Add more detail to missing-key warning

I have a component in which I must be using an array and not setting keys because I get this warning:

Warning: Each child in an array or iterator should have a unique "key" prop.
Check the render method of `Blah`.
See https://fb.me/react-warning-keys for more information.

The problem is that render methods aren’t always simple and sometimes it’s quite hard to find out where the problematic array is.

It would be awesome it the warning could be enhanced to provide some more information about the problematic dom. Something like:

Warning: Each child in an array or iterator should have a unique "key" prop.
Check the render method of `Blah` when rendering: <ol><li>One</li><li>Two</li></ol>
See https://fb.me/react-warning-keys for more information.

or even

Warning: Each child in an array or iterator should have a unique "key" prop.
Check the render method of `Blah`.
The head element renders to: <li>One</li>
See https://fb.me/react-warning-keys for more information.

[gaearon]

This was fixed in https://github.com/facebook/react/pull/6799—now we have an exact stack trace.

[troydemonbreun]

Cool, that would be helpful info.