Partial support for intelligent paste operation

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

Index: pkg/analysis_server/lib/src/computer/import_elements_computer.dart
diff --git a/pkg/analysis_server/lib/src/computer/import_elements_computer.dart b/pkg/analysis_server/lib/src/computer/import_elements_computer.dart
index 0826e39c2702e9860ee72fa1ba56a71fb69ffe97..f9328f4351017bd7e3b8ac8be9cae3af4abaf707 100644
--- a/pkg/analysis_server/lib/src/computer/import_elements_computer.dart
+++ b/pkg/analysis_server/lib/src/computer/import_elements_computer.dart
@@ -2,55 +2,409 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'dart:async';
+
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analyzer/dart/analysis/results.dart';
-import 'package:analyzer/dart/analysis/session.dart';
+import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/ast_factory.dart';
+import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/element/element.dart';
-import 'package:analyzer_plugin/protocol/protocol_common.dart';
+import 'package:analyzer/file_system/file_system.dart';
+import 'package:analyzer/src/dart/ast/ast_factory.dart';
+import 'package:analyzer/src/dart/ast/token.dart';
+import 'package:analyzer/src/dart/resolver/scope.dart';
+import 'package:analyzer/src/generated/source.dart';
+import 'package:analyzer_plugin/protocol/protocol_common.dart' hide Element;
 import 'package:analyzer_plugin/utilities/change_builder/change_builder_dart.dart';
+import 'package:analyzer_plugin/utilities/range_factory.dart';
+import 'package:front_end/src/base/syntactic_entity.dart';
+import 'package:path/src/context.dart';
 
 /**
- * An object used to compute the edits required to ensure that a list of
- * elements is imported into a given library.
+ * An object used to compute a set of edits to add imports to a given library in
+ * order to make a given set of elements visible.
+ *
+ * This is used to implement the `edit.importElements` request.
  */
 class ImportElementsComputer {
   /**
-   * The analysis session used to compute the unit.
+   * The resource provider used to access the file system.
    */
-  final AnalysisSession session;
+  final ResourceProvider resourceProvider;
 
   /**
-   * The library element representing the library to which the imports are to be
-   * added.
+   * The resolution result associated with the defining compilation unit of the
+   * library to which imports might be added.
    */
-  final LibraryElement libraryElement;
+  final ResolveResult libraryResult;
 
   /**
-   * The path of the defining compilation unit of the library.
+   * Initialize a newly created builder.
    */
-  final String path;
+  ImportElementsComputer(this.resourceProvider, this.libraryResult);
 
   /**
-   * The elements that are to be imported into the library.
+   * Create the edits that will cause the list of [importedElements] to be
+   * imported into the library at the given [path].
    */
-  final List<ImportedElements> elements;
+  Future<SourceChange> createEdits(
+      List<ImportedElements> importedElementsList) async {
+    List<ImportedElements> filteredImportedElements =
+        _filterImportedElements(importedElementsList);
+    LibraryElement libraryElement = libraryResult.libraryElement;
+    SourceFactory sourceFactory = libraryElement.context.sourceFactory;

[scheglov, 2017/07/27 20:54:15]

It might be worth eventually to expose SourceFactory from AnalysisSession.
With the final goal to remove AnalysisContext.

[Brian Wilkerson, 2017/07/27 20:55:33]

I agree. I'll try to tackle that soon.

