Add ConvertToF#LambdaSyntax code fixer

src/fsharp/service/ServiceUntypedParse.fs

@@ -99,6 +99,30 @@ type FSharpParseFileResults(errors: FSharpErrorInfo[], input: ParsedInput option
     member scope.ParseHadErrors = parseHadErrors
 
     member scope.ParseTree = input
+
+    member scope.TryRangeOfParenEnclosingOpEqualsGreaterUsage opGreaterEqualPos =
+        let (|Ident|_|) ofName =
+            function | SynExpr.Ident ident when ident.idText = ofName -> Some ()
+                     | _ -> None
+        let (|InfixAppOfOpEqualsGreater|_|) =
+          function | SynExpr.App(ExprAtomicFlag.NonAtomic, false, SynExpr.App(ExprAtomicFlag.NonAtomic, true, Ident "op_EqualsGreater", actualParamListExpr, _), actualLambdaBodyExpr, _) ->
+                        Some (actualParamListExpr, actualLambdaBodyExpr)
+                   | _ -> None
+
+        match scope.ParseTree with
+        | Some parseTree ->
+            AstTraversal.Traverse(opGreaterEqualPos, parseTree, { new AstTraversal.AstVisitorBase<_>() with
+                member _.VisitExpr(_, _, defaultTraverse, expr) =
+                    match expr with
+                    | SynExpr.Paren((InfixAppOfOpEqualsGreater(lambdaArgs, lambdaBody) as app), _, _, _) ->
+                        Some (app.Range, lambdaArgs.Range, lambdaBody.Range)
+                    | _ -> defaultTraverse expr
+                member _.VisitBinding(defaultTraverse, binding) =
+                    match binding with
+                    | SynBinding.Binding (_, SynBindingKind.NormalBinding, _, _, _, _, _, _, _, (InfixAppOfOpEqualsGreater(lambdaArgs, lambdaBody) as app), _, _) ->
+                        Some(app.Range, lambdaArgs.Range, lambdaBody.Range)
+                    | _ -> defaultTraverse binding })
+        | None -> None
 
     member scope.TryRangeOfExprInYieldOrReturn pos =
         match scope.ParseTree with

src/fsharp/service/ServiceUntypedParse.fsi

@@ -19,6 +19,9 @@ type public FSharpParseFileResults =
     /// The syntax tree resulting from the parse
     member ParseTree : ParsedInput option
 
+    /// Attempts to find the range of an attempted lambda expression or pattern, the argument range, and the expr range when writing a C#-style "lambda" (which is actually an operator application)
+    member TryRangeOfParenEnclosingOpEqualsGreaterUsage: opGreaterEqualPos: pos -> Option<range * range * range>
+
     /// Attempts to find the range of an expression `expr` contained in a `yield expr`  or `return expr` expression (and bang-variants).
     member TryRangeOfExprInYieldOrReturn: pos: pos -> Option<range>
 

tests/FSharp.Compiler.Service.Tests/SurfaceArea.netstandard.fs

@@ -22755,6 +22755,7 @@ FSharp.Compiler.SourceCodeServices.FSharpParseFileResults: FSharp.Compiler.Sourc
 FSharp.Compiler.SourceCodeServices.FSharpParseFileResults: Microsoft.FSharp.Core.FSharpOption`1[FSharp.Compiler.Range+range] TryRangeOfRefCellDereferenceContainingPos(pos)
 FSharp.Compiler.SourceCodeServices.FSharpParseFileResults: Microsoft.FSharp.Core.FSharpOption`1[FSharp.Compiler.Range+range] TryRangeOfRecordExpressionContainingPos(pos)
 FSharp.Compiler.SourceCodeServices.FSharpParseFileResults: Microsoft.FSharp.Core.FSharpOption`1[FSharp.Compiler.Range+range] TryRangeOfExprInYieldOrReturn(pos)
+FSharp.Compiler.SourceCodeServices.FSharpParseFileResults: Microsoft.FSharp.Core.FSharpOption`1[System.Tuple`3[FSharp.Compiler.Range+range,FSharp.Compiler.Range+range,FSharp.Compiler.Range+range]] TryRangeOfParenEnclosingOpEqualsGreaterUsage(pos)
 FSharp.Compiler.SourceCodeServices.FSharpParseFileResults: Microsoft.FSharp.Core.FSharpOption`1[FSharp.Compiler.Range+range] ValidateBreakpointLocation(pos)
 FSharp.Compiler.SourceCodeServices.FSharpParseFileResults: Microsoft.FSharp.Core.FSharpOption`1[FSharp.Compiler.SourceCodeServices.FSharpNoteworthyParamInfoLocations] FindNoteworthyParamInfoLocations(pos)
 FSharp.Compiler.SourceCodeServices.FSharpParseFileResults: Boolean IsPositionContainedInACurriedParameter(pos)

