services:intl locales leaking into user-space options

If your options object happens to be persistent across calls to t, then you can run into a situation where the current locale(s) leak out into that instance and override the default locale stored in the service

let recipient = {who: 'World'};
intl.setLocale('en-us');
intl.t('say.hello', recipient); // 'Hello World'

// At this point, recipient contains a locale property and will override the default in the service

intl.setLocale('es');
intl.t('say.hello', recipient); // 'Hello World' ... expected 'Hola World'

Possible Bug Location

In services:intl, the function returned by formatterProxy appears to directly update the provided options value with the service’s _locale. I think the bug might be in the extend call. Not exactly sure how the custom extend util works, but if it’s like other libraries, an empty seed object could be used to clone the provided object rather than directly manipulating it.

[jasonmit]

2.10.0 contains this

[justinaray]

Awesome!!! Thanks!

Null-safe Issue (#334)