+    List<ImportDirective> existingImports = <ImportDirective>[];
+    for (var directive in libraryResult.unit.directives) {
+      if (directive is ImportDirective) {
+        existingImports.add(directive);
+      }
+    }
+
+    DartChangeBuilder builder = new DartChangeBuilder(libraryResult.session);
+    await builder.addFileEdit(libraryResult.path,
+        (DartFileEditBuilder builder) {
+      for (ImportedElements importedElements in filteredImportedElements) {
+        List<ImportDirective> matchingImports =
+            _findMatchingImports(existingImports, importedElements);
+        if (matchingImports.isEmpty) {
+          //
+          // The required library is not being imported with a matching prefix,
+          // so we need to add an import.
+          //
+          File importedFile = resourceProvider.getFile(importedElements.path);
+          Uri uri = sourceFactory.restoreUri(importedFile.createSource());
+          Source importedSource = importedFile.createSource(uri);
+          String importUri =
+              _getLibrarySourceUri(libraryElement, importedSource);
+          int offset = _offsetForInsertion(importUri);
+          builder.addInsertion(offset, (DartEditBuilder builder) {
+            builder.writeln();
+            builder.write("import '");
+            builder.write(importUri);
+            builder.write("'");
+            if (importedElements.prefix.isNotEmpty) {
+              builder.write(' as ');
+              builder.write(importedElements.prefix);
+            }
+            builder.write(';');
+          });
+        } else {
+          //
+          // There are some imports of the library with a matching prefix. We
+          // need to determine whether the names are already visible or whether
+          // we need to make edits to make them visible.
+          //
+          // Compute the edits that need to be made.
+          //
+          Map<ImportDirective, _ImportUpdate> updateMap =
+              <ImportDirective, _ImportUpdate>{};
+          for (String requiredName in importedElements.elements) {
+            _computeUpdate(updateMap, matchingImports, requiredName);
+          }
+          //
+          // Apply the edits.
+          //
+          for (ImportDirective directive in updateMap.keys) {
+            _ImportUpdate update = updateMap[directive];
+            List<String> namesToUnhide = update.namesToUnhide;
+            List<String> namesToShow = update.namesToShow;
+            namesToShow.sort();
+            NodeList<Combinator> combinators = directive.combinators;
+            int combinatorCount = combinators.length;
+            for (int combinatorIndex = 0;
+                combinatorIndex < combinatorCount;
+                combinatorIndex++) {
+              Combinator combinator = combinators[combinatorIndex];
+              if (combinator is HideCombinator && namesToUnhide.isNotEmpty) {
+                NodeList<SimpleIdentifier> hiddenNames = combinator.hiddenNames;
+                int nameCount = hiddenNames.length;
+                int first = -1;
+                for (int nameIndex = 0; nameIndex < nameCount; nameIndex++) {
+                  if (namesToUnhide.contains(hiddenNames[nameIndex].name)) {
+                    if (first < 0) {
+                      first = nameIndex;
+                    }
+                  } else {
+                    if (first >= 0) {
+                      // Remove a range of names.
+                      builder.addDeletion(range.startStart(
+                          hiddenNames[first], hiddenNames[nameIndex]));
+                      first = -1;
+                    }
+                  }
+                }
+                if (first == 0) {
+                  // Remove the whole combinator.
+                  if (combinatorIndex == 0) {
+                    if (combinatorCount > 1) {
+                      builder.addDeletion(range.startStart(
+                          combinator, combinators[combinatorIndex + 1]));
+                    } else {
+                      SyntacticEntity precedingNode = directive.prefix ??
+                          directive.deferredKeyword ??
+                          directive.uri;
+                      if (precedingNode == null) {
+                        builder.addDeletion(range.node(combinator));
+                      } else {
+                        builder.addDeletion(
+                            range.endEnd(precedingNode, combinator));
+                      }
+                    }
+                  } else {
+                    builder.addDeletion(range.endEnd(
+                        combinators[combinatorIndex - 1], combinator));
+                  }
+                } else if (first > 0) {
+                  // Remove a range of names that includes the last name.
+                  builder.addDeletion(range.endEnd(
+                      hiddenNames[first - 1], hiddenNames[nameCount - 1]));
+                }
+              } else if (combinator is ShowCombinator &&
+                  namesToShow.isNotEmpty) {
+                // TODO(brianwilkerson) Add the names in alphabetic order.
+                builder.addInsertion(combinator.shownNames.last.end,
+                    (DartEditBuilder builder) {
+                  for (String nameToShow in namesToShow) {
+                    builder.write(', ');
+                    builder.write(nameToShow);
+                  }
+                });
+              }
+            }
+          }
+        }
+      }
+    });
+    return builder.sourceChange;
+  }
 
