Merge pull request scala#3502 from retronym/ticket/8258

Fix regression for using Scala IDE on scala-library

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/interactive/scala/tools/nsc/interactive/Global.scala

@@ -534,7 +534,6 @@ class Global(settings: Settings, _reporter: Reporter, projectName: String = "")
     threadId += 1
     compileRunner = new PresentationCompilerThread(this, projectName)
     compileRunner.setDaemon(true)
-    compileRunner.start()
     compileRunner
   }
 
@@ -1253,11 +1252,21 @@ class Global(settings: Settings, _reporter: Reporter, projectName: String = "")
 
   forceSymbolsUsedByParser()
 
+  /** Start the compiler background thread and turn on thread confinement checks */
+  private def finishInitialization(): Unit = {
+    // this flag turns on `assertCorrectThread checks`
+    initializing = false
+
+    // Only start the thread if initialization was successful. A crash while forcing symbols (for example
+    // if the Scala library is not on the classpath) can leave running threads behind. See Scala IDE #1002016
+    compileRunner.start()
+  }
+
   /** The compiler has been initialized. Constructors are evaluated in textual order,
-   *  so this is set to true only after all super constructors and the primary constructor
+   *  if we reached here, all super constructors and the primary constructor
    *  have been executed.
    */
-  initializing = false
+  finishInitialization()
 }
 
 object CancelException extends Exception

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 {