Refactor the cake so SymbolTable does not depend on Global

This is rather large commit so I'll first explain the motivation
behind it and then go through all changes in detail explaining
the choices I made.

The motivation behind this refactoring was to make SymbolTable
unit testable. I wanted a lightweight way of initializing
SymbolTable and then writing unit tests for subtyping algorithm,
various functionality related to Symbols, etc.
All of that should be possible by precisely controlling what we
test, e.g., create types and symbols by hand and not have them
defined in source code as we normally do in partest (functional)
tests.

The other motivation was to reduce and clarify dependencies we
have in the compiler. Explicit dependencies lead to cleaner
design. Also, explicit and reduces dependencies help incremental
compilation which is a big problem for us in compiler's code
base at the moment.

One of the challenges I faced during that refactoring was
cyclic dependency between Platform and SymbolLoaders.

Platform depended on `SymbolLoaders.SymbolLoader` because it
would define a root loader. SymbolLoaders depended on Platform
for numerous reasons like deferring decision how to load a given
symbol based on some Platform-specific hooks.

I decided to break that cycle by removing methods related to
symbol loading from Platform interface. One could argue, that
better fix would be to make SymbolLoaders to not depend on Platform
(backend) concept but that would be much bigger refactoring. Also,
we have a new concept for dealing with symbol loading: Mirrors.

For those reasons both `newClassLoader` and `rootLoader`
were dropped from Platform interface.

Note that JavaPlatform still depends on Global so it can
access phases defined in Global to implement `platformPhases`
method.

Both GenICode and BCodeBodyBuilder have some Platform specific
logic that requires casting because pattern matcher doesn't narrow
types to give them a proper refinement. Check the changes for details.

Some logging utilities has been moved from Global to SymbolTable
because they are accessed by SymbolTable. Since Global inherits from
SymbolTable this should be a source compatible change.

The SymbolLoaders has dependency on `compileLate` method defined in Global.
The purpose behind `compileLate` is not clear to me but the dependency looks
a little bit dubious. At least we made that dependency explicit.

ScaladocGlobal and Global defined in interactive has been adapted in a way
that makes them compile both with quick.comp and 2.11.0-M4 so my refactorings
are not blocking the modularization effort.

4 files changed, 55 insertions, 20 deletions

diff --git a/src/compiler/scala/tools/nsc/symtab/BrowsingLoaders.scala b/src/compiler/scala/tools/nsc/symtab/BrowsingLoaders.scala
index f93be78a3f..0d756fd309 100644
--- a/src/compiler/scala/tools/nsc/symtab/BrowsingLoaders.scala
+++ b/src/compiler/scala/tools/nsc/symtab/BrowsingLoaders.scala
@@ -13,8 +13,11 @@ import scala.tools.nsc.io.AbstractFile
  *  are managed automatically.
  */
 abstract class BrowsingLoaders extends SymbolLoaders {
-  import global._
+  val global: Global
+  val symbolTable: global.type
+  protected def compileLate(srcfile: AbstractFile) = global.currentRun.compileLate(srcfile)
 
+  import global._
   import syntaxAnalyzer.{OutlineParser, MalformedInput}
 
   /*
diff --git a/src/compiler/scala/tools/nsc/symtab/SymbolLoaders.scala b/src/compiler/scala/tools/nsc/symtab/SymbolLoaders.scala
index 201a2315ab..d22352154b 100644
--- a/src/compiler/scala/tools/nsc/symtab/SymbolLoaders.scala
+++ b/src/compiler/scala/tools/nsc/symtab/SymbolLoaders.scala
@@ -20,13 +20,23 @@ import scala.reflect.io.{ AbstractFile, NoAbstractFile }
  *  @version 1.0
  */
 abstract class SymbolLoaders {
-  val global: Global
-  import global._
-
+  val symbolTable: symtab.SymbolTable {
+    def settings: Settings
+  }
+  val platform: backend.Platform {
+    val symbolTable: SymbolLoaders.this.symbolTable.type
+  }
+  import symbolTable._
   /**
    * Required by ClassfileParser. Check documentation in that class for details.
    */
   protected def lookupMemberAtTyperPhaseIfPossible(sym: Symbol, name: Name): Symbol
+  /**
+   * Should forward to `Run.compileLate`. The more principled fix would be to
+   * determine why this functionality is needed and extract it into a separate
+   * interface.
+   */
+  protected def compileLate(srcfile: AbstractFile): Unit
   import SymbolLoadersStats._
 
