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..5103c930b264352808c297d56e9af2c00a4f7000 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.
+   */
+  LibraryElement containingLibrary;

[scheglov, 2017/07/31 22:08:04]

Make all these fields final?

[Brian Wilkerson, 2017/08/01 14:44:15]

Not sure I see the point, given that they're in a private class, but done.

+
+  /**
+   * The offset of the start of the region of text being copied.
+   */
+  int startOffset;
+
+  /**
+   * The offset of the end of the region of text being copied.
+   */
+  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.offset <= endOffset && node.end >= startOffset) {
+      Element nodeElement = node.bestElement;

[scheglov, 2017/07/31 22:08:04]

Hm... I thought that we are interested in names of top-level declarations that
are explicitly written in code. So, these names are always statically resolved.
So, maybe this should be "node.staticElement".

[Brian Wilkerson, 2017/08/01 14:44:15]

Done

+      if (nodeElement != null &&
+          nodeElement.enclosingElement is CompilationUnitElement) {
+        LibraryElement nodeLibrary = nodeElement.library;
+        if (nodeLibrary != containingLibrary) {

[scheglov, 2017/07/31 22:08:04]

Why not?

If we copy a use of a class defined in the library A from the library A to the
library B, we want to insert an import of A into B. OTOH, if we paste into A, we
don't need to re-import itself.

So, this check should be moved to paste.

[Brian Wilkerson, 2017/08/01 14:44:15]

Good point. Done.

+          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.bestElement;

[scheglov, 2017/07/31 22:08:04]

Same here - prefixes are resolved statically.

[Brian Wilkerson, 2017/08/01 14:44:15]

Done

+              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;
   }
 }