Merge pull request #2440 from retronym/ticket/6771

SI-6771 Alias awareness for checkableType in match analysis.

4 files changed, 32 insertions, 0 deletions

diff --git a/test/files/neg/t6771b.check b/test/files/neg/t6771b.check
new file mode 100644
index 0000000000..ba99e9178d
--- /dev/null
+++ b/test/files/neg/t6771b.check
@@ -0,0 +1,6 @@
+t6771b.scala:14: error: type mismatch;
+ found   : x.type (with underlying type String)
+ required: Test.a.type
+  b = b match { case x => x }
+                          ^
+one error found
diff --git a/test/files/neg/t6771b.scala b/test/files/neg/t6771b.scala
new file mode 100644
index 0000000000..78f11f7750
--- /dev/null
+++ b/test/files/neg/t6771b.scala
@@ -0,0 +1,16 @@
+// Currently, the pattern matcher widens the type of the
+// scrutinee, so this doesn't typecheck. This test just
+// confirms this behaviour, although it would be an improvement
+// to change this and make this a `pos` test.
+//
+// But, to the intrepid hacker who works on this, a few notes:
+// You'll have to look into places in the pattern matcher that
+// call `dealias`, and see if they need to be `dealiasWiden`.
+// For example, if `checkableType` used only `dealias`, `pos/t6671.scala`
+// would fail.
+object Test {
+  val a = ""; var b: a.type = a
+
+  b = b match { case x => x }
+}
+
diff --git a/test/files/pos/t6771.flags b/test/files/pos/t6771.flags
new file mode 100644
index 0000000000..e8fb65d50c
--- /dev/null
+++ b/test/files/pos/t6771.flags
@@ -0,0 +1 @@
+-Xfatal-warnings
\ No newline at end of file
diff --git a/test/files/pos/t6771.scala b/test/files/pos/t6771.scala
new file mode 100644
index 0000000000..0f0bd4e4a0
--- /dev/null
+++ b/test/files/pos/t6771.scala
@@ -0,0 +1,9 @@
+object Test {
+  type Id[X] = X
+  val a: Id[Option[Int]] = None
+
+  a match {
+     case Some(x) => println(x)
+     case None    =>
+  }
+}