SI-6968 Simple Tuple patterns aren't irrefutable

Reverts part of c82ecab. The parser can't assume that
a pattern `(a, b)` will match, as results of
`.isInstanceOf[Tuple2]` can't be statically known until
after the typer.

The reopens SI-1336, SI-5589 and SI-4574, in exchange for fixing
this regression SI-6968. Keeping all of those fixed will require
a better definition of irrefutability, and some acrobatics to
ensure safe passage to the ambiguous trees through typechecking.

6 files changed, 101 insertions, 0 deletions

diff --git a/test/pending/neg/t5589neg.check b/test/pending/neg/t5589neg.check
new file mode 100644
index 0000000000..f1dad94df3
--- /dev/null
+++ b/test/pending/neg/t5589neg.check
@@ -0,0 +1,37 @@
+t5589neg.scala:2: warning: `withFilter' method does not yet exist on scala.util.Either.RightProjection[Int,String], using `filter' method instead
+  def f5(x: Either[Int, String])        = for ((y1, y2: String) <- x.right) yield ((y1, y2))
+                                                                     ^
+t5589neg.scala:2: error: constructor cannot be instantiated to expected type;
+ found   : (T1, T2)
+ required: String
+  def f5(x: Either[Int, String])        = for ((y1, y2: String) <- x.right) yield ((y1, y2))
+                                               ^
+t5589neg.scala:3: warning: `withFilter' method does not yet exist on scala.util.Either.RightProjection[Int,String], using `filter' method instead
+  def f6(x: Either[Int, String])        = for ((y1, y2: Any) <- x.right) yield ((y1, y2))
+                                                                  ^
+t5589neg.scala:3: error: constructor cannot be instantiated to expected type;
+ found   : (T1, T2)
+ required: String
+  def f6(x: Either[Int, String])        = for ((y1, y2: Any) <- x.right) yield ((y1, y2))
+                                               ^
+t5589neg.scala:4: error: constructor cannot be instantiated to expected type;
+ found   : (T1,)
+ required: (String, Int)
+  def f7(x: Either[Int, (String, Int)]) = for (y1 @ Tuple1(y2) <- x.right) yield ((y1, y2))
+                                                    ^
+t5589neg.scala:4: error: not found: value y2
+  def f7(x: Either[Int, (String, Int)]) = for (y1 @ Tuple1(y2) <- x.right) yield ((y1, y2))
+                                                                                       ^
+t5589neg.scala:5: error: constructor cannot be instantiated to expected type;
+ found   : (T1, T2, T3)
+ required: (String, Int)
+  def f8(x: Either[Int, (String, Int)]) = for ((y1, y2, y3) <- x.right) yield ((y1, y2))
+                                               ^
+t5589neg.scala:5: error: not found: value y1
+  def f8(x: Either[Int, (String, Int)]) = for ((y1, y2, y3) <- x.right) yield ((y1, y2))
+                                                                                ^
+t5589neg.scala:5: error: not found: value y2
+  def f8(x: Either[Int, (String, Int)]) = for ((y1, y2, y3) <- x.right) yield ((y1, y2))
+                                                                                    ^
+two warnings found
+7 errors found
diff --git a/test/pending/neg/t5589neg.scala b/test/pending/neg/t5589neg.scala
new file mode 100644
index 0000000000..31ff2c3693
--- /dev/null
+++ b/test/pending/neg/t5589neg.scala
@@ -0,0 +1,6 @@
+class A {
+  def f5(x: Either[Int, String])        = for ((y1, y2: String) <- x.right) yield ((y1, y2))
