NgUpgrade for Performance's `downgradeModule` can only be called once

I’m submitting a…

[ ] Regression (a behavior that used to work and stopped working in a new release)
[ ] Bug report  
[ ] Performance issue
[ ] Feature request
[x] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question
[ ] Other... Please describe:

Current behavior

A call like:

module('demoApp', [downgradeModule(Ng2Mod1), downgradeModule(Ng2Mod2)])

succeeds but only the first module is usable.

Expected behavior

Either both modules are available or an error is throw describing the limitation. The workaround is not too bad IMHO, just import Ng2Mod1 and Ng2Mod2 into a single module, but without an error this is confusing to users.

Minimal reproduction of the problem with instructions

https://stackblitz.com/edit/ngupgradelite-multi-downgrademodule?file=ng1%2Fdemo-app.module.ts

[jrabbe]

Seems like #26084 is the PR for better throwing, #26062 is the number of this issue.

#26217 looks like it would solve my use case, and would solve the use cases where you are migrating multiple different parts of an AngularJS application.

I am unsure what the value of #26084 is. If you can’t downgrade multiple modules you would need to have one root Angular module to downgrade, and depend on it at the earliest common root of the different places of the application you are migrating. Wouldn’t you just end up having to depend on the downgraded root Angular module almost from the outset, mitigating most of the benefit in using “Upgrade for performance” and the possibility of delaying the loading of Angular and its dependencies?

[jrabbe]

I don’t have a problem manually mapping components to modules for downgrading purposes.