Make observable transform a barback transform.

pkg/observe/lib/transform.dart

+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+/**
+ * Code transform for @observable. The core transformation is relatively
+ * straightforward, and essentially like an editor refactoring.
+ */
+library observe.transform;
+
+import 'dart:async';
+import 'package:path/path.dart' as path;
+import 'package:analyzer_experimental/src/generated/ast.dart';
+import 'package:analyzer_experimental/src/generated/error.dart';
+import 'package:analyzer_experimental/src/generated/parser.dart';
+import 'package:analyzer_experimental/src/generated/scanner.dart';
+import 'package:barback/barback.dart';
+import 'package:source_maps/refactor.dart';
+import 'package:source_maps/span.dart' show SourceFile;
+
+/**
+ * A [Transformer] that replaces observables based on dirty-checking with an
+ * implementation based on change notifications. 
+ *
+ * The transformation adds hooks for field setters and notifies the observation
+ * system of the change.
+ */
+class ObservableTransformer extends Transformer {
+
+  Future<bool> isPrimary(Asset input) {
+    if (input.id.extension != '.dart') return new Future.value(false);
+    // Note: technically we should parse the file to find accurately the
+    // observable annotation, but that seems expensive. It would require almost
+    // as much work as applying the transform. We rather have some false
+    // positives here, and then generate no outputs when we apply this
+    // transform.
+    return input.readAsString().then((c) => c.contains("@observable"));
+  }
+
+  Future apply(Transform transform) {
+    return transform.primaryInput
+        .then((input) => input.readAsString().then((content) {
+      var id = transform.primaryId;
+      // TODO(sigmund): improve how we compute this url
+      var url = id.path.startsWith('lib/')
+            ? 'package:${id.package}/${id.path.substring(4)}' : id.path;
+      var sourceFile = new SourceFile.text(url, content);
+      var transaction = _transformCompilationUnit(
+          content, sourceFile, transform.logger);
+      if (!transaction.hasEdits) {
+        transform.addOutput(input);
+        return;
+      }
+      var printer = transaction.commit();
+      // TODO(sigmund): emit source maps when barback supports it (see
+      // dartbug.com/12340)
+      printer.build(url);
+      transform.addOutput(new Asset.fromString(id, printer.text));
+    }));
+  }
+}
+
+TextEditTransaction _transformCompilationUnit(
+    String inputCode, SourceFile sourceFile, TransformLogger logger) {
+  var unit = _parseCompilationUnit(inputCode);
+  return transformObservables(unit, sourceFile, inputCode, logger);
+}
+
+// TODO(sigmund): make this private. This is currently public so it can be used
+// by the polymer.dart package which is not yet entirely migrated to use
+// pub-serve and pub-deploy.
+TextEditTransaction transformObservables(CompilationUnit unit,
+    SourceFile sourceFile, String content, TransformLogger logger) {
+  var code = new TextEditTransaction(content, sourceFile);
+  for (var directive in unit.directives) {
+    if (directive is LibraryDirective && _hasObservable(directive)) {
+      logger.warning('@observable on a library no longer has any effect. '
+          'It should be placed on individual fields.',
+          _getSpan(sourceFile, directive));
+      break;
+    }
+  }
+
+  for (var declaration in unit.declarations) {
+    if (declaration is ClassDeclaration) {
+      _transformClass(declaration, code, sourceFile, logger);
+    } else if (declaration is TopLevelVariableDeclaration) {
+      if (_hasObservable(declaration)) {
+        logger.warning('Top-level fields can no longer be observable. '
+            'Observable fields should be put in an observable objects.',
+            _getSpan(sourceFile, declaration));
+      }
+    }
+  }
+  return code;
+}
+
+/** Parse [code] using analyzer_experimental. */
+CompilationUnit _parseCompilationUnit(String code) {
+  var errorListener = new _ErrorCollector();
+  var scanner = new StringScanner(null, code, errorListener);
+  var token = scanner.tokenize();
+  var parser = new Parser(null, errorListener);
+  return parser.parseCompilationUnit(token);
+}
+
+class _ErrorCollector extends AnalysisErrorListener {
+  final errors = <AnalysisError>[];
+  onError(error) => errors.add(error);
+}
+
+_getSpan(SourceFile file, ASTNode node) => file.span(node.offset, node.end);
+
+/** True if the node has the `@observable` annotation. */
+bool _hasObservable(AnnotatedNode node) => _hasAnnotation(node, 'observable');
+
+bool _hasAnnotation(AnnotatedNode node, String name) {
+  // TODO(jmesserly): this isn't correct if the annotation has been imported
+  // with a prefix, or cases like that. We should technically be resolving, but
+  // that is expensive.
