Test case for scala#12927

Author: griggt

sbt-test/opaques/i12927/build.sbt

@@ -0,0 +1 @@
+scalaVersion := sys.props("plugin.scalaVersion")

sbt-test/opaques/i12927/changes/Foo.scala

@@ -0,0 +1,7 @@
+object Foo:
+  opaque type BlaBla[+T, D] = Int
+  extension [T, D](token: BlaBla[T, D]) def data: D = ???
+
+//To cause the crash, after initial clean compilation
+//replace `???` with `value.data` to cause the compiler crash
+def foo[W <: Int](value: Bar.BlaBla[W]): Unit = value.data

sbt-test/opaques/i12927/src/main/scala/Bar.scala

@@ -0,0 +1,4 @@
+object Bar:
+  type Fuzzy[W <: Int] = Int
+  opaque type BlaBla[W <: Int] <: Foo.BlaBla[Fuzzy[W], Int] =
+    Foo.BlaBla[Fuzzy[W], Int]

sbt-test/opaques/i12927/src/main/scala/Foo.scala

@@ -0,0 +1,7 @@
+object Foo:
+  opaque type BlaBla[+T, D] = Int
+  extension [T, D](token: BlaBla[T, D]) def data: D = ???
+
+//To cause the crash, after initial clean compilation
+//replace `???` with `value.data` to cause the compiler crash
+def foo[W <: Int](value: Bar.BlaBla[W]): Unit = ??? //value.data

sbt-test/opaques/i12927/test

@@ -0,0 +1,3 @@
+> compile
+$ copy-file changes/Foo.scala src/main/scala/Foo.scala
+> compile