SI-4577 singleton type pattern test should use `eq`, not `==`

I find it hard to imagine anyone is relying on `case x: foo.type =>`
erroneously being compiled to `foo == x` instead of the spec'ed `foo eq x`,
so let's finally fix this.

1 files changed, 38 insertions, 0 deletions

diff --git a/test/files/run/t4577.scala b/test/files/run/t4577.scala
new file mode 100644
index 0000000000..b08100d3ea
--- /dev/null
+++ b/test/files/run/t4577.scala
@@ -0,0 +1,38 @@
+object Test {
+  val bippy    = new Symbol("bippy")
+  val imposter = new Symbol("bippy")
+  val notBippy = new Symbol("not-bippy")
+  val syms = List(bippy, imposter, notBippy)
+
+  // the equals method should only be used for case `bippy`,
+  // for the singleton type pattern, case _: bippy.type, the spec mandates `bippy eq _` as the test
+  class Symbol(val name: String) {
+    override def equals(other: Any) = other match {
+      case x: Symbol  => name == x.name
+      case _          => false
+    }
+    override def toString = name
+  }
+
+  // TODO: test bytecode equality for f and fDirect (and g and gDirect),
+  // for now the optimizer doesn't quite get from `f` to `fDirect`
+  def f(s: Symbol) = s match {
+    case _: bippy.type  => true
+    case _              => false
+  }
+  def fDirect(s: Symbol) = bippy eq s
+
+  def g(s: Symbol) = s match {
+    case _: bippy.type => 1
+    case `bippy`       => 2
+    case _             => 3
+  }
+  def gDirect(s: Symbol) = if (bippy eq s) 1 else if (bippy == s) 2 else 3
+  
+  def main(args: Array[String]): Unit = {
+    // `syms map f` should be: true false false
+    assert(syms forall (s => f(s) == fDirect(s)))
+    // `syms map g` should be: 1 2 3
+    assert(syms forall (s => g(s) == gDirect(s)))
+  }
+}
\ No newline at end of file