Merge branch 'main' into update-fsdocs

Author: nojaf

CHANGELOG.md

@@ -11,6 +11,7 @@
 - Multiline `val` body in signature files was not indented correctly. [#3269](https://github.com/fsprojects/fantomas/pull/3269)
 - `///` doc comment without associated declaration (e.g. at end of file) was duplicated when formatting. [#2499](https://github.com/fsprojects/fantomas/issues/2499)
 - NamedIndexedPropertySet with two SynLongIdent removed space. [#3273](https://github.com/fsprojects/fantomas/issues/3273)
+- `%%` (double-percent) infix operator moved to new line, producing invalid F#. [#2107](https://github.com/fsprojects/fantomas/issues/2107)
 
 ## [8.0.0-alpha-007] - 2026-03-10
 

src/Fantomas.Core/CodePrinter.fs

@@ -8,10 +8,17 @@ open Microsoft.FSharp.Core.CompilerServices
 let noBreakInfixOps = set [| "="; ">"; "<"; "%"; "%%" |]
 let newLineInfixOps = set [ "|>"; "||>"; "|||>"; ">>"; ">>=" ]
 
+let isFirstCharUppercase (v: string) =
+    match Seq.tryHead v with
+    | Some c -> Char.IsUpper c
+    | None -> false
+
 let rec (|UppercaseType|LowercaseType|) (t: Type) : Choice<unit, unit> =
     let upperOrLower (v: string) =
-        let isUpper = Seq.tryHead v |> Option.map Char.IsUpper |> Option.defaultValue false
-        if isUpper then UppercaseType else LowercaseType
+        if isFirstCharUppercase v then
+            UppercaseType
+        else
+            LowercaseType
 
     match t with
     | Type.LongIdent node ->
@@ -32,8 +39,10 @@ let rec (|UppercaseType|LowercaseType|) (t: Type) : Choice<unit, unit> =
 
 let rec (|UppercaseExpr|LowercaseExpr|) (expr: Expr) =
     let upperOrLower (v: string) =
-        let isUpper = Seq.tryHead v |> Option.map Char.IsUpper |> Option.defaultValue false
-        if isUpper then UppercaseExpr else LowercaseExpr
+        if isFirstCharUppercase v then
+            UppercaseExpr
+        else
+            LowercaseExpr
 
     let lastFragmentInList (identList: IdentListNode) =
         match List.tryLast identList.Content with