Closure Compiler no longer able to determine type - google-closure-compiler

Question

I've been using Google's Closure Compiler for most of my projects, and a few of them in advanced mode with 100% typed.
One of my projects though no longer gets stated as 100% typed and I get warnings for things that I didn't used to get them for, and I can't seem to be able to figure out why. This is the message I get
WARNING - could not determine the type of this expression
v['children'].map(v => new _ChildLineItem(v['child'], v['option'], v['quantity'], v['price'])))))),
^
There's 42 more warnings like it, all about the same code, which I have here
/**
* #constructor
* #param {Array<!_Quote>} quotes
* #param {string} email
* #param {?string} quoteid
*/
function _GetQuotes(quotes, email, quoteid) {
this.quotes = quotes;
this.email = email;
this.quoteid = quoteid;
}
/**
* #constructor
* #param {string} quoteid
* #param {boolean} shipping
* #param {Array<!_Proof>} proofs
* #param {Array<!_LineItem>} lineitems
*/
function _Quote(quoteid, shipping, proofs, lineitems) {
this.quoteid = quoteid;
this.shipping = shipping;
this.proofs = proofs;
this.lineitems = lineitems;
}
/**
* #constructor
* #param {string} number
* #param {string} main
* #param {string} thumbnail
*/
function _Proof(number, main, thumbnail) {
this.number = number;
this.main = main;
this.thumbnail = thumbnail;
}
/**
* #constructor
* #param {string} name
* #param {number} quantity
* #param {number} price
* #param {Array<!_ChildLineItem>} children
* */
function _LineItem(name, quantity, price, children) {
this.name = name;
this.quantity = quantity;
this.price = price;
this.children = children;
}
/**
* #constructor
* #param {string} child
* #param {string} option
* #param {number} quantity
* #param {number} price
* */
function _ChildLineItem(child, option, quantity, price) {
this.child = child;
this.option = option;
this.quantity = quantity;
this.price = price;
}
Ajax({
url: '/ajax/getquotes',
data: Data,
success: function (/** !_GetQuotes */ data) {
var d = new _GetQuotes(
data['quotes'].map(v => new _Quote(v['quoteid'], v['shipping'],
v['proofs'].map(v => new _Proof(v['number'], v['main'], v['thumbnail'])),
v['lineitems'].map(v => new _LineItem(v['name'], v['quantity'], v['price'],
v['children'].map(v => new _ChildLineItem(v['child'], v['option'], v['quantity'], v['price'])))))),
data['email'], data['quoteid']);
...
I can rewrite the closures to specify the types of the objects coming through like this
v['children'].map(function( /** !_ChildLineItem */ v) { new _ChildLineItem(v['child'], v['option'], v['quantity'], v['price'])}
But shouldn't it be able to figure that out from the constructor definitions?
Actually me specifying all of them like this isn't even working
var d = new _GetQuotes(
data['quotes'].map((/** !_Quote */ v) => new _Quote(v['quoteid'], v['shipping'],
v['proofs'].map((/** !_Proof */ v) => new _Proof(v['number'], v['main'], v['thumbnail'])),
v['lineitems'].map((/** !_LineItem */ v) => new _LineItem(v['name'], v['quantity'], v['price'],
v['children'].map((/** !_ChildLineItem */ v) => new _ChildLineItem(v['child'], v['option'], v['quantity'], v['price'])))))),
data['email'], data['quoteid']);
With this warning
WARNING - could not determine the type of this expression
v['children'].map((/** !_ChildLineItem */ v) => new _ChildLineItem(v['child'], v['option'], v['quantity'], v['price'])))))),
^^^^^^^^^^^^^^^^^

Answer 1

The problem you are facing is that the compiler generally treats computed and dot property accesses differently. Computed property accesses are treated as the 'unknown' type unless you give a type signature the [] operator (i.e. the class implements IArrayLike as Array does or IObject[2] for map like objects).
Although, the compiler could understand that x.foo and x['foo'] are reference the same property, it does not currently do this.
[1] https://github.com/google/closure-compiler/wiki/Special-types-in-the-Closure-Type-System