Add F# code snippets (Ctrl+K,Ctrl+X / Ctrl+K,Ctrl+S)

[xperiandri]

Fixes #1498

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]

❗ Release notes required

You can open this PR in browser to add release notes: open in github.dev

---

✅ Found changes and release notes in following paths:

Change path	Release notes path	Description
`vsintegration/src`	docs/release-notes/.VisualStudio/18.vNext.md

[xperiandri]

[github-actions]

🔍 Tooling Safety Check — Affects-Build-Infra, Affects-Design-Time, Affects-Test-Tooling
Affects-Build-Infra: Changes VSIX targets and packaged build content.
Affects-Design-Time: Adds editor services executing inside Visual Studio.
Affects-Test-Tooling: Changes test content-copy and compilation configuration.

Generated by PR Tooling Safety Check · gpt56 1.3M · ◷

[xperiandri]

/azp run fsharp-ci

[azure-pipelines]

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

[T-Gro]

🤖 🕵️ AI review — verify independently.

[T-Gro]

🤖 🕵️ Wrong branch for [<RequireQualifiedAccess>] unions: generated A/B patterns bind variables instead of testing cases, so U.B takes the first arm.

[<RequireQualifiedAccess>]
type U = A | B
let value = U.B
// Insert match for value; fill the generated bodies with 0 and 1.
let run () =
    match value with
    | A -> 0
    | B -> 1
// run () returns 0, not 1; the patterns need U.A and U.B.

[T-Gro]

🤖 🕵️ Surround With changes multiline string values: wrapping this assignment in if true changes "a\nb" to "a\n b".

let mutable captured = ""
// Select the following two lines and surround with if true:
captured <- """a
b"""

[T-Gro]

🤖 🕵️ Inserting equals inside a nested module generates :? Outer.C, which fails with FS0039 because Outer is not in scope yet.

module Outer =
    type C() =
        member _.Value = 0
        // Insert equals here: ClassName() produces Outer.C instead of C.

[T-Gro]

🤖 🕵️ Matching a function application generates cases from its final argument instead of its result, producing FS0001 rather than valid match arms.

type Input = X | Y
type Output = A | B
let make (_: Input) = B
let value = Y
// Insert match with expression make value; generated arms:
match make value with
| X -> () // FS0001: expected Output, got Input
| Y -> ()

[T-Gro]

🤖 🕵️ Surround With puts ) inside a selected trailing // comment, leaving lock with an unmatched (. Keep the closing parenthesis on its own line.

let gate = obj()
lock gate (fun () ->
    printfn "working" // retained user comment
)

[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]

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