From cb7a8e0ac7548b8d9f97577fcce91803d46de393 Mon Sep 17 00:00:00 2001
From: dawe <dawedawe@posteo.de>
Date: Thu, 30 May 2024 14:14:20 +0200
Subject: [PATCH] Check if we just wrote a DotLambda before deciding on space
 before parens, 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                              |  5 ++
 src/Fantomas.Core.Tests/DotLambdaTests.fs | 72 +++++++++++++++++++++++
 src/Fantomas.Core/CodePrinter.fs          |  7 ++-
 3 files changed, 83 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0f7dd2ef31..f957a1d03f 100644
--- a/CHANGELOG.md
+++ b/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
diff --git a/src/Fantomas.Core.Tests/DotLambdaTests.fs b/src/Fantomas.Core.Tests/DotLambdaTests.fs
index 376a4b92a6..45285c3e32 100644
--- a/src/Fantomas.Core.Tests/DotLambdaTests.fs
+++ b/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 ())
+"""
diff --git a/src/Fantomas.Core/CodePrinter.fs b/src/Fantomas.Core/CodePrinter.fs
index 2491ef4f17..658f5fcdd1 100644
--- a/src/Fantomas.Core/CodePrinter.fs
+++ b/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 =