Delegate with many parameters result in a compilation error.

[MNie]

Issue created from fantomas-online

Code

type SomeWin32Callback = delegate of (NastyWinApi32Type * int * int * int * NastyWinApi32Type * int * int * int * int * NastyWinApi32Type * int * int) -> bool

Result

type SomeWin32Callback = delegate of
    (NastyWinApi32Type * int * int * int * NastyWinApi32Type * int * int * int * int * NastyWinApi32Type * int * int) ->
    bool

Problem description

I want to create a WinApi32 type in my application because this type is a delegate that accepts 8 nasty WinApi32 parameters after Fantomas autosave autoformats generate not compilable code.

I assume that in such a scenario it shouldn't format it at all(?) or use some indentation in new lines.

like:

type SomeWin32Callback = delegate of (NastyWinApi32Type * int * int * int * NastyWinApi32Type * int * int * int * int * NastyWinApi32Type * int * int) -> bool

or

type SomeWin32Callback = delegate of 
                               (NastyWinApi32Type * int * int * int * NastyWinApi32Type * int * int * int * int * NastyWinApi32Type * int * int) -> 
                               bool

Extra information

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

If this is indeed an issue I would be glad to help fix it : )

Options

Fantomas version: 4.5.0-alpha-001
Master at 03/08/2021 19:16:36 - a2fd887

Default Fantomas configuration

[nojaf]

Hello Michal, thank you for reporting this issue.
I would expect the output to be:

type SomeWin32Callback = 
    delegate of 
         NastyWinApi32Type *
         int *
         int *
         int *
         NastyWinApi32Type *
         int *
         int *
         int *
         int *
         NastyWinApi32Type *
         int *
         int
        -> bool

in this case.

To solve this, there are two parts.
The first is moving the delegate of to the next line when it crossed the max_line_length.

fantomas/src/Fantomas/CodePrinter.fs

Lines 3617 to 3622 in a2fd887

	| ObjectModel (TCDelegate (FunType ts), _, _) ->
	typeName
	+> sepEq
	+> sepSpace
	+> !- "delegate of "
	+> genTypeList astContext ts

Change this to:

    | ObjectModel (TCDelegate (FunType ts), _, _) ->
        let short =
            typeName
            +> sepEq
            +> sepSpace
            +> !- "delegate of "
            +> genTypeList astContext ts
        let long =
            typeName
            +> sepEq
            +> indent
            +> sepNln
            +> !- "delegate of "
            +> genTypeList astContext ts
            +> unindent
        expressionFitsOnRestOfLine short long

The next part is trickier, because of the long tupled definition I would also be splitted on separate lines.
We already do this when there are no parenthesis in genTypeList (example)

fantomas/src/Fantomas/CodePrinter.fs

Lines 4246 to 4299 in a2fd887

	and genTypeList astContext node =
	let gt (t, args: SynArgInfo list) =
	match t, args with
	| TTuple ts', _ ->
	let hasBracket = not node.IsEmpty
	let gt sepBefore =
	if args.Length = ts'.Length then
	col
	sepBefore
	(Seq.zip args (Seq.map snd ts'))
	(fun ((ArgInfo (ats, so, isOpt)), t) ->
	genOnelinerAttributes astContext ats
	+> opt
	sepColon
	so
	(if isOpt then
	(sprintf "?%s" >> (!-))
	else
	(!-))
	+> genType astContext hasBracket t)
	else
	col sepBefore ts' (snd >> genType astContext hasBracket)
	let shortExpr = gt sepStar
	let longExpr = gt (sepNln +> sepStarFixed)
	expressionFitsOnRestOfLine shortExpr longExpr
	| _, [ ArgInfo (ats, so, isOpt) ] ->
	match t with
	| TTuple _ -> not node.IsEmpty
	| TFun _ -> true // Fun is grouped by brackets inside 'genType astContext true t'
	| _ -> false
	|> fun hasBracket ->
	genOnelinerAttributes astContext ats
	+> opt
	sepColon
	so
	(if isOpt then
	(sprintf "?%s" >> (!-))
	else
	(!-))
	+> genType astContext hasBracket t
	| _ -> genType astContext false t
	let shortExpr = col sepArrow node gt
	let longExpr =
	indent
	+> sepNln
	+> col (sepArrow +> sepNln) node gt
	+> unindent
	expressionFitsOnRestOfLine shortExpr longExpr

Add something like:

        | TParen (TTuple ts'), _ ->
            !- "TODO: something clever"

Are you interested in submitting a PR?
If so please check out our Contribution Guidelines (and add a test to TypeDeclarationTests).

[MNie]

@nojaf thanks! I will take a look if I could prepare something : )

[nojaf]

Thank you, feel free to ask questions you might have along the way.