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.

1 files changed, 0 insertions, 22 deletions

diff --git a/test/files/pos/t5589.scala b/test/files/pos/t5589.scala
deleted file mode 100644
index 69cbb20391..0000000000
--- a/test/files/pos/t5589.scala
+++ /dev/null
@@ -1,22 +0,0 @@
-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
-**/
-}