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Support explicit struct optional args (?x=…) #19113

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fa324a8
Add test
brianrourkeboll Nov 22, 2025
669a6bb
Support explicit struct optional args
brianrourkeboll Nov 22, 2025
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8 changes: 8 additions & 0 deletions src/Compiler/Checking/ConstraintSolver.fs
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Expand Up @@ -3213,6 +3213,10 @@ and ArgsMustSubsumeOrConvert
match usesTDC with
| TypeDirectedConversionUsed.Yes(warn, _, _) -> do! WarnD(warn csenv.DisplayEnv)
| TypeDirectedConversionUsed.No -> ()
let callerTy =
let g = csenv.g
if isValueOptionTy g calledArgTy && isOptionTy g callerTy then mkValueOptionTy g (destOptionTy g callerTy)
else callerTy
do! SolveTypeSubsumesTypeWithReport csenv ndeep m trace cxsln (Some calledArg.CalledArgumentType) calledArgTy callerTy
if g.langVersion.SupportsFeature(LanguageFeature.WarnWhenUnitPassedToObjArg) && isUnitTy g callerTy && isObjTyAnyNullness g calledArgTy then
do! WarnD(Error(FSComp.SR.tcUnitToObjSubsumption(), m))
Expand Down Expand Up @@ -3246,6 +3250,10 @@ and ArgsMustSubsumeOrConvertWithContextualReport
match usesTDC with
| TypeDirectedConversionUsed.Yes(warn, _, _) -> do! WarnD(warn csenv.DisplayEnv)
| TypeDirectedConversionUsed.No -> ()
let callerArgTy =
let g = csenv.g
if isValueOptionTy g calledArgTy && isOptionTy g callerArgTy then mkValueOptionTy g (destOptionTy g callerArgTy)
else callerArgTy
do! SolveTypeSubsumesTypeWithWrappedContextualReport csenv ndeep m trace cxsln (Some calledArg.CalledArgumentType) calledArgTy callerArgTy (fun e -> ArgDoesNotMatchError(e :?> _, calledMeth, calledArg, callerArg))
return usesTDC
}
Expand Down
26 changes: 25 additions & 1 deletion src/Compiler/Checking/Expressions/CheckExpressions.fs
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Expand Up @@ -10092,7 +10092,31 @@ and TcMethodApplication_CheckArguments
// This is the case where some explicit arguments have been given.

let unnamedCurriedCallerArgs = unnamedCurriedCallerArgs |> List.mapSquared (fun (argExpr, argTy, mArg) -> CallerArg(argTy, mArg, false, argExpr))
let namedCurriedCallerArgs = namedCurriedCallerArgs |> List.mapSquared (fun (id, isOpt, argExpr, argTy, mArg) -> CallerNamedArg(id, CallerArg(argTy, mArg, isOpt, argExpr)))
let namedCurriedCallerArgs =
if
g.langVersion.SupportsFeature LanguageFeature.SupportValueOptionsAsOptionalParameters
&& namedCurriedCallerArgs |> List.existsSquared (fun (_, isOpt, _, _, _) -> isOpt)
then
let voptionParams =
(Set.empty, preArgumentTypeCheckingCalledMethGroup)
||> List.fold (fun acc calledMeth ->
(acc, calledMeth.AssignedNamedArgs)
||> List.fold (fun acc args ->
(acc, args)
||> List.fold (fun acc arg ->
match arg.CalledArg.OptArgInfo, arg.NamedArgIdOpt with
| CalleeSide, Some argId when isValueOptionTy g arg.CalledArg.CalledArgumentType && arg.CallerArg.IsExplicitOptional -> acc |> Set.add argId.idText
| _ -> acc)))

namedCurriedCallerArgs |> List.mapSquared (fun (id : Ident, isOpt, argExpr, argTy, mArg) ->
let argTy =
if isOpt && voptionParams |> Set.contains id.idText && isOptionTy g argTy then mkValueOptionTy g (destOptionTy g argTy)
else argTy
Comment on lines +10112 to +10114
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@brianrourkeboll brianrourkeboll Nov 22, 2025

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This is a bit of hack and might cause other problems.

I wonder if it could/should be done here instead?

fsharp/src/Compiler/Checking/Expressions/CheckExpressions.fs

Line 9945 in cfda5f6

and TcMethodApplication_UniqueOverloadInference

fsharp/src/Compiler/Checking/Expressions/CheckExpressions.fs

Lines 9966 to 9968 in cfda5f6

// Build the CallerArg values for the caller's arguments.
// Fake up some arguments if this is the use of a method as a first class function
let unnamedCurriedCallerArgs, namedCurriedCallerArgs, returnTy =

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@brianrourkeboll brianrourkeboll Nov 22, 2025

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...Lol, yeah, it broke a bunch of stuff.

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@brianrourkeboll brianrourkeboll Nov 22, 2025

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Meh. Won't work there, either.

We'd really need to somehow defer checking the kind of the optional param till overload resolution...

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@brianrourkeboll brianrourkeboll Nov 23, 2025

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Oh, silly. I forgot to check whether the caller arg was an explicit optional arg here:

fsharp/src/Compiler/Checking/ConstraintSolver.fs

Lines 3216 to 3219 in 669a6bb

let callerTy =
let g = csenv.g
if isValueOptionTy g calledArgTy && isOptionTy g callerTy then mkValueOptionTy g (destOptionTy g callerTy)
else callerTy

But even if I did check that, this approach seems potentially wrong: is it possible to know here that a different overload wouldn't be picked if we didn't swap out the caller arg type? Would doing some subset of the overload resolution analysis here be enough, e.g., at least making sure that the explicit optional caller arg's position lined up with at least one struct optional arg's position on a candidate method?


CallerNamedArg(id, CallerArg(argTy, mArg, isOpt, argExpr)))
else
namedCurriedCallerArgs |> List.mapSquared (fun (id, isOpt, argExpr, argTy, mArg) -> CallerNamedArg(id, CallerArg(argTy, mArg, isOpt, argExpr)))


// Collect the information for F# 3.1 lambda propagation rule, and apply the caller's object type to the method's object type if the rule is relevant.
let lambdaPropagationInfo =
Expand Down
6 changes: 6 additions & 0 deletions ...Conformance/BasicGrammarElements/MemberDefinitions/OptionalArguments/OptionalArguments.fs
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Expand Up @@ -115,6 +115,12 @@ module MemberDefinitions_OptionalArguments =
|> verifyCompileAndRun
|> shouldSucceed

[<Theory; Directory(__SOURCE_DIRECTORY__, Includes=[|"RefAndStructOptionalArgParity.fs"|])>]
let ``RefAndStructOptionalArgParity_fs`` compilation =
compilation
|> verifyCompileAndRun
|> shouldSucceed

[<Fact>]
let ``Optional Arguments can't be a ValueOption+StructAttribute attribute with langversion=9`` () =
let source =
Expand Down
17 changes: 17 additions & 0 deletions ...BasicGrammarElements/MemberDefinitions/OptionalArguments/RefAndStructOptionalArgParity.fs
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@@ -0,0 +1,17 @@
module M

type T =
static member MRef (?x : int) = ()
static member MStruct ([<Struct>] ?x : int) = ()

T.MRef 3
T.MRef ()
T.MRef (x=3)
T.MRef (?x=None)
T.MRef (?x=Some 3)

T.MStruct 3
T.MStruct ()
T.MStruct (x=3)
T.MStruct (?x=ValueNone)
T.MStruct (?x=ValueSome 3)
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