Invalid location of comma when using named parameters for a class

[MNie]

Issue created from fantomas-online

Code

type MyCSharpClass() =
    member val Prop = 0.0m with get, set
    member val Prop2 = 0.0m with get, set

type FSharpType = {
    SomeValue: string option
}

let v = { SomeValue = Some "str" }

let instance = 
    MyClass(
        Prop = 
            match value.SomeValue with 
            | Some _ -> 0.0m
            | None -> 0.0m
        ,
        Prop2 =
            match value.SomeValue with
            | Some _ -> 0.0m
            | None -> 0.0m
    )

Result

type MyCSharpClass() =
    member val Prop = 0.0m with get, set
    member val Prop2 = 0.0m with get, set

type FSharpType = { SomeValue: string option }

let v = { SomeValue = Some "str" }

let instance =
    MyClass(
        Prop =
            match value.SomeValue with
            | Some _ -> 0.0m
            | None -> 0.0m,
        Prop2 =
            match value.SomeValue with
            | Some _ -> 0.0m
            | None -> 0.0m
    )

Problem description

It seems that when we have multiple match statements passed to named parameters for a class it places the , in the wrong place. That results in a dotnet fantomas error.

Known workarounds are:

1. surround the match statement with (),

let instance = 
    MyClass(
        (Prop = 
            match value.SomeValue with 
            | Some _ -> 0.0m
            | None -> 0.0m)
        ,
        (Prop2 =
            match value.SomeValue with
            | Some _ -> 0.0m
            | None -> 0.0m)
    )

2. extract the match statement to an explicit variable.

let instance = 
    let v1 =
            match value.SomeValue with 
            | Some _ -> 0.0m
            | None -> 0.0m
    let v2 =
            match value.SomeValue with 
            | Some _ -> 0.0m
            | None -> 0.0m
    MyClass(
        Prop = v1,
        Prop2 = v2
    )

Extra information

• The formatted result breaks my code.
• The formatted result gives compiler warnings.
• I or my company would be willing to help fix this.

Options

Fantomas main branch at 2023-04-20T16:04:28Z - 4ed1e9d

Default Fantomas configuration

• Fantomas v6,
• .NET6

[nojaf]

Hello,

Thank you for reporting this issue!
I think you could extend this check to include your use-case:

fantomas/src/Fantomas.Core/CodePrinter.fs

Lines 1876 to 1895 in f144756

	let containsLambdaOrMatchExpr =
	// If the any items (expect the last) is a match/lambda
	node.Items
	|> List.chunkBySize 2
	|> List.exists (fun pair ->
	match pair with
	| [ Choice1Of2 e; Choice2Of2 _ ] ->
	match e with
	| Expr.Match _
	| Expr.Lambda _ -> true
	| Expr.InfixApp node ->
	match node.RightHandSide with
	| Expr.Lambda _ -> true
	| _ -> false
	| Expr.SameInfixApps node ->
	match List.last node.SubsequentExpressions with
	| _, Expr.Lambda _ -> true
	| _ -> false
	| _ -> false
	| _ -> false)

Are you interested in submitting a PR for this?

[MNie]

@nojaf will try to do so at the end of this week : )