Add a refactoring between ?x and [<Struct>] ?x optional parameters

[xperiandri]

Offers Ctrl+. on a member's optional parameter to switch it between option and voption (F# 10). defaultArg, Option functions and match cases on it in the body, and ?x = value arguments at call sites across the solution, are rewritten to match.

Not offered when a use of the parameter would change type (passed on, Option.map), for overrides, abstract slots and constructors, or when the file has a paired .fsi.

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[github-actions]

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✅ Found changes and release notes in following paths:

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

[github-actions]

🔍 Tooling Safety Check — Affects-Design-Time
Affects-Design-Time: Modifies Visual Studio code executed while projects are open.

Generated by PR Tooling Safety Check · gpt56 1.8M · ◷

[T-Gro]

🤖🕵️ Please shorten the description using this guidance. Focus on the problem and why the change is needed, in simplified technical English. Leave the implementation inventory to the Files tab and retain necessary caveats.

[xperiandri]

Covered cases

Converts

• Parameter and body: member _.Greet(name: string, ?greeting: string) with defaultArg greeting "Hello" → [<Struct>] ?greeting: string with defaultValueArg greeting "Hello"
• Call sites in the same file: ?greeting = Some "Hey" → ?greeting = ValueSome "Hey", and ?greeting = g (with g: string option) → ?greeting = ValueOption.ofOption g; Greet("Ada") and greeting = "Hi" stay as they are
• Converting that whole file back gives back the original exactly (ValueSome "Hey" → Some "Hey", ValueOption.ofOption g → g)
• match on the parameter: | Some s -> s | None -> 1 → | ValueSome s -> s | ValueNone -> 1, both ways
• Option module functions, called directly or through a pipe, in a static member: Option.isSome step && step.IsSome then step |> Option.defaultValue 0 → ValueOption.isSome step && step.IsSome then step |> ValueOption.defaultValue 0 (IsSome unchanged), both ways
• Expression argument at a call site: ?step = (if true then step else None) → ?step = ValueOption.ofOption (if true then step else None), both ways
• A voption passed to a struct parameter, when converting back: ?step = step (with step: int voption) → ?step = ValueOption.toOption step
• Action titles: Use 'voption' for optional parameter / Use 'option' for optional parameter, exactly one action each
• Each converted document type-checks without errors

Not offered

• Parameter passed to a function the conversion does not handle: static member M(?x: int) = printfn "%A" x
• Option module function that is not supported: Option.map string x
• Override of an abstract slot: abstract M: ?x: int -> int with default _.M(?x) = defaultArg x 0
• Caret on the member name (M() instead of the parameter
• Parameter that is not optional: static member M(x: int option) = defaultArg x 0
• Before F# 10 (--langversion:9.0): static member M(?x: int) = defaultArg x 0
• File that has a signature file: static member M: ?x: int -> int