Return type hints (#14998)

src/Compiler/Service/FSharpParseFileResults.fs

@@ -398,6 +398,35 @@ type FSharpParseFileResults(diagnostics: FSharpDiagnostic[], input: ParsedInput,
 
         SyntaxTraversal.Traverse(expressionPos, input, visitor)
 
+    member _.TryRangeOfReturnTypeHint(symbolUseStart: pos, ?skipLambdas) =
+        let skipLambdas = defaultArg skipLambdas true
+
+        SyntaxTraversal.Traverse(
+            symbolUseStart,
+            input,
+            { new SyntaxVisitorBase<_>() with
+                member _.VisitExpr(_path, _traverseSynExpr, defaultTraverse, expr) = defaultTraverse expr
+
+                override _.VisitBinding(_path, defaultTraverse, binding) =
+                    match binding with
+                    | SynBinding(expr = SynExpr.Lambda _) when skipLambdas -> defaultTraverse binding
+
+                    // Skip manually type-annotated bindings
+                    | SynBinding(returnInfo = Some (SynBindingReturnInfo(typeName = SynType.LongIdent _))) -> defaultTraverse binding
+
+                    // Let binding
+                    | SynBinding (trivia = { EqualsRange = Some equalsRange }; range = range) when range.Start = symbolUseStart ->
+                        Some equalsRange.StartRange
+
+                    // Member binding
+                    | SynBinding (headPat = SynPat.LongIdent(longDotId = SynLongIdent(id = _ :: ident :: _))
+                                  trivia = { EqualsRange = Some equalsRange }) when ident.idRange.Start = symbolUseStart ->
+                        Some equalsRange.StartRange
+
+                    | _ -> defaultTraverse binding
+            }
+        )
+
     member _.FindParameterLocations pos = ParameterLocations.Find(pos, input)
 
     member _.IsPositionContainedInACurriedParameter pos =

src/Compiler/Service/FSharpParseFileResults.fsi

@@ -52,6 +52,10 @@ type public FSharpParseFileResults =
     /// Gets the range of an expression being dereferenced. For `!expr`, gives the range of `expr`
     member TryRangeOfExpressionBeingDereferencedContainingPos: expressionPos: pos -> range option
 
+    /// Gets the range of where a return type hint could be placed for a function binding. This will be right in front of the equals sign.
+    /// Returns None if type annotation is present.
+    member TryRangeOfReturnTypeHint: symbolUseStart: pos * ?skipLambdas: bool -> range option
+
     /// Notable parse info for ParameterInfo at a given location
     member FindParameterLocations: pos: pos -> ParameterLocations option
 

src/Compiler/Symbols/Symbols.fs

@@ -2331,24 +2331,20 @@ type FSharpMemberOrFunctionOrValue(cenv, d:FSharpMemberOrValData, item) =
             |> LayoutRender.toArray
 
     member x.GetReturnTypeLayout (displayContext: FSharpDisplayContext) =
-        match x.IsMember, d with
-        | true, _ ->
-            None
-        | false, _ ->
-            checkIsResolved()
-            match d with 
-            | E _
-            | P _
-            | C _ -> None
-            | M m ->
-                let retTy = m.GetFSharpReturnType(cenv.amap, range0, m.FormalMethodInst)
-                NicePrint.layoutType (displayContext.Contents cenv.g) retTy
-                |> LayoutRender.toArray
-                |> Some
-            | V v ->
-                NicePrint.layoutOfValReturnType (displayContext.Contents cenv.g) v
-                |> LayoutRender.toArray
-                |> Some
+        checkIsResolved()
+        match d with 
+        | E _
+        | P _
+        | C _ -> None
+        | M m ->
+            let retTy = m.GetFSharpReturnType(cenv.amap, range0, m.FormalMethodInst)
+            NicePrint.layoutType (displayContext.Contents cenv.g) retTy
+            |> LayoutRender.toArray
+            |> Some
+        | V v ->
+            NicePrint.layoutOfValReturnType (displayContext.Contents cenv.g) v
+            |> LayoutRender.toArray
+            |> Some
     
     member x.GetWitnessPassingInfo() = 
         let witnessInfos = 

tests/FSharp.Compiler.Service.Tests/FSharp.Compiler.Service.SurfaceArea.netstandard20.debug.bsl