tests/service/ServiceUntypedParseTests.fs

@@ -407,4 +407,58 @@ let f x =
         |> tups
         |> shouldEqual ((3, 11), (3, 12))
     | None ->
-        Assert.Fail("Expected to get a range back, but got none.")
+        Assert.Fail("Expected to get a range back, but got none.")
+
+[<Test>]
+let ``TryRangeOfParenEnclosingOpEqualsGreaterUsage - not correct operator``() =
+    let source = """
+let x = y |> y + 1
+"""
+    let parseFileResults, _ = getParseAndCheckResults source
+    let res = parseFileResults.TryRangeOfParenEnclosingOpEqualsGreaterUsage (mkPos 2 8)
+    Assert.True(res.IsNone, "Expected not to find any ranges.")
+
+[<Test>]
+let ``TryRangeOfParenEnclosingOpEqualsGreaterUsage - error arg pos``() =
+    let source = """
+let x = y => y + 1
+"""
+    let parseFileResults, _ = getParseAndCheckResults source
+    let res = parseFileResults.TryRangeOfParenEnclosingOpEqualsGreaterUsage (mkPos 2 8)
+    match res with
+    | Some (overallRange, argRange, exprRange) ->
+        [overallRange; argRange; exprRange]
+        |> List.map tups
+        |> shouldEqual [((2, 8), (2, 18)); ((2, 8), (2, 9)); ((2, 13), (2, 18))]
+    | None ->
+        Assert.Fail("Expected to get a range back, but got none.")
+
+[<Test>]
+let ``TryRangeOfParenEnclosingOpEqualsGreaterUsage - error expr pos``() =
+    let source = """
+let x = y => y + 1
+"""
+    let parseFileResults, _ = getParseAndCheckResults source
+    let res = parseFileResults.TryRangeOfParenEnclosingOpEqualsGreaterUsage (mkPos 2 13)
+    match res with
+    | Some (overallRange, argRange, exprRange) ->
+        [overallRange; argRange; exprRange]
+        |> List.map tups
+        |> shouldEqual [((2, 8), (2, 18)); ((2, 8), (2, 9)); ((2, 13), (2, 18))]
+    | None ->
+        Assert.Fail("Expected to get a range back, but got none.")
+
+[<Test>]
+let ``TryRangeOfParenEnclosingOpEqualsGreaterUsage - parenthesized lambda``() =
+    let source = """
+[1..10] |> List.map (x => x + 1)
+"""
+    let parseFileResults, _ = getParseAndCheckResults source
+    let res = parseFileResults.TryRangeOfParenEnclosingOpEqualsGreaterUsage (mkPos 2 21)
+    match res with
+    | Some (overallRange, argRange, exprRange) ->
+        [overallRange; argRange; exprRange]
+        |> List.map tups
+        |> shouldEqual [((2, 21), (2, 31)); ((2, 21), (2, 22)); ((2, 26), (2, 31))]
+    | None ->
+        Assert.Fail("Expected to get a range back, but got none.")

