Add space around dots when negative floats are inside Expr.TripleNumb…

…erIndexRange (#3106)

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Changelog
 
+## 6.3.11 - 2024-08-16
+
+### Fixed
+* F# Range Operator (\.\.) with negative numbers produces invalid F# code and idempotent. [#3105](https://github.com/fsprojects/fantomas/issues/3105)
+
 ## 6.3.10 - 2024-07-12
 
 ### Changed

src/Fantomas.Core.Tests/ListTests.fs

@@ -2292,3 +2292,17 @@ let fns =
     Functions[Checked false
               OnChange(fun _ -> s |> updateSettings)]
 """
+
+[<Test>]
+let ``negative numbers in range operator, 3105`` () =
+    formatSourceString
+        """
+[|-24.0 .. -1.0 .. -30.0|]
+"""
+        config
+    |> prepend newline
+    |> should
+        equal
+        """
+[| -24.0 .. -1.0 .. -30.0 |]
+"""

src/Fantomas.Core/CodePrinter.fs

@@ -1546,10 +1546,19 @@ let genExpr (e: Expr) =
         |> genNode node
     | Expr.IndexRangeWildcard node -> genSingleTextNode node
     | Expr.TripleNumberIndexRange node ->
+        let isNegativeFloat (text: string) =
+            text.StartsWith("-", StringComparison.Ordinal) && text.Contains(".")
+
+        let genDots (before: SingleTextNode) (dots: SingleTextNode) (after: SingleTextNode) =
+            if not (isNegativeFloat before.Text) && not (isNegativeFloat after.Text) then
+                genSingleTextNode dots
+            else
+                sepSpace +> genSingleTextNode dots +> sepSpace
+
         genSingleTextNode node.Start
-        +> genSingleTextNode node.StartDots
+        +> genDots node.Start node.StartDots node.Center
         +> genSingleTextNode node.Center
-        +> genSingleTextNode node.EndDots
+        +> genDots node.Center node.EndDots node.EndDots
         +> genSingleTextNode node.End
         |> genNode node
     | Expr.IndexRange node ->