SI-6937 core type tags are no longer referentially unique

Type tag factory used to evaluate the provided type creator in the
context of the initial mirror in order to maintain referential equality
of instances of standard tags. Unfortunately this evaluation might fail
if the mirror provided doesn't contain the classes being referred to.
Therefore I think we should avoid evaluating type creators there.

Note that failure of evaluation doesn't mean that there's something
bad going on. When one creates a type tag, the correct mirror /
classloader to interpret that tag in might be unknown (like it happens
here). This is okay, and this is exactly what the 2.10.0-M4 refactoring
has addressed.

Something like `res2.typeTag[A].in(currentMirror)` should be okay.

12 files changed, 59 insertions, 21 deletions

diff --git a/test/files/run/macro-expand-nullary-generic.check b/test/files/run/macro-expand-nullary-generic.check
index 133840c469..42976f4baf 100644
--- a/test/files/run/macro-expand-nullary-generic.check
+++ b/test/files/run/macro-expand-nullary-generic.check
@@ -1,6 +1,6 @@
-it works TypeTag[Int]
-it works TypeTag[Int]
-it works TypeTag[Int]
-it works TypeTag[Int]
-it works TypeTag[Int]
+it works WeakTypeTag[Int]
+it works WeakTypeTag[Int]
+it works WeakTypeTag[Int]
+it works WeakTypeTag[Int]
+it works WeakTypeTag[Int]
 kkthxbai
diff --git a/test/files/run/macro-expand-tparams-explicit.check b/test/files/run/macro-expand-tparams-explicit.check
index e7e6718406..b6b4f6fa3a 100644
--- a/test/files/run/macro-expand-tparams-explicit.check
+++ b/test/files/run/macro-expand-tparams-explicit.check
@@ -1 +1 @@
-TypeTag[Int]
+WeakTypeTag[Int]
diff --git a/test/files/run/macro-expand-tparams-implicit.check b/test/files/run/macro-expand-tparams-implicit.check
index fa6b335afb..a9bf55423e 100644
--- a/test/files/run/macro-expand-tparams-implicit.check
+++ b/test/files/run/macro-expand-tparams-implicit.check
@@ -1,2 +1,2 @@
-TypeTag[Int]
+WeakTypeTag[Int]
 WeakTypeTag[String]
diff --git a/test/files/run/macro-expand-tparams-prefix-a.check b/test/files/run/macro-expand-tparams-prefix-a.check
index 0bf3c55bbe..ca44a4f652 100644
--- a/test/files/run/macro-expand-tparams-prefix-a.check
+++ b/test/files/run/macro-expand-tparams-prefix-a.check
@@ -1,4 +1,4 @@
-TypeTag[Int]
-TypeTag[Int]
+WeakTypeTag[Int]
+WeakTypeTag[Int]
 WeakTypeTag[String]
-TypeTag[Boolean]
+WeakTypeTag[Boolean]
diff --git a/test/files/run/macro-expand-tparams-prefix-b.check b/test/files/run/macro-expand-tparams-prefix-b.check
index 77c2ee9051..2ff2ce435d 100644
--- a/test/files/run/macro-expand-tparams-prefix-b.check
+++ b/test/files/run/macro-expand-tparams-prefix-b.check
@@ -1,2 +1,2 @@
-TypeTag[Boolean] TypeTag[Int]
-TypeTag[Boolean] WeakTypeTag[String]
+WeakTypeTag[Boolean] WeakTypeTag[Int]
+WeakTypeTag[Boolean] WeakTypeTag[String]
diff --git a/test/files/run/macro-expand-tparams-prefix-c1.check b/test/files/run/macro-expand-tparams-prefix-c1.check
index f0dd5b9cd8..0f24f74db1 100644
--- a/test/files/run/macro-expand-tparams-prefix-c1.check
