Reformatting multiple array index operators (v6 style) adds spaces that are invalid

[richardcox13]

Issue created from fantomas-online

Code

let a = Array.create 10 -1
let b = Array.create 10 a

printfn "%d -> %d" a[0] (b[0][0])

Result

let a = Array.create 10 -1
let b = Array.create 10 a

printfn "%d -> %d" a[0] (b [ 0 ] [ 0 ])

Problem description

See above for the simplest repro I could come up with (real case had expressions for the indexes. Note using pre-v6 indexing (.[…]) works.

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 2022-03-11T15:23:45Z - 1531c68

Default Fantomas configuration

_{Did you know that you can ignore files when formatting from fantomas-tool or the FAKE targets by using a .fantomasignore file?}

[nojaf]

Hello Richard, thank you for creating this issue.
The new index syntax in F# 6 is not fully supported yet in Fantomas.

To fix this, I believe we need to extend:

fantomas/src/Fantomas/SourceParser.fs

Lines 906 to 918 in 9059695

	// expr1[expr2]
	// ref: https://github.com/fsharp/fslang-design/blob/main/FSharp-6.0/FS-1110-index-syntax.md
	let (|IndexWithoutDotExpr|_|) =
	function
	| SynExpr.App (ExprAtomicFlag.Atomic, false, identifierExpr, SynExpr.ArrayOrListComputed (false, indexExpr, _), _) ->
	Some(identifierExpr, indexExpr)
	| SynExpr.App (ExprAtomicFlag.NonAtomic,
	false,
	identifierExpr,
	(SynExpr.ArrayOrListComputed (isArray = false; expr = indexExpr) as argExpr),
	_) when (RangeHelpers.isAdjacentTo identifierExpr.Range argExpr.Range) ->
	Some(identifierExpr, indexExpr)
	| _ -> None

and capture the AST shape of b[0][0]

Are you interested in submitting a PR for this?

[richardcox13]

Having had a brief look at that, it it somewhat beyond my current level of F# and parsing expertise. Sorry.

[richardcox13]

Thanks for the fix.

[nojaf]

I'll publish a new version tomorrow.

[richardcox13]

Fix confirmed.