From c419411afea9f11f5cec603badeb3ddaf6355c5e Mon Sep 17 00:00:00 2001
From: Florian Verdonck <florian.verdonck@outlook.com>
Date: Fri, 22 Oct 2021 11:56:11 +0200
Subject: [PATCH] Don't add a newline if there are no additional arguments
 before lambda. (#1923)

Fixes #1922.
---
 src/Fantomas.Tests/LambdaTests.fs | 23 +++++++++++++++++++++++
 src/Fantomas/CodePrinter.fs       |  2 +-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/src/Fantomas.Tests/LambdaTests.fs b/src/Fantomas.Tests/LambdaTests.fs
index f47fe6754a..5f96a03b4a 100644
--- a/src/Fantomas.Tests/LambdaTests.fs
+++ b/src/Fantomas.Tests/LambdaTests.fs
@@ -1069,3 +1069,26 @@ leadingExpressionIsMultiline
      | Ok _ -> true
      | Error _ -> false)
 """
+
+[<Test>]
+let ``multiline lambda argument, 1922`` () =
+    formatSourceString
+        false
+        """
+let g =
+    Array.groupBy
+        (fun { partNumber = p
+               revisionNumber = r
+               processName = pn } -> p, r, pn)
+"""
+        config
+    |> prepend newline
+    |> should
+        equal
+        """
+let g =
+    Array.groupBy
+        (fun { partNumber = p
+               revisionNumber = r
+               processName = pn } -> p, r, pn)
+"""
diff --git a/src/Fantomas/CodePrinter.fs b/src/Fantomas/CodePrinter.fs
index 1f65697564..9ae540eb14 100644
--- a/src/Fantomas/CodePrinter.fs
+++ b/src/Fantomas/CodePrinter.fs
@@ -2211,7 +2211,7 @@ and genExpr astContext synExpr ctx =
                             +> indent
                             +> sepNln
                             +> col sepNln es (genExpr astContext)
-                            +> sepNln
+                            +> onlyIfNot (List.isEmpty es) sepNln
                             +> (sepOpenTFor lpr
                                 +> (!- "fun "
                                     +> col sepSpace pats (genPat astContext)