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 0d631a0c192829fb51726b968157ebbf13c3b554..b7d83172d1606a0b7924772af55fe04d272ab4a9 100644
--- a/pkg/observe/lib/src/path_observer.dart
+++ b/pkg/observe/lib/src/path_observer.dart
@@ -83,7 +83,10 @@ class PathObserver extends _Observer implements Bindable {
 
 /// A dot-delimieted property path such as "foo.bar" or "foo.10.bar".

[Jennifer Messerly, 2014/03/25 22:32:44]

this was an issue before but: do you mind adding a newline after this intro
sentence?

[Siggi Cherem (dart-lang), 2014/03/26 00:32:07]

Done.

 /// The path specifies how to get a particular value from an object graph, where
-/// the graph can include arrays.
+/// 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 an [StringIndexer], while integer values are read as indexes in an array.

[Jennifer Messerly, 2014/03/25 22:32:44]

should be "a [StringIndexer]"

also, this was an issue with the old comment too, but I think "indexes in a
[List]" is more accurate

[Siggi Cherem (dart-lang), 2014/03/26 00:32:07]

Done.

 // TODO(jmesserly): consider specialized subclasses for:
 // * empty path
 // * "value"
@@ -180,7 +183,7 @@ class PropertyPath {
     return 0x1fffffff & (hash + ((0x00003fff & hash) << 15));
   }
 
-  /// Returns the current of the path from the provided [obj]ect.
+  /// Returns the current value of the path from the provided [obj]ect.
   getValueFrom(Object obj) {
     if (!isValid) return null;
     for (var segment in _segments) {
@@ -233,6 +236,13 @@ 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;
 
@@ -241,21 +251,25 @@ _getObjectProperty(object, property) {
       return object[property];
     }
   } else if (property is Symbol) {
-    final type = object.runtimeType;
+    var name = smoke.symbolToName(property);

[Jennifer Messerly, 2014/03/25 22:32:44]

move this inside the if, below? and make _MAP_PROPERTIES use symbols then?

[Siggi Cherem (dart-lang), 2014/03/26 00:32:07]

Done.

+    // 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 StringIndexer ||
+        object is Map && !_MAP_PROPERTIES.contains(name)) {
+      return object[name];
+    }
     try {
-      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) {
+      return smoke.read(object, property);
+    } on NoSuchMethodError catch (e, s) {
       // Rethrow, unless the type implements noSuchMethod, in which case we
       // interpret the exception as a signal that the method was not found.
-      if (!smoke.hasNoSuchMethod(type)) rethrow;
+      if (!smoke.hasNoSuchMethod(object.runtimeType)) {
+        new Completer().completeError(e, s);

[Jennifer Messerly, 2014/03/25 22:32:44]

hmmm. Upon second look I'm not sure this is the right place to throw the error
async. _getObjectProperty is used by PropertyPath, which is just a normal sync
API, and therefore should throw errors synchronously, IMO. So any
catch-rethrow-async must happen at a higher level. 

I think it would be better to leave this code rethrowing, and we can file a bug
if we find cases where template_binding is not rendering other things after a
binding throws. 

BTW, I'm really sorry for leading you down a wild goose chase of async-ifying
this :-(. It didn't click for me until seeing the code in _getObjectProperty why
I had intentionally made it a synchronous throw.

I went ahead and filed https://code.google.com/p/dart/issues/detail?id=17789

[Siggi Cherem (dart-lang), 2014/03/26 00:32:07]

No worries, changed it back to sync. Thanks for filing the bug.

+      }
     }
   }
 
@@ -274,19 +288,20 @@ bool _setObjectProperty(object, property, value) {
       return true;
     }
   } else if (property is Symbol) {
-    final type = object.runtimeType;
+    // Support indexer if available, e.g. Maps or polymer_expressions Scope.
+    var name = smoke.symbolToName(property);
+    if (object is StringIndexer ||
+        object is Map && !_MAP_PROPERTIES.contains(name)) {
+      object[name] = value;
+      return true;
+    }
     try {
-      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;
+      smoke.write(object, property, value);
+      return true;
+    } on NoSuchMethodError catch (e, s) {
+      if (!smoke.hasNoSuchMethod(object.runtimeType)) {
+        new Completer().completeError(e, s);
       }
-    } on NoSuchMethodError catch (e) {
-      if (!smoke.hasNoSuchMethod(type)) rethrow;
     }
   }
 
@@ -470,6 +485,13 @@ 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 StringIndexer {

[Siggi Cherem (dart-lang), 2014/03/25 21:44:25]

I was not sure about the name. Other ideas/suggestions?

[Jennifer Messerly, 2014/03/25 22:32:44]

Indexable<K, V>? then do the is check for Indexable<String, dynamic>.

[Siggi Cherem (dart-lang), 2014/03/26 00:32:07]

Done.

+  operator [](String name);
+  operator []=(index, value);
+}
+
 const _observerSentinel = const _ObserverSentinel();
 class _ObserverSentinel { const _ObserverSentinel(); }