SI-9567 Fix latent bugs in patmat's reasoning about mutability

Under -optimize, the pattern matcher tries to avoid local variables
in favour of directly accessing to non-var case class accessors.

However, the code that analysed the patterns failed to account
properly for repeated parameters, which could either lead to
a compiler crash (when assuming that the n-th subpattern must have
a corresponding param accessor), or could lead to a correctness
problem (when failing to eagerly the bound elements from the
sequence.)

The test case that tried to cover seems only to have been working
because of a separate bug (the primary subject of SI-9567) related
to method-local case classes: they were treated during typechecking
as extractors, rather than native case classes.

The subsequent commit will fix that problem, but first we must
pave the way with this commit that emits local vals for bound
elements of case class repeated params.

1 files changed, 29 insertions, 0 deletions

diff --git a/test/files/run/t9567c.scala b/test/files/run/t9567c.scala
new file mode 100644
index 0000000000..560bea8821
--- /dev/null
+++ b/test/files/run/t9567c.scala
@@ -0,0 +1,29 @@
+case class CaseSequenceTopLevel(as: Int*)
+
+object Test {
+   def main(args: Array[String]): Unit = {
+
+    val buffer1 = collection.mutable.Buffer(0, 0)
+    CaseSequenceTopLevel(buffer1: _*) match {
+      case CaseSequenceTopLevel(_, i) =>
+        buffer1(1) = 1
+        assert(i == 0, i) // fails in 2.11.7 -optimize
+    }
+
+    case class CaseSequence(as: Int*)
+    val buffer2 = collection.mutable.Buffer(0, 0)
+    CaseSequence(buffer2: _*) match {
+      case CaseSequence(_, i) =>
+        buffer2(1) = 1
+        assert(i == 0, i)
+    }
+
+    case class CaseSequenceWithVar(var x: Any, as: Int*)
+    val buffer3 = collection.mutable.Buffer(0, 0)
+    CaseSequenceWithVar("", buffer3: _*) match {
+      case CaseSequenceWithVar(_, _, i) => // crashes in 2.11.7
+        buffer2(1) = 1
+        assert(i == 0, i)
+    }
+  }
+}