SI-8258 Revert "SI-7335 Remove special case for import of Predef._

This reverts commit 6690455.

Conflicts:
    src/reflect/scala/reflect/internal/TreeInfo.scala

As evidenced by the highlights of the stack trace in Scala IDE,
my assertion in the 6690455 wasn't universally true.

The change was only motivated by removing a special case, not in
order to fix some other problem. So the revert is the most straight
forward course of action for now.

I haven't pinned this down with a test outside of Eclipse, and
given the lateness of the hour wrt 2.11.0, I'll have to submit
without one.

    2013-03-10 08:38:04,690 ERROR [main] - org.scala-ide.sdt.core - org.scala-ide.sdt.core - org.scala-ide.sdt.core - 0 - Error during askOption
    scala.reflect.internal.Symbols$CyclicReference: illegal cyclic reference involving object Predef
    ...
    at scala.reflect.internal.Symbols$Symbol.lock(Symbols.scala:482)
    at scala.reflect.internal.Symbols$Symbol.info(Symbols.scala:1216)
    at scala.reflect.internal.Symbols$Symbol.tpe(Symbols.scala:1200)
    at scala.reflect.internal.Symbols$Symbol.tpeHK(Symbols.scala:1201)
    at scala.reflect.internal.Types$Type.computeMemberType(Types.scala:784)
    at scala.reflect.internal.Types$Type.memberType(Types.scala:781)
    at scala.reflect.internal.TreeGen.mkAttributedSelect(TreeGen.scala:203)
    ...
    at scala.reflect.internal.TreeGen.mkAttributedStableRef(TreeGen.scala:162)
    at scala.tools.nsc.ast.TreeGen.mkWildcardImport(TreeGen.scala:39)
    at scala.tools.nsc.typechecker.Contexts$Context.makeNewImport(Contexts.scala:308)
    at scala.tools.nsc.typechecker.Contexts$class.rootContext(Contexts.scala:69)
    at scala.tools.nsc.Global$$anon$1.rootContext(Global.scala:492)
    at scala.tools.nsc.typechecker.Contexts$class.rootContext(Contexts.scala:64)
    at scala.tools.nsc.Global$$anon$1.rootContext(Global.scala:492)
    at scala.tools.nsc.typechecker.Analyzer$namerFactory$$anon$1.apply(Analyzer.scala:43)
    at scala.tools.nsc.Global$GlobalPhase.applyPhase(Global.scala:463)
    ...
    at scala.tools.nsc.Global$Run.compileLate(Global.scala:1681)
    at scala.tools.nsc.Global$Run.compileLate(Global.scala:1671)
    at scala.tools.nsc.symtab.SymbolLoaders$SourcefileLoader.doComplete(SymbolLoaders.scala:284)
    at scala.tools.nsc.symtab.SymbolLoaders$SymbolLoader.complete(SymbolLoaders.scala:187)
    at scala.reflect.internal.Symbols$Symbol.info(Symbols.scala:1229)
    at scala.reflect.internal.Symbols$Symbol.tpe(Symbols.scala:1200)
    at scala.reflect.internal.Symbols$Symbol.tpeHK(Symbols.scala:1201)
    at scala.reflect.internal.Types$Type.computeMemberType(Types.scala:784)
    at scala.reflect.internal.Types$Type.memberType(Types.scala:781)
    at scala.reflect.internal.TreeGen.mkAttributedSelect(TreeGen.scala:203)
    at scala.reflect.internal.TreeGen.mkAttributedRef(TreeGen.scala:124)
    at scala.reflect.internal.TreeGen.mkAttributedRef(TreeGen.scala:130)
    at scala.reflect.internal.TreeGen.mkAttributedStableRef(TreeGen.scala:162)
    at scala.tools.nsc.ast.TreeGen.mkWildcardImport(TreeGen.scala:39)
    ...
    at scala.tools.nsc.Global$$anon$1.rootContext(Global.scala:492)
    at scala.tools.nsc.typechecker.Analyzer$namerFactory$$anon$1.apply(Analyzer.scala:43)
    at scala.tools.nsc.Global$GlobalPhase.applyPhase(Global.scala:463)
    ...
    at scala.tools.nsc.Global$Run.compileLate(Global.scala:1671)
    at scala.tools.nsc.symtab.SymbolLoaders$SourcefileLoader.doComplete(SymbolLoaders.scala:284)
    at scala.tools.nsc.symtab.SymbolLoaders$SymbolLoader.complete(SymbolLoaders.scala:187)
    at scala.reflect.internal.Symbols$Symbol.info(Symbols.scala:1229)
    at scala.reflect.internal.Symbols$Symbol.initialize(Symbols.scala:1365)
    ...
    at scala.collection.immutable.HashSet$HashSet1.foreach(HashSet.scala:153)
    at scala.collection.immutable.HashSet$HashTrieSet.foreach(HashSet.scala:306)
    at scala.tools.eclipse.javaelements.ScalaJavaMapper$class.initializeRequiredSymbols(ScalaJavaMapper.scala:29)
    ...
    at scala.tools.nsc.util.InterruptReq.execute(InterruptReq.scala:26)
    at scala.tools.nsc.interactive.Global.pollForWork(Global.scala:340)

