SI-7678 Don't cache member symbols of TypeTags in Definitions.

It we can only safely use vals in Definitions for top-level symbols.
Otherwise, when the IDE switches to loading the symbol from source,
we can hold on to a stale symbol, which in turn impedes implicit
materialization of TypeTags.

This commit moves (most) of the accessors for member symbols
into RunDefinitions, and changes calling code accordingly.
This is a win for presentation compiler correctness, and
might even shave of a few cycles.

In a few cases, I have had to leave a `def` to a member symbol
in Definitions so we can get to it from the SymbolTable cake,
which doesn't see RunDefinitions.

The macro FastTrack facility now correctly recreates the mapping
from Symbol to macro implementation each run, using a new facility
in perRunCaches to create a run-indexed cache.

The enclosed test recreates the situation reported in the ticket,
in which TypeTags.scala is loaded from source.

1 files changed, 4 insertions, 2 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index c385e7533a..a9bb81c691 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -115,6 +115,8 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
     import context0.unit
     import typeDebug.{ ptTree, ptBlock, ptLine, inGreen, inRed }
     import TyperErrorGen._
+    val runDefinitions = currentRun.runDefinitions
+    import runDefinitions._
 
     val infer = new Inferencer(context0) {
       // See SI-3281 re undoLog
@@ -3847,7 +3849,7 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
         if (sameLength(tparams, args)) {
           val targs = args map (_.tpe)
           checkBounds(tree, NoPrefix, NoSymbol, tparams, targs, "")
-          if (fun.symbol == Predef_classOf)
+          if (isPredefClassOf(fun.symbol))
             typedClassOf(tree, args.head, noGen = true)
           else {
             if (!isPastTyper && fun.symbol == Any_isInstanceOf && targs.nonEmpty) {
@@ -4807,7 +4809,7 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
               typed1(This(sym.owner) setPos tree.pos, mode, pt)
           // Inferring classOf type parameter from expected type.  Otherwise an
           // actual call to the stubbed classOf method is generated, returning null.
-            else if (isPredefMemberNamed(sym, nme.classOf) && pt.typeSymbol == ClassClass && pt.typeArgs.nonEmpty)
+            else if (isPredefClassOf(sym) && pt.typeSymbol == ClassClass && pt.typeArgs.nonEmpty)
             typedClassOf(tree, TypeTree(pt.typeArgs.head))
           else {
               val pre1  = if (sym.isTopLevel) sym.owner.thisType else if (qual == EmptyTree) NoPrefix else qual.tpe