Add the F# Interactive window on the JSON-RPC protocol by xperiandri · Pull Request #20565 · dotnet/fsharp

xperiandri · 2026-09-16T13:46:10Z

Replaces the Visual Studio F# Interactive window with one hosted on Microsoft.VisualStudio.InteractiveWindow — the same REPL engine C# Interactive and Python Interactive use — driving fsi over the JSON-RPC protocol fsi gained in #20396 instead of parsing SERVER-PROMPT> text on stdin.

github-actions · 2026-09-16T13:46:27Z

✅ No release notes required

T-Gro · 2026-09-16T19:52:31Z

+
+  <ItemGroup>
+    <ProjectReference Include="$(FSharpSourcesRoot)\FSharp.Core\FSharp.Core.fsproj" />
+    <ProjectReference Include="$(FSharpSourcesRoot)\Compiler\FSharp.Compiler.Service.fsproj" />


How would the architecture need to change for the window to locate the SDK, and start the JSON-RPC server from the SDK? i.e. the Window NOT having a reference to FSharp.Compiler.Service.fsproj

That way, we decouple VS versions and SDK versions (steered via global.json).
We would also gain parity of CLI fsi, CLI build VS FSI - guaranteed to use same compiler bits.

And more importantly, the VS FSI could then be powered by net11 F# compiler, benefiting from any perf improvements on the .NET side.

Done in the last commit: the session starts in the solution folder with the dotnet a shell there would run, so the host resolves the SDK from global.json exactly as dotnet fsi does — nothing in the window re-implements that, and the fsi it evaluates on is the SDK's. The FCS reference that remains serves the tokenizer only (Enter-vs-newline in SubmissionAnalysis, lexical colouring) — the same FCS FSharp.Editor already loads; it plays no part in evaluation.

🤖🕵️ @xperiandri This is still occurring.

<ProjectReference Include="$(FSharpSourcesRoot)\Compiler\FSharp.Compiler.Service.fsproj" />

SDK selection is fixed; the requested no-FCS window boundary is not.

You are right, and my earlier answer only covered evaluation. The window no longer references FSharp.Compiler.Service.fsproj, and cannot compile against it: DisableTransitiveProjectReferences stops FSharp.VS.FSI (which keeps the compiler for the old window) from handing it on. What the window used the compiler for was its lexer, to colour input and output and to decide when Enter submits. That is now ILexicalScannerFactory in LexicalScanning.fs, and FSharp.Editor, which already runs on the compiler Visual Studio ships, exports the implementation. The session's own compiler stays the SDK's, in the dotnet fsi process. The submission rule is still tested, with the editor's scanner, in SubmissionAnalysisTests.

T-Gro · 2026-09-16T20:02:14Z

+        UICultureLcid: int
+    }
+
+module internal FsiLocator =


This should use the SDK locator as if you launched dotnet fsi from the solution folder (i.e. following global.json).

Also as long as we keep the legacy FSI in current shape, the new window via JSON-RPC could be netcoreapp only and not offer any of the .NET Framework options.

Both done: the platform choice, the desktop executables and the shadow-copy switch are gone from this window (they stay with the old one), and the session starts in the solution folder so global.json picks the SDK. When a session comes up the window prints which fsi answered, on what runtime and where.

xperiandri · 2026-09-20T20:28:04Z

Re-stacked on xperiandri/fsharp@c5501123 (#20396 after its second pass: the server is .NET-only, the pipe is CurrentUserOnly, and EvalInteraction evaluates a whole selection, so the window no longer relies on the server splitting on ;;). The only change here is that the window passes --fsi-server-client-pid, so a Visual Studio that dies between launching fsi and connecting no longer leaves a session waiting on the pipe.

Two things from the review are still open and are the next steps for this PR rather than for #20396:

Locating fsi through the SDK that global.json resolves to, instead of FSHARP_INTERACTIVE_PATH or dotnet from PATH — @T-Gro's thread on InteractiveHost.fs.
Dropping the .NET Framework platform choices from this window. The server now exists only in the .NET fsi, so picking a desktop platform ends with fsi's own "The JSON-RPC server mode is not available in this build of F# Interactive." on the error stream.

