SI-8158 compiler hangs printing out fancy types

Apparently, even though the compiler has safeguards against infinite type
printouts, having a depth counter, we didn’t account for the cases when
printouts are both self-referential and self-multiplying.

For one, SI-8158 provides an example of such a type, which is a structural
type that refers to itself twice in return types of its methods. At first,
printing such a type would go deeper and deeper, but then it will hit
the depth limit and start multiply indefinitely.

This commit fixes this particular problem by recognizing self-references
as this.type’s and printing them out as such. The subsequent commit will
introduce a more general facility.

2 files changed, 48 insertions, 0 deletions

diff --git a/test/files/neg/t8158/Macros_1.scala b/test/files/neg/t8158/Macros_1.scala
new file mode 100644
index 0000000000..b84e3ed8d3
--- /dev/null
+++ b/test/files/neg/t8158/Macros_1.scala
@@ -0,0 +1,34 @@
+import scala.language.experimental.macros
+import scala.reflect.macros.whitebox.Context
+
+object Max {
+  def impl(c: Context)(any: c.Expr[Any]): c.Expr[Any] = {
+    import c.universe._
+    def fail(msg: String) = c.abort(c.enclosingPosition, msg)
+    val t = c.macroApplication match {
+      case q"$_.unapply($unargs)" =>
+        /* hangs
+        */
+        q"""
+          new {
+            def isEmpty = false
+            def get = this
+            def unapply(x: String) = this
+          }.unapply($unargs)
+        """
+        /*
+        if get returns Unit or Boolean:
+        wrong number of patterns for <$anon: AnyRef> offering Unit: expected 1, found 0
+        */
+        /* straightforward
+        q"""
+          new {
+            def unapply(x: String) = true
+          }.unapply($unargs)
+        """
+        */
+      case _ => fail("bad appl")
+    }
+    c.Expr[Any](t)
+  }
+}
\ No newline at end of file
diff --git a/test/files/neg/t8158/Test_2.scala b/test/files/neg/t8158/Test_2.scala
new file mode 100644
index 0000000000..f5ac6616bb
--- /dev/null
+++ b/test/files/neg/t8158/Test_2.scala
@@ -0,0 +1,14 @@
+import scala.language.experimental.macros
+
+object X {
+  def unapply(any: Any): Any = macro Max.impl
+}
+
+class BugTest {
+  def bug(): Unit = {
+    "any" match {
+      case X() =>
+      case _ => ???
+    }
+  }
+}
\ No newline at end of file