No longer crash on NoSymbol.owner.

Historically calling NoSymbol.owner has crashed the compiler.
With this commit, NoSymbol owns itself. This is consistent with
the way ownership chains are handled elsewhere in the compiler
(e.g. NoContext.owner is NoContext, NoSymbol.enclClass is
NoSymbol, and so on) and frees every call site which handles
symbols from having to perform precondition tests against
NoSymbol.

Since calling NoSymbol.owner sometimes (not always) indicates
a bug which we'd like to catch sooner than later, I have
introduced a couple more methods for selected call sites.

  def owner: Symbol       // NoSymbol.owner is self, log if -Xdev
  def safeOwner: Symbol   // NoSymbol.owner is self, ignore
  def assertOwner: Symbol // NoSymbol.owner is fatal

The idea is that everyone can call sym.owner without undue anxiety
or paranoid null-like tests. When compiling under -Xdev calls to
`owner` are logged with a stack trace, so any call sites for which
that is an expected occurrence should call safeOwner instead to
communicate the intention and stay out of the log. Conversely, any
call site where crashing on the owner call was a desirable behavior
can opt into calling assertOwner.

This commit also includes all the safeOwner calls necessary to
give us a silent log when compiling scala.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala b/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
index 30b923e2a1..66dff792b6 100644
--- a/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
@@ -216,7 +216,7 @@ abstract class RefChecks extends InfoTransform with scala.reflect.internal.trans
             val inherited = clazz.info.nonPrivateMemberAdmitting(member.name, VBRIDGE)
 
             // Delaying calling memberType as long as possible
-            if (inherited ne NoSymbol) {
+            if (inherited.exists) {
               val jtpe = toJavaRepeatedParam(self memberType member)
               // this is a bit tortuous: we look for non-private members or bridges
               // if we find a bridge everything is OK. If we find another member,
@@ -1521,7 +1521,7 @@ abstract class RefChecks extends InfoTransform with scala.reflect.internal.trans
       checkCompileTimeOnly(sym, tree.pos)
       checkDelayedInitSelect(qual, sym, tree.pos)
 
-      if (sym eq NoSymbol)
+      if (!sym.exists)
         devWarning("Select node has NoSymbol! " + tree + " / " + tree.tpe)
       else if (sym.hasLocalFlag)
         varianceValidator.checkForEscape(sym, currentClass)