Fantoms breaks anonymous records in interpolated strings

[marcpiechura]

Issue created from fantomas-online

Code

$"""{ {| Prop = "XYZ" |} }"""

Result

$"""{{| Prop = "XYZ" |}}"""

Problem description

I'm using Fable and include the React/JSX part in F# via string interpolation like this:

JSX.jsx $"""
<Paper sx={ {| padding = theme.spacing 2 |} }>
...
</Paper>
"""

After Fantomas has reformatted the code and removed the space, the anonymous record is no longer recognized and becomes part of the string because {{ }} are for escaping a { } .
I can workaround it by defining a variable with the anonymous record, but it's quite annoying to do that for every style I need to apply.

let paperSx = {| padding = theme.spacing 2 |} 
JSX.jsx $"""
<Paper sx={paperSx}>
...
</Paper>
"""

Thanks.

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.
• I would like a release if this problem is solved.

Options

Fantomas main branch at ? - ?

Default Fantomas configuration

_{Did you know that you can ignore files when formatting by using a .fantomasignore file?
PS: It's unlikely that someone else will solve your specific issue, as it's something that you have a personal stake in.}

[nojaf]

Thank you for reporting this issue!
Are you interested in sending a PR for this?

[marcpiechura]

Sure, I'll try. Do you have a hint where I should look for fixing it?

[nojaf]

I think you could add a check here:

fantomas/src/Fantomas.Core/CodePrinter.fs

Lines 1541 to 1550 in 938160e

	col sepNone node.Parts (fun part ->
	match part with
	| Choice1Of2 stringNode -> genSingleTextNode stringNode
	| Choice2Of2 fillNode ->
	fun ctx ->
	let genFill =
	genInterpolatedFillExpr fillNode.Expr
	+> optSingle (fun format -> sepColonFixed +> genSingleTextNode format) fillNode.Ident
	genFill ctx)

If the expression is an (anonymous) record, add an additional sepSpace before and after.

More general information about the project can be found over at: https://fsprojects.github.io/fantomas/docs/contributors/Getting%20Started.html

[brianrourkeboll]

Note that this also appears to affect sequence expressions without seq ({ 1..10 }), which were deprecated in dotnet/fsharp#17772, but which are still technically legal.

[brianrourkeboll]

I can workaround it by defining a variable with the anonymous record, but it's quite annoying to do that for every style I need to apply.

Another workaround is to wrap the record/anonymous record in parentheses.

$"""{({| Prop = "XYZ" |})}"""