One limit worth knowing: the client side cannot ask for PipeOptions.CurrentUserOnly on net472, so the GUID pipe name is what stands between the window and a pipe squatter until the window itself targets .NET.

T-Gro · 2026-09-21T13:59:53Z

@xperiandri Current head 0e32fd1 is conflicting. Build MacOS Batch2, Build CheckCodeFormatting, fsharp-ci, and check_release_notes are failing.

T-Gro

🤖🕵️ Review follow-up.

T-Gro · 2026-09-21T13:59:53Z

+        addSwitch $"{CommandLine.ServerOption}{pipeName}"
+        // How the host names itself: a session whose host dies, even before the handshake, exits instead of
+        // waiting on the pipe forever.
+        addSwitch $"--fsi-server-client-pid:{clientProcessId}"


🤖🕵️ @xperiandri user arguments can override the trusted owner PID; closing VS leaves FSI alive.

trusted: --fsi-server-client-pid:<VS pid> UserArguments: --fsi-server-client-pid:0 owner exits -> server_alive=true

// Reject duplicate ownership switches, or append the trusted PID after UserArguments.

Fixed. The window's own switches now come last, after the user's arguments, and for --fsi-server-jsonrpc and --fsi-server-client-pid the last occurrence wins, so --fsi-server-client-pid:0 in the arguments no longer names the owner. the last owner named on the command line is the one that counts starts a session with two owners and closes the first; the session keeps serving.

The filter sits on every F# editor view, so answering S_OK for the whole VsStd11 group hid the status of every other command in it from the targets behind. Commands it does not handle now go to the next target. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

The exit handler reports an exit only once the session is current, so one that exited between the handshake and the install was dropped and the dead session installed. The install now checks the session under the same lock and reports the exit as a failed start. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

The origin was cleared only after the session started, so a send while fsi could not start left it for the next text typed into the window. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Closing disposed the evaluator but kept the window and evaluator fields, so the next open submitted through the disposed host. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Registration, the VSIX entry and the editor commands have landed; only the debugger commands are left. Also drop a stray prefix from the title. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

…fewer comments Round one of the NoBloat and code-compaction pass asked for in review. Removed from the pull request: - docs/ide/FSI-Modern-Interactive-Window-Plan.md, the plan and status of the work; - .claude/rules/CcrOptout.md, an agent rule that is no part of this feature; - members nothing calls: the host client's IsRunning, EvaluatingProcessId, Initialization, ExecuteFileAsync and SetPathsAsync, the session's EvaluatingProcessId and Process, the evaluator's EvaluatingProcessId and Host, the provider's Window and Evaluator, the package's Provider and its InitializeAsync override that only called the base; - TolerateUnusedBindings: the project compiles with unused bindings as errors; - comments that restated the code, told its history or defended the design. Reused instead of repeated: - PredefinedInteractiveContentTypes and PredefinedClassificationTypeNames for the names the classifier spelled as literals; - TextWriter.Null for a window that is not there, in place of four null-checking writers; - Result.bind, Result.map and List.sortBy where the host matched and filtered by hand. Extracted: - HeldOutput, the buffer that keeps a starting session's output back until its handshake; - SessionProcess, for the command line, the output pumps and the quiet teardown; - one way to build a candidate that runs on the dotnet host, one to describe an early exit, and one to install a started session; - the evaluator's subscriptions as one list, and one function that reports a failed start; - LexicalToken.IsWithin, the bounds check the classifier and the submission rule both made. The send-to-interactive active pattern yields the kind, so Exec has one arm for both commands, and the continuation tokens are three lines of text instead of fifty-five of list. FsiCommandService.fs keeps the byte-order mark it has on main. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

