xperiandri · Aug 30, 2026 · Aug 30, 2026 · Aug 30, 2026 · Aug 30, 2026 · Aug 30, 2026
@@ -108,6 +108,9 @@
     <Project Path="vsintegration/src/FSharp.Editor/FSharp.Editor.fsproj">
       <BuildType Solution="Proto|*" Project="Release" />
     </Project>
+    <Project Path="vsintegration/src/FSharp.Interactive.Window/FSharp.Interactive.Window.fsproj">
+      <BuildType Solution="Proto|*" Project="Release" />
+    </Project>
     <Project Path="vsintegration/src/FSharp.ProjectSystem.PropertyPages/FSharp.ProjectSystem.PropertyPages.vbproj">
       <BuildType Solution="Proto|*" Project="Release" />
     </Project>

@@ -2,6 +2,7 @@
 
 * Add maintainer-requested F# Apex Visual Studio integration tests on DartLab-1ES CloudTest, using PR pipeline definitions pinned to an explicitly requested commit SHA. ([PR #20625](https://github.com/dotnet/fsharp/pull/20625))
 * Code-fixes for FS3888 (compiler-semantic attribute on the `.fs` but not the `.fsi`): copy the attribute into the `.fsi`, or remove it from the `.fs`. ([Issue #19560](https://github.com/dotnet/fsharp/issues/19560), [PR #19880](https://github.com/dotnet/fsharp/pull/19880))
+* The F# Interactive window is rebuilt on the Interactive Window package and talks to `dotnet fsi` over its JSON-RPC server mode: the input and output are coloured, Enter submits only a complete interaction, diagnostics carry positions in the submitted file, and the session starts in the solution folder, so the SDK that `global.json` names supplies the compiler; until the .NET SDK includes the server (11.0.200), Visual Studio installs an F# Interactive of its own for the window to fall back to. ([PR #20565](https://github.com/dotnet/fsharp/pull/20565))
 * Expand `<inheritdoc/>` in IDE tooltips, completion, and signature help, inheriting XML documentation from base classes, interfaces, overridden members, and constructors. ([Issue #19175](https://github.com/dotnet/fsharp/issues/19175), [PR #19188](https://github.com/dotnet/fsharp/pull/19188))
 * Added a **Tools > Options > F# Tools > Compiler** option, **"Use the .NET SDK F# compiler for builds"**, on by default. Visual Studio uses the .NET SDK F# compiler when the project supplies SDK paths, matching `dotnet build`. Otherwise, it uses the bundled .NET Framework compiler. Turn the option off to use the bundled compiler for all projects. Changes are saved on Apply or OK; Cancel discards unsaved changes. Command-line builds are unaffected. ([Issue #20484](https://github.com/dotnet/fsharp/issues/20484), [PR #20485](https://github.com/dotnet/fsharp/pull/20485))
 * F# types, modules, members and values now appear in the GitHub Copilot Chat `#` mention picker, and attach their declaration source as context. ([PR #20409](https://github.com/dotnet/fsharp/pull/20409))
@@ -21,6 +22,7 @@
 * Make Alt+F1 (momentary toggle) work for inlay hints. ([PR #19421](https://github.com/dotnet/fsharp/pull/19421))
 * Fix doubled F# diagnostics in tooltips. ([Issue #16360](https://github.com/dotnet/fsharp/issues/16360))
 * Fix `NotSupportedException` in the memory-mapped-file optimization when copying `ReadOnlyMemory` into `MemoryMappedFileViewStream`. ([Issue #20263](https://github.com/dotnet/fsharp/issues/20263))
+* Handle unavailable document and classification information in the F# Interactive window with the updated Visual Studio SDK. ([PR #20565](https://github.com/dotnet/fsharp/pull/20565))
 * Reduce allocations in the VS project options reactor: the command-line options and project options caches and the mailbox reply payloads now hold struct tuples, and `IProjectSite.CompilationBinOutputPath` returns `string voption` picked with a new `Array.tryPickV`. ([PR #20413](https://github.com/dotnet/fsharp/pull/20413))
 * Build a single-file project's `OtherOptions` reference flags with one array comprehension instead of two `Array.ofSeq` calls and an `Array.append`. ([PR #20499](https://github.com/dotnet/fsharp/pull/20499))
 * Fix syntax coloring being lost for a whole file when one symbol resolves into metadata that could not be read. ([Issue #20269](https://github.com/dotnet/fsharp/issues/20269), [PR #20274](https://github.com/dotnet/fsharp/pull/20274))

