Avoid cycles in Symbol toString under -Ydebug

This is the first of two commits to restore workingness
to the compiler under `-Ydebug`.

`ResetAttrs` is now called during case class unapply synthesis,
after the UnTyper was recently banished.

But, this class has some low-level tracing that is triggered
under `-Ydebug` (irrespective of any `-Ylog` settings.)

This tracing code calls `Symbol#toString`, which, in an attempt
to discriminate primary from secondary constructors, accesses
the info of its owner. This is sufficient to hit a dreaded
`CyclicReferenceError`.

The enclosed test compiles a case class under this option
to show that things now compile. It still spews out unwanted
output; this will be removed in the next commit.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/reflect/scala/reflect/internal/Symbols.scala b/src/reflect/scala/reflect/internal/Symbols.scala
index e15b33e5d7..c2689fe7e9 100644
--- a/src/reflect/scala/reflect/internal/Symbols.scala
+++ b/src/reflect/scala/reflect/internal/Symbols.scala
@@ -2419,7 +2419,7 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
         else if (isTrait) ("trait", "trait", "TRT")
         else if (isClass) ("class", "class", "CLS")
         else if (isType) ("type", "type", "TPE")
-        else if (isClassConstructor && isPrimaryConstructor) ("primary constructor", "constructor", "PCTOR")
+        else if (isClassConstructor && (owner.hasCompleteInfo && isPrimaryConstructor)) ("primary constructor", "constructor", "PCTOR")
         else if (isClassConstructor) ("constructor", "constructor", "CTOR")
         else if (isSourceMethod) ("method", "method", "METH")
         else if (isTerm) ("value", "value", "VAL")