@@ -2091,6 +2091,7 @@ FSharp.Compiler.CodeAnalysis.FSharpParseFileResults: Microsoft.FSharp.Core.FShar
 FSharp.Compiler.CodeAnalysis.FSharpParseFileResults: Microsoft.FSharp.Core.FSharpOption`1[FSharp.Compiler.Text.Range] TryRangeOfNameOfNearestOuterBindingContainingPos(FSharp.Compiler.Text.Position)
 FSharp.Compiler.CodeAnalysis.FSharpParseFileResults: Microsoft.FSharp.Core.FSharpOption`1[FSharp.Compiler.Text.Range] TryRangeOfRecordExpressionContainingPos(FSharp.Compiler.Text.Position)
 FSharp.Compiler.CodeAnalysis.FSharpParseFileResults: Microsoft.FSharp.Core.FSharpOption`1[FSharp.Compiler.Text.Range] TryRangeOfRefCellDereferenceContainingPos(FSharp.Compiler.Text.Position)
+FSharp.Compiler.CodeAnalysis.FSharpParseFileResults: Microsoft.FSharp.Core.FSharpOption`1[FSharp.Compiler.Text.Range] TryRangeOfReturnTypeHint(FSharp.Compiler.Text.Position, Microsoft.FSharp.Core.FSharpOption`1[System.Boolean])
 FSharp.Compiler.CodeAnalysis.FSharpParseFileResults: Microsoft.FSharp.Core.FSharpOption`1[FSharp.Compiler.Text.Range] TryRangeOfStringInterpolationContainingPos(FSharp.Compiler.Text.Position)
 FSharp.Compiler.CodeAnalysis.FSharpParseFileResults: Microsoft.FSharp.Core.FSharpOption`1[FSharp.Compiler.Text.Range] ValidateBreakpointLocation(FSharp.Compiler.Text.Position)
 FSharp.Compiler.CodeAnalysis.FSharpParseFileResults: Microsoft.FSharp.Core.FSharpOption`1[Microsoft.FSharp.Collections.FSharpList`1[FSharp.Compiler.Text.Range]] GetAllArgumentsForFunctionApplicationAtPosition(FSharp.Compiler.Text.Position)

tests/FSharp.Compiler.Service.Tests/FSharp.Compiler.Service.SurfaceArea.netstandard20.release.bsl

@@ -2091,6 +2091,7 @@ FSharp.Compiler.CodeAnalysis.FSharpParseFileResults: Microsoft.FSharp.Core.FShar
 FSharp.Compiler.CodeAnalysis.FSharpParseFileResults: Microsoft.FSharp.Core.FSharpOption`1[FSharp.Compiler.Text.Range] TryRangeOfNameOfNearestOuterBindingContainingPos(FSharp.Compiler.Text.Position)
 FSharp.Compiler.CodeAnalysis.FSharpParseFileResults: Microsoft.FSharp.Core.FSharpOption`1[FSharp.Compiler.Text.Range] TryRangeOfRecordExpressionContainingPos(FSharp.Compiler.Text.Position)
 FSharp.Compiler.CodeAnalysis.FSharpParseFileResults: Microsoft.FSharp.Core.FSharpOption`1[FSharp.Compiler.Text.Range] TryRangeOfRefCellDereferenceContainingPos(FSharp.Compiler.Text.Position)
+FSharp.Compiler.CodeAnalysis.FSharpParseFileResults: Microsoft.FSharp.Core.FSharpOption`1[FSharp.Compiler.Text.Range] TryRangeOfReturnTypeHint(FSharp.Compiler.Text.Position, Microsoft.FSharp.Core.FSharpOption`1[System.Boolean])
 FSharp.Compiler.CodeAnalysis.FSharpParseFileResults: Microsoft.FSharp.Core.FSharpOption`1[FSharp.Compiler.Text.Range] TryRangeOfStringInterpolationContainingPos(FSharp.Compiler.Text.Position)
 FSharp.Compiler.CodeAnalysis.FSharpParseFileResults: Microsoft.FSharp.Core.FSharpOption`1[FSharp.Compiler.Text.Range] ValidateBreakpointLocation(FSharp.Compiler.Text.Position)
 FSharp.Compiler.CodeAnalysis.FSharpParseFileResults: Microsoft.FSharp.Core.FSharpOption`1[Microsoft.FSharp.Collections.FSharpList`1[FSharp.Compiler.Text.Range]] GetAllArgumentsForFunctionApplicationAtPosition(FSharp.Compiler.Text.Position)

