         <source>Use 'upcast'</source>
         <target state="new">Use 'upcast'</target>

vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.zh-Hant.xlf

@@ -192,6 +192,11 @@
         <target state="translated">格式化</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseMutationWhenValueIsMutable">
+        <source>Use '&lt;-' to mutate value</source>
+        <target state="new">Use '&lt;-' to mutate value</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseUpcastKeyword">
         <source>Use 'upcast'</source>
         <target state="new">Use 'upcast'</target>