Initial implementation of the import-aware copy support

pkg/analysis_server/lib/src/computer/imported_elements_computer.dart

Index: pkg/analysis_server/lib/src/computer/imported_elements_computer.dart
diff --git a/pkg/analysis_server/lib/src/computer/imported_elements_computer.dart b/pkg/analysis_server/lib/src/computer/imported_elements_computer.dart
index 058a6ec1dac3f42e1f9956fee223684c1bf3b930..56671aa821ab46a1035ec828a34a68fcd1304989 100644
--- a/pkg/analysis_server/lib/src/computer/imported_elements_computer.dart
+++ b/pkg/analysis_server/lib/src/computer/imported_elements_computer.dart
@@ -4,6 +4,8 @@
 
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/visitor.dart';
+import 'package:analyzer/dart/element/element.dart';
 
 /**
  * An object used to compute the list of elements referenced within a given
@@ -37,7 +39,85 @@ class ImportedElementsComputer {
    * Compute and return the list of imported elements.
    */
   List<ImportedElements> compute() {
-    // TODO(brianwilkerson) Implement this.
-    return <ImportedElements>[];
+    _Visitor visitor =
+        new _Visitor(unit.element.library, offset, offset + length);
+    unit.accept(visitor);
+    return visitor.importedElements.values.toList();
+  }
+}
+
+/**
+ * The visitor used by an [ImportedElementsComputer] to record the names of all
+ * imported elements.
+ */
+class _Visitor extends UnifyingAstVisitor<Object> {
+  /**
+   * The element representing the library containing the code being visited.
+   */
+  final LibraryElement containingLibrary;
+
+  /**
+   * The offset of the start of the region of text being copied.
+   */
+  final int startOffset;
+
+  /**
+   * The offset of the end of the region of text being copied.
+   */
+  final int endOffset;
+
+  /**
+   * A table mapping library path and prefix keys to the imported elements from
+   * that library.
+   */
+  Map<String, ImportedElements> importedElements = <String, ImportedElements>{};
+
+  /**
+   * Initialize a newly created visitor to visit nodes within a specified
+   * region.
+   */
+  _Visitor(this.containingLibrary, this.startOffset, this.endOffset);
+
+  @override
+  Object visitNode(AstNode node) {
+    if (node.offset <= endOffset && node.end >= startOffset) {
+      node.visitChildren(this);
+    }
+    return null;
+  }
+
+  @override
+  Object visitSimpleIdentifier(SimpleIdentifier node) {
+    if (!node.inDeclarationContext() &&
+        node.offset <= endOffset &&
+        node.end >= startOffset) {
+      Element nodeElement = node.staticElement;
+      if (nodeElement != null &&
+          nodeElement.enclosingElement is CompilationUnitElement) {
+        LibraryElement nodeLibrary = nodeElement.library;
+        String path = nodeLibrary.definingCompilationUnit.source.fullName;
+        String prefix = '';
+        AstNode parent = node.parent;
+        if (parent is PrefixedIdentifier && parent.identifier == node) {
+          SimpleIdentifier prefixIdentifier = parent.prefix;
+          if (prefixIdentifier.offset <= endOffset &&
+              prefixIdentifier.end >= startOffset) {
+            Element prefixElement = prefixIdentifier.staticElement;
+            if (prefixElement is PrefixElement) {
+              prefix = prefixElement.name;
+            }
+          }
+        }
+        String key = '$prefix;$path';
+        ImportedElements elements = importedElements.putIfAbsent(
+            key, () => new ImportedElements(path, prefix, <String>[]));
+        List<String> elementNames = elements.elements;
+        String elementName = nodeElement.name;
+        if (!elementNames.contains(elementName)) {
+          elementNames.add(elementName);
+        }
+      }
+    }
+    return null;
   }
 }