Take single tuple parameter in lambda into account to capture lambda …

…body. Fixes #1789. (#1790)

src/Fantomas.Tests/LambdaTests.fs

@@ -897,3 +897,37 @@ let x =
         """
 let x = fun _ -> fun _ -> "hello"
 """
+
+[<Test>]
+let ``wild card parameters in lambda, 1789`` () =
+    formatSourceString
+        false
+        """
+let elifs =
+    es
+    |> List.collect (fun (e1, e2, _, _, _) -> [ visit e1; visit e2 ])
+"""
+        config
+    |> prepend newline
+    |> should
+        equal
+        """
+let elifs =
+    es
+    |> List.collect (fun (e1, e2, _, _, _) -> [ visit e1; visit e2 ])
+"""
+
+[<Test>]
+let ``leading and trailing wild card parameters in lambda`` () =
+    formatSourceString
+        false
+        """
+List.map (fun (_, _, _, _, body, _) -> visit body) andBangs
+"""
+        config
+    |> prepend newline
+    |> should
+        equal
+        """
+List.map (fun (_, _, _, _, body, _) -> visit body) andBangs
+"""

src/Fantomas/SourceParser.fs

@@ -1250,7 +1250,10 @@ let (|Clause|) (SynMatchClause.Clause (p, eo, e, _, _)) = (p, e, eo)
 let (|Lambda|_|) =
     function
     | SynExpr.Lambda (_, _, _, _, Some (pats, body), range) ->
-        let maxDepth = List.length pats
+        let maxDepth =
+            match pats with
+            | [ PatParen (PatTuple ts) ] -> List.length ts
+            | _ -> List.length pats
         // find the body expression from the last lambda
         let rec visit (currentDepth: int) (e: SynExpr) : SynExpr =
             if currentDepth < maxDepth then