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

@@ -137,6 +137,7 @@
     <Compile Include="AutomaticCompletion\BraceCompletionSessionProvider.fs" />
     <Compile Include="Hints\Hints.fs" />
     <Compile Include="Hints\InlineTypeHints.fs" />
+    <Compile Include="hints\InlineReturnTypeHints.fs" />
     <Compile Include="Hints\InlineParameterNameHints.fs" />
     <Compile Include="Hints\HintService.fs" />
     <Compile Include="Hints\NativeToRoslynHintConverter.fs" />

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

@@ -224,6 +224,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</value>

vsintegration/src/FSharp.Editor/Hints/HintService.fs

@@ -17,6 +17,9 @@ module HintService =
         Seq.filter (InlineTypeHints.isValidForHint parseResults symbol)
         >> Seq.collect (InlineTypeHints.getHints symbol)
 
+    let inline private getReturnTypeHints parseResults symbol =
+        Seq.collect (InlineReturnTypeHints(parseResults, symbol).getHints)
+
     let inline private getHintsForMemberOrFunctionOrValue (sourceText: SourceText) parseResults symbol : NativeHintResolver =
         Seq.filter (InlineParameterNameHints.isMemberOrFunctionOrValueValidForHint symbol)
         >> Seq.collect (InlineParameterNameHints.getHintsForMemberOrFunctionOrValue sourceText parseResults symbol)
@@ -35,6 +38,10 @@ module HintService =
                     match symbol with
                     | :? FSharpMemberOrFunctionOrValue as symbol -> getTypeHints parseResults symbol |> Some
                     | _ -> None
+                | HintKind.ReturnTypeHint ->
+                    match symbol with
+                    | :? FSharpMemberOrFunctionOrValue as symbol -> getReturnTypeHints parseResults symbol |> Some
+                    | _ -> None
                 | HintKind.ParameterNameHint ->
                     match symbol with
                     | :? FSharpMemberOrFunctionOrValue as symbol ->
@@ -45,7 +52,7 @@ module HintService =
                 :: resolvers
                 |> resolve hintKinds
 
-         in resolve hintKinds []
+        resolve hintKinds []
 
     let private getHintsForSymbol (sourceText: SourceText) parseResults hintKinds (symbol: FSharpSymbol, symbolUses: FSharpSymbolUse seq) =
         symbol

vsintegration/src/FSharp.Editor/Hints/Hints.fs

@@ -9,6 +9,7 @@ module Hints =
     type HintKind =
         | TypeHint
         | ParameterNameHint
+        | ReturnTypeHint
 
