First Draft for AddExplicitReturnType (dotnet#15562) with exploration…

… test and resource file entry

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

@@ -99,6 +99,7 @@
     <Compile Include="Commands\HelpContextService.fs" />
     <Compile Include="Commands\FsiCommandService.fs" />
     <Compile Include="Commands\XmlDocCommandService.fs" />
+    <Compile Include="Refactor\AddExplicitReturnType.fs" />
     <Compile Include="Refactor\ChangeTypeofWithNameToNameofExpression.fs" />
     <Compile Include="Refactor\AddExplicitTypeToParameter.fs" />
     <Compile Include="Refactor\ChangeDerefToValueRefactoring.fs" />

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

@@ -352,6 +352,9 @@ Use live (unsaved) buffers for analysis</value>
   <data name="ConvertCSharpUsingToFSharpOpen" xml:space="preserve">
     <value>Convert C# 'using' to F# 'open'</value>
   </data>
+  <data name="AddExplicitReturnTypeAnnotation" xml:space="preserve">
+    <value>Add explicit return type annotation</value>
+  </data>
   <data name="RemoveUnnecessaryParentheses" xml:space="preserve">
     <value>Remove unnecessary parentheses</value>
   </data>

vsintegration/src/FSharp.Editor/Refactor/AddExplicitReturnType.fs

@@ -0,0 +1,109 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+namespace Microsoft.VisualStudio.FSharp.Editor
+
+open System
+open System.Composition
+open System.Threading
+open System.Threading.Tasks
+
+open FSharp.Compiler
+open FSharp.Compiler.CodeAnalysis
+open FSharp.Compiler.Symbols
+open FSharp.Compiler.Text
+open FSharp.Compiler.Syntax
+
+open Microsoft.CodeAnalysis.Text
+open Microsoft.CodeAnalysis.CodeRefactorings
+open Microsoft.CodeAnalysis.CodeActions
+open CancellableTasks
+
+[<ExportCodeRefactoringProvider(FSharpConstants.FSharpLanguageName, Name = "AddExplicitReturnType"); Shared>]
+type internal AddExplicitReturnType [<ImportingConstructor>] () =
+    inherit CodeRefactoringProvider()
+
+    static member isValidMethodWithoutTypeAnnotation (funcOrValue: FSharpMemberOrFunctionOrValue) (symbolUse: FSharpSymbolUse) (parseFileResults:FSharpParseFileResults) =
+        let isLambdaIfFunction =
+            funcOrValue.IsFunction
+            && parseFileResults.IsBindingALambdaAtPosition symbolUse.Range.Start
+
+        (not funcOrValue.IsValue || not isLambdaIfFunction)
+        && not (funcOrValue.ReturnParameter.Type.IsUnresolved)
+        && not (parseFileResults.IsTypeAnnotationGivenAtPosition symbolUse.Range.Start)
+
+
+    static member refactor (context:CodeRefactoringContext) (symbolUse:FSharpSymbolUse,memberFunc:FSharpMemberOrFunctionOrValue,symbolSpan) =
+        let typeString = memberFunc.FullType.FormatWithConstraints symbolUse.DisplayContext
+        let title = SR.AddExplicitReturnTypeAnnotation()
+
+        let getChangedText (sourceText: SourceText) =
+            let debugInfo = $"{sourceText} : {typeString} : {symbolSpan}"
+            debugInfo
+            let sub = sourceText.ToString(symbolSpan)
+
+            let newSub =
+                sub.Replace("=", $" :{memberFunc.ReturnParameter.Type.TypeDefinition.DisplayName}=")
+
+            sourceText.Replace(symbolSpan, newSub)
+
+        let codeActionFunc = (fun (cancellationToken: CancellationToken) ->
+            backgroundTask  {
+                let! sourceText = context.Document.GetTextAsync(cancellationToken)
+                let changedText = getChangedText sourceText
+                return context.Document.WithText(changedText)
+            }
+        )
+        let codeAction = 
+                CodeAction.Create(
+                    title,
+                    codeActionFunc,
+                    title
+                )
+
+
+        do context.RegisterRefactoring(codeAction)
+
+    override _.ComputeRefactoringsAsync context =
+        backgroundTask {
+            let document = context.Document
+            let position = context.Span.Start
+            let! sourceText = document.GetTextAsync()
+            let textLine = sourceText.Lines.GetLineFromPosition position
+            let textLinePos = sourceText.Lines.GetLinePosition position
+            let fcsTextLineNumber = Line.fromZ textLinePos.Line
+
+            let! ct = Async.CancellationToken
+
+            let! lexerSymbol =
+                document.TryFindFSharpLexerSymbolAsync(position, SymbolLookupKind.Greedy, false, false, nameof (AddExplicitReturnType))
+
+
+            let! (parseFileResults,checkFileResults) =
+                document.GetFSharpParseAndCheckResultsAsync(nameof (AddExplicitReturnType))
+                |> CancellableTask.start ct
+
+            let res = 
+                lexerSymbol
+                |> Option.bind(fun lexer -> 
+                    checkFileResults.GetSymbolUseAtLocation(
+                    fcsTextLineNumber,
+                    lexer.Ident.idRange.EndColumn,
+                    textLine.ToString(),
+                    lexer.FullIsland
+                ))
+                |> Option.bind(fun symbolUse->
+                        match symbolUse.Symbol with
+                        | :? FSharpMemberOrFunctionOrValue as v 
+                            when AddExplicitReturnType.isValidMethodWithoutTypeAnnotation v symbolUse parseFileResults->
+                                Some (symbolUse,v)
+                        | _ -> None
+                )
+                |> Option.bind(fun (symbolUse,memberFunc)->
+                        match RoslynHelpers.TryFSharpRangeToTextSpan(sourceText, symbolUse.Range) with
+                        | Some span -> Some(symbolUse,memberFunc,span)
+                        | None -> None
+                )
+                |> Option.map(fun (symbolUse,memberFunc,textSpan) -> AddExplicitReturnType.refactor context (symbolUse,memberFunc,textSpan))
+
+            return res
+        }