   /**
-   * Initialize a newly created computer to compute the edits required to ensure
-   * that the given list of [elements] is imported into a given [library].
+   * Choose the import for which the least amount of work is required,
+   * preferring to do no work in there is an import that already makes the name
+   * visible, and preferring to remove hide combinators rather than add show
+   * combinators.
+   *
+   * The name is visible without needing any changes if:
+   * - there is an import with no combinators,
+   * - there is an import with only hide combinators and none of them hide the
+   *   name,
+   * - there is an import that shows the name and doesn't subsequently hide the
+   *   name.
    */
-  ImportElementsComputer(ResolveResult result, this.path, this.elements)
-      : session = result.session,
-        libraryElement = result.libraryElement;
+  void _computeUpdate(Map<ImportDirective, _ImportUpdate> updateMap,
+      List<ImportDirective> matchingImports, String requiredName) {
+    /**
+     * Return `true` if the [requiredName] is in the given list of [names].
+     */
+    bool nameIn(NodeList<SimpleIdentifier> names) {
+      for (SimpleIdentifier name in names) {
+        if (name.name == requiredName) {
+          return true;
+        }
+      }
+      return false;
+    }
+
+    ImportDirective preferredDirective = null;
+    int bestEditCount = -1;
+    bool deleteHide = false;
+    bool addShow = false;
+
+    for (ImportDirective directive in matchingImports) {
+      NodeList<Combinator> combinators = directive.combinators;
+      if (combinators.isEmpty) {
+        return;
+      }
+      bool hasHide = false;
+      bool needsShow = false;
+      int editCount = 0;
+      for (Combinator combinator in combinators) {
+        if (combinator is HideCombinator) {
+          if (nameIn(combinator.hiddenNames)) {
+            hasHide = true;
+            editCount++;
+          }
+        } else if (combinator is ShowCombinator) {
+          if (needsShow || !nameIn(combinator.shownNames)) {
+            needsShow = true;
+            editCount++;
+          }
+        }
+      }
+      if (editCount == 0) {
+        return;
+      } else if (bestEditCount < 0 || editCount < bestEditCount) {
+        preferredDirective = directive;
+        bestEditCount = editCount;
+        deleteHide = hasHide;
+        addShow = needsShow;
+      }
+    }
+
+    _ImportUpdate update = updateMap.putIfAbsent(
+        preferredDirective, () => new _ImportUpdate(preferredDirective));
+    if (deleteHide) {
+      update.unhide(requiredName);
+    }
+    if (addShow) {
+      update.show(requiredName);
+    }
+  }
 
