Check if we just wrote a DotLambda before deciding on space before pa…

…rens, fix 3050 (#3051)

* fix an idempotency issue with dot lambdas, 3050

* add changelog entry

* fix warning from analysers

* fix by using Oak knowledge and altering the config for the dotlambda construction

* instead of using a potentially wrong config for argument nodes, check if the node.Expr is an AppSingleParenArg and just be always atomic in that case when writing the FunctionExpr

* release notes for 6.3.5

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Changelog
 
+## 6.3.5 - 2024-05-30
+
+### Fixed
+* Idempotency problem when _.Property shorthand. [#3050](https://github.com/fsprojects/fantomas/issues/3050)
+
 ## 6.3.4 - 2024-04-16
 
 ### Fixed

src/Fantomas.Core.Tests/DotLambdaTests.fs

@@ -59,3 +59,75 @@ let c = _.foo().Length
         """
 let c = _.foo().Length
 """
+
+[<Test>]
+let ``idempotency problem when _.Property shorthand, 3050`` () =
+    formatSourceString
+        """
+"ABC" |> _.ToLower()
+"""
+        { config with
+            SpaceBeforeUppercaseInvocation = true }
+    |> prepend newline
+    |> should
+        equal
+        """
+"ABC" |> _.ToLower()
+"""
+
+[<Test>]
+let ``idempotency problem when _.property shorthand lowercase, 3050`` () =
+    formatSourceString
+        """
+"ABC" |> _.toLower()
+"""
+        { config with
+            SpaceBeforeLowercaseInvocation = true }
+    |> prepend newline
+    |> should
+        equal
+        """
+"ABC" |> _.toLower()
+"""
+
+[<Test>]
+let ``idempotency problem when _.property shorthand quoted, 3050`` () =
+    formatSourceString
+        """
+"ABC" |> _.``to Lower``()
+"""
+        { config with
+            SpaceBeforeLowercaseInvocation = true }
+    |> prepend newline
+    |> should
+        equal
+        """
+"ABC" |> _.``to Lower``()
+"""
+
+[<Test>]
+let ``idempotency problem when _.Property shorthand with app arg, 3050`` () =
+    formatSourceString
+        """
+let Meh () = 1
+
+type Bar() =
+    member this.Foo(v:int):int = v + 1
+
+let b = Bar()
+b |> _.Foo(Meh ())
+"""
+        { config with
+            SpaceBeforeUppercaseInvocation = true }
+    |> prepend newline
+    |> should
+        equal
+        """
+let Meh () = 1
+
+type Bar() =
+    member this.Foo(v: int) : int = v + 1
+
+let b = Bar ()
+b |> _.Foo(Meh ())
+"""

src/Fantomas.Core/CodePrinter.fs

@@ -1553,9 +1553,14 @@ let genExpr (e: Expr) =
     | Expr.IndexFromEnd node -> !- "^" +> genExpr node.Expr |> genNode node
     | Expr.Typar node -> genSingleTextNode node
     | Expr.DotLambda node ->
+        let genDotLambdaExpr expr =
+            match expr with
+            | Expr.AppSingleParenArg p -> genExpr p.FunctionExpr +> genExpr p.ArgExpr // be always atomic, see 3050
+            | _ -> genExpr expr
+
         genSingleTextNode node.Underscore
         +> genSingleTextNode node.Dot
-        +> genExpr node.Expr
+        +> genDotLambdaExpr node.Expr
         |> genNode node
     | Expr.BeginEnd node ->
         let short =