+++ b/test/files/run/macro-expand-tparams-prefix-c1.check
@@ -1,3 +1,3 @@
-TypeTag[Int]
+WeakTypeTag[Int]
 WeakTypeTag[String]
-TypeTag[Boolean]
+WeakTypeTag[Boolean]
diff --git a/test/files/run/macro-expand-tparams-prefix-c2.check b/test/files/run/macro-expand-tparams-prefix-c2.check
index f0dd5b9cd8..0f24f74db1 100644
--- a/test/files/run/macro-expand-tparams-prefix-c2.check
+++ b/test/files/run/macro-expand-tparams-prefix-c2.check
@@ -1,3 +1,3 @@
-TypeTag[Int]
+WeakTypeTag[Int]
 WeakTypeTag[String]
-TypeTag[Boolean]
+WeakTypeTag[Boolean]
diff --git a/test/files/run/macro-expand-tparams-prefix-d1.check b/test/files/run/macro-expand-tparams-prefix-d1.check
index c5aaaf5a09..7832503256 100644
--- a/test/files/run/macro-expand-tparams-prefix-d1.check
+++ b/test/files/run/macro-expand-tparams-prefix-d1.check
@@ -1,3 +1,3 @@
 WeakTypeTag[T]
 WeakTypeTag[U]
-TypeTag[Boolean]
+WeakTypeTag[Boolean]
diff --git a/test/files/run/macro-undetparams-consfromsls.check b/test/files/run/macro-undetparams-consfromsls.check
index b10a90043e..3fee58d9c1 100644
--- a/test/files/run/macro-undetparams-consfromsls.check
+++ b/test/files/run/macro-undetparams-consfromsls.check
@@ -1,5 +1,5 @@
-A = TypeTag[Int]
-B = TypeTag[Nothing]
+A = WeakTypeTag[Int]
+B = WeakTypeTag[Nothing]
 List(1)
-A = TypeTag[Any]
+A = WeakTypeTag[Any]
 List(abc, 1)
diff --git a/test/files/run/macro-undetparams-macroitself.check b/test/files/run/macro-undetparams-macroitself.check
index fa6b335afb..a9bf55423e 100644
--- a/test/files/run/macro-undetparams-macroitself.check
+++ b/test/files/run/macro-undetparams-macroitself.check
@@ -1,2 +1,2 @@
-TypeTag[Int]
+WeakTypeTag[Int]
 WeakTypeTag[String]
diff --git a/test/files/run/t6937.check b/test/files/run/t6937.check
new file mode 100644
index 0000000000..9a1fa4cfaf
--- /dev/null
+++ b/test/files/run/t6937.check
@@ -0,0 +1,26 @@
+Type in expressions to have them evaluated.
+Type :help for more information.
+
+scala> 
+
+scala>     import scala.reflect.runtime.{universe => ru}
+import scala.reflect.runtime.{universe=>ru}
+
+scala>     import scala.reflect.runtime.{currentMirror => cm}
+import scala.reflect.runtime.{currentMirror=>cm}
+
+scala>     import scala.reflect.api.{Universe => ApiUniverse}
+import scala.reflect.api.{Universe=>ApiUniverse}
+
+scala>     class A
+defined class A
+
+scala>     lazy val apiru = ru: ApiUniverse
+apiru: scala.reflect.api.Universe = <lazy>
+
+scala>     apiru.typeTag[A].in(cm)
+res0: reflect.runtime.universe.TypeTag[A] = TypeTag[A]
+
+scala> 
+
+scala> 
diff --git a/test/files/run/t6937.scala b/test/files/run/t6937.scala
new file mode 100644
index 0000000000..4b30894bf3
--- /dev/null
+++ b/test/files/run/t6937.scala
@@ -0,0 +1,12 @@
+import scala.tools.partest.ReplTest
+
+object Test extends ReplTest {
+  def code = """
+    import scala.reflect.runtime.{universe => ru}
+    import scala.reflect.runtime.{currentMirror => cm}
+    import scala.reflect.api.{Universe => ApiUniverse}
+    class A
+    lazy val apiru = ru: ApiUniverse
+    apiru.typeTag[A].in(cm)
+  """
+}
\ No newline at end of file