+  def f6(x: Either[Int, String])        = for ((y1, y2: Any) <- x.right) yield ((y1, y2))
+  def f7(x: Either[Int, (String, Int)]) = for (y1 @ Tuple1(y2) <- x.right) yield ((y1, y2))
+  def f8(x: Either[Int, (String, Int)]) = for ((y1, y2, y3) <- x.right) yield ((y1, y2))
+}
diff --git a/test/pending/neg/t5589neg2.scala b/test/pending/neg/t5589neg2.scala
new file mode 100644
index 0000000000..b7c7ab7218
--- /dev/null
+++ b/test/pending/neg/t5589neg2.scala
@@ -0,0 +1,13 @@
+class A {
+  def f1(x: List[((((Int, (Double, (Float, String))), List[String]), List[Int]), List[Float])]) = {
+    for (((((a, (b, (c, d))), es), fs), gs) <- x) yield (d :: es).mkString(", ") // ok
+  }
+
+  def f2(x: List[((((Int, (Double, (Float, String))), List[String]), List[Int]), List[Float])]) = {
+    for (((((a, (b, (c, (d1, d2)))), es), fs), gs) <- x) yield (d :: es).mkString(", ") // not ok
+  }
+
+  def f3(x: List[((((Int, (Double, (Float, String))), List[String]), List[Int]), List[Float])]) = {
+    for (((((a, (b, _)), es), fs), gs) <- x) yield (es ::: fs).mkString(", ") // ok
+  }
+}
\ No newline at end of file
diff --git a/test/pending/pos/t1336.scala b/test/pending/pos/t1336.scala
new file mode 100644
index 0000000000..63967985c7
--- /dev/null
+++ b/test/pending/pos/t1336.scala
@@ -0,0 +1,10 @@
+object Foo {
+  def foreach( f : ((Int,Int)) => Unit ) {
+    println("foreach")
+    f(1,2)
+  }
+
+  for( (a,b) <- this ) {
+    println((a,b))
+  }
+}
diff --git a/test/pending/pos/t5589.scala b/test/pending/pos/t5589.scala
new file mode 100644
index 0000000000..69cbb20391
--- /dev/null
+++ b/test/pending/pos/t5589.scala
@@ -0,0 +1,22 @@
+class A {
+  // First three compile.
+  def f1(x: Either[Int, String])        = x.right map (y => y)
+  def f2(x: Either[Int, String])        = for (y <- x.right) yield y
+  def f3(x: Either[Int, (String, Int)]) = x.right map { case (y1, y2) => (y1, y2) }
+  // Last one fails.
+  def f4(x: Either[Int, (String, Int)]) = for ((y1, y2) <- x.right) yield ((y1, y2))
+/**
+./a.scala:5: error: constructor cannot be instantiated to expected type;
+ found   : (T1, T2)
+ required: Either[Nothing,(String, Int)]
+  def f4(x: Either[Int, (String, Int)]) = for ((y1, y2) <- x.right) yield ((y1, y2))
+                                               ^
+./a.scala:5: error: not found: value y1
+  def f4(x: Either[Int, (String, Int)]) = for ((y1, y2) <- x.right) yield ((y1, y2))
+                                                                            ^
+./a.scala:5: error: not found: value y2
+  def f4(x: Either[Int, (String, Int)]) = for ((y1, y2) <- x.right) yield ((y1, y2))
+                                                                                ^
+three errors found
+**/
+}
diff --git a/test/pending/run/t4574.scala b/test/pending/run/t4574.scala
new file mode 100644
index 0000000000..1dde496aca
--- /dev/null
+++ b/test/pending/run/t4574.scala
@@ -0,0 +1,13 @@
+object Test {
+  val xs: List[(Int, Int)] = List((2, 2), null)
+  
+  def expectMatchError[T](msg: String)(body: => T) {
+    try { body ; assert(false, "Should not succeed.") }
+    catch { case _: MatchError => println(msg) }
+  }
+
+  def main(args: Array[String]): Unit = {
+    expectMatchError("I hereby refute null!")( for ((x, y) <- xs) yield x )
+    expectMatchError("I denounce null as unListLike!")( (null: Any) match { case List(_*) => true } )
+  }
+}