   protected def enterIfNew(owner: Symbol, member: Symbol, completer: SymbolLoader): Symbol = {
@@ -80,14 +90,14 @@ abstract class SymbolLoaders {
           name+"\none of them needs to be removed from classpath"
         )
       else if (settings.termConflict.value == "package") {
-        global.warning(
+        warning(
           "Resolving package/object name conflict in favor of package " +
           preExisting.fullName + ".  The object will be inaccessible."
         )
         root.info.decls.unlink(preExisting)
       }
       else {
-        global.warning(
+        warning(
           "Resolving package/object name conflict in favor of object " +
           preExisting.fullName + ".  The package will be inaccessible."
         )
@@ -149,12 +159,12 @@ abstract class SymbolLoaders {
       case (Some(bin), Some(src))
       if platform.needCompile(bin, src) && !binaryOnly(owner, classRep.name) =>
         if (settings.verbose) inform("[symloader] picked up newer source file for " + src.path)
-        global.loaders.enterToplevelsFromSource(owner, classRep.name, src)
+        enterToplevelsFromSource(owner, classRep.name, src)
       case (None, Some(src)) =>
         if (settings.verbose) inform("[symloader] no class, picked up source file for " + src.path)
-        global.loaders.enterToplevelsFromSource(owner, classRep.name, src)
+        enterToplevelsFromSource(owner, classRep.name, src)
       case (Some(bin), _) =>
-        global.loaders.enterClassAndModule(owner, classRep.name, platform.newClassLoader(bin))
+        enterClassAndModule(owner, classRep.name, new ClassfileLoader(bin))
     }
   }
 
@@ -250,12 +260,23 @@ abstract class SymbolLoaders {
 
   class ClassfileLoader(val classfile: AbstractFile) extends SymbolLoader with FlagAssigningCompleter {
     private object classfileParser extends {
-      val global: SymbolLoaders.this.global.type = SymbolLoaders.this.global
+      val symbolTable: SymbolLoaders.this.symbolTable.type = SymbolLoaders.this.symbolTable
     } with ClassfileParser {
       override protected type ThisConstantPool = ConstantPool
       override protected def newConstantPool: ThisConstantPool = new ConstantPool
       override protected def lookupMemberAtTyperPhaseIfPossible(sym: Symbol, name: Name): Symbol =
         SymbolLoaders.this.lookupMemberAtTyperPhaseIfPossible(sym, name)
+      /*
+       * The type alias and the cast (where the alias is used) is needed due to problem described
+       * in SI-7585. In this particular case, the problem is that we need to make sure that symbol
+       * table used by symbol loaders is exactly the same as they one used by classfileParser.
+       * If you look at the path-dependent types we have here everything should work out ok but
+       * due to issue described in SI-7585 type-checker cannot tie the knot here.
+       *
+       */
+      private type SymbolLoadersRefined = SymbolLoaders { val symbolTable: classfileParser.symbolTable.type }
+      val loaders = SymbolLoaders.this.asInstanceOf[SymbolLoadersRefined]
+      val classPath = platform.classPath
     }
 
     protected def description = "class file "+ classfile.toString
@@ -282,7 +303,7 @@ abstract class SymbolLoaders {
     protected def description = "source file "+ srcfile.toString
     override def fromSource = true
     override def sourcefile = Some(srcfile)
-    protected def doComplete(root: Symbol): Unit = global.currentRun.compileLate(srcfile)
+    protected def doComplete(root: Symbol): Unit = compileLate(srcfile)
   }
 
   object moduleClassLoader extends SymbolLoader with FlagAssigningCompleter {
diff --git a/src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala b/src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala
index 4743260c79..ad2b024935 100644
--- a/src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala
+++ b/src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala
@@ -17,6 +17,7 @@ import scala.reflect.internal.{ JavaAccFlags }
 import scala.reflect.internal.pickling.{PickleBuffer, ByteCodecs}
 import scala.tools.nsc.io.AbstractFile
 
+import util.ClassPath
 
 /** This abstract class implements a class file parser.
  *
@@ -24,9 +25,14 @@ import scala.tools.nsc.io.AbstractFile
  *  @version 1.0
  */
 abstract class ClassfileParser {
-  val global: Global
-  import global._
+  val symbolTable: SymbolTable {
+    def settings: Settings
+  }
+  val loaders: SymbolLoaders {
+    val symbolTable: ClassfileParser.this.symbolTable.type
+  }
 
