From 90df4598c0fbbc42f7eefdd4a07588f8610231d6 Mon Sep 17 00:00:00 2001
From: Nicolas Stucki <nicolas.stucki@gmail.com>
Date: Wed, 29 Nov 2017 13:33:47 +0100
Subject: [PATCH] Fix #3588: Do not emit switch when matching on non switchable
 types

---
 .../tools/dotc/transform/PatternMatcher.scala |  3 +-
 .../dotty/tools/dotc/CompilationTests.scala   |  2 +
 tests/neg-custom-args/i3589-a.scala           | 10 ++++
 tests/pos-special/i3589-b.scala               |  7 +++
 tests/pos/i3588.scala                         | 51 +++++++++++++++++++
 5 files changed, 72 insertions(+), 1 deletion(-)
 create mode 100644 tests/neg-custom-args/i3589-a.scala
 create mode 100644 tests/pos-special/i3589-b.scala
 create mode 100644 tests/pos/i3588.scala

diff --git a/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala b/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala
index 8d217cf96e0d..a562410b262c 100644
--- a/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala
+++ b/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala
@@ -812,7 +812,8 @@ object PatternMatcher {
           plan :: Nil
       }
 
-      recur(plan)
+      if (isSwitchableType(scrutinee.tpe.widen)) recur(plan)
+      else Nil
     }
 
     /** Emit cases of a switch */
diff --git a/compiler/test/dotty/tools/dotc/CompilationTests.scala b/compiler/test/dotty/tools/dotc/CompilationTests.scala
index e1057838ddbe..a73def1f66ed 100644
--- a/compiler/test/dotty/tools/dotc/CompilationTests.scala
+++ b/compiler/test/dotty/tools/dotc/CompilationTests.scala
@@ -55,6 +55,7 @@ class CompilationTests extends ParallelTesting {
     compileFile("../tests/pos-scala2/rewrites.scala", scala2Mode.and("-rewrite")).copyToTarget() +
     compileFile("../tests/pos-special/utf8encoded.scala", explicitUTF8) +
     compileFile("../tests/pos-special/utf16encoded.scala", explicitUTF16) +
+    compileFile("../tests/pos-special/i3589-b.scala", defaultOptions.and("-Xfatal-warnings")) +
     compileList(
       "compileMixed",
       List(
@@ -181,6 +182,7 @@ class CompilationTests extends ParallelTesting {
     compileFile("../tests/neg-custom-args/overloadsOnAbstractTypes.scala", allowDoubleBindings) +
     compileFile("../tests/neg-custom-args/xfatalWarnings.scala", defaultOptions.and("-Xfatal-warnings")) +
     compileFile("../tests/neg-custom-args/pureStatement.scala", defaultOptions.and("-Xfatal-warnings")) +
+    compileFile("../tests/neg-custom-args/i3589-a.scala", defaultOptions.and("-Xfatal-warnings")) +
     compileFile("../tests/neg-custom-args/phantom-overload.scala", allowDoubleBindings) +
     compileFile("../tests/neg-custom-args/phantom-overload-2.scala", allowDoubleBindings) +
     compileFile("../tests/neg-custom-args/structural.scala", defaultOptions.and("-Xfatal-warnings"))
diff --git a/tests/neg-custom-args/i3589-a.scala b/tests/neg-custom-args/i3589-a.scala
new file mode 100644
index 000000000000..f6621b430ddf
--- /dev/null
+++ b/tests/neg-custom-args/i3589-a.scala
@@ -0,0 +1,10 @@
+object Test {
+  case class IntAnyVal(x: Int) extends AnyVal
+
+  def test(x: IntAnyVal) = (x: @annotation.switch) match { //error: warning: could not emit switch
+    case IntAnyVal(1) => 1
+    case IntAnyVal(2) => 2
+    case IntAnyVal(3) => 3
+    case _ => 4
+  }
+}
diff --git a/tests/pos-special/i3589-b.scala b/tests/pos-special/i3589-b.scala
new file mode 100644
index 000000000000..e6fb462736e1
--- /dev/null
+++ b/tests/pos-special/i3589-b.scala
@@ -0,0 +1,7 @@
+class Test {
+  def test(x: 1) = (x: @annotation.switch) match {
+    case 1 => 1
+    case 2 => 2
+    case 3 => 3
+  }
+}
diff --git a/tests/pos/i3588.scala b/tests/pos/i3588.scala
new file mode 100644
index 000000000000..17aea68dc7b2
--- /dev/null
+++ b/tests/pos/i3588.scala
@@ -0,0 +1,51 @@
+class Foo {
+  val a: Any = 3
+  a match {
+    case 1 =>
+    case 2 =>
+    case 3 =>
+    case _ =>
+  }
+}
+
+class Bar[T] {
+  val a: T = ???
+  a match {
+    case 1 =>
+    case 2 =>
+    case 3 =>
+    case _ =>
+  }
+}
+
+class Baz {
+  val a: Double = 1.0
+  a match {
+    case 1 =>
+    case 2 =>
+    case 3 =>
+    case _ =>
+  }
+}
+
+class Foo2 {
+  val a: AnyVal = 3
+  a match {
+    case 1 =>
+    case 2 =>
+    case 3 =>
+    case _ =>
+  }
+}
+
+
+case class A(i: Int) extends AnyVal
+class Foo3 {
+  val a: A = new A(3)
+  a match {
+    case A(1) =>
+    case A(2) =>
+    case A(3) =>
+    case _ =>
+  }
+}