From 71f5b3aac74bcd8d45d0cac8afb816cc70fdcc62 Mon Sep 17 00:00:00 2001
From: Liu Fengyun <liu@fengy.me>
Date: Tue, 28 Apr 2020 11:02:18 +0200
Subject: [PATCH] Fix #8757: check wildcard star patterns by tree instead of
 type

---
 .../src/dotty/tools/dotc/transform/patmat/Space.scala  |  4 ++--
 tests/patmat/i8757.check                               |  1 +
 tests/patmat/i8757.scala                               | 10 ++++++++++
 3 files changed, 13 insertions(+), 2 deletions(-)
 create mode 100644 tests/patmat/i8757.check
 create mode 100644 tests/patmat/i8757.scala

diff --git a/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala b/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
index 776ebf076aa3..bc74d9542a61 100644
--- a/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
+++ b/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
@@ -481,8 +481,8 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
   def projectSeq(pats: List[Tree]): Space = {
     if (pats.isEmpty) return Typ(scalaNilType, false)
 
-    val (items, zero) = if (pats.last.tpe.isRepeatedParam)
-      (pats.init, Typ(scalaListType.appliedTo(pats.last.tpe.argTypes.head), false))
+    val (items, zero) = if (isWildcardStarArg(pats.last))
+      (pats.init, Typ(scalaListType.appliedTo(pats.last.tpe.elemType), false))
     else
       (pats, Typ(scalaNilType, false))
 
diff --git a/tests/patmat/i8757.check b/tests/patmat/i8757.check
new file mode 100644
index 000000000000..a0606bf625c6
--- /dev/null
+++ b/tests/patmat/i8757.check
@@ -0,0 +1 @@
+8: Pattern Match Exhaustivity: C()
diff --git a/tests/patmat/i8757.scala b/tests/patmat/i8757.scala
new file mode 100644
index 000000000000..2056bfb74527
--- /dev/null
+++ b/tests/patmat/i8757.scala
@@ -0,0 +1,10 @@
+sealed trait T
+
+case class C(xs: Int*) extends T
+
+def f(): Unit = (C(42): T) match { case C(xs: _*) => }
+def g(): Unit = (C(42): T) match { case C(_: _*) => }
+
+def h(): Unit = (C(42): T) match
+  case C(5, _: _*) =>
+  case C(x, xs: _*) =>