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

@@ -0,0 +1,59 @@
+// 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 Microsoft.CodeAnalysis.Text
+open Microsoft.CodeAnalysis.CodeFixes
+
+[<ExportCodeFixProvider(FSharpConstants.FSharpLanguageName, Name = "ConvertCSharpLambdaToFSharpLambda"); Shared>]
+type internal FSharpConvertCSharpLambdaToFSharpLambdaCodeFixProvider
+    [<ImportingConstructor>]
+    (
+        checkerProvider: FSharpCheckerProvider, 
+        projectInfoManager: FSharpProjectOptionsManager
+    ) =
+    inherit CodeFixProvider()
+
+    static let userOpName = "ConvertCSharpLambdaToFSharpLambda"
+    let fixableDiagnosticIds = set ["FS0039"; "FS0043"]
+
+    override _.FixableDiagnosticIds = Seq.toImmutableArray fixableDiagnosticIds
+
+    override _.RegisterCodeFixesAsync context =
+        asyncMaybe {
+            let! sourceText = context.Document.GetTextAsync(context.CancellationToken)
+            let! parsingOptions, _ = projectInfoManager.TryGetOptionsForEditingDocumentOrProject(context.Document, context.CancellationToken, userOpName)
+            let! parseResults = checkerProvider.Checker.ParseFile(context.Document.FilePath, sourceText.ToFSharpSourceText(), parsingOptions, userOpName) |> liftAsync
+
+            let errorRange = RoslynHelpers.TextSpanToFSharpRange(context.Document.FilePath, context.Span, sourceText)
+
+            let! fullParenRange, lambdaArgRange, lambdaBodyRange = parseResults.TryRangeOfParenEnclosingOpEqualsGreaterUsage errorRange.Start
+
+            let! fullParenSpan = RoslynHelpers.TryFSharpRangeToTextSpan(sourceText, fullParenRange)
+            let! lambdaArgSpan = RoslynHelpers.TryFSharpRangeToTextSpan(sourceText, lambdaArgRange)
+            let! lambdaBodySpan = RoslynHelpers.TryFSharpRangeToTextSpan(sourceText, lambdaBodyRange)
+
+            let replacement =
+                let argText = sourceText.GetSubText(lambdaArgSpan).ToString()
+                let bodyText = sourceText.GetSubText(lambdaBodySpan).ToString()
+                TextChange(fullParenSpan, "fun " + argText + " -> " + bodyText)
+
+            let diagnostics =
+                context.Diagnostics
+                |> Seq.filter (fun x -> fixableDiagnosticIds |> Set.contains x.Id)
+                |> Seq.toImmutableArray
+
+            let title = SR.UseFSharpLambda()
+
+            let codeFix =
+                CodeFixHelpers.createTextChangeCodeFix(
+                    title,
+                    context,
+                    (fun () -> asyncMaybe.Return [| replacement |]))
+
+            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\ConvertCSharpLambdaToFSharpLambda.fs" />
     <Compile Include="CodeFix\RemoveReturnOrYield.fs" />
     <Compile Include="CodeFix\ConvertToAnonymousRecord.fs" />
     <Compile Include="CodeFix\UseMutationWhenValueIsMutable.fs" />

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

@@ -261,4 +261,7 @@
   <data name="UseMutationWhenValueIsMutable" xml:space="preserve">
     <value>Use '&lt;-' to mutate value</value>
   </data>
+  <data name="UseFSharpLambda" xml:space="preserve">
+    <value>Use F# lambda syntax</value>
+  </data>
 </root>

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

@@ -217,6 +217,11 @@
         <target state="translated">Formátování</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseFSharpLambda">
+        <source>Use F# lambda syntax</source>
+        <target state="new">Use F# lambda syntax</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseMutationWhenValueIsMutable">
         <source>Use '&lt;-' to mutate value</source>
         <target state="new">Use '&lt;-' to mutate value</target>

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

@@ -217,6 +217,11 @@
         <target state="translated">Formatierung</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseFSharpLambda">
+        <source>Use F# lambda syntax</source>
+        <target state="new">Use F# lambda syntax</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseMutationWhenValueIsMutable">
         <source>Use '&lt;-' to mutate value</source>
         <target state="new">Use '&lt;-' to mutate value</target>

