Trivia not restored after long identifier in SynField

[pbiggar]

Issue created from fantomas-online

Code

type X = 
  | A of int // This comment survives
  | B of C.D // This comment disappears!

Result

type X =
    | A of int // This comment survives
    | B of C.D

Problem description

The comment labelled "This comment disappears" disappears! I played around a bit and it seems that the key thing is the variant type to be in the form A.B.

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.

Options

Fantomas master branch at 1/1/1990

Default Fantomas configuration

[nojaf]

Hey Paul, thanks for raising this issue.
This is again another subtle trivia bug I'm afraid.

The comment that disappears is linked to the D Ident:

and it is not being handled in CodePrinter:

fantomas/src/Fantomas/CodePrinter.fs

Lines 4348 to 4355 in 10d0dcb

	| TLongIdent s ->
	ifElseCtx
	(fun ctx ->
	not ctx.Config.StrictMode
	&& astContext.IsCStylePattern)
	(!-(if s = "unit" then "void" else s))
	(!-s)
	|> genTriviaFor Ident_ current.Range

Because the TLongIdent active pattern does not keep track of the range an individual Ident, it just returns the combined string.

fantomas/src/Fantomas/SourceParser.fs

Lines 1503 to 1506 in 10d0dcb

	let (|TLongIdent|_|) =
	function
	| SynType.LongIdent (LongIdentWithDots s) -> Some s
	| _ -> None

Are you interested in submitting a PR for this one?

[pbiggar]

Are you interested in submitting a PR for this one?

Alas a busy time for me. If it's still here in a few months I might give it a go.