@@ -76,6 +76,7 @@
     <PackageVersion Include="Microsoft.VisualStudio.Extensibility.Sdk" Version="17.13.39620" />
     <PackageVersion Include="Microsoft.VisualStudio.Extensibility.Testing.SourceGenerator" Version="$(MicrosoftVisualStudioExtensibilityTestingVersion)" />
     <PackageVersion Include="Microsoft.VisualStudio.Extensibility.Testing.Xunit" Version="$(MicrosoftVisualStudioExtensibilityTestingVersion)" />
+    <PackageVersion Include="Microsoft.VisualStudio.InteractiveWindow" Version="4.0.0" />
     <PackageVersion Include="Microsoft.VisualStudio.Language.Intellisense" Version="$(VisualStudioEditorPackagesVersion)" />
     <PackageVersion Include="Microsoft.VisualStudio.Language.StandardClassification" Version="$(VisualStudioEditorPackagesVersion)" />
     <!-- Pinned to 17.13.9 (not the projects' 17.13.6-preview floor) because Protocol.Internal 17.13.9,
@@ -93,6 +94,9 @@
     <PackageVersion Include="Microsoft.VisualStudio.ProjectSystem" Version="18.0.1237-pre" />
     <PackageVersion Include="Microsoft.VisualStudio.ProjectSystem.Managed" Version="2.3.6152103" />
     <PackageVersion Include="Microsoft.VisualStudio.ProjectSystem.Query" Version="17.13.66" />
+    <!-- Match the minimum required by Shell.Design, Package.LanguageService.15.0, and the Roslyn IDE packages. -->
+    <PackageVersion Include="Microsoft.VisualStudio.Shell.15.0" Version="18.12.772" />
+    <PackageVersion Include="Microsoft.VisualStudio.VsInteractiveWindow" Version="4.0.0" />
     <PackageVersion Include="Microsoft.VisualStudio.Shell.Design" Version="18.12.772" />
     <PackageVersion Include="Microsoft.VisualStudio.Shell.Immutable.10.0" Version="10.0.30319" />
     <PackageVersion Include="Microsoft.VisualStudio.Shell.Immutable.11.0" Version="11.0.50727" />

@@ -101,7 +101,7 @@
          via Microsoft.CodeAnalysis.EditorFeatures / .LanguageServices.ExternalAccess 5.11.0). Full NU1109
          rationale lives there, next to the 18.9.x pins. -->
     <VisualStudioEditorPackagesVersion>18.12.46</VisualStudioEditorPackagesVersion>
-    <MicrosoftVisualStudioExtensibilityTestingVersion>0.1.800-beta</MicrosoftVisualStudioExtensibilityTestingVersion>
+    <MicrosoftVisualStudioExtensibilityTestingVersion>5.6.0-2.26151.2</MicrosoftVisualStudioExtensibilityTestingVersion>
 
     <!-- Apex VS integration-test packages, consumed by-name via $(...) in
          vsintegration/tests/FSharp.Editor.Apex.IntegrationTests, so they stay properties here. -->

@@ -9,6 +9,13 @@
     <ProjectReference Include="$(FSharpSourcesRoot)\fsc\fscAnyCpuProject\fscAnyCpu.fsproj" />
     <ProjectReference Include="$(FSharpSourcesRoot)\fsc\fscArm64Project\fscArm64.fsproj" />
     <ProjectReference Include="$(FSharpSourcesRoot)\fsi\fsiProject\fsi.fsproj" />
+    <!-- The .NET build of fsi, the only one with the JSON-RPC server: the F# Interactive window falls
+         back to it when the SDK's `dotnet fsi` has none. -->
+    <ProjectReference Include="$(FSharpSourcesRoot)\fsi\fsiProject\fsi.fsproj"
+                      SetTargetFramework="TargetFramework=$(FSharpNetCoreProductTargetFramework)"
+                      ReferenceOutputAssembly="false"
+                      SkipGetTargetFrameworkProperties="true"
+                      Private="false" />
     <ProjectReference Include="$(FSharpSourcesRoot)\fsi\fsiAnyCpuProject\fsiAnyCpu.fsproj" />
     <ProjectReference Include="$(FSharpSourcesRoot)\fsi\fsiArm64Project\fsiArm64.fsproj" />
     <ProjectReference Include="$(FSharpSourcesRoot)\FSharp.Build\FSharp.Build.fsproj" />
@@ -40,8 +47,43 @@
     </CreateItem>
   </Target>
 