     // Relatively convenient for testing
     type NativeHint =
@@ -22,3 +23,4 @@ module Hints =
         match kind with
         | TypeHint -> "type"
         | ParameterNameHint -> "parameterName"
+        | ReturnTypeHint -> "returnType"

vsintegration/src/FSharp.Editor/Hints/InlineReturnTypeHints.fs

+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+namespace Microsoft.VisualStudio.FSharp.Editor.Hints
+
+open Microsoft.VisualStudio.FSharp.Editor
+open FSharp.Compiler.CodeAnalysis
+open FSharp.Compiler.Symbols
+open FSharp.Compiler.Text
+open Hints
+
+type InlineReturnTypeHints(parseFileResults: FSharpParseFileResults, symbol: FSharpMemberOrFunctionOrValue) =
+
+    let getHintParts (symbolUse: FSharpSymbolUse) =
+        symbol.GetReturnTypeLayout symbolUse.DisplayContext
+        |> Option.map (fun typeInfo ->
+            [
+                TaggedText(TextTag.Text, ": ")
+                yield! typeInfo |> Array.toList
+                TaggedText(TextTag.Space, " ")
+            ])
+
+    let getHint symbolUse range =
+        getHintParts symbolUse
+        |> Option.map (fun parts ->
+            {
+                Kind = HintKind.ReturnTypeHint
+                Range = range
+                Parts = parts
+            })
+
+    member _.getHints(symbolUse: FSharpSymbolUse) =
+        [
+            if symbol.IsFunction then
+                yield!
+                    parseFileResults.TryRangeOfReturnTypeHint symbolUse.Range.Start
+                    |> Option.bind (getHint symbolUse)
+                    |> Option.toList
+        ]

vsintegration/src/FSharp.Editor/Hints/OptionParser.fs

@@ -15,4 +15,7 @@ module OptionParser =
 
                 if options.IsInlineParameterNameHintsEnabled then
                     HintKind.ParameterNameHint
+
+                if options.IsInlineReturnTypeHintsEnabled then
+                    HintKind.ReturnTypeHint
             ]

vsintegration/src/FSharp.Editor/LanguageService/LanguageService.fs

@@ -137,6 +137,9 @@ type internal FSharpWorkspaceServiceFactory [<System.Composition.ImportingConstr
 
                             let isInlineTypeHintsEnabled = editorOptions.Advanced.IsInlineTypeHintsEnabled
 
+                            let isInlineReturnTypeHintsEnabled =
+                                editorOptions.Advanced.IsInlineReturnTypeHintsEnabled
+
                             let enablePartialTypeChecking =
                                 editorOptions.LanguageServicePerformance.EnablePartialTypeChecking
 
@@ -169,6 +172,7 @@ type internal FSharpWorkspaceServiceFactory [<System.Composition.ImportingConstr
                                     nameof enableFastFindReferences, enableFastFindReferences
                                     nameof isInlineParameterNameHintsEnabled, isInlineParameterNameHintsEnabled
                                     nameof isInlineTypeHintsEnabled, isInlineTypeHintsEnabled
+                                    nameof isInlineReturnTypeHintsEnabled, isInlineReturnTypeHintsEnabled
                                     nameof enablePartialTypeChecking, enablePartialTypeChecking
                                 ]
 

vsintegration/src/FSharp.Editor/Options/EditorOptions.fs

@@ -105,6 +105,7 @@ type AdvancedOptions =
         IsOutliningEnabled: bool
         IsInlineTypeHintsEnabled: bool
         IsInlineParameterNameHintsEnabled: bool
+        IsInlineReturnTypeHintsEnabled: bool
         IsLiveBuffersEnabled: bool
     }
 
@@ -114,6 +115,7 @@ type AdvancedOptions =
             IsOutliningEnabled = true
             IsInlineTypeHintsEnabled = false
             IsInlineParameterNameHintsEnabled = false
+            IsInlineReturnTypeHintsEnabled = false
             IsLiveBuffersEnabled = FSharpExperimentalFeaturesEnabledAutomatically
         }
 

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

@@ -34,6 +34,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</source>
@@ -43,6 +44,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</target>

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

@@ -34,6 +34,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</source>
@@ -43,6 +44,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</target>

