add checks for early references to global names

[nicks]

this class of error seems to hit me a bunch:

// ==ClosureCompiler==
// @compilation_level ADVANCED_OPTIMIZATIONS
// @output_file_name default.js
// ==/ClosureCompiler==

var x = {};
alert(x.y);
x.y = 3;

closure-compiler does not warn about this today, but I think it should. I was thinking about either moving theVariableReferenceCheck after CollapseProperties, or doing something clever in CheckGlobalNames.

any thoughts or advice on this?

[dimvar]

This is sth that should be caught by type checking.

We shouldn't do sth that depends on CollapseProperties running during checks. We currently have it there to check constants on namespaces, but we will do that in the new type inference, so we'll eventually remove CollapseProperties from the checks.

[nicks]

does the new type system catch this?

[dimvar]

yeah it does. For some reason I can't see the warning on the debugger, but I see it when I add a unit test. (Will have a patch out with that test later today.)