Add F# code snippets (Ctrl+K,Ctrl+X / Ctrl+K,Ctrl+S) by xperiandri · Pull Request #20521 · dotnet/fsharp

xperiandri · 2026-09-11T07:42:18Z

Adds Visual Studio code-snippet support for F#: Ctrl+K,Ctrl+X inserts a snippet, Ctrl+K,Ctrl+S surrounds a selection, and a snippet shortcut expands on Tab. Ships a built-in catalog matching C#'s (declarations, members, control flow, computation expressions); ctor/equals fill in the enclosing type name and match generates the cases of the union or enum it is given.

Verified by hand in the experimental hive in addition to the added tests.

Not in scope: snippet shortcuts as an IntelliSense completion item (as C# offers), localized snippet folders, <Imports>/<References> support, and snippets for test methods.

Checklist

Test cases added
Performance benchmarks added in case of performance changes — not applicable, no existing path changes
Release notes entry updated

🤖 Generated with Claude Code

github-actions · 2026-09-11T07:42:29Z

✅ Release notes checked

✅ Found changes and release notes in following paths:

Change path Release notes path Description

`vsintegration/src` docs/release-notes/.VisualStudio/18.vNext.md

xperiandri · 2026-09-11T10:08:27Z

xperiandri · 2026-09-11T14:48:18Z

/azp run fsharp-ci

azure-pipelines · 2026-09-11T14:48:24Z

Commenter does not have sufficient privileges for PR 20521 in repo dotnet/fsharp

T-Gro

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T-Gro

🤖🕵️ If this fixes an issue or implements an RFC/suggestion, link it (Fixes #... when applicable). Otherwise, give a short management-level summary in simplified technical English: what user scenario improves and what this achieves.

Please apply this PR-description guidance. Remove the implementation inventory already visible in Files, but keep necessary scope, compatibility, and dependency caveats.

xperiandri · 2026-09-14T15:19:00Z

Rewrote per the guidance — description is now Fixes #1498 + one paragraph on user-visible behavior + scope/compatibility caveats, implementation inventory removed.

T-Gro

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github-actions · 2026-09-23T19:40:23Z

🔍 Tooling Safety Check — Affects-Design-Time
Affects-Design-Time: Modifies FCS services used by editor tooling.

Generated by PR Tooling Safety Check · gpt56 2.3M · ◷

Insert Snippet and Surround With have had nothing to offer in an F# file: the Code Snippets Manager has no F# entry and this repository contains no `.snippet` file at all. Adds 40 snippets covering the part of the C# set that has an F# analogue - declarations, members, control flow, computation expressions - together with the registration and packaging that lets Visual Studio find them. `Languages\CodeExpansions\FSharp` is written into the pkgdef rather than produced by `ProvideLanguageCodeExpansionAttribute`, which does not expose the `Package` value that `DisplayName` resolves against; C#, VB, XAML, XML and TypeScript all register by hand for the same reason. Only 1033 is registered, and outright rather than as `%LCID%`: registering both would enumerate every snippet twice on an English VS. The shipped directory is `Snippets\1033\FSharp`, not `Visual F#`, because a '#' in a VSIX part URI reads as a URI fragment and the packaging step refuses it. `SnippetsIndex.xml` supplies the folder name the Code Snippets Manager shows. Bodies are authored at column 0 with 4-space relative indentation - absolute indentation is applied at insertion time - and every snippet carries an explicit `$end$`, which is what lets the expansion client avoid reading the snippet XML back out of the live session. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Insert Snippet (Ctrl+K,Ctrl+X), Surround With (Ctrl+K,Ctrl+S), Tab expansion of a snippet shortcut, and the keys that drive a live expansion session. Nothing here reuses Roslyn: its snippet stack is `internal` under `LanguageServices.Implementation.Snippets` with no ExternalAccess surface, so F# writes its own `IVsExpansionClient` the way it already writes its own brace completion. The commands come in through one MEF `ICommandHandler<_>` part, ordered after the completion handler so that Tab still commits an open completion list first. Indentation is the F#-specific part. The expansion engine inserts snippet text verbatim, and C# gets away with that because Roslyn's formatter reflows the result afterwards; F# has no formatter, so `FormatSpan` computes the columns. That arithmetic lives in `SnippetIndentation`, free of editor types so that it can be tested on its own - the policy is where the mistakes live, not the buffer edit that applies it. A directive wrapper is its own line kind: `#if`/`#else`/`#endif` and the scoped `#nowarn`/`#warnon` pair read at the left margin whatever they wrap, so the code they cover keeps the column it had. Two things worth knowing for anyone reading `IVsExpansionClient` next to Roslyn's: `tsInsertPos` is the range `InsertNamedExpansion` replaces, so handing it the selection deletes the code a SurroundsWith snippet was meant to wrap; and `GetFieldSpan "selected"` does not answer for that special literal, so the substituted range is derived from the template's own `$selected$` line plus the line count the command handler took before the insertion. `ClassName()` and `GenerateMatchCases()` back the `ctor`, `equals` and `match` snippets. Both are synchronous COM callbacks, so they block; `ClassName()` blocks on a parse and `GenerateMatchCases()` on the stale-tolerant check-results path, falling back to a visible `| _ -> ()` rather than waiting unbounded. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

