Fix 2954 by using mkIdent in SynPat.OptionalVal

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Changelog
 
+## [Unreleased]
+
+### Fixed
+* Backticks in optional parameter gets removed [#2954](https://github.com/fsprojects/fantomas/issues/2954)
+
 ## 6.2.0 - 2023-08-29
 
 ### Changed

src/Fantomas.Core.Tests/TypeDeclarationTests.fs

@@ -3593,6 +3593,23 @@ type ArrayBuffer =
     abstract slice: ``begin``: int * ?``end``: int -> ArrayBuffer
 """
 
+[<Test>]
+let ``optional member parameter with ticks, 2954`` () =
+    formatSourceString
+        false
+        """
+type C() =
+    static member foo(?``type``) = ``type``
+"""
+        config
+    |> prepend newline
+    |> should
+        equal
+        """
+type C() =
+    static member foo(?``type``) = ``type``
+"""
+
 [<Test>]
 let ``trivia before comma in primary constructor`` () =
     formatSourceString

src/Fantomas.Core/ASTTransformer.fs

@@ -1630,7 +1630,9 @@ let mkPat (creationAide: CreationAide) (p: SynPat) =
     let patternRange = p.Range
 
     match p with
-    | SynPat.OptionalVal(ident, _) -> stn $"?{ident.idText}" patternRange |> Pattern.OptionalVal
+    | SynPat.OptionalVal(ident, _) ->
+        let identNode = mkIdent ident
+        SingleTextNode($"?{identNode.Text}", patternRange) |> Pattern.OptionalVal
     | PatParameter(ats, pat, t) ->
         PatParameterNode(
             mkAttributes creationAide ats,