vsintegration/tests/FSharp.Editor.Tests/FSharp.Editor.Tests.fsproj

@@ -12,6 +12,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+
     <Content Include="xunit.runner.json" CopyToOutputDirectory="PreserveNewest" />
   </ItemGroup>
 
@@ -71,6 +72,7 @@
     <Compile Include="CodeFixes\ConvertCSharpUsingToFSharpOpenTests.fs" />
     <Compile Include="CodeFixes\ReplaceWithSuggestionTests.fs" />
     <Compile Include="CodeFixes\RemoveUnnecessaryParenthesesTests.fs" />
+    <Compile Include="Refactors\AddExplicitReturnType.fs" />
     <Compile Include="Hints\HintTestFramework.fs" />
     <Compile Include="Hints\OptionParserTests.fs" />
     <Compile Include="Hints\InlineParameterNameHintTests.fs" />

vsintegration/tests/FSharp.Editor.Tests/Refactors/AddExplicitReturnType.fs

@@ -0,0 +1,52 @@
+module FSharp.Editor.Tests.Refactors.AddExplicitReturnType
+
+open Microsoft.VisualStudio.FSharp.Editor
+open Xunit
+open System
+open System.Collections.Immutable
+open System.Text.RegularExpressions
+
+open Microsoft.CodeAnalysis
+open Microsoft.CodeAnalysis.CodeFixes
+open Microsoft.CodeAnalysis.Text
+open Microsoft.VisualStudio.FSharp.Editor
+open Microsoft.VisualStudio.FSharp.Editor.CancellableTasks
+
+open FSharp.Compiler.Diagnostics
+open FSharp.Editor.Tests.Helpers
+
+open Microsoft.CodeAnalysis.CodeRefactorings
+open NUnit.Framework
+
+
+[<Fact>]
+let ``Refactor changes something`` () =
+    task {
+        let code =
+            """
+            let sum a b = a + b
+            """
+
+        let! ct = Async.CancellationToken
+
+        let sourceText = SourceText.From code
+        let document = RoslynTestHelpers.GetFsDocument code
+        let spanStart = code.IndexOf "sum"
+        let span = TextSpan(spanStart, 3)
+
+        let mutable refactorContext =
+            CodeRefactoringContext(document, span, Action<CodeActions.CodeAction>(fun a -> ()), ct)
+
+        let refactorProvider = AddExplicitReturnType()
+        let expected = None
+
+        do! refactorProvider.ComputeRefactoringsAsync refactorContext
+        let newText = match refactorContext.TextDocument.TryGetText() with
+            | true,result -> result
+            | false,_ -> sourceText
+
+        let! text = refactorContext.TextDocument.GetTextAsync( ct)
+        Assert.AreNotEqual(sourceText.ToString(),newText.ToString(),"")
+
+        ()
+    }