…onstructor Round two of the NoBloat and code-compaction pass asked for in review. - SubmissionAnalysisTests: eleven facts that each asserted a list of inputs become one theory over named scenarios, and the terminator test a second one. The 32 pairs of input and expectation are the same. - FsiLocator builds its three candidates through one function, and the dotnet host is dotnet.exe without asking the platform: the assembly only loads in Visual Studio. - The output pump is a loop under the quiet wrapper the teardown uses, not a recursive function in a try inside a thread's lambda. - The execute request takes its two optional fields through ValueOption.toObj and toNullable. - The exit code is read in one place, the session's own member. - The project no longer references PresentationCore, PresentationFramework and WindowsBase, which nothing in it uses. - What an SDK too old for the server does is said once, where the candidates are ordered. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

xperiandri · 2026-10-11T09:50:47Z

@T-Gro Two rounds are pushed, 9b95f7a and 512effa. The diff against main went from 2357 added lines to 1644, the comment lines in it from 210 to 105 and the let/member definitions from 258 to 214; the server tests pass (79 cases, the submission rule's eleven facts now being one theory over the same 29 inputs), and FSharp.Editor and FSharp.Interactive.Window build with -p:Optimize=true. The process artifact, docs/ide/FSI-Modern-Interactive-Window-Plan.md, is removed, together with a stray .claude/rules/CcrOptout.md and the members nothing called yet (SetPathsAsync, ExecuteFileAsync, EvaluatingProcessId, IsRunning and their like). Extracted or reused: HeldOutput and SessionProcess came out of the host client, the fsi candidates share one constructor, the evaluator's four null-checking writers became TextWriter.Null and its subscriptions one list, the classifier takes its names from PredefinedClassificationTypeNames and PredefinedInteractiveContentTypes, and the send-to-interactive active pattern yields the kind, so Exec has one arm for both commands.

T-Gro

The diff is still way too big - apply the NoBloat instructions and CodeCompaction skill.

Especially the massive code comments would benefit not just with drastic reduction, but ideally with well named functions/arguments/bindings/types making the intention clear.

If a well named piece of code just tells what the comment says - delete the comment.

This diff adds 88 new code comment lines and 7116 new code comment chars.
Comments bypass the type system and become stale maintenance state. Keep only durable public contracts; express implementation intent through names, functions, active patterns, discriminated unions, and types.

T-Gro

🤖🕵️ AI review — verify independently.

…fewer comments Round one of the NoBloat and code-compaction pass asked for in review. Removed from the pull request: - docs/ide/FSI-Modern-Interactive-Window-Plan.md, the plan and status of the work; - .claude/rules/CcrOptout.md, an agent rule that is no part of this feature; - members nothing calls: the host client's IsRunning, EvaluatingProcessId, Initialization, ExecuteFileAsync and SetPathsAsync, the session's EvaluatingProcessId and Process, the evaluator's EvaluatingProcessId and Host, the provider's Window and Evaluator, the package's Provider and its InitializeAsync override that only called the base; - TolerateUnusedBindings: the project compiles with unused bindings as errors; - comments that restated the code, told its history or defended the design. Reused instead of repeated: - PredefinedInteractiveContentTypes and PredefinedClassificationTypeNames for the names the classifier spelled as literals; - TextWriter.Null for a window that is not there, in place of four null-checking writers; - Result.bind, Result.map and List.sortBy where the host matched and filtered by hand. Extracted: - HeldOutput, the buffer that keeps a starting session's output back until its handshake; - SessionProcess, for the command line, the output pumps and the quiet teardown; - one way to build a candidate that runs on the dotnet host, one to describe an early exit, and one to install a started session; - the evaluator's subscriptions as one list, and one function that reports a failed start; - LexicalToken.IsWithin, the bounds check the classifier and the submission rule both made. The send-to-interactive active pattern yields the kind, so Exec has one arm for both commands, and the continuation tokens are three lines of text instead of fifty-five of list. FsiCommandService.fs keeps the byte-order mark it has on main. This is 9b95f7a of dotnet#20565 without its two deletions: docs/ide/FSI-Modern-Interactive-Window-Plan.md and .claude/rules/CcrOptout.md leave the pull request only and stay on this branch. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

T-Gro

🤖🕵️ AI review — verify independently.

