Fix bug where `this` was referring to the fields of a parent facet, not the facet currently being constructed

js/compiler/compiler.js

@@ -55,9 +55,9 @@ function buildActor(nameExpOpt, block, withReact) {
 }
 
 function reactWrap(blockCode) {
-  return '{ Syndicate.Actor.Facet.build((function () { ' +
+  return '{ Syndicate.Actor.Facet.build(function () { ' +
     blockCode +
-    ' }).bind(this)); }';
+    ' }); }';
 }
 
 function buildOnEvent(isTerminal, eventType, subscription, projection, bindings, body) {

js/compiler/demo-bad-this.js

@@ -0,0 +1,59 @@
+// bin/syndicatec compiler/demo-bad-this.js | node
+//
+// Bug with this-ness. Symptomatic output:
+//
+// + render one false
+// + render two false
+// present one
+// - render one false
+// - render two false
+// + render one one
+// + render two one
+//
+// Good output:
+//
+// + render one false
+// + render two false
+// present one
+// - render one false
+// + render one one
+
+var Syndicate = require('./src/main.js');
+
+assertion type user(who);
+assertion type present(who);
+assertion type rendered(who, isPresent);
+
+ground dataspace {
+  actor {
+    assert user('one');
+    assert present('one');
+  }
+
+  actor {
+    assert user('two');
+    // assert present('two');
+  }
+
+  actor {
+    during user($who) {
+      field this.isPresent = false;
+      on asserted present(who) {
+        console.log('present', who);
+        this.isPresent = who;
+      }
+      on retracted present(who) {
+        console.log('absent', who);
+        this.isPresent = false;
+      }
+      assert rendered(who, this.isPresent);
+    }
+  }
+
+  actor {
+    during rendered($who, $isPresent) {
+      on start { console.log('+ render', who, isPresent); }
+      on stop { console.log('- render', who, isPresent); }
+    }
+  }
+}

js/src/actor.js

@@ -139,7 +139,9 @@ Facet.current = null;
 
 Facet.build = function(f) {
   var facet = new Facet(Dataspace.activeBehavior());
-  withCurrentFacet(facet, f);
+  withCurrentFacet(facet, function () {
+    f.call(facet.fields);
+  });
   facet.completeBuild();
 };