Treat nested imports more carefully

This commit overworks the way nested imports are treated when calculating
compilation unit dependencies. Prior to this commit, nested imports were
often simply ignored, resulting in breakage like ticket #1002613. To mitigate
this problem, it was necessary to add more bookkeeping to the dependency
calculation algorithm.

Fixes #1002613

src/main/scala/scala/tools/refactoring/analysis/CompilationUnitDependencies.scala

@@ -169,7 +169,7 @@ trait CompilationUnitDependencies extends CompilerApiExtensions with ScalaVersio
         t match {
           case Select(Ident(name), _) if name startsWith nme.EVIDENCE_PARAM_PREFIX =>
             ()
-          case t @ Select(qual, _) if !isQualifierFromLocalImport(qual) =>
+          case t @ Select(qual, _) if !isRelativeToLocalImports(qual) =>
             addToResult(t)
           case _ =>
             ()
@@ -199,14 +199,6 @@ trait CompilationUnitDependencies extends CompilerApiExtensions with ScalaVersio
         t.qualifier.symbol != null && (!t.qualifier.symbol.isTerm || t.qualifier.symbol.isStable)
       }
 
-      @tailrec
-      def isRelativeToPreviousImports(tree: Tree): Boolean = tree match {
-        case Select(qualifier, _) =>
-          if (qualifier.pos.isRange) isRelativeToPreviousImports(qualifier)
-          else true
-        case _ => false
-      }
-
       val language = newTermName("language")
 
       def isScopeForLocalImports(tree: Tree) = tree match {
@@ -217,16 +209,68 @@ trait CompilationUnitDependencies extends CompilerApiExtensions with ScalaVersio
       var inScopeForLocalImports = false
       var localImports: List[Import] = Nil
       var localImportsForParent: List[Import] = Nil
+      var topLevelImports: List[Import] = Nil
+      var pkgDefStack: List[RefTree] = Nil
+
+      def isRelativeToLocalImports(tree: Tree): Boolean = {
+        (hasImplicitQualifier(tree) && isRelativeTo(localImports, tree)) \\ { res =>
+          trace("Tree %s is relative to local imports: %s", tree, res)
+        }
+      }
+
+      def isRelativeToTopLevelImports(tree: Tree): Boolean = {
+        (hasImplicitQualifier(tree) && !isRelativeTo(localImports, tree) && isRelativeTo(topLevelImports, tree)) \\ { res =>
+          trace("Tree %s is relative to top level imports: %s", tree, res)
+        }
+      }
+
+      def isRelativeToEnclosingPackage(tree: Tree): Boolean = {
+        !hasImplicitQualifier(tree) && {
+          val owningPkg = getOwningPkg(tree.symbol)
 
-      def isQualifierFromLocalImport(qualifier: Tree): Boolean = {
-        localImports.exists { imp =>
-          imp.expr.symbol == qualifier.symbol
+          pkgDefStack.exists { pid =>
+            owningPkg.toString == pid.symbol.toString
+          }
         }
+      } \\ { res =>
+        trace("Tree %s is relative to enclosing package: %s", tree, res)
+      }
+
+      @tailrec
+      def getOwningPkg(symbol: Symbol): Symbol = {
+        if (symbol.hasPackageFlag) symbol
+        else getOwningPkg(symbol.owner)
+      }
+
+      def isRelativeTo(imports: List[Import], tree: Tree): Boolean = {
+        imports.exists { imp =>
+          def compareSyms = imp.expr.symbol == tree.symbol
+
+          imp.selectors match {
+            case List(singleSelector) =>
+              tree match {
+                case Select(q, n) =>
+                  compareSyms || (q.symbol == imp.expr.symbol && (n == singleSelector.name || singleSelector.name == nme.WILDCARD))
+                case _ => compareSyms
+              }
+            case _ => compareSyms
+          }
+        }
+      }
+
+      @tailrec
+      def hasImplicitQualifier(tree: Tree): Boolean = tree match {
+        case Select(q, _) =>
+          if (q.pos.isRange) hasImplicitQualifier(q)
+          else true
+        case _: Ident => !tree.pos.isRange
+        case _ => false
       }
 
       override def traverse(tree: Tree) = {
         var resetInScopeForLocalImports = false
         var restoreLocalImports = false
+        var popPkgDefStack = false
 
         if (isScopeForLocalImports(tree)) {
           localImportsForParent = localImports
@@ -245,15 +289,18 @@ trait CompilationUnitDependencies extends CompilerApiExtensions with ScalaVersio
               feature foreach (selector => addToResult(Select(select, selector.name)))
 
             case imp @ Import(qualifier, selector)  => {
-              if (inScopeForLocalImports && !qualifier.symbol.isLocal) {
-                localImports ::= imp
-
-                if (!isRelativeToPreviousImports(qualifier)) {
-                  fakeSelectTree(qualifier.tpe, qualifier.symbol, qualifier) match {
-                    case select: Select => addToResult(select)
-                    case _ => ()
+              if (inScopeForLocalImports) {
+                if (!qualifier.symbol.isLocal && !qualifier.symbol.isVal) {
+                  if (isRelativeToTopLevelImports(qualifier) || isRelativeToEnclosingPackage(qualifier)) {
+                    fakeSelectTree(qualifier.tpe, qualifier.symbol, qualifier) match {
+                      case select: Select => addToResult(select)
+                      case _ => ()
+                    }
                   }
                 }
+                localImports ::= imp
+              } else {
+                topLevelImports ::= imp
               }
             }
 
@@ -318,7 +365,7 @@ trait CompilationUnitDependencies extends CompilerApiExtensions with ScalaVersio
                   && t.name != nme.WILDCARD
                   && hasStableQualifier(t)
                   && !t.symbol.isLocal
-                  && !isQualifierFromLocalImport(qual)
+                  && !isRelativeToLocalImports(qual)
                   && !isDefinedLocallyAndQualifiedWithEnclosingPackage(t)) {
                 addToResult(t)
               }
@@ -367,6 +414,11 @@ trait CompilationUnitDependencies extends CompilerApiExtensions with ScalaVersio
               super.traverse(tree)
             }
 
+            case t @ PackageDef(pid, stats) =>
+              pkgDefStack ::= pid
+              popPkgDefStack = true
+              stats.foreach(traverse)
+
             case _ =>
               super.traverse(tree)
           }
@@ -378,6 +430,10 @@ trait CompilationUnitDependencies extends CompilerApiExtensions with ScalaVersio
           if (restoreLocalImports) {
             localImports = localImportsForParent
           }
+
+          if (popPkgDefStack && pkgDefStack.nonEmpty) {
+            pkgDefStack = pkgDefStack.tail
+          }
         }
       }