Incompatibility between `ember-cli-addon-guard` and `ember-intl` >= `4.2.1`

[BillyRayPreachersSon]

The problem

On a project containing [email protected] and [email protected], when starting my Ember server, I get an error Cannot read property 'paths' of undefined, with this stack trace:

  - broccoliBuilderErrorStack: [undefined]
  - code: [undefined]
  - codeFrame: [undefined]
  - errorMessage: Cannot read property 'paths' of undefined
  - errorType: [undefined]
  - location:
    - column: [undefined]
    - file: [undefined]
    - line: [undefined]
  - message: Cannot read property 'paths' of undefined
  - name: TypeError
  - nodeAnnotation: [undefined]
  - nodeName: [undefined]
  - originalErrorMessage: [undefined]
  - stack: TypeError: Cannot read property 'paths' of undefined
    at Class.cacheKeyForTree (/Users/dan.nye/new/Documents/code/platform/node_modules/ember-intl/index.js:47:32)
    at traverseAddons (/Users/dan.nye/new/Documents/code/platform/node_modules/ember-cli-addon-guard/lib/utils/review-project.js:54:66)
    at traverseAddons (/Users/dan.nye/new/Documents/code/platform/node_modules/ember-cli-addon-guard/lib/utils/review-project.js:76:13)
    at traverseAddons (/Users/dan.nye/new/Documents/code/platform/node_modules/ember-cli-addon-guard/lib/utils/review-project.js:76:13)
    at traverseAddons (/Users/dan.nye/new/Documents/code/platform/node_modules/ember-cli-addon-guard/lib/utils/review-project.js:76:13)
    at Object.reviewProject [as default] (/Users/dan.nye/new/Documents/code/platform/node_modules/ember-cli-addon-guard/lib/utils/review-project.js:28:5)
    at Class.included (/Users/dan.nye/new/Documents/code/platform/node_modules/ember-cli-addon-guard/index.js:35:49)
    at Class.superWrapper [as included] (/Users/dan.nye/new/Documents/code/platform/node_modules/core-object/lib/assign-properties.js:34:20)
    at /Users/dan.nye/new/Documents/code/platform/node_modules/ember-cli/lib/broccoli/ember-app.js:629:15
    at Array.forEach (<anonymous>)

The diagnosis

Adding in some logging, it appears that when ember-cli-addon-guard tries to call ember-intl's cacheKeyForTree method, an error is thrown because the cacheKeyForTree method refers to a property that is only set up if the included method is called first.

Reproduction steps

I've tried on our setup:

• [email protected]
• [email protected]
• [email protected]
• [email protected]
• [email protected]

I've also tried the same but with our target Ember upgrade versions:

• [email protected]
• [email protected]

I've also tried using out-of-the-box LTS versions of Ember and Node:

• [email protected]
• [email protected]
• [email protected]
• [email protected]
• [email protected]
• [email protected]

In all cases, running ember s will throw the above error.

Where to go from here

I'm trying to work out which addon is at fault here - ember-intl or ember-cli-addon-guard. I'm leaning towards ember-intl being the culprit, as neither https://rfcs.emberjs.com/id/0090-addon-tree-caching/ nor https://ember-cli.com/api/classes/addon#method_cacheKeyForTree state that included should be called before cacheKeyForTree in order for cacheKeyForTree to work.

As such, I've raised https://github.com/ember-intl/ember-intl/issues/1926. However, I thought it worth raising this bug here for two reasons:

1. I could be wrong, and it could well be that included should always be called before cacheKeyForTree
2. Anyone with the same problem searching issues here