structural invocation in nsc.ast.Scanners, easy to remove performance penalty

[scabug]

There's a structural invocation in nsc.ast.parser.Scanners. Not sure whether there's a performance impact, but doing away with it is easy. Rather than defining lookaheadReader (in CharArrayReader.scala) to have a refinement type, give a name to its class:

  /** A new reader that takes off at the current character position */
  def lookaheadReader = new CharArrayReaderForLookahead 

  class CharArrayReaderForLookahead extends CharArrayReader {  
    val buf = self.buf
    charOffset = self.charOffset
    ch = self.ch
    override def decodeUni = self.decodeUni
    def error(offset: Int, msg: String) = self.error(offset, msg)
    /** A mystery why CharArrayReader.nextChar() returns Unit */
    def getc() = { nextChar() ; ch }
  }

Besides that one, there are three other cases of dynamic dispatch in the compiler sources (granted, forMSIL without -optimize) found after placing a breakpoint at CleanUp on:

case ad@ApplyDynamic(qual0, params) =>

(1)
    pos: scala\\tools\\nsc\\typechecker\\Implicits.scala,line-857,offset=39632
    qual = "ImplicitSearch.this.scala$$tools$$nsc$$typechecker$$Implicits$$ImplicitSearch$$$$$$outer().global().erasure().erasure()"
    args = "List(parents)"
    symbol = "method intersectionDominator"

(2) 
    pos: scala\\tools\\nsc\\io\\File.scala,line-31,offset=1334
    qual = "target"
    args = "List()"
    symbol = "method close"

(3) 
    pos: "scala\\tools\\nsc\\io\\ZipArchive.scala,line-265,offset=8462"
    qual = "x.traverser()"
    args = "List()"
    symbol = "method zis"

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-3974?orig=1
Reporter: @magarciaEPFL

[scabug]

@paulp said:
It occurs to me that the ZipFile bug I've been dealing with for an eternity (which I enclose the stack trace of here because it just hit me again: partest hangs and this is always among the threads) could well be related. I think I will tackle this right now.

"ForkJoinPool-1-worker-3" daemon prio=5 tid=196240800 nid=0x1973de000 runnable [1973dc000]
   java.lang.Thread.State: RUNNABLE
	at java.util.zip.ZipFile.getNextEntry(Native Method)
	at java.util.zip.ZipFile.access$$400(ZipFile.java:29)
	at java.util.zip.ZipFile$$2.nextElement(ZipFile.java:313)
	- locked <141623488> (a java.util.zip.ZipFile)
	at java.util.zip.ZipFile$$2.nextElement(ZipFile.java:299)
	at scala.tools.nsc.io.ZipArchive$$$$anon$$1$$$$anon$$2.next(ZipArchive.scala:253)
	at scala.tools.nsc.io.ZipArchive$$$$anon$$1$$$$anon$$2.next(ZipArchive.scala:250)
	at scala.collection.Iterator$$class.foreach(Iterator.scala:631)
	at scala.tools.nsc.io.ZipArchive$$$$anon$$1$$$$anon$$2.foreach(ZipArchive.scala:250)
	at scala.collection.IterableLike$$class.foreach(IterableLike.scala:79)
	at scala.tools.nsc.io.ZipArchive$$$$anon$$1.foreach(ZipArchive.scala:248)
	at scala.tools.nsc.io.ZipContainer$$ZipRootCreator.apply(ZipArchive.scala:145)
	at scala.tools.nsc.io.ZipArchive.root(ZipArchive.scala:206)
	- locked <1416234e8> (a scala.tools.nsc.io.ZipArchive)
	at scala.tools.nsc.io.ZipContainer$$class.iterator(ZipArchive.scala:172)
	at scala.tools.nsc.io.ZipArchive.iterator(ZipArchive.scala:199)
	at scala.collection.IterableLike$$class.foreach(IterableLike.scala:79)
	at scala.tools.nsc.io.AbstractFile.foreach(AbstractFile.scala:84)
	at scala.collection.TraversableLike$$class.collect(TraversableLike.scala:271)
	at scala.tools.nsc.io.AbstractFile.collect(AbstractFile.scala:84)
	at scala.tools.nsc.util.DirectoryClassPath.classes(ClassPath.scala:315)
	- locked <141623570> (a scala.tools.nsc.util.DirectoryClassPath)
	at scala.tools.nsc.util.MergedClassPath$$$$anonfun$$classes$$3.apply(ClassPath.scala:342)
	at scala.tools.nsc.util.MergedClassPath$$$$anonfun$$classes$$3.apply(ClassPath.scala:342)
	at scala.collection.LinearSeqOptimized$$class.foreach(LinearSeqOptimized.scala:61)
	at scala.collection.immutable.List.foreach(List.scala:45)
	at scala.tools.nsc.util.MergedClassPath.classes(ClassPath.scala:342)
	- locked <141623638> (a scala.tools.nsc.util.JavaClassPath)
	at scala.tools.nsc.symtab.SymbolLoaders$$PackageLoader.doComplete(SymbolLoaders.scala:150)
	at scala.tools.nsc.symtab.SymbolLoaders$$SymbolLoader.complete(SymbolLoaders.scala:58)
	at scala.tools.nsc.symtab.SymbolLoaders$$SymbolLoader.complete(SymbolLoaders.scala:32)
	at scala.tools.nsc.symtab.Symbols$$Symbol.info(Symbols.scala:690)
	at scala.tools.nsc.symtab.Definitions$$definitions$$.init(Definitions.scala:828)
	at scala.tools.nsc.Global$$Run.<init>(Global.scala:602)
	at scala.tools.partest.nest.DirectCompiler.compile(CompileManager.scala:100)
	at scala.tools.partest.nest.CompileManager.shouldCompile(CompileManager.scala:165)
	at scala.tools.partest.nest.Worker$$$$anonfun$$runTestCommon$$1$$1$$$$anonfun$$10.apply(Worker.scala:496)
	at scala.tools.partest.nest.Worker$$$$anonfun$$runTestCommon$$1$$1$$$$anonfun$$10.apply(Worker.scala:496)
	at scala.tools.partest.nest.Worker$$$$anonfun$$runTestCommon$$1$$1.apply(Worker.scala:498)
	at scala.tools.partest.nest.Worker$$$$anonfun$$runTestCommon$$1$$1.apply(Worker.scala:487)
	at scala.tools.partest.nest.Worker.runInContext$$1(Worker.scala:432)
	at scala.tools.partest.nest.Worker.runTestCommon$$1(Worker.scala:487)
	at scala.tools.partest.nest.Worker.processSingleFile$$1(Worker.scala:558)
	at scala.tools.partest.nest.Worker$$$$anonfun$$runTests$$2$$$$anonfun$$apply$$2.apply$$mcV$$sp(Worker.scala:1069)

[scabug]

@paulp said:
(In r23423) Sprinkling in some names to avoid reflective calls in the compiler
as suggested by magarcia. Closes #3974, no review.