Author: retronym

src/compiler/scala/tools/nsc/typechecker/Contexts.scala

@@ -89,6 +89,8 @@ trait Contexts { self: Analyzer =>
     if (settings.noimports) Nil
     else if (unit.isJava) RootImports.javaList
     else if (settings.nopredef || treeInfo.noPredefImportForUnit(unit.body)) {
+      // SI-8258 Needed for the presentation compiler using -sourcepath, otherwise cycles can occur. See the commit
+      //         message for this ticket for an example.
       debuglog("Omitted import of Predef._ for " + unit)
       RootImports.javaAndScalaList
     }

src/reflect/scala/reflect/internal/TreeInfo.scala

@@ -735,6 +735,17 @@ abstract class TreeInfo {
       unapply(dissectApplied(tree))
   }
 
+  /** Does list of trees start with a definition of
+   *  a class of module with given name (ignoring imports)
+   */
+  def firstDefinesClassOrObject(trees: List[Tree], name: Name): Boolean = trees match {
+    case Import(_, _) :: xs             => firstDefinesClassOrObject(xs, name)
+    case Annotated(_, tree1) :: _       => firstDefinesClassOrObject(List(tree1), name)
+    case ModuleDef(_, `name`, _) :: _   => true
+    case ClassDef(_, `name`, _, _) :: _ => true
+    case _                              => false
+  }
+
   /** Locates the synthetic Apply node corresponding to an extractor's call to
    *  unapply (unwrapping nested Applies) and returns the fun part of that Apply.
    */
@@ -750,8 +761,7 @@ abstract class TreeInfo {
   }
 
   /** Is this file the body of a compilation unit which should not
-   *  have Predef imported? This is the case iff the first import in the
-   *  unit explicitly refers to Predef.
+   *  have Predef imported?
    */
   def noPredefImportForUnit(body: Tree) = {
     // Top-level definition whose leading imports include Predef.
@@ -760,7 +770,13 @@ abstract class TreeInfo {
       case Import(expr, _)      => isReferenceToPredef(expr)
       case _                    => false
     }
-    isLeadingPredefImport(body)
+    // Compilation unit is class or object 'name' in package 'scala'
+    def isUnitInScala(tree: Tree, name: Name) = tree match {
+      case PackageDef(Ident(nme.scala_), defs) => firstDefinesClassOrObject(defs, name)
+      case _                                   => false
+    }
+
+    isUnitInScala(body, nme.Predef) || isLeadingPredefImport(body)
   }
 
   def isAbsTypeDef(tree: Tree) = tree match {