Not possible to compile latest Angular 2 due to literal types

[alfaproject]

TypeScript Version: nightly (2.1.0-dev.20161022)

Code
https://github.com/angular/angular/blob/master/modules/%40angular/compiler/src/expression_parser/lexer.ts#L296

Expected behavior:
No compiler errors.

Actual behavior:

› ./node_modules/.bin/tsc --version
Version 2.1.0-dev.20161022

› ./node_modules/.bin/tsc -p ./modules/tsconfig.json
modules/@angular/compiler/src/expression_parser/lexer.ts(296,13): error TS2365: Operator '==' cannot be applied to types '92' and '117'.

It looks like literal type inference went a bit aggressive with this particular piece of code.
Funnily enough, I've tried to isolate the issue in a more concise class with just a scan method but works all the time, so it must be some weird combination of things going on here, which I couldn't figure out. ):

[alfaproject]

Forgot to say that it is possible to prevent that error by widening the literal type to number, like this:

if (this.peek == <number>chars.$u) {
  // ...
}

But still looks like some weird bug to me.

[ahejlsberg]

This is an effect of #11587. In the if (this.peek == chars.$BACKSLASH) test we narrow this.peek to the literal type 92 (the value of chars.$BACKSLASH). We then complain when you try to compare this literal type to the literal type 117 (the value of chars.$u). The issue of course is that we don't know that this.advance() has a side effect on the value of this.peek.

Interestingly, we had a very similar issue with TypeScript's own parser as described here. We opted to use an accessor function to obtain the value of the side effected variable.