From f1e553ecfbea25bcc7e13294f6104d599336f460 Mon Sep 17 00:00:00 2001
From: Jason Zaugg <jzaugg@gmail.com>
Date: Sat, 29 Aug 2015 21:42:29 +1000
Subject: SI-9029 Fix regression in extractor patterns

The unified treatment of classical and named-based pattern matching
does not correctly handle the generalization of "tuple capture".

By "tuple capture", I mean:

```
scala> object Extractor { def unapply(a: Any): Option[(Int, String)] = Some((1, "2")) }
defined object Extractor

scala> "" match { case Extractor(x: Int, y: String) => }

scala> "" match { case Extractor(xy : (Int, String)) => }
warning: there was one deprecation warning; re-run with -deprecation for details

scala> :warnings
<console>:9: warning: object Extractor expects 2 patterns to hold (Int, String) but crushing into 2-tuple to fit single pattern (SI-6675)
              "" match { case Extractor(xy : (Int, String)) => }
                              ^
```

Name based pattern matching, new in Scala 2.11, allows one to
deconstruct the elements that structurally resembles `ProductN`:

```
scala> class P2(val _1: Int, val _2: String)
defined class P2

scala> object Extractor { def unapply(a: Any): Option[P2] = Some(new P2(1, "2")) }
defined object Extractor

scala> "" match { case Extractor(x: Int, y: String) => }
```

However, attempting to extract the `P2` in its entirety leads to
an internal error:

```
scala> "" match { case Extractor(p2: P2) => }
<console>:10: warning: fruitless type test: a value of type (Int, String) cannot also be a P2
              "" match { case Extractor(p2: P2) => }
                                            ^
<console>:10: error: error during expansion of this match (this is a scalac bug).
The underlying error was: type mismatch;
 found   : P2
 required: (Int, String)
              "" match { case Extractor(p2: P2) => }
                 ^
```

Note that this match was legal and warning free in 2.10.

This commit avoids the hard-coded assumption that the "tuple capture"
results in a `TupleN`, and instead keeps track of the product-ish
type from which we extracted the element types. I have also opted not
to limit the deprecation warning to `TupleN` extractors.
---
 test/files/run/t9029.scala | 15 +++++++++++++++
 1 file changed, 15 insertions(+)
 create mode 100644 test/files/run/t9029.scala

(limited to 'test/files/run/t9029.scala')

diff --git a/test/files/run/t9029.scala b/test/files/run/t9029.scala
new file mode 100644
index 0000000000..c01033b76e
--- /dev/null
+++ b/test/files/run/t9029.scala
@@ -0,0 +1,15 @@
+class Y(val _2: Int, val _1: String)
+
+object X { def unapply(u: Unit): Option[Y] = Some(new Y(42, "!")) }
+
+object Test {
+  def test1 = {
+    val X(y) = ()
+    val yy: Y = y
+    assert(yy._1 == "!")
+    assert(yy._2 == 42)
+  }
+  def main(args: Array[String]): Unit = {
+    test1
+  }
+}
-- 
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