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

@@ -34,6 +34,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</source>
@@ -43,6 +44,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</target>

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

@@ -34,6 +34,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</source>
@@ -43,6 +44,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</target>

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

@@ -34,6 +34,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</source>
@@ -43,6 +44,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</target>

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

@@ -34,6 +34,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</source>
@@ -43,6 +44,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</target>

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

@@ -34,6 +34,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</source>
@@ -43,6 +44,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</target>

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

@@ -34,6 +34,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</source>
@@ -43,6 +44,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</target>

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

@@ -34,6 +34,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</source>
@@ -43,6 +44,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</target>

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

@@ -34,6 +34,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</source>
@@ -43,6 +44,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</target>

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

@@ -34,6 +34,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</source>
@@ -43,6 +44,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</target>

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

@@ -34,6 +34,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</source>
@@ -43,6 +44,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</target>

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

@@ -34,6 +34,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</source>
@@ -43,6 +44,7 @@ Outlining;
 Show outlining and collapsible nodes for F# code;
 Inline hints;
 Display inline type hints (preview);
+Display return type hints (preview);
 Display inline parameter name hints (preview);Beer;
 Live Buffers;
 Use live (unsaved) buffers for checking</target>

vsintegration/src/FSharp.UIResources/AdvancedOptionsControl.xaml

@@ -28,6 +28,8 @@
                     <StackPanel>
                         <CheckBox x:Name="toggleInlineTypeHints" IsChecked="{Binding IsInlineTypeHintsEnabled}"
                                   Content="{x:Static local:Strings.Show_Inline_Type_Hints}"/>
+                        <CheckBox x:Name="toggleReturnTypeHints" IsChecked="{Binding IsInlineReturnTypeHintsEnabled}"
+                                  Content="{x:Static local:Strings.Show_Return_Type_Hints}"/>
                         <CheckBox x:Name="toggleParameterNameHints" IsChecked="{Binding IsInlineParameterNameHintsEnabled}"
                                   Content="{x:Static local:Strings.Show_Inline_Parameter_Name_Hints}"/>
                     </StackPanel>

vsintegration/src/FSharp.UIResources/Strings.Designer.cs

@@ -402,6 +402,15 @@ public class Strings {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Display return type hints (preview).
+        /// </summary>
+        public static string Show_Return_Type_Hints {
+            get {
+                return ResourceManager.GetString("Show_Return_Type_Hints", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Simplify names (remove unnecessary qualifiers).
         /// </summary>

vsintegration/src/FSharp.UIResources/Strings.resx

@@ -261,4 +261,7 @@
   <data name="Tooltip_preferred_description_width_in_characters" xml:space="preserve">
     <value>Format signature to the given width by adding line breaks conforming with F# syntax rules. </value>
   </data>
+  <data name="Show_Return_Type_Hints" xml:space="preserve">
+    <value>Display return type hints (preview)</value>
+  </data>
 </root>
\ No newline at end of file

vsintegration/src/FSharp.UIResources/xlf/Strings.cs.xlf

@@ -107,6 +107,11 @@
         <target state="needs-review-translation">Zobrazení tipů pro vložený typ (experimentální)</target>
         <note />
       </trans-unit>
+      <trans-unit id="Show_Return_Type_Hints">
+        <source>Display return type hints (preview)</source>
+        <target state="new">Display return type hints (preview)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Show_all_symbols">
         <source>Show s_ymbols in unopened namespaces</source>
         <target state="translated">Zobrazit s_ymboly v neotevřených oborech názvů</target>

vsintegration/src/FSharp.UIResources/xlf/Strings.de.xlf

@@ -107,6 +107,11 @@
         <target state="needs-review-translation">Hinweise für Inlinetypen anzeigen (experimentell)</target>
         <note />
       </trans-unit>
+      <trans-unit id="Show_Return_Type_Hints">
+        <source>Display return type hints (preview)</source>
+        <target state="new">Display return type hints (preview)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Show_all_symbols">
         <source>Show s_ymbols in unopened namespaces</source>
         <target state="translated">S_ymbole in nicht geöffneten Namespaces anzeigen</target>

