Revert "Change path-observer to lookup properties aggressively and report errors"

pkg/observe/lib/src/path_observer.dart

Index: pkg/observe/lib/src/path_observer.dart
diff --git a/pkg/observe/lib/src/path_observer.dart b/pkg/observe/lib/src/path_observer.dart
index cfaab187764caf34f630bca86db670e101073256..0d631a0c192829fb51726b968157ebbf13c3b554 100644
--- a/pkg/observe/lib/src/path_observer.dart
+++ b/pkg/observe/lib/src/path_observer.dart
@@ -82,12 +82,8 @@ class PathObserver extends _Observer implements Bindable {
 }
 
 /// A dot-delimieted property path such as "foo.bar" or "foo.10.bar".
-///
 /// The path specifies how to get a particular value from an object graph, where
-/// the graph can include arrays and maps. Each segment of the path describes
-/// how to take a single step in the object graph. Properties like 'foo' or
-/// 'bar' are read as properties on objects, or as keys if the object is a [Map]
-/// or a [Indexable], while integer values are read as indexes in a [List].
+/// the graph can include arrays.
 // TODO(jmesserly): consider specialized subclasses for:
 // * empty path
 // * "value"
@@ -184,7 +180,7 @@ class PropertyPath {
     return 0x1fffffff & (hash + ((0x00003fff & hash) << 15));
   }
 
-  /// Returns the current value of the path from the provided [obj]ect.
+  /// Returns the current of the path from the provided [obj]ect.
   getValueFrom(Object obj) {
     if (!isValid) return null;
     for (var segment in _segments) {
@@ -237,12 +233,6 @@ bool _changeRecordMatches(record, key) {
   return false;
 }
 
-/// Properties in [Map] that need to be read as properties and not as keys in
-/// the map. We exclude methods ('containsValue', 'containsKey', 'putIfAbsent',
-/// 'addAll', 'remove', 'clear', 'forEach') because there is no use in reading
-/// them as part of path-observer segments.
-const _MAP_PROPERTIES = const [#keys, #values, #length, #isEmpty, #isNotEmpty];
-
 _getObjectProperty(object, property) {
   if (object == null) return null;
 
@@ -251,24 +241,21 @@ _getObjectProperty(object, property) {
       return object[property];
     }
   } else if (property is Symbol) {
-    // Support indexer if available, e.g. Maps or polymer_expressions Scope.
-    // This is the default syntax used by polymer/nodebind and
-    // polymer/observe-js PathObserver.
-    // TODO(sigmund): should we also support using checking dynamically for
-    // whether the type practically implements the indexer API
-    // (smoke.hasInstanceMethod(type, const Symbol('[]')))?
-    if (object is Indexable<String, dynamic> ||
-        object is Map<String, dynamic> && !_MAP_PROPERTIES.contains(property)) {
-      return object[smoke.symbolToName(property)];
-    }
+    final type = object.runtimeType;
     try {
-      return smoke.read(object, property);
+      if (smoke.hasGetter(type, property) || smoke.hasNoSuchMethod(type)) {
+        return smoke.read(object, property);
+      }
+      // Support indexer if available, e.g. Maps or polymer_expressions Scope.
+      // This is the default syntax used by polymer/nodebind and
+      // polymer/observe-js PathObserver.
+      if (smoke.hasInstanceMethod(type, const Symbol('[]'))) {
+        return object[smoke.symbolToName(property)];
+      }
     } on NoSuchMethodError catch (e) {
       // Rethrow, unless the type implements noSuchMethod, in which case we
       // interpret the exception as a signal that the method was not found.
-      // Dart note: getting invalid properties is an error, unlike in JS where
-      // it returns undefined.
-      if (!smoke.hasNoSuchMethod(object.runtimeType)) rethrow;
+      if (!smoke.hasNoSuchMethod(type)) rethrow;
     }
   }
 
@@ -287,17 +274,19 @@ bool _setObjectProperty(object, property, value) {
       return true;
     }
   } else if (property is Symbol) {
-    // Support indexer if available, e.g. Maps or polymer_expressions Scope.
-    if (object is Indexable<String, dynamic> ||
-        object is Map<String, dynamic> && !_MAP_PROPERTIES.contains(property)) {
-      object[smoke.symbolToName(property)] = value;
-      return true;
-    }
+    final type = object.runtimeType;
     try {
-      smoke.write(object, property, value);
-      return true;
-    } on NoSuchMethodError catch (e, s) {
-      if (!smoke.hasNoSuchMethod(object.runtimeType)) rethrow;
+      if (smoke.hasSetter(type, property) || smoke.hasNoSuchMethod(type)) {
+        smoke.write(object, property, value);
+        return true;
+      }
+      // Support indexer if available, e.g. Maps or polymer_expressions Scope.
+      if (smoke.hasInstanceMethod(type, const Symbol('[]='))) {
+        object[smoke.symbolToName(property)] = value;
+        return true;
+      }
+    } on NoSuchMethodError catch (e) {
+      if (!smoke.hasNoSuchMethod(type)) rethrow;
     }
   }
 
@@ -481,13 +470,6 @@ class CompoundObserver extends _Observer implements Bindable {
   }
 }
 
-/// An object accepted by [PropertyPath] where properties are read and written
-/// as indexing operations, just like a [Map].
-abstract class Indexable<K, V> {
-  V operator [](K key);
-  operator []=(K key, V value);
-}
-
 const _observerSentinel = const _ObserverSentinel();
 class _ObserverSentinel { const _ObserverSentinel(); }