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

@@ -217,6 +217,11 @@
         <target state="translated">Formato</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseFSharpLambda">
+        <source>Use F# lambda syntax</source>
+        <target state="new">Use F# lambda syntax</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseMutationWhenValueIsMutable">
         <source>Use '&lt;-' to mutate value</source>
         <target state="new">Use '&lt;-' to mutate value</target>

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

@@ -217,6 +217,11 @@
         <target state="translated">Mise en forme</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseFSharpLambda">
+        <source>Use F# lambda syntax</source>
+        <target state="new">Use F# lambda syntax</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseMutationWhenValueIsMutable">
         <source>Use '&lt;-' to mutate value</source>
         <target state="new">Use '&lt;-' to mutate value</target>

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

@@ -217,6 +217,11 @@
         <target state="translated">Formattazione</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseFSharpLambda">
+        <source>Use F# lambda syntax</source>
+        <target state="new">Use F# lambda syntax</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseMutationWhenValueIsMutable">
         <source>Use '&lt;-' to mutate value</source>
         <target state="new">Use '&lt;-' to mutate value</target>

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

@@ -217,6 +217,11 @@
         <target state="translated">書式設定</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseFSharpLambda">
+        <source>Use F# lambda syntax</source>
+        <target state="new">Use F# lambda syntax</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseMutationWhenValueIsMutable">
         <source>Use '&lt;-' to mutate value</source>
         <target state="new">Use '&lt;-' to mutate value</target>

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

@@ -217,6 +217,11 @@
         <target state="translated">서식</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseFSharpLambda">
+        <source>Use F# lambda syntax</source>
+        <target state="new">Use F# lambda syntax</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseMutationWhenValueIsMutable">
         <source>Use '&lt;-' to mutate value</source>
         <target state="new">Use '&lt;-' to mutate value</target>

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

@@ -217,6 +217,11 @@
         <target state="translated">Formatowanie</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseFSharpLambda">
+        <source>Use F# lambda syntax</source>
+        <target state="new">Use F# lambda syntax</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseMutationWhenValueIsMutable">
         <source>Use '&lt;-' to mutate value</source>
         <target state="new">Use '&lt;-' to mutate value</target>

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

@@ -217,6 +217,11 @@
         <target state="translated">Formatação</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseFSharpLambda">
+        <source>Use F# lambda syntax</source>
+        <target state="new">Use F# lambda syntax</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseMutationWhenValueIsMutable">
         <source>Use '&lt;-' to mutate value</source>
         <target state="new">Use '&lt;-' to mutate value</target>

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

@@ -217,6 +217,11 @@
         <target state="translated">Форматирование</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseFSharpLambda">
+        <source>Use F# lambda syntax</source>
+        <target state="new">Use F# lambda syntax</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseMutationWhenValueIsMutable">
         <source>Use '&lt;-' to mutate value</source>
         <target state="new">Use '&lt;-' to mutate value</target>

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

@@ -217,6 +217,11 @@
         <target state="translated">Biçimlendirme</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseFSharpLambda">
+        <source>Use F# lambda syntax</source>
+        <target state="new">Use F# lambda syntax</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseMutationWhenValueIsMutable">
         <source>Use '&lt;-' to mutate value</source>
         <target state="new">Use '&lt;-' to mutate value</target>

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

@@ -217,6 +217,11 @@
         <target state="translated">正在格式化</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseFSharpLambda">
+        <source>Use F# lambda syntax</source>
+        <target state="new">Use F# lambda syntax</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseMutationWhenValueIsMutable">
         <source>Use '&lt;-' to mutate value</source>
         <target state="new">Use '&lt;-' to mutate value</target>

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

@@ -217,6 +217,11 @@
         <target state="translated">格式化</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseFSharpLambda">
+        <source>Use F# lambda syntax</source>
+        <target state="new">Use F# lambda syntax</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseMutationWhenValueIsMutable">
         <source>Use '&lt;-' to mutate value</source>
         <target state="new">Use '&lt;-' to mutate value</target>