vsintegration/src/FSharp.UIResources/xlf/Strings.es.xlf

@@ -107,6 +107,11 @@
         <target state="needs-review-translation">Mostrar sugerencias de tipo insertadas (experimental)</target>
         <note />
       </trans-unit>
+      <trans-unit id="Show_Return_Type_Hints">
+        <source>Display return type hints (preview)</source>
+        <target state="new">Display return type hints (preview)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Show_all_symbols">
         <source>Show s_ymbols in unopened namespaces</source>
         <target state="translated">Mostrar sím_bolos en espacios de nombres sin abrir</target>

vsintegration/src/FSharp.UIResources/xlf/Strings.fr.xlf

@@ -107,6 +107,11 @@
         <target state="needs-review-translation">Afficher les indicateurs de type inline (expérimental)</target>
         <note />
       </trans-unit>
+      <trans-unit id="Show_Return_Type_Hints">
+        <source>Display return type hints (preview)</source>
+        <target state="new">Display return type hints (preview)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Show_all_symbols">
         <source>Show s_ymbols in unopened namespaces</source>
         <target state="translated">Afficher les sym_boles dans les espaces de noms non ouverts</target>

vsintegration/src/FSharp.UIResources/xlf/Strings.it.xlf

@@ -107,6 +107,11 @@
         <target state="needs-review-translation">Visualizzare suggerimenti di tipo inline (sperimentale)</target>
         <note />
       </trans-unit>
+      <trans-unit id="Show_Return_Type_Hints">
+        <source>Display return type hints (preview)</source>
+        <target state="new">Display return type hints (preview)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Show_all_symbols">
         <source>Show s_ymbols in unopened namespaces</source>
         <target state="translated">Mostra si_mboli in spazi dei nomi non aperti</target>

vsintegration/src/FSharp.UIResources/xlf/Strings.ja.xlf

@@ -107,6 +107,11 @@
         <target state="needs-review-translation">インライン型のヒントを表示する (試験段階)</target>
         <note />
       </trans-unit>
+      <trans-unit id="Show_Return_Type_Hints">
+        <source>Display return type hints (preview)</source>
+        <target state="new">Display return type hints (preview)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Show_all_symbols">
         <source>Show s_ymbols in unopened namespaces</source>
         <target state="translated">開かれていない名前空間の記号を表示する(_Y)</target>

vsintegration/src/FSharp.UIResources/xlf/Strings.ko.xlf

@@ -107,6 +107,11 @@
         <target state="needs-review-translation">인라인 유형 힌트 표시(실험적)</target>
         <note />
       </trans-unit>
+      <trans-unit id="Show_Return_Type_Hints">
+        <source>Display return type hints (preview)</source>
+        <target state="new">Display return type hints (preview)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Show_all_symbols">
         <source>Show s_ymbols in unopened namespaces</source>
         <target state="translated">열려 있지 않은 네임스페이스에 기호 표시(_Y)</target>

vsintegration/src/FSharp.UIResources/xlf/Strings.pl.xlf

@@ -107,6 +107,11 @@
         <target state="needs-review-translation">Wyświetl wskazówki typu wbudowanego (eksperymentalne)</target>
         <note />
       </trans-unit>
+      <trans-unit id="Show_Return_Type_Hints">
+        <source>Display return type hints (preview)</source>
+        <target state="new">Display return type hints (preview)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Show_all_symbols">
         <source>Show s_ymbols in unopened namespaces</source>
         <target state="translated">Pokaż s_ymbole w nieotwartych przestrzeniach nazw</target>