   /**
-   * Compute and return the list of edits.
+   * Filter the given list of imported elements ([originalList]) so that only
+   * the names that are not already defined still remain. Names that are already
+   * defined are removed even if they might not resolve to the same name as in
+   * the original source.
    */
-  List<SourceEdit> compute() {
-    DartChangeBuilder builder = new DartChangeBuilder(session);
-    builder.addFileEdit(path, (DartFileEditBuilder builder) {
-      // TODO(brianwilkerson) Implement this.
-    });
-    return <SourceEdit>[]; // builder.sourceChange
+  List<ImportedElements> _filterImportedElements(
+      List<ImportedElements> originalList) {
+    LibraryElement libraryElement = libraryResult.libraryElement;
+    LibraryScope libraryScope = new LibraryScope(libraryElement);
+    AstFactory factory = new AstFactoryImpl();
+    List<ImportedElements> filteredList = <ImportedElements>[];
+    for (ImportedElements elements in originalList) {
+      List<String> originalElements = elements.elements;
+      List<String> filteredElements = originalElements.toList();
+      for (String name in originalElements) {
+        Identifier identifier = factory
+            .simpleIdentifier(new StringToken(TokenType.IDENTIFIER, name, -1));
+        if (elements.prefix.isNotEmpty) {
+          SimpleIdentifier prefix = factory.simpleIdentifier(
+              new StringToken(TokenType.IDENTIFIER, elements.prefix, -1));
+          Token period = new SimpleToken(TokenType.PERIOD, -1);
+          identifier = factory.prefixedIdentifier(prefix, period, identifier);
+        }
+        Element element = libraryScope.lookup(identifier, libraryElement);
+        if (element != null) {
+          filteredElements.remove(name);
+        }
+      }
+      if (originalElements.length == filteredElements.length) {
+        filteredList.add(elements);
+      } else if (filteredElements.isNotEmpty) {
+        filteredList.add(new ImportedElements(
+            elements.path, elements.prefix, filteredElements));
+      }
+    }
+    return filteredList;
+  }
+
+  /**
+   * Return all of the import elements in the list of [existingImports] that
+   * match the given specification of [importedElements], or an empty list if
+   * there are no such imports.
+   */
+  List<ImportDirective> _findMatchingImports(
+      List<ImportDirective> existingImports,
+      ImportedElements importedElements) {
+    List<ImportDirective> matchingImports = <ImportDirective>[];
+    for (ImportDirective existingImport in existingImports) {
+      if (_matches(existingImport, importedElements)) {
+        matchingImports.add(existingImport);
+      }
+    }
+    return matchingImports;
+  }
+
+  /**
+   * Computes the best URI to import [what] into [from].
+   *
+   * Copied from DartFileEditBuilderImpl.
+   */
+  String _getLibrarySourceUri(LibraryElement from, Source what) {
+    String whatPath = what.fullName;
+    // check if an absolute URI (such as 'dart:' or 'package:')
+    Uri whatUri = what.uri;
+    String whatUriScheme = whatUri.scheme;
+    if (whatUriScheme != '' && whatUriScheme != 'file') {
+      return whatUri.toString();
+    }
+    // compute a relative URI
+    Context context = resourceProvider.pathContext;
+    String fromFolder = context.dirname(from.source.fullName);
+    String relativeFile = context.relative(whatPath, from: fromFolder);
+    return context.split(relativeFile).join('/');
+  }
+
+  /**
+   * Return `true` if the given [import] matches the given specification of
+   * [importedElements]. They will match if they import the same library using
+   * the same prefix.
+   */
+  bool _matches(ImportDirective import, ImportedElements importedElements) {
+    return (import.element as ImportElement).importedLibrary.source.fullName ==
+            importedElements.path &&
+        (import.prefix?.name ?? '') == importedElements.prefix;
+  }
+
+  /**
+   * Return the offset at which an import of the given [importUri] should be
+   * inserted.
+   *
+   * Partially copied from DartFileEditBuilderImpl.
+   */
+  int _offsetForInsertion(String importUri) {
+    // TODO(brianwilkerson) Fix this to find the right location.
+    // See DartFileEditBuilderImpl._addLibraryImports for inspiration.
+    CompilationUnit unit = libraryResult.unit;
+    LibraryDirective libraryDirective;
+    List<ImportDirective> importDirectives = <ImportDirective>[];
+    for (Directive directive in unit.directives) {
+      if (directive is LibraryDirective) {
+        libraryDirective = directive;
+      } else if (directive is ImportDirective) {
+        importDirectives.add(directive);
+      }
+    }
+    if (importDirectives.isEmpty) {
+      if (libraryDirective == null) {
+        return 0;
+      }
+      return libraryDirective.end;
+    }
+    return importDirectives.last.end;
+  }
+}
+
+/**
+ * Information about how a given import directive needs to be updated in order
+ * to make the required names visible.
+ */
+class _ImportUpdate {
+  /**
+   * The import directive to be updated.
+   */
+  final ImportDirective import;
+
+  /**
+   * The list of names that are currently hidden that need to not be hidden.
+   */
+  final List<String> namesToUnhide = <String>[];
+
+  /**
+   * The list of names that need to be added to show clauses.
+   */
+  final List<String> namesToShow = <String>[];
+
+  /**
+   * Initialize a newly created information holder to hold information about
+   * updates to the given [import].
+   */
+  _ImportUpdate(this.import);
+
+  /**
+   * Record that the given [name] needs to be added to show combinators.
+   */
+  void show(String name) {
+    namesToShow.add(name);
+  }
+
+  /**
+   * Record that the given [name] needs to be removed from hide combinators.
+   */
+  void unhide(String name) {
+    namesToUnhide.add(name);
   }
 }