A RequireQualifiedAccess union rejects a bare case pattern (`A`, not `U.A`) - the generated pattern binds a fresh variable instead of testing the case, so it takes the first arm regardless of the actual value. matchRulesFor now qualifies with the entity's DisplayName when the union carries the attribute, the same way it already does for enums. ClassName() used the navigation item's LogicalName, which is qualified by every enclosing module ("Outer.C") - it does not resolve from a constructor sitting inside C's own scope. Strips to the name after the last '.'. GenerateMatchCases() resolved the lexer symbol nearest the field's end position, which is whatever identifier happens to sit there - for `f x`, that is `x`, not the call `f x`. Reads the type the checker captured for the field's whole span instead (TryGetCapturedType), so it matches the expression's own result type regardless of its shape. Surround With reindented every non-first selected line uniformly, including a line that is itself inside a multi-line string continued from an earlier selected line - inserting indentation there changes the string's value, not just its position. classifyLines now threads the lexer's color state across the span and classifies such a line as InsideString, left untouched like a blank line. lock.snippet closed the lambda on the same line as $selected$$end$, so a selection whose last line ends in a trailing // comment swallowed the closing paren into the comment, leaving the call unclosed. Moved onto its own line, matching how the other wrapping snippets already close. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

A match on a union or enum now spells its cases with the shortest qualifier that resolves at the insertion point, asked of the checked file the way the simplify-names analyzer asks it, instead of assuming `DisplayName.` is reachable: a `[<RequireQualifiedAccess>]` union in an unopened module produced `U.A`, which does not resolve. The expression's captured type is used as it stands, so matching a function value no longer generates the arms of its result type. Indentation is measured in visual columns. A snippet expanded after a tab took the character count as its column and came out one space in, and Surround With over tab-indented code wrapped it at the wrong column. A cancelled Surround With never reports back, so its pending selection was still set when the next shortcut expanded; the shortcut path now clears it. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Expands and surrounds like `task`, for code that has to run off the caller's context. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Copilot

Copilot review overview

🟡 Changes recommended

Unresolved insertion-crash, interface-snippet, line-ending, and expansion-session issues remain.

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Review effort: Lite
Findings: 1 · 1

Open (2)

Zero-length indentation causes out-of-range snapshot access · New
Custom function paths lack focused regression tests · New

What changed in this PR

Adds Visual Studio snippet support for F#, including insertion, surround-with, Tab expansion, dynamic type-name and match-case generation, packaging, tests, localization, and release notes.

