SI-7694 Add @uncheckedBounds to the library

Followup to the previous commit that added the compiler support
for opting out of bounds checking.

With both pieces, we can test that the temporaries introduced
by the named/default arguments transform don't trigger bounds
violations.

3 files changed, 60 insertions, 0 deletions

diff --git a/src/reflect/scala/reflect/internal/annotations/uncheckedBounds.scala b/src/reflect/scala/reflect/internal/annotations/uncheckedBounds.scala
new file mode 100644
index 0000000000..a44bb54734
--- /dev/null
+++ b/src/reflect/scala/reflect/internal/annotations/uncheckedBounds.scala
@@ -0,0 +1,13 @@
+package scala.reflect
+package internal
+package annotations
+
+/**
+ * An annotation that designates the annotated type should not be checked for violations of
+ * type parameter bounds in the `refchecks` phase of the compiler. This can be used by synthesized
+ * code the uses an inferred type of an expression as the type of an artifict val/def (for example,
+ * a temporary value introduced by an ANF transform). See [[https://issues.scala-lang.org/browse/SI-7694]].
+ *
+ * @since  2.10.3
+ */
+final class uncheckedBounds extends scala.annotation.StaticAnnotation
diff --git a/test/files/neg/t7694b.check b/test/files/neg/t7694b.check
new file mode 100644
index 0000000000..ea3d7736f8
--- /dev/null
+++ b/test/files/neg/t7694b.check
@@ -0,0 +1,7 @@
+t7694b.scala:8: error: type arguments [_3,_4] do not conform to trait L's type parameter bounds [A2,B2 <: A2]
+  def d = if (true) (null: L[A, A]) else (null: L[B, B])
+      ^
+t7694b.scala:9: error: type arguments [_1,_2] do not conform to trait L's type parameter bounds [A2,B2 <: A2]
+  val v = if (true) (null: L[A, A]) else (null: L[B, B])
+      ^
+two errors found
diff --git a/test/files/pos/t7694.scala b/test/files/pos/t7694.scala
new file mode 100644
index 0000000000..9852d5ec79
--- /dev/null
+++ b/test/files/pos/t7694.scala
@@ -0,0 +1,40 @@
+trait A
+trait B
+
+trait L[A2, B2 <: A2] {
+  def bar(a: Any, b: Any) = 0
+}
+
+object Lub {
+  // use named args transforms to include TypeTree(<lub.tpe>) in the AST before refchecks.
+  def foo(a: L[_, _], b: Any) = 0
+
+  foo(b = 0, a = if (true) (null: L[A, A]) else (null: L[B, B]))
+
+  (if (true) (null: L[A, A]) else (null: L[B, B])).bar(b = 0, a = 0)
+}
+
+/*
+The LUB ends up as:
+
+TypeRef(
+  TypeSymbol(
+    abstract trait L#7038[A2#7039, B2#7040 <: A2#7039] extends AnyRef#2197
+
+  )
+  args = List(
+    AbstractTypeRef(
+      AbstractType(
+        type _1#13680 >: A#7036 with B#7037 <: Object#1752
+      )
+    )
+    AbstractTypeRef(
+      AbstractType(
+        type _2#13681 >: A#7036 with B#7037 <: Object#1752
+      )
+    )
+  )
+)
+
+Note that type _2#13681 is *not* bound by _1#13680
+*/