"Property never defined" warning when compiling subset of code

[Steve]

I have a large JS application with which I use Closure.  I also use the PrototypeJS library, so for my

compilation I have a custom externs.js file, select externs from the Closure sources, and the

--use_only_custom_externs option.  Also using advanced optimizations.

The first JS file in my application is "base.js" which contains some utilities used throughout the

application.  Currently I'm attempting to compile just the "base.js" and another file for use elsewhere on the

site, and Closure is throwing "Property xxx never defined on yyy" warnings that I don't see when compiling the

entire application.  I'm including the same externs.

It does this with v20130823 and v20131118 but not v20121212.  (This is not an exhaustive bisect, just the

versions I happen to have on hand.)

Why would I get different warnings when compiling a subset of a larger application?

The warning:

base.js:510: WARNING - Property onFailure never defined on Ajax.Base.prototype.options

(request.options.onTimeout || request.options.onFailure || Prototype.emptyFunction)(response, response.headerJSON);

Relevant lines from externs.js:

var Ajax = {};

/** @constructor */

Ajax.Base = function(){};

/** @type {Object} */

Ajax.Base.prototype.options;

/** @type {function(Ajax.Response, Object)|undefined} */

Ajax.Base.prototype.options.onFailure;

(Incidentally, I don't use Ajax in the two-file subset I'm attempting to compile.)

[Dimitris Vardoulakis]

I just filed

https://code.google.com/p/closure-compiler/issues/detail?id=1164

Thanks for the report. For now, you can rewrite your externs slightly to sidestep the issue. (See the workaround in the bug report.)

[Steve]

Thanks, Dimitris.  The record type workaround works for me, although it's not as flexible as the @type annotation.

[Chad Killingsworth]

Often in this case we either use private constructors or interfaces for these cases. Not as convenient, but it get's the job done. Here's an example from the Google Feed API extern: https://code.google.com/p/closure-compiler/source/browse/contrib/externs/google_feed_api.js#94

Chad Killingsworth