+  <PropertyGroup>
+    <_InteractiveBinaries>$(BinariesFolder)fsi\$(Configuration)\$(FSharpNetCoreProductTargetFramework)\</_InteractiveBinaries>
+    <_InteractiveInstallDir>InstallDir:Common7\IDE\CommonExtensions\Microsoft\FSharp\Tools\Interactive</_InteractiveInstallDir>
+    <_SwrNewLine><![CDATA[
+]]></_SwrNewLine>
+  </PropertyGroup>
+
+  <!-- Under `dotnet exec` and without fsi.deps.json the host loads the assemblies next to fsi.dll, so the
+       folder is those and the runtime configuration. The block is one item, as the other blocks are:
+       MSBuild trims the indentation from the start of each item. -->
+  <Target Name="_GenerateInteractiveSwrFileContents">
+    <ItemGroup>
+      <_InteractiveFile Include="$(_InteractiveBinaries)*.dll;$(_InteractiveBinaries)fsi.runtimeconfig.json" />
+    </ItemGroup>
+    <PropertyGroup>
+      <_InteractiveBlock>folder "$(_InteractiveInstallDir)"$(_SwrNewLine)@(_InteractiveFile->'  file source="%(FullPath)"', '$(_SwrNewLine)')$(_SwrNewLine)</_InteractiveBlock>
+    </PropertyGroup>
+    <ItemGroup>
+      <_BuiltSwrLines Include="$(_InteractiveBlock)" />
+    </ItemGroup>
+  </Target>
+
   <!-- For each localization language, include the appropriate satellite assemblies. -->
   <Target Name="_GenerateLocSwrFileContents" DependsOnTargets="_GenerateLanguageList" Outputs="%(_XlfLanguages.Identity)">
+    <PropertyGroup>
+      <_Language>%(_XlfLanguages.Identity)</_Language>
+    </PropertyGroup>
+    <ItemGroup>
+      <_InteractiveSatellite Remove="@(_InteractiveSatellite)" />
+      <_InteractiveSatellite Include="$(_InteractiveBinaries)$(_Language)\*.resources.dll" />
+    </ItemGroup>
+    <PropertyGroup>
+      <_InteractiveSatelliteBlock>folder "$(_InteractiveInstallDir)\$(_Language)"$(_SwrNewLine)@(_InteractiveSatellite->'  file source="%(FullPath)"', '$(_SwrNewLine)')$(_SwrNewLine)</_InteractiveSatelliteBlock>
+    </PropertyGroup>
+    <ItemGroup>
+      <_BuiltSwrLines Include="$(_InteractiveSatelliteBlock)" Condition="'@(_InteractiveSatellite)' != ''" />
+    </ItemGroup>
     <PropertyGroup>
       <_Line>
 <![CDATA[
@@ -64,7 +106,7 @@ folder "InstallDir:Common7\IDE\CommonExtensions\Microsoft\FSharp\Tools\%(_XlfLan
     </PropertyGroup>
   </Target>
 
-  <Target Name="_GenerateSwrFile" AfterTargets="Build" BeforeTargets="SwixBuild" DependsOnTargets="_SetSwrFilePath;_GenerateLocSwrFileContents" Outputs="$(_SwrFilePath)">
+  <Target Name="_GenerateSwrFile" AfterTargets="Build" BeforeTargets="SwixBuild" DependsOnTargets="_SetSwrFilePath;_GenerateInteractiveSwrFileContents;_GenerateLocSwrFileContents" Outputs="$(_SwrFilePath)">
 
     <PropertyGroup>
       <_Lines>

@@ -38,6 +38,10 @@ module Methods =
     [<Literal>]
     let Shutdown = "fsi/shutdown"
 
+module CommandLine =
+    [<Literal>]
+    let ServerOption = "--fsi-server-jsonrpc:"
+
 [<CLIMutable>]
 type InitializeResult =
     {
@@ -67,7 +71,7 @@ type ExecuteRequest =
         /// with <c>startLine</c> this makes diagnostics point at the user's own source rather than
         /// at a position within the submission.
         /// </summary>
-        sourcePath: string
+        sourcePath: string | null
 
         startLine: System.Nullable<int>
     }
@@ -78,7 +82,7 @@ type ExecuteFileRequest = { path: string }
 [<CLIMutable>]
 type SetPathsRequest =
     {
-        includePaths: string[]
+        includePaths: string[] | null
         workingDirectory: string
     }
 
@@ -123,8 +127,8 @@ type ExecutionResult =
         success: bool
 
         cancelled: bool
-        diagnostics: DiagnosticInfo[]
-        ``exception``: ExceptionInfo
+        diagnostics: DiagnosticInfo[] | null
+        ``exception``: ExceptionInfo | null
         values: ValueInfo[]
 