Changes:

Adds and registers 41 built-in F# snippets.
Implements snippet commands, expansion sessions, indentation, and dynamic functions.
Adds catalog and indentation tests plus localized resources.

File	Description
`vsintegration/Vsix/VisualFSharpFull/VisualFSharp.Core.targets`	Packages snippet assets.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/SnippetsIndex.xml`	Registers the snippet catalog.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/while.snippet`	Adds the `while` snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/use.snippet`	Adds the `use` snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/tryf.snippet`	Adds the `try/finally` snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/try.snippet`	Adds the `try` snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/task.snippet`	Adds the `task` snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/struct.snippet`	Adds the `struct` snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/seq.snippet`	Adds the sequence snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/record.snippet`	Adds the record snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/propfull.snippet`	Adds the full property snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/prop.snippet`	Adds the property snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/pp_if.snippet`	Adds the conditional compilation snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/pfn.snippet`	Adds the function snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/override.snippet`	Adds the override snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/nowarn.snippet`	Adds the warning suppression snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/module.snippet`	Adds the module snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/member.snippet`	Adds the member snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/matchvo.snippet`	Adds the value-option match snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/matcht.snippet`	Adds the tuple match snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/matchr.snippet`	Adds the record match snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/matcho.snippet`	Adds the option match snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/match.snippet`	Adds the dynamic match snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/main.snippet`	Adds the main function snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/lock.snippet`	Adds the lock snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/interface.snippet`	Adds the interface declaration snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/ife.snippet`	Adds the `if/else` expression snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/iface.snippet`	Adds the interface implementation snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/if.snippet`	Adds the `if` snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/forr.snippet`	Adds the range loop snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/for.snippet`	Adds the `for` loop snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/ext.snippet`	Adds the extension snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/exn.snippet`	Adds the exception snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/equals.snippet`	Adds the equality override snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/enum.snippet`	Adds the enum snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/du.snippet`	Adds the discriminated union snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/dispose.snippet`	Adds the disposal snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/ctor.snippet`	Adds the constructor snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/class.snippet`	Adds the class snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/backgroundTask.snippet`	Adds the background task snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/attribute.snippet`	Adds the attribute snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/async.snippet`	Adds the async snippet.
`vsintegration/Vsix/VisualFSharpFull/snippets/1033/FSharp/abstract.snippet`	Adds the abstract member snippet.
`vsintegration/Vsix/RegisterFsharpPackage.pkgdef`	Registers snippet paths and language metadata.
`vsintegration/tests/FSharp.Editor.Tests/Snippets/SnippetIndentationTests.fs`	Tests snippet indentation.
`vsintegration/tests/FSharp.Editor.Tests/Snippets/SnippetCatalogTests.fs`	Validates the snippet catalog.
`vsintegration/tests/FSharp.Editor.Tests/FSharp.Editor.Tests.fsproj`	Includes snippet tests and assets.
`vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.zh-Hant.xlf`	Adds Traditional Chinese resources.
`vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.zh-Hans.xlf`	Adds Simplified Chinese resources.
`vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.tr.xlf`	Adds Turkish resources.
`vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.ru.xlf`	Adds Russian resources.
`vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.pt-BR.xlf`	Adds Brazilian Portuguese resources.
`vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.pl.xlf`	Adds Polish resources.
`vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.ko.xlf`	Adds Korean resources.
`vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.ja.xlf`	Adds Japanese resources.
`vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.it.xlf`	Adds Italian resources.
`vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.fr.xlf`	Adds French resources.
`vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.es.xlf`	Adds Spanish resources.
`vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.de.xlf`	Adds German resources.
`vsintegration/src/FSharp.Editor/xlf/FSharp.Editor.cs.xlf`	Adds Czech resources.
`vsintegration/src/FSharp.Editor/Snippets/SnippetIndentation.fs`	Implements expansion indentation.
`vsintegration/src/FSharp.Editor/Snippets/SnippetFunctions.fs`	Implements dynamic snippet functions.
`vsintegration/src/FSharp.Editor/Snippets/SnippetExpansionClient.fs`	Manages expansion sessions.
`vsintegration/src/FSharp.Editor/Snippets/SnippetCommandHandler.fs`	Handles snippet commands and shortcuts.
`vsintegration/src/FSharp.Editor/LanguageService/FSharpEditorFactory.fs`	Adds the command-handler name.
`vsintegration/src/FSharp.Editor/FSharp.Editor.resx`	Adds command resources.
`vsintegration/src/FSharp.Editor/FSharp.Editor.fsproj`	Includes snippet implementation files.
`vsintegration/src/FSharp.Editor/Common/Vs.fs`	Exposes the expansion manager.
`vsintegration/src/FSharp.Editor/Common/Extensions.fs`	Adds line-ending detection.
`docs/release-notes/.VisualStudio/18.vNext.md`	Documents the feature.