+  return node.metadata.any((m) => m.name.name == name &&
+      m.constructorName == null && m.arguments == null);
+}
+
+void _transformClass(ClassDeclaration cls, TextEditTransaction code,
+    SourceFile file, TransformLogger logger) {
+
+  if (_hasObservable(cls)) {
+    logger.warning('@observable on a class no longer has any effect. '
+        'It should be placed on individual fields.',
+        _getSpan(file, cls));
+  }
+
+  // We'd like to track whether observable was declared explicitly, otherwise
+  // report a warning later below. Because we don't have type analysis (only
+  // syntactic understanding of the code), we only report warnings that are
+  // known to be true.
+  var declaresObservable = false;
+  if (cls.extendsClause != null) {
+    var id = _getSimpleIdentifier(cls.extendsClause.superclass.name);
+    if (id.name == 'ObservableBase') {
+      code.edit(id.offset, id.end, 'ChangeNotifierBase');
+      declaresObservable = true;
+    } else if (id.name == 'ChangeNotifierBase') {
+      declaresObservable = true;
+    } else if (id.name != 'PolymerElement' && id.name != 'CustomElement'
+        && id.name != 'Object') {
+      // TODO(sigmund): this is conservative, consider using type-resolution to
+      // improve this check.
+      declaresObservable = true;
+    }
+  }
+
+  if (cls.withClause != null) {
+    for (var type in cls.withClause.mixinTypes) {
+      var id = _getSimpleIdentifier(type.name);
+      if (id.name == 'ObservableMixin') {
+        code.edit(id.offset, id.end, 'ChangeNotifierMixin');
+        declaresObservable = true;
+        break;
+      } else if (id.name == 'ChangeNotifierMixin') {
+        declaresObservable = true;
+        break;
+      } else {
+        // TODO(sigmund): this is conservative, consider using type-resolution
+        // to improve this check.
+        declaresObservable = true;
+      }
+    }
+  }
+
+  if (!declaresObservable && cls.implementsClause != null) {
+    // TODO(sigmund): consider adding type-resolution to give a more precise
+    // answer.
+    declaresObservable = true;
+  }
+
+  // Track fields that were transformed.
+  var instanceFields = new Set<String>();
+  var getters = new List<String>();
+  var setters = new List<String>();
+
+  for (var member in cls.members) {
+    if (member is FieldDeclaration) {
+      bool isStatic = _hasKeyword(member.keyword, Keyword.STATIC);
+      if (isStatic) {
+        if (_hasObservable(member)){
+          logger.warning('Static fields can no longer be observable. '
+              'Observable fields should be put in an observable objects.',
+              _getSpan(file, member));
+        }
+        continue;
+      }
+      if (_hasObservable(member)) {
+        if (!declaresObservable) {
+          logger.warning('Observable fields should be put in an observable'
+              ' objects. Please declare that this class extends from '
+              'ObservableBase, includes ObservableMixin, or implements '
+              'Observable.',
+              _getSpan(file, member));
+
+        }
+        _transformFields(member.fields, code, member.offset, member.end);
+
+        var names = member.fields.variables.map((v) => v.name.name);
+
+        getters.addAll(names);
+        if (!_isReadOnly(member.fields)) {
+          setters.addAll(names);
+          instanceFields.addAll(names);
+        }
+      }
+    }
+    // TODO(jmesserly): this is a temporary workaround until we can remove
+    // getValueWorkaround and setValueWorkaround.
+    if (member is MethodDeclaration) {
+      if (_hasKeyword(member.propertyKeyword, Keyword.GET)) {
+        getters.add(member.name.name);
+      } else if (_hasKeyword(member.propertyKeyword, Keyword.SET)) {
+        setters.add(member.name.name);
+      }
+    }
+  }
+
+  // If nothing was @observable, bail.
