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, 10 insertions, 0 deletions

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))
+  }
+}