Active patterns with defined with otherwise invalid name is incorrectly re-formatted

[josh-degraw]

Issue created from fantomas-online

Code

let (|``Custom Prefix``|_|) (p: string) (s: string) =
  if s.StartsWith(p) then
    Some(s.Substring(p.Length))
  else
    None

Result

let (|Custom Prefix|_|) (p: string) (s: string) =
    if s.StartsWith(p) then
        Some(s.Substring(p.Length))
    else
        None

Problem description

Please describe here the Fantomas problem you encountered.
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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 1/1/1990

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]

You should snatch the original ident text from source code in

fantomas/src/Fantomas.Core/ASTTransformer.fs

Line 42 in 06d86ad

| Some(IdentTrivia.HasParenthesis _) -> stn $"(%s{ident.idText})" ident.idRange

using creationAide.TextFromSource fallback range.

[nojaf]

Actually, we should reuse the logic of

fantomas/src/Fantomas.Core/ASTTransformer.fs

Lines 25 to 42 in 06d86ad

	let mkIdent (ident: Ident) =
	let width = ident.idRange.EndColumn - ident.idRange.StartColumn
	let text =
	if ident.idText.Length + 4 = width then
	// add backticks
	$"``%s{ident.idText}``"
	else
	ident.idText
	stn text ident.idRange
	let mkSynIdent (SynIdent(ident, trivia)) =
	match trivia with
	| None -> mkIdent ident
	| Some(IdentTrivia.OriginalNotation text) -> stn text ident.idRange
	| Some(IdentTrivia.OriginalNotationWithParen(_, text, _)) -> stn $"(%s{text})" ident.idRange
	| Some(IdentTrivia.HasParenthesis _) -> stn $"(%s{ident.idText})" ident.idRange

instead (ident.idText.Length + 4 = width) perhaps.