         /// Reported after every interaction so that the host can keep its own view of the session

@@ -24,6 +24,18 @@
     <Compile Include="$(FSharpSourcesRoot)\fsi\interactiveProtocol.fs">
       <Link>interactiveProtocol.fs</Link>
     </Compile>
+    <!-- The Visual Studio window's submission rule and the editor's lexer it runs on, linked here so
+         that testing the two together needs no Windows-only host. -->
+    <Compile Include="$(MSBuildThisFileDirectory)..\..\vsintegration\src\FSharp.Interactive.Window\LexicalScanning.fs">
+      <Link>LexicalScanning.fs</Link>
+    </Compile>
+    <Compile Include="$(MSBuildThisFileDirectory)..\..\vsintegration\src\FSharp.Editor\Commands\InteractiveLexicalScanner.fs">
+      <Link>InteractiveLexicalScanner.fs</Link>
+    </Compile>
+    <Compile Include="$(MSBuildThisFileDirectory)..\..\vsintegration\src\FSharp.Interactive.Window\SubmissionAnalysis.fs">
+      <Link>SubmissionAnalysis.fs</Link>
+    </Compile>
+    <Compile Include="SubmissionAnalysisTests.fs" />
     <Compile Include="FsiServerHarness.fs" />
     <Compile Include="FsiJsonRpcServerTests.fs" />
   </ItemGroup>

@@ -667,6 +667,24 @@ let ``the session exits when its host process exits`` () =
 
     Assert.True(session.WaitForExit 30_000, "the session outlived its host process")
 
+[<Fact>]
+let ``the last owner named on the command line is the one that counts`` () =
+    // A host puts its own switches after the user's arguments to keep them from naming another owner,
+    // which holds only if the last occurrence wins.
+    use earlier = new FsiServerHarness()
+
+    use session =
+        new FsiServerHarness(
+            serverSwitches = fun pipeName -> [ $"--fsi-server-client-pid:{earlier.ProcessId}"; $"--fsi-server-jsonrpc:{pipeName}" ]
+        )
+
+    session.Initialize() |> ignore
+
+    (earlier :> IDisposable).Dispose()
+
+    Assert.False(session.WaitForExit 5_000, "the session followed the owner named first")
+    Assert.True(succeeded (session.Execute "1 + 1"))
+
 //-------------------------------------------------------------------------
 // What ships
 //-------------------------------------------------------------------------

@@ -111,7 +111,7 @@ type FsiServerHarness
             locateFsi (defaultArg fsiDirectory (fsiOutputDirectory ()))
 
         let serverSwitches =
-            defaultArg serverSwitches (fun pipeName -> [ $"--fsi-server-jsonrpc:{pipeName}" ])
+            defaultArg serverSwitches (fun pipeName -> [ $"{CommandLine.ServerOption}{pipeName}" ])
 
         let arguments =
             [
@@ -229,7 +229,7 @@ type FsiServerHarness
         let deadline = DateTime.UtcNow + defaultArg timeout (TimeSpan.FromSeconds 30.0)
 
         let rec wait () =
-            if this.StandardOutput.Contains text then true
+            if this.StandardOutput.Contains(text, StringComparison.Ordinal) then true
             elif DateTime.UtcNow > deadline then false
             else
                 Thread.Sleep 50
@@ -331,10 +331,10 @@ let diagnostics (result: ExecutionResult) =
     | items -> items
 
 let errors result =
-    diagnostics result |> Array.filter (fun d -> d.severity = "error")
+    diagnostics result |> Array.filter (fun d -> String.Equals(d.severity, "error", StringComparison.Ordinal))
 
 let warnings result =
-    diagnostics result |> Array.filter (fun d -> d.severity = "warning")
+    diagnostics result |> Array.filter (fun d -> String.Equals(d.severity, "warning", StringComparison.Ordinal))
 