+  if (instanceFields.length == 0) return;
+
+  // Fix initializers, because they aren't allowed to call the setter.
+  for (var member in cls.members) {
+    if (member is ConstructorDeclaration) {
+      _fixConstructor(member, code, instanceFields);
+    }
+  }
+}
+
+SimpleIdentifier _getSimpleIdentifier(Identifier id) =>
+    id is PrefixedIdentifier ? (id as PrefixedIdentifier).identifier : id;
+
+
+bool _hasKeyword(Token token, Keyword keyword) =>
+    token is KeywordToken && (token as KeywordToken).keyword == keyword;
+
+String _getOriginalCode(TextEditTransaction code, ASTNode node) =>
+    code.original.substring(node.offset, node.end);
+
+void _fixConstructor(ConstructorDeclaration ctor, TextEditTransaction code,
+    Set<String> changedFields) {
+
+  // Fix normal initializers
+  for (var initializer in ctor.initializers) {
+    if (initializer is ConstructorFieldInitializer) {
+      var field = initializer.fieldName;
+      if (changedFields.contains(field.name)) {
+        code.edit(field.offset, field.end, '__\$${field.name}');
+      }
+    }
+  }
+
+  // Fix "this." initializer in parameter list. These are tricky:
+  // we need to preserve the name and add an initializer.
+  // Preserving the name is important for named args, and for dartdoc.
+  // BEFORE: Foo(this.bar, this.baz) { ... }
+  // AFTER:  Foo(bar, baz) : __$bar = bar, __$baz = baz { ... }
+
+  var thisInit = [];
+  for (var param in ctor.parameters.parameters) {
+    if (param is DefaultFormalParameter) {
+      param = param.parameter;
+    }
+    if (param is FieldFormalParameter) {
+      var name = param.identifier.name;
+      if (changedFields.contains(name)) {
+        thisInit.add(name);
+        // Remove "this." but keep everything else.
+        code.edit(param.thisToken.offset, param.period.end, '');
+      }
+    }
+  }
+
+  if (thisInit.length == 0) return;
+
+  // TODO(jmesserly): smarter formatting with indent, etc.
+  var inserted = thisInit.map((i) => '__\$$i = $i').join(', ');
+
+  int offset;
+  if (ctor.separator != null) {
+    offset = ctor.separator.end;
+    inserted = ' $inserted,';
+  } else {
+    offset = ctor.parameters.end;
+    inserted = ' : $inserted';
+  }
+
+  code.edit(offset, offset, inserted);
+}
+
+bool _isReadOnly(VariableDeclarationList fields) {
+  return _hasKeyword(fields.keyword, Keyword.CONST) ||
+      _hasKeyword(fields.keyword, Keyword.FINAL);
+}
+
+void _transformFields(VariableDeclarationList fields, TextEditTransaction code,
+    int begin, int end) {
+
+  if (_isReadOnly(fields)) return;
+
+  var indent = guessIndent(code.original, begin);
+  var replace = new StringBuffer();
+
+  // Unfortunately "var" doesn't work in all positions where type annotations
+  // are allowed, such as "var get name". So we use "dynamic" instead.
+  var type = 'dynamic';
+  if (fields.type != null) {
+    type = _getOriginalCode(code, fields.type);
+  }
+
+  for (var field in fields.variables) {
+    var initializer = '';
+    if (field.initializer != null) {
+      initializer = ' = ${_getOriginalCode(code, field.initializer)}';
+    }
+
+    var name = field.name.name;
+
+    // TODO(jmesserly): should we generate this one one line, so source maps
+    // don't break?
+    if (replace.length > 0) replace.write('\n\n$indent');
+    replace.write('''
+$type __\$$name$initializer;
+$type get $name => __\$$name;
+set $name($type value) {
+  __\$$name = notifyPropertyChange(const Symbol('$name'), __\$$name, value);
+}
+'''.replaceAll('\n', '\n$indent'));
+  }
+
+  code.edit(begin, end, '$replace');
+}