From 045508cf4b970e42a7ab4a79fc577cf008f2ff82 Mon Sep 17 00:00:00 2001
From: liu fengyun <liu@fengy.me>
Date: Tue, 20 Feb 2018 18:07:09 +0100
Subject: [PATCH] fix #3200: bind var for singleton pattern get scrutinee type

Related issues:

https://issues.scala-lang.org/browse/SI-1503
https://github.com/lampepfl/dotty/issues/1463
---
 compiler/src/dotty/tools/dotc/typer/Typer.scala | 7 ++++++-
 tests/neg/i3200.scala                           | 6 ++++++
 tests/neg/i3200b.scala                          | 5 +++++
 3 files changed, 17 insertions(+), 1 deletion(-)
 create mode 100644 tests/neg/i3200.scala
 create mode 100644 tests/neg/i3200b.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
index 8c2cfab986c4..2a5937b42571 100644
--- a/compiler/src/dotty/tools/dotc/typer/Typer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -1320,7 +1320,12 @@ class Typer extends Namer
       case _ =>
         if (tree.name == nme.WILDCARD) body1
         else {
-          val sym = ctx.newPatternBoundSymbol(tree.name, body1.tpe.underlyingIfRepeated(isJava = false), tree.pos)
+          // for a singleton pattern like `x @ Nil`, `x` should get the type from the scrutinee
+          // see tests/neg/i3200b.scala and SI-1503
+          val symTp =
+            if (body1.tpe.isInstanceOf[TermRef]) pt1
+            else body1.tpe.underlyingIfRepeated(isJava = false)
+          val sym = ctx.newPatternBoundSymbol(tree.name, symTp, tree.pos)
           if (ctx.mode.is(Mode.InPatternAlternative))
             ctx.error(i"Illegal variable ${sym.name} in pattern alternative", tree.pos)
           assignType(cpy.Bind(tree)(tree.name, body1), sym)
diff --git a/tests/neg/i3200.scala b/tests/neg/i3200.scala
new file mode 100644
index 000000000000..7d905810b6ab
--- /dev/null
+++ b/tests/neg/i3200.scala
@@ -0,0 +1,6 @@
+object Test {
+  case object Bob { override def equals(other: Any) = true }
+  def main(args: Array[String]): Unit = {
+    val m : Bob.type = (5: Any) match { case x @ Bob => x }  // error
+  }
+}
diff --git a/tests/neg/i3200b.scala b/tests/neg/i3200b.scala
new file mode 100644
index 000000000000..522f4e3d63ea
--- /dev/null
+++ b/tests/neg/i3200b.scala
@@ -0,0 +1,5 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    val a : Nil.type = (Vector(): Any) match { case n @ Nil => n } // error
+  }
+}