Keep the existing 18.12.772 pin and remove the older duplicate that causes NU1506 during restore. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 1750b0a0-85af-4cd4-b6a1-c4b5cc8240fb

Align Shell.15.0 with the newer VS dependencies, handle nullable editor API results, and update the integration-test generator and UI-thread checks. Replace the build-completion semaphore with a cancellable asynchronous signal. Verified clean bootstrap and full Debug VisualFSharp solution build; 53 focused editor classification tests passed. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 1750b0a0-85af-4cd4-b6a1-c4b5cc8240fb

abonie · 2026-10-22T15:20:06Z

/azp run

azure-pipelines · 2026-10-22T15:20:21Z

Azure Pipelines: Successfully started running 1 pipeline(s).

T-Gro

🤖 🕵️ Re-reviewed all recent changes as of 09f9fa9; LGTM

…fewer comments Round one of the NoBloat and code-compaction pass asked for in review. Removed from the pull request: - docs/ide/FSI-Modern-Interactive-Window-Plan.md, the plan and status of the work; - .claude/rules/CcrOptout.md, an agent rule that is no part of this feature; - members nothing calls: the host client's IsRunning, EvaluatingProcessId, Initialization, ExecuteFileAsync and SetPathsAsync, the session's EvaluatingProcessId and Process, the evaluator's EvaluatingProcessId and Host, the provider's Window and Evaluator, the package's Provider and its InitializeAsync override that only called the base; - TolerateUnusedBindings: the project compiles with unused bindings as errors; - comments that restated the code, told its history or defended the design. Reused instead of repeated: - PredefinedInteractiveContentTypes and PredefinedClassificationTypeNames for the names the classifier spelled as literals; - TextWriter.Null for a window that is not there, in place of four null-checking writers; - Result.bind, Result.map and List.sortBy where the host matched and filtered by hand. Extracted: - HeldOutput, the buffer that keeps a starting session's output back until its handshake; - SessionProcess, for the command line, the output pumps and the quiet teardown; - one way to build a candidate that runs on the dotnet host, one to describe an early exit, and one to install a started session; - the evaluator's subscriptions as one list, and one function that reports a failed start; - LexicalToken.IsWithin, the bounds check the classifier and the submission rule both made. The send-to-interactive active pattern yields the kind, so Exec has one arm for both commands, and the continuation tokens are three lines of text instead of fifty-five of list. FsiCommandService.fs keeps the byte-order mark it has on main. This is 9b95f7a of dotnet#20565 without its two deletions: docs/ide/FSI-Modern-Interactive-Window-Plan.md and .claude/rules/CcrOptout.md leave the pull request only and stay on this branch. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

An editor send left its source file and line in a single slot that the next send overwrote, so with two sends in a row the first ran with the second's origin and the second with none. The evaluator now keeps the origins in the order they were sent, and a submission takes the one that belongs to its own text. Text typed into the window takes none, and an origin whose submission never ran is dropped once a later one runs. Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

The review found the added comments too many: 88 lines, 7116 characters. 23 lines, 2409 characters remain, 13 of them licence headers. What went restated a name or a test, defended a design the PR body already covers, or was wrong: the window package never replaces its output buffer, which one comment claimed. Where a comment made up for a name, the name took over (readAndAdvanceCaret, OneBasedStartLine, pumpWithoutWaitingForNewline, OutputHeldUntilHandshake, SessionExitedUnexpectedly, installUnlessExited, unguessablePipeName, carriesStateAcrossLines = true at the call sites). The solution directory lookup asserts the UI thread instead of saying so: its try would have hidden a call from another thread. Kept: the persisted tool-window id, the F# content type name, the Tools\Interactive layout, the rule that the last --fsi-server-* switch wins, Process.Exited being raised once, no CurrentUserOnly on net472, FS3511 and the global.json note on the working directory. Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

xperiandri · 2026-10-29T22:01:38Z

Went through the diff with the code-compaction skill (three reviewers from different model families for the comments, one for reuse).

Comments added by the PR, counted the same way as in the review (added // lines in *.fs): 88 lines / 7116 chars → 23 lines / 2409 chars, 13 of them licence headers. What stayed are cross-file contracts and the FS3511 workaround; the rest became names (readAndAdvanceCaret, OneBasedStartLine, pumpWithoutWaitingForNewline, SessionExitedUnexpectedly, …) or went away. One of the removed comments was wrong: the window package never replaces its output buffer.

