Fix issue #19074: Support voption with optional parameter syntax (?x=)

Revert incorrect attribute changes and fix the actual issue where using
?x=ValueNone or ?x=ValueSome with optional parameters expecting voption
was failing with type mismatch.

The fix allows the type inference to determine whether to use option or
voption based on the parameter type when the language feature is enabled.

Co-authored-by: T-Gro <[email protected]>

Author: Copilot

src/Compiler/Checking/Expressions/CheckExpressions.fs

@@ -9934,7 +9934,7 @@ and TcMethodApplication_SplitSynArguments
                 // named optional arguments should always have option type
                 // STRUCT OPTIONS: if we allow struct options as optional arguments then we should relax this and rely
                 // on later inference to work out if this is a struct option or ref option
-                let ty = if isOpt then mkOptionTy denv.g ty else ty
+                let ty = if isOpt && not (denv.g.langVersion.SupportsFeature LanguageFeature.SupportValueOptionsAsOptionalParameters) then mkOptionTy denv.g ty else ty
                 nm, isOpt, x, ty, x.Range)
 
             (Some (unnamedCurriedCallerArgs, namedCurriedCallerArgs), None, exprTy)

src/Compiler/Checking/PostInferenceChecks.fs

@@ -1974,8 +1974,6 @@ and CheckAttribArgExpr cenv env expr =
     | AttribBitwiseOrExpr g (arg1, arg2) ->
         CheckAttribArgExpr cenv env arg1
         CheckAttribArgExpr cenv env arg2
-    | Expr.Op (TOp.UnionCase _, _, args, _) ->
-        List.iter (CheckAttribArgExpr cenv env) args
     | _ ->
         if cenv.reportErrors then
            errorR (Error (FSComp.SR.chkInvalidCustAttrVal(), expr.Range))

src/Compiler/TypedTree/TypedTreeOps.fs

@@ -10329,9 +10329,6 @@ let rec EvalAttribArgExpr suppressLangFeatureCheck (g: TcGlobals) (x: Expr) =
         | _ ->
             errorR (Error ( FSComp.SR.tastNotAConstantExpression(), x.Range))
             x
-    | Expr.Op (TOp.UnionCase _, _, _args, _) ->
-        // Union cases (like ValueNone, Some x) are valid constant expressions for attributes
-        x
     | _ -> 
         errorR (Error ( FSComp.SR.tastNotAConstantExpression(), x.Range))
         x
@@ -10341,8 +10338,6 @@ and EvaledAttribExprEquality g e1 e2 =
     | Expr.Const (c1, _, _), Expr.Const (c2, _, _) -> c1 = c2
     | TypeOfExpr g ty1, TypeOfExpr g ty2 -> typeEquiv g ty1 ty2
     | TypeDefOfExpr g ty1, TypeDefOfExpr g ty2 -> typeEquiv g ty1 ty2
-    | Expr.Op (TOp.UnionCase (UnionCaseRef(tc1, nm1)), _, args1, _), Expr.Op (TOp.UnionCase (UnionCaseRef(tc2, nm2)), _, args2, _) ->
-        tyconRefEq g tc1 tc2 && nm1 = nm2 && (args1.Length = args2.Length) && List.forall2 (EvaledAttribExprEquality g) args1 args2
     | _ -> false
 
 [<return: Struct>]