Issue 7236 - Handle sub properties in abort-on-property snippets

lib/content/snippets.js

Index: lib/content/snippets.js
===================================================================
--- a/lib/content/snippets.js
+++ b/lib/content/snippets.js
@@ -695,21 +695,45 @@
   // 2176782336 - 60466176 = 2116316160. This ensure to always have 6
   // chars even if Math.random() returns its minimum value 0.0
   //
   return Math.floor(Math.random() * 2116316160 + 60466176).toString(36);
 }
 
 function wrapPropertyAccess(object, property, descriptor)
 {
-  let currentDescriptor = Object.getOwnPropertyDescriptor(object, property);
+  let dot = property.indexOf(".");
+  if (dot == -1)
+  {
+    // simple property case.
+    let currentDescriptor = Object.getOwnPropertyDescriptor(object, property);
+    if (currentDescriptor && !currentDescriptor.configurable)
+      return false;
+
+    Object.defineProperty(object, property, descriptor);
+    return true;
+  }
+  let name = property.slice(0, dot);
+  property = property.slice(dot + 1);
+  let value = object[name];
+  if (value && typeof value == "object")
+    return wrapPropertyAccess(value, property, descriptor);
+
+  let currentDescriptor = Object.getOwnPropertyDescriptor(object, name);
   if (currentDescriptor && !currentDescriptor.configurable)
     return false;
 
-  Object.defineProperty(object, property, descriptor);
+  let v;

[Manish Jethani, 2019/02/20 06:20:46]

There are two things missing in this implementation:

 1.  If `typeof value` is not object (let's say it's number), the getter below
will return undefined instead of the value

 2.  When wrapping `foo.bar.lambda`, if `foo.bar` exists and is an object, and
if `foo.bar` is reassigned a different object, the wrapper is gone; however this
is not the case if the `foo.bar` does not exist initially (asymmetry)

[Manish Jethani, 2019/02/20 06:28:53]

Let me elaborate a little ...
Suppose we are wrapping `foo.bar.lambda` but only `foo.bar` exists and the value
is 4. Our getter for `foo.bar` returns `undefined`, the original value 4 is
lost.
Once again, suppose we are wrapping `foo.bar.lambda`. There are two scenarios
(asymmetry):

Scenario 1: `foo.bar` does not exist. In this case, when `foo.bar` is assigned a
value that is an object, the setter ensures that `foo.bar.lambda` is wrapped.

Scenario 2: `foo.bar` exists and is an object. In this case, when
`foo.bar.lambda` is wrapped; however, unlike the previous case, if `foo.bar` is
assigned a different object (i.e. `foo.bar = {}`), the new `foo.bar.lambda` is
not wrapped. In the previous case, no matter how many different objects are
assigned to `foo.bar`, each new assignment is always wrapped.

So these asymmetries and inconsistencies is something we could address. I don't
know if it means much in practice, at least for now, but in the long run it's
always better to have a robust implementation.

[hub, 2019/02/22 17:36:19]

Fixed them.

+  let setter = a =>
+  {
+    v = a;
+    if (a && typeof a == "object")
+      wrapPropertyAccess(a, property, descriptor);
+  };
+  Object.defineProperty(object, name, {get: () => v, set: setter});
   return true;
 }
 
 /**
  * Overrides the <code>onerror</code> handler to discard tagged error messages
  * from our property wrapping.
  *
  * @param {string} magic The magic string that tags the error message.