Bug in build-optimizer or uglify-es (AOT output bug)

As per @trotyl on https://github.com/angular/angular/issues/25800 I post this here:

Bug Report or Feature Request (mark with an x)

- [ X] bug report -> please search issues before submitting
- [ ] feature request

Command (mark with an x)

- [ ] new
- [ X] build
- [ ] serve
- [ ] test
- [ ] e2e
- [ ] generate
- [ ] add
- [ ] update
- [ ] lint
- [ ] xi18n
- [ ] run
- [ ] config
- [ ] help
- [ ] version
- [ ] doc

Versions

Angular CLI: 6.0.8 Node: 10.4.0 OS: darwin x64 Angular: 6.1.6

Repro steps

Current behavior

The following Typescript code:

let table1 = [null, "hello"];
let table2 = [null, "world"];

let i = -1;
for (const row of table1) {
  i++;
  if (!row) {
    continue;
  }
  console.log(row, table2[i])
}

when compiled with AOT in an Angular project (ng build --prod --build-optimizer --vendor-chunk=true --aot), produces the following “compiled” code:

for (var l = [null, "world"], n = -1, u = 0, a = [null, "hello"]; u < a.length; u++) {
   var o = a[u];
   o && console.log(o, l[++n])
}

The compiled code checks for null first before it increments i, the written Typescript codes increments i before the null check.

When run in a browser the AOT code prints hello null

Expected behavior

The AOT compiled code in a browser should print hello world

Minimal reproduction of the problem with instructions

Copy above Typescript snipped into a newly created Angular project and build it with AOT.

What is the motivation / use case for changing the behavior?

We expect AOT compiled code to do exactly what the code intends to do

[michaelbaur]

I guess this is the same problem with pure_getters: true that is already discussed in issue 11439

[fbernhard]

Thank you for re-opening the issue.

These type of changes are very dangerous for your users; We have more than 100k lines of code since Angular 2. We don’t see these type of issues in tests as the they only appear in the AOT compilation. We have to “read” the code to find out where else this problem might occur.

On Tue, Sep 4, 2018, 19:04 Alan Agius [e-mail] wrote:

Reopened #12082 https://github.com/angular/angular-cli/issues/12082.

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