Don't add parenthesis if last clause is single line. Fixes #1698

src/Fantomas.Tests/PatternMatchingTests.fs

@@ -1754,3 +1754,30 @@ match x with
 match x with
 | :? (int) as i -> ()
 """
+
+[<Test>]
+let ``don't add parenthesis if last clause is single line, 1698`` () =
+    formatSourceString
+        false
+        """
+  let select px =
+    match px with
+    | Shared.Foo _ -> "foo"
+    | Shared.LongerFoobarFoo -> "lf"
+    | Shared.Barry -> "barry"
+    |> List.singleton
+    |> instr "ziggy"
+"""
+        { config with IndentSize = 2 }
+    |> prepend newline
+    |> should
+        equal
+        """
+let select px =
+  match px with
+  | Shared.Foo _ -> "foo"
+  | Shared.LongerFoobarFoo -> "lf"
+  | Shared.Barry -> "barry"
+  |> List.singleton
+  |> instr "ziggy"
+"""

src/Fantomas/CodePrinter.fs

@@ -1698,7 +1698,18 @@ and genExpr astContext synExpr ctx =
                 (match e with
                  | SynExpr.IfThenElse _
                  | SynExpr.Match _ when (ctx.Config.IndentSize <= operatorText.Length) ->
-                     autoParenthesisIfExpressionExceedsPageWidth (genExpr astContext e)
+                     (fun ctx ->
+                         let ctxAfterMatch = genExpr astContext e ctx
+
+                         let barOnLastLine =
+                             match List.tryHead ctxAfterMatch.WriterModel.Lines with
+                             | Some line -> line.TrimStart().StartsWith("| ")
+                             | None -> false
+
+                         if barOnLastLine then
+                             ctxAfterMatch
+                         else
+                             autoParenthesisIfExpressionExceedsPageWidth (genExpr astContext e) ctx)
                  | _ -> genExpr astContext e)
                 +> sepNln
                 +> col