From b8fad2bb6dfb24ced2f633b774bf123092082a99 Mon Sep 17 00:00:00 2001
From: Win Wang <winw@twitter.com>
Date: Tue, 1 Oct 2019 15:06:33 -0700
Subject: [PATCH] Fix parenthesization of ascribed function types with single
 tuple argument

---
 .../src/main/scala/rsc/tests/BetterRscCompat.scala  |  7 +++++++
 .../src/main/scala/rsc/tests/BetterRscCompat.scala  |  7 +++++++
 .../scala/rsc/rules/pretty/SemanticdbPrinter.scala  | 13 +++++++++++--
 3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/scalafix/input/src/main/scala/rsc/tests/BetterRscCompat.scala b/scalafix/input/src/main/scala/rsc/tests/BetterRscCompat.scala
index 2a49d69b..d11c23c2 100644
--- a/scalafix/input/src/main/scala/rsc/tests/BetterRscCompat.scala
+++ b/scalafix/input/src/main/scala/rsc/tests/BetterRscCompat.scala
@@ -283,4 +283,11 @@ object BetterRscCompat_Test {
 
     class H extends V
   }
+
+  object FunctionTypes {
+
+    val f1 = (_: (Int, Int)) => ()
+
+    def f2 = (_: (Int, Int), _: Int) => ()
+  }
 }
diff --git a/scalafix/output/src/main/scala/rsc/tests/BetterRscCompat.scala b/scalafix/output/src/main/scala/rsc/tests/BetterRscCompat.scala
index 9ed8b5e0..1f6fb81e 100644
--- a/scalafix/output/src/main/scala/rsc/tests/BetterRscCompat.scala
+++ b/scalafix/output/src/main/scala/rsc/tests/BetterRscCompat.scala
@@ -283,4 +283,11 @@ object BetterRscCompat_Test {
 
     class H extends V
   }
+
+  object FunctionTypes {
+
+    val f1: ((Int, Int)) => Unit = (_: (Int, Int)) => ()
+
+    def f2: ((Int, Int), Int) => Unit = (_: (Int, Int), _: Int) => ()
+  }
 }
diff --git a/scalafix/rules/src/main/scala/rsc/rules/pretty/SemanticdbPrinter.scala b/scalafix/rules/src/main/scala/rsc/rules/pretty/SemanticdbPrinter.scala
index 921380e7..321590f8 100644
--- a/scalafix/rules/src/main/scala/rsc/rules/pretty/SemanticdbPrinter.scala
+++ b/scalafix/rules/src/main/scala/rsc/rules/pretty/SemanticdbPrinter.scala
@@ -30,13 +30,22 @@ class SemanticdbPrinter(
             rep(args, ", ")(normal)
             str(")")
           } else if (sym.startsWith("scala/Function")) {
-            var params :+ ret = args
+            val params :+ ret = args
             val hasByNameArg = params.exists(_.isInstanceOf[s.ByNameType])
             val hasFunctionArg = params.exists {
               case s.TypeRef(pre, sym, args) if sym.startsWith("scala/Function") => true
               case _ => false
             }
-            val needsExtraParens = hasFunctionArg || hasByNameArg || (params.length != 1)
+            val singleTupleArg = params.length == 1 && (params.head match {
+              case s.TypeRef(_, argSym, _) => argSym.startsWith("scala/Tuple")
+              case _ => false
+            })
+
+            val needsExtraParens = hasFunctionArg ||
+              hasByNameArg ||
+              singleTupleArg ||
+              (params.length != 1)
+
             if (needsExtraParens) str("(")
             rep(params, ", ") { normal }
             if (needsExtraParens) str(")")