+  import symbolTable._
   /**
    * If typer phase is defined then perform member lookup of a symbol
    * `sym` at typer phase. This method results from refactoring. The
@@ -37,6 +43,9 @@ abstract class ClassfileParser {
    */
   protected def lookupMemberAtTyperPhaseIfPossible(sym: Symbol, name: Name): Symbol
 
+  /** The compiler classpath. */
+  def classPath: ClassPath[AbstractFile]
+
   import definitions._
   import scala.reflect.internal.ClassfileConstants._
   import Flags._
@@ -64,7 +73,7 @@ abstract class ClassfileParser {
 
   def srcfile = srcfile0
 
-  private def optimized         = global.settings.optimise.value
+  private def optimized         = settings.optimise.value
   private def currentIsTopLevel = !(currentClass.decodedName containsChar '$')
 
   // u1, u2, and u4 are what these data types are called in the JVM spec.
@@ -84,7 +93,7 @@ abstract class ClassfileParser {
   private def readType()            = pool getType u2
 
   private object unpickler extends scala.reflect.internal.pickling.UnPickler {
-    val global: ClassfileParser.this.global.type = ClassfileParser.this.global
+    val symbolTable: ClassfileParser.this.symbolTable.type = ClassfileParser.this.symbolTable
   }
 
   private def handleMissing(e: MissingRequirementError) = {
@@ -344,7 +353,7 @@ abstract class ClassfileParser {
   }
 
   private def loadClassSymbol(name: Name): Symbol = {
-    val file = global.classPath findSourceFile ("" +name) getOrElse {
+    val file = classPath findSourceFile ("" +name) getOrElse {
       // SI-5593 Scaladoc's current strategy is to visit all packages in search of user code that can be documented
       // therefore, it will rummage through the classpath triggering errors whenever it encounters package objects
       // that are not in their correct place (see bug for details)
@@ -352,7 +361,7 @@ abstract class ClassfileParser {
         warning(s"Class $name not found - continuing with a stub.")
       return NoSymbol.newClass(name.toTypeName)
     }
-    val completer     = new global.loaders.ClassfileLoader(file)
+    val completer     = new loaders.ClassfileLoader(file)
     var owner: Symbol = rootMirror.RootClass
     var sym: Symbol   = NoSymbol
     var ss: Name      = null
@@ -990,7 +999,7 @@ abstract class ClassfileParser {
 
     def enterClassAndModule(entry: InnerClassEntry, file: AbstractFile) {
       def jflags      = entry.jflags
-      val completer   = new global.loaders.ClassfileLoader(file)
+      val completer   = new loaders.ClassfileLoader(file)
       val name        = entry.originalName
       val sflags      = jflags.toScalaFlags
       val owner       = ownerForFlags(jflags)
@@ -998,7 +1007,7 @@ abstract class ClassfileParser {
       val innerClass  = owner.newClass(name.toTypeName, NoPosition, sflags) setInfo completer
       val innerModule = owner.newModule(name.toTermName, NoPosition, sflags) setInfo completer
 
-      innerModule.moduleClass setInfo global.loaders.moduleClassLoader
+      innerModule.moduleClass setInfo loaders.moduleClassLoader
       List(innerClass, innerModule.moduleClass) foreach (_.associatedFile = file)
 
       scope enter innerClass
@@ -1019,7 +1028,7 @@ abstract class ClassfileParser {
     for (entry <- innerClasses.entries) {
       // create a new class member for immediate inner classes
       if (entry.outerName == currentClass) {
-        val file = global.classPath.findSourceFile(entry.externalName.toString) getOrElse {
+        val file = classPath.findSourceFile(entry.externalName.toString) getOrElse {
           throw new AssertionError(entry.externalName)
         }
         enterClassAndModule(entry, file)
diff --git a/src/compiler/scala/tools/nsc/symtab/classfile/ICodeReader.scala b/src/compiler/scala/tools/nsc/symtab/classfile/ICodeReader.scala
index 5c8819945a..f704d8ac89 100644
--- a/src/compiler/scala/tools/nsc/symtab/classfile/ICodeReader.scala
+++ b/src/compiler/scala/tools/nsc/symtab/classfile/ICodeReader.scala
@@ -20,6 +20,8 @@ import scala.reflect.internal.JavaAccFlags
  */
 abstract class ICodeReader extends ClassfileParser {
   val global: Global
+  val symbolTable: global.type
+  val loaders: global.loaders.type
   import global._
   import icodes._