Also fixed in this push: queued editor sends no longer overwrite each other's source origin (the open AI-review thread), with tests.

…fewer comments Round one of the NoBloat and code-compaction pass asked for in review. Removed from the pull request: - docs/ide/FSI-Modern-Interactive-Window-Plan.md, the plan and status of the work; - .claude/rules/CcrOptout.md, an agent rule that is no part of this feature; - members nothing calls: the host client's IsRunning, EvaluatingProcessId, Initialization, ExecuteFileAsync and SetPathsAsync, the session's EvaluatingProcessId and Process, the evaluator's EvaluatingProcessId and Host, the provider's Window and Evaluator, the package's Provider and its InitializeAsync override that only called the base; - TolerateUnusedBindings: the project compiles with unused bindings as errors; - comments that restated the code, told its history or defended the design. Reused instead of repeated: - PredefinedInteractiveContentTypes and PredefinedClassificationTypeNames for the names the classifier spelled as literals; - TextWriter.Null for a window that is not there, in place of four null-checking writers; - Result.bind, Result.map and List.sortBy where the host matched and filtered by hand. Extracted: - HeldOutput, the buffer that keeps a starting session's output back until its handshake; - SessionProcess, for the command line, the output pumps and the quiet teardown; - one way to build a candidate that runs on the dotnet host, one to describe an early exit, and one to install a started session; - the evaluator's subscriptions as one list, and one function that reports a failed start; - LexicalToken.IsWithin, the bounds check the classifier and the submission rule both made. The send-to-interactive active pattern yields the kind, so Exec has one arm for both commands, and the continuation tokens are three lines of text instead of fifty-five of list. FsiCommandService.fs keeps the byte-order mark it has on main. This is 9b95f7a of dotnet#20565 without its two deletions: docs/ide/FSI-Modern-Interactive-Window-Plan.md and .claude/rules/CcrOptout.md leave the pull request only and stay on this branch. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

github-project-automation Bot added this to F# Compiler and Tooling Sep 16, 2026

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Add a JSON-RPC server mode to F# Interactive #20396

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xperiandri force-pushed the modern-repl branch from 0bdeb79 to 1990f9e Compare September 20, 2026 20:25

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F# Interactive window: IntelliSense and semantic colouring in the input buffer #20608

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xperiandri and others added 5 commits October 10, 2026 23:40

Forget an editor submission's origin when its execution fails

c9b1932

The origin was cleared only after the session started, so a send while fsi could not start left it for the next text typed into the window. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Open a new window after the old one is closed

b543537

Closing disposed the evaluator but kept the window and evaluator fields, so the next open submitted through the disposed host. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Bring the interactive window plan's status up to date

d74dfcc

Registration, the VSIX entry and the editor commands have landed; only the debugger commands are left. Also drop a stray prefix from the title. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

xperiandri force-pushed the modern-repl branch from 09338b1 to d74dfcc Compare October 10, 2026 22:28

xperiandri and others added 2 commits October 11, 2026 11:32

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github-project-automation Bot moved this from New to In Progress in F# Compiler and Tooling Oct 13, 2026

T-Gro reviewed Oct 17, 2026

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Comment thread vsintegration/src/FSharp.Interactive.Window/FSharpVsInteractiveWindowProvider.fs Resolved

Merge branch 'main' into modern-repl

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T-Gro reviewed Oct 22, 2026

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Comment thread eng/Packages.props Resolved

abonie and others added 2 commits October 22, 2026 11:01

Remove duplicate Shell.Design central package version

aa8e698

Keep the existing 18.12.772 pin and remove the older duplicate that causes NU1506 during restore. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: 1750b0a0-85af-4cd4-b6a1-c4b5cc8240fb

T-Gro reviewed Oct 23, 2026

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xperiandri and others added 3 commits October 29, 2026 21:05

Merge remote-tracking branch 'origin/main' into modern-repl

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xperiandri requested review from T-Gro and abonie October 30, 2026 17:43

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