From 052008313d5f72ffbbfe12fef6baf759f80be0eb Mon Sep 17 00:00:00 2001
From: liu fengyun <liu@fengy.me>
Date: Sat, 24 Dec 2016 23:26:02 +0100
Subject: [PATCH] Fix #1716: avoid crash in type checking f[_]

---
 compiler/src/dotty/tools/dotc/typer/TypeAssigner.scala | 7 ++++++-
 tests/neg/i1716.scala                                  | 8 ++++++++
 tests/neg/i1716b.scala                                 | 5 +++++
 3 files changed, 19 insertions(+), 1 deletion(-)
 create mode 100644 tests/neg/i1716.scala
 create mode 100644 tests/neg/i1716b.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/TypeAssigner.scala b/compiler/src/dotty/tools/dotc/typer/TypeAssigner.scala
index 4a97648f5825..ca219d8b3af1 100644
--- a/compiler/src/dotty/tools/dotc/typer/TypeAssigner.scala
+++ b/compiler/src/dotty/tools/dotc/typer/TypeAssigner.scala
@@ -368,7 +368,12 @@ trait TypeAssigner {
         }
         else {
           val argTypes = args.tpes
-          if (sameLength(argTypes, paramNames) || ctx.phase.prev.relaxedTyping) pt.instantiate(argTypes)
+          if (sameLength(argTypes, paramNames) || ctx.phase.prev.relaxedTyping) {
+            val index = argTypes.indexWhere(!_.isInstanceOf[TermType])
+            if (index != -1)
+              errorType(i"Incorrect type parameter `${args(index)}` for ${err.exprStr(fn)}", args(index).pos)
+            else pt.instantiate(argTypes)
+          }
           else wrongNumberOfTypeArgs(fn.tpe, pt.typeParams, args, tree.pos)
         }
       case _ =>
diff --git a/tests/neg/i1716.scala b/tests/neg/i1716.scala
new file mode 100644
index 000000000000..61b573512f1a
--- /dev/null
+++ b/tests/neg/i1716.scala
@@ -0,0 +1,8 @@
+object Fail {
+  def f(m: Option[Int]): Unit = {
+     m match {
+      case x @ Some[_] =>       // error
+      case _       =>
+    }
+  }
+}
\ No newline at end of file
diff --git a/tests/neg/i1716b.scala b/tests/neg/i1716b.scala
new file mode 100644
index 000000000000..b125a9328fbd
--- /dev/null
+++ b/tests/neg/i1716b.scala
@@ -0,0 +1,5 @@
+object Fail {
+  def f: Unit = {
+    Some[_]        // error
+  }
+}
\ No newline at end of file