+        for offset in 0 .. length - 1 do
+            column <- SnippetIndentation.advanceColumn tabSize column snapshot[start + offset]


+    /// The match rules covering the union or enum `$expression$` evaluates to, or ValueNone for any
+    /// other type.
+    let tryGetMatchRules (document: Document) (span: VsTextSpan) =
+        cancellableTask {
+            let! _, checkResults = document.GetFSharpParseAndCheckResultsAsync userOpName
+            let! ct = CancellableTask.getCancellationToken ()
+            let! sourceText = document.GetTextAsync ct
+
+            let range =
+                Range.mkRange
+                    document.FilePath
+                    (Position.mkPos (span.iStartLine + 1) span.iStartIndex)
+                    (Position.mkPos (span.iEndLine + 1) span.iEndIndex)
+
+            let position = sourceText.Lines[span.iEndLine].Start + span.iEndIndex
+
+            let rules =
+                match checkResults.TryGetCapturedType range with
+                | Some fsharpType ->
+                    let fsharpType = fsharpType.StripAbbreviations()
+
+                    if fsharpType.HasTypeDefinition then
+                        matchRulesFor checkResults range.Start fsharpType.TypeDefinition
+                    else
+                        Seq.empty
+                | None -> Seq.empty
+
+            return
+                match String.Join(sourceText.LineBreakAt position, rules) with


github-project-automation Bot added this to F# Compiler and Tooling Sep 11, 2026

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xperiandri marked this pull request as ready for review September 11, 2026 09:51

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xperiandri changed the title ~~Code snippets for F# in Visual Studio (Ctrl+K,Ctrl+X / Ctrl+K,Ctrl+S)~~ Code snippets for F# in Visual Studio (Ctrl+K,Ctrl+X / Ctrl+K,Ctrl+S) Sep 11, 2026

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xperiandri changed the title ~~Code snippets for F# in Visual Studio (Ctrl+K,Ctrl+X / Ctrl+K,Ctrl+S)~~ Add F# code snippets (Ctrl+K,Ctrl+X / Ctrl+K,Ctrl+S) Sep 14, 2026

xperiandri force-pushed the feature/vs-code-snippets branch 2 times, most recently from 50be8a5 to 77bccb8 Compare September 17, 2026 22:51

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Comment thread vsintegration/src/FSharp.Editor/Snippets/SnippetExpansionClient.fs

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Comment thread vsintegration/src/FSharp.Editor/Snippets/SnippetFunctions.fs Outdated

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xperiandri force-pushed the feature/vs-code-snippets branch from 080f662 to e7775f7 Compare September 23, 2026 18:38

xperiandri and others added 6 commits September 24, 2026 13:36

Link the snippets release note to its issue and pull request

d6ea391

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Add a backgroundTask snippet

80593e5

Expands and surrounds like `task`, for code that has to run off the caller's context. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

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		for offset in 0 .. length - 1 do
		column <- SnippetIndentation.advanceColumn tabSize column snapshot[start + offset]

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