v5.7.0 to v6.0.0 migration: Assertion failed error

• [X ] I am on the latest ember-intl version
• [ X] I have searched the issues of this repo and believe that this is not a duplicate

Environment

• Ember Version: 3.28.3
• Ember CLI Version: 3.28.3
• Ember Intl Version: 6.0.0
• Browser(s): Chrome 93.0
• Node Version: 14.7.6

Steps to Reproduce

• Update ember-intl from 5.7.0 t0 6.0.0 via npm
• ember test

not ok 1 Chrome 93.0 - [131 ms] - Integration | Component | navbar: it renders

    ---

        stack: >

            Error: Assertion Failed: You attempted to update '_locale' on '<(unknown):ember171>', but it had already been used previously in the same computation.  Attempting to update a value after using it in a computation can cause logical errors, infinite revalidation bugs, and performance issues, and is not supported.

            '_locale' was first used:
            
            - While rendering:
              -top-level
                application
                  index
                    navbar
                      bs-navbar
                        bs-navbar/content
                          bs-collapse
                            bs-navbar/nav
                              bs-nav/item
                                bs-navbar/link-to
                                  bs-link-to
                                    link-to
            
            Stack trace for the update:
                at dirtyTagFor (http://localhost:7357/assets/vendor.js:58515:37)
                at setter (http://localhost:7357/assets/vendor.js:58801:7)
                at _class2.set [as _locale] (http://localhost:7357/assets/vendor.js:16458:7)
                at _class2.set locale [as locale] (http://localhost:7357/assets/vendor.js:121125:22)
                at _class2.setLocale (http://localhost:7357/assets/vendor.js:121351:19)
                at new _class2 (http://localhost:7357/assets/vendor.js:121182:12)
                at Function.create (http://localhost:7357/assets/vendor.js:29497:20)
        message: >
            global failure: Error: Assertion Failed: You attempted to update `_locale` on `<(unknown):ember171>`, but it had already been used previously in the same computation.  Attempting to update a value after using it in a computation can cause logical errors, infinite revalidation bugs, and performance issues, and is not supported.
            
            `_locale` was first used:
            
            - While rendering:
              -top-level
                application
                  index
                    navbar
                      bs-navbar
                        bs-navbar/content
                          bs-collapse
                            bs-navbar/nav
                              bs-nav/item
                                bs-navbar/link-to
                                  bs-link-to
                                    link-to
            
            Stack trace for the update:
        negative: >
            false
        browser log: |
            {"type":"warn","text":"DEPRECATION: Versions of modifier manager capabilities prior to 3.22 have been deprecated. You must update to the 3.22 capabilities. [deprecation id: manager-capabilities.modifiers-3-13] See https://deprecations.emberjs.com/v3.x#toc_manager-capabilities-modifiers-3-13 for more details.\n        at logDeprecationStackTrace (http://localhost:7357/assets/vendor.js:36565:21)\n        at HANDLERS.<computed> (http://localhost:7357/assets/vendor.js:36698:9)\n        at raiseOnDeprecation (http://localhost:7357/assets/vendor.js:36592:9)\n        at HANDLERS.<computed> (http://localhost:7357/assets/vendor.js:36698:9)\n        at http://localhost:7357/assets/test-support.js:6638:10\n        at HANDLERS.<computed> (http://localhost:7357/assets/vendor.js:36698:9)\n        at invoke (http://localhost:7357/assets/vendor.js:36710:9)\n        at deprecate (http://localhost:7357/assets/vendor.js:36666:28)\n        at modifierCapabilities$1 (http://localhost:7357/assets/vendor.js:11683:62)"}
            {"type":"error","text":"\n\nError occurred:\n\n- While rendering:\n  -top-level\n    application\n      index\n        navbar\n          bs-navbar\n            bs-navbar/content\n              bs-collapse\n                bs-navbar/nav\n                  bs-nav/item\n                    bs-navbar/link-to\n                      bs-link-to\n                        link-to\n\n"}
            {"type":"error","text":"\n\nError occurred:\n\n\n\n"}
    ...

[charlesfries]

Figured it out. We need to call setLocale before any t helpers in templates are invoked to prevent the double mutation, a good place is probably the ApplicationRoute constructor. This is still probably an issue that needs resolving, though.

import Route from '@ember/routing/route';
import { inject as service } from '@ember/service';

export default class ApplicationRoute extends Route {
  @service intl;

  constructor() {
    super(...arguments);

    this.intl.setLocale('en-us');
  }
}

[xomaczar]

I am also seeing this failure but only in tests. Adding setupIntl(hooks) to a given test module resolves the issue for me.