 let succeeded (result: ExecutionResult) = result.success
 

@@ -0,0 +1,46 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+/// The rule that decides whether Enter submits an interaction or adds another line.
+module FSharp.Compiler.Interactive.Server.Tests.SubmissionAnalysisTests
+
+open Xunit
+
+open Microsoft.VisualStudio.FSharp.Editor
+open Microsoft.VisualStudio.FSharp.Interactive
+
+let private scanners = FSharpLexicalScannerFactory() :> ILexicalScannerFactory
+
+let private scenario (completes: bool) (name: string) (texts: string list) : obj[] list =
+    texts |> List.map (fun text -> [| box name; box completes; box text |])
+
+let private submits = scenario true
+let private takesAnotherLine = scenario false
+
+let scenarios: obj[] seq =
+    [
+        submits "an explicit terminator always submits, even mid-construct" [ "1 + 1;;"; "let f x =\n    x + 1\n;;"; "let xs = [1; 2];;" ]
+        submits "a finished expression submits without a terminator" [ "1 + 1"; "printfn \"hi\""; "let x = 40"; "let f a b =\n    a + b" ]
+        takesAnotherLine "a line that visibly continues" [ "let x ="; "fun x ->"; "1 +"; "if true then" ]
+        takesAnotherLine "an unclosed bracket" [ "printfn (\"a\""; "let xs = [1; 2"; "let xs = [| 1; 2"; "let r = {| A = 1" ]
+        submits "closed brackets do not hold the submission open" [ "printfn (\"a\")"; "let xs = [1; 2]"; "let xs = [| 1; 2 |]" ]
+        takesAnotherLine "an unterminated string or comment" [ "let s = \"abc"; "(* comment" ]
+        submits "brackets and terminators inside a string do not count" [ "let s = \"([{\""; "let s = \"a;;b\"" ]
+        submits "a string literal can end a submission: the last token is the literal, not the '=' before it" [ "let greeting = \"hello\"" ]
+        takesAnotherLine "a terminator inside a string is not a terminator" [ "let s = \";;" ]
+        submits "a comment does not change what the last token was" [ "let x = 1 // ([\n"; "(* c *) let x = 1" ]
+        takesAnotherLine "a comment does not change what the last token was" [ "let x = // nothing yet" ]
+        submits "an empty submission, which the window uses to start a session that has gone away" [ ""; "   \n  " ]
+    ]
+    |> Seq.concat
+
+[<Theory>]
+[<MemberData(nameof scenarios)>]
+let ``Enter submits only what is visibly finished`` (scenario: string) (completes: bool) (text: string) =
+    Assert.True((SubmissionAnalysis.isComplete scanners text = completes), $"{scenario}: <<{text}>>")
+
+[<Theory>]
+[<InlineData("1 + 1;;", "1 + 1;;")>]
+[<InlineData("1 + 1", "1 + 1\n;;")>]
+[<InlineData("let s = \"a;;b\"", "let s = \"a;;b\"\n;;")>]
+let ``the terminator is added only when it is missing`` (text: string) (expected: string) =
+    Assert.Equal(expected, SubmissionAnalysis.withTerminator scanners text)
@@ -8,6 +8,8 @@
     <VSSDKTargetPlatformRegRootSuffix>$(VSRootSuffix)</VSSDKTargetPlatformRegRootSuffix>
     <!-- Path to the locally built F# compiler for use during VSIX debugging -->
     <FSharpCompilerPathForDebuggingLocally>$(ArtifactsDir)bin\fscAnyCpu\$(Configuration)\net472\</FSharpCompilerPathForDebuggingLocally>
+    <!-- Same for F# Interactive: the .NET build, the one with the JSON-RPC server, run on the repository's dotnet -->
+    <FSharpInteractivePathForDebuggingLocally>$(ArtifactsDir)bin\fsi\$(Configuration)\$(FSharpNetCoreProductTargetFramework)\fsi.dll</FSharpInteractivePathForDebuggingLocally>
     <CreateVsixContainer>true</CreateVsixContainer>
     <PublishUrl>publish\</PublishUrl>
     <Install>true</Install>

@@ -12,7 +12,8 @@
         "FSharpPreferAnyCpuTools": "true",
         "Fsc_NetFramework_ToolPath": "$(FSharpCompilerPathForDebuggingLocally)",
         "Fsc_NetFramework_AnyCpu_ToolExe": "fscAnyCpu.exe",
-        "FSHARP_OTEL_EXPORT": ""
+        "FSHARP_OTEL_EXPORT": "",
+        "FSHARP_INTERACTIVE_PATH": "$(FSharpInteractivePathForDebuggingLocally)"
       }
     },
     "OTEL Export": {
@@ -27,7 +28,8 @@
         "FSharpPreferAnyCpuTools": "true",
         "Fsc_NetFramework_ToolPath": "$(FSharpCompilerPathForDebuggingLocally)",
         "Fsc_NetFramework_AnyCpu_ToolExe": "fscAnyCpu.exe",
-        "FSHARP_OTEL_EXPORT": "http://127.0.0.1:4317"
+        "FSHARP_OTEL_EXPORT": "http://127.0.0.1:4317",
+        "FSHARP_INTERACTIVE_PATH": "$(FSharpInteractivePathForDebuggingLocally)"
       }
     }
   }