vsintegration/src/FSharp.UIResources/xlf/Strings.pt-BR.xlf

@@ -107,6 +107,11 @@
         <target state="needs-review-translation">Exibir as dicas de tipo embutido (experimental)</target>
         <note />
       </trans-unit>
+      <trans-unit id="Show_Return_Type_Hints">
+        <source>Display return type hints (preview)</source>
+        <target state="new">Display return type hints (preview)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Show_all_symbols">
         <source>Show s_ymbols in unopened namespaces</source>
         <target state="translated">Mostrar s_ímbolos em namespaces não abertos</target>

vsintegration/src/FSharp.UIResources/xlf/Strings.ru.xlf

@@ -107,6 +107,11 @@
         <target state="needs-review-translation">Отображать подсказки для встроенных типов (экспериментальная версия)</target>
         <note />
       </trans-unit>
+      <trans-unit id="Show_Return_Type_Hints">
+        <source>Display return type hints (preview)</source>
+        <target state="new">Display return type hints (preview)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Show_all_symbols">
         <source>Show s_ymbols in unopened namespaces</source>
         <target state="translated">По_казать символы в неоткрытых пространствах имен</target>

vsintegration/src/FSharp.UIResources/xlf/Strings.tr.xlf

@@ -107,6 +107,11 @@
         <target state="needs-review-translation">Satır içi tür ipuçlarını göster (deneysel)</target>
         <note />
       </trans-unit>
+      <trans-unit id="Show_Return_Type_Hints">
+        <source>Display return type hints (preview)</source>
+        <target state="new">Display return type hints (preview)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Show_all_symbols">
         <source>Show s_ymbols in unopened namespaces</source>
         <target state="translated">Açılmamış ad alanlarında s_embolleri göster</target>

vsintegration/src/FSharp.UIResources/xlf/Strings.zh-Hans.xlf

@@ -107,6 +107,11 @@
         <target state="needs-review-translation">显示内联类型提示(实验性)</target>
         <note />
       </trans-unit>
+      <trans-unit id="Show_Return_Type_Hints">
+        <source>Display return type hints (preview)</source>
+        <target state="new">Display return type hints (preview)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Show_all_symbols">
         <source>Show s_ymbols in unopened namespaces</source>
         <target state="translated">显示未打开的命名空间中的符号(_Y)</target>

vsintegration/src/FSharp.UIResources/xlf/Strings.zh-Hant.xlf

@@ -107,6 +107,11 @@
         <target state="needs-review-translation">顯示內嵌類型提示 (實驗性)</target>
         <note />
       </trans-unit>
+      <trans-unit id="Show_Return_Type_Hints">
+        <source>Display return type hints (preview)</source>
+        <target state="new">Display return type hints (preview)</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Show_all_symbols">
         <source>Show s_ymbols in unopened namespaces</source>
         <target state="translated">顯示未開啟之命名空間中的符號(_Y)</target>

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

@@ -34,6 +34,7 @@
     <Compile Include="Hints\OptionParserTests.fs" />
     <Compile Include="Hints\InlineParameterNameHintTests.fs" />
     <Compile Include="Hints\InlineTypeHintTests.fs" />
+    <Compile Include="hints\InlineReturnTypeHintTests.fs" />
     <Compile Include="Hints\OverallHintExperienceTests.fs" />
     <Compile Include="EditorFormattingServiceTests.fs" />
     <Compile Include="RoslynSourceTextTests.fs" />

vsintegration/tests/FSharp.Editor.Tests/Hints/HintTestFramework.fs

@@ -64,11 +64,16 @@ module HintTestFramework =
         |> Async.RunSynchronously
 
     let getTypeHints document =
-        getHints document (Set.empty.Add(HintKind.TypeHint))
+        getHints document (set [ HintKind.TypeHint ])
+
+    let getReturnTypeHints document =
+        getHints document (set [ HintKind.ReturnTypeHint ])
 
     let getParameterNameHints document =
-        getHints document (Set.empty.Add(HintKind.ParameterNameHint))
+        getHints document (set [ HintKind.ParameterNameHint ])
 
     let getAllHints document =
-        let hintKinds = Set.empty.Add(HintKind.TypeHint).Add(HintKind.ParameterNameHint)
+        let hintKinds =
+            set [ HintKind.TypeHint; HintKind.ParameterNameHint; HintKind.ReturnTypeHint ]
+
         getHints document hintKinds

vsintegration/tests/FSharp.Editor.Tests/Hints/InlineReturnTypeHintTests.fs

+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+module FSharp.Editor.Tests.Hints.InlineReturnTypeHintTests
+
+open Xunit
+open HintTestFramework
+open FSharp.Test
+
+[<Fact>]
+let ``Hints are shown for let-bound function return types`` () =
+    let code =
+        """
+let func () = 3
+let func2 x = x + 1
+let setConsoleOut = System.Console.SetOut
+"""
+
+    let document = getFsDocument code
+
+    let result = getReturnTypeHints document
+
+    let expected =
+        [
+            {
+                Content = ": int "
+                Location = (1, 13)
+            }
+            {
+                Content = ": int "
+                Location = (2, 13)
+            }
+            {
+                Content = ": unit "
+                Location = (3, 19)
+            }
+        ]
+
+    Assert.Equal(expected, result)
+
+[<Fact>]
+let ``Hints are shown for method return types`` () =
+    let code =
+        """
+type Test() =
+    member this.Func() = 3
+"""
+
+    let document = getFsDocument code
+
+    let result = getReturnTypeHints document
+
+    let expected =
+        [
+            {
+                Content = ": int "
+                Location = (2, 24)
+            }
+        ]
+
+    Assert.Equal(expected, result)
+
+[<Fact>]
+let ``Hints are shown for generic functions`` () =
+    let code = "let func _a = 5"
+
+    let document = getFsDocument code
+
+    let result = getReturnTypeHints document
+
+    let expected =
+        [
+            {
+                Content = ": int "
+                Location = (0, 13)
+            }
+        ]
+
+    Assert.Equal(expected, result)
+
+[<Fact>]
+let ``Hints are shown for functions within expressions`` () =
+    let code =
+        """
+    let _ =
+        let func () = 2
+"""
+
+    let document = getFsDocument code
+
+    let result = getReturnTypeHints document
+
+    let expected =
+        [
+            {
+                Content = ": int "
+                Location = (2, 21)
+            }
+        ]
+
+    Assert.Equal(expected, result)
+
+[<Fact>]
+let ``Hints are not shown for lambda bindings`` () =
+    let code = "let func = fun () -> 3"
+
+    let document = getFsDocument code
+
+    let result = getReturnTypeHints document
+
+    Assert.Empty result
+
+[<Fact>]
+let ``Hints are not shown when there's type annotation`` () =
+    let code = "let func x : int = x"
+
+    let document = getFsDocument code
+
+    let result = getReturnTypeHints document
+
+    Assert.Empty result

vsintegration/tests/FSharp.Editor.Tests/Hints/OverallHintExperienceTests.fs

@@ -26,7 +26,7 @@ let a = Square 1
 let b = Rectangle (1, 2)
 
 type C (blahFirst: int) =
-    member _.Normal (what: string) = 1 
+    member _.Normal (what: string) = 1
 
 let a = C 1
 let cc = a.Normal "hmm"
@@ -40,6 +40,10 @@ let cc = a.Normal "hmm"
                     Content = ": Song"
                     Location = (2, 18)
                 }
+                {
+                    Content = ": string "
+                    Location = (2, 19)
+                }
                 {
                     Content = "song = "
                     Location = (4, 23)
@@ -68,6 +72,10 @@ let cc = a.Normal "hmm"
                     Content = ": Shape"
                     Location = (11, 6)
                 }
+                {
+                    Content = ": int "
+                    Location = (14, 36)
+                }
                 {
                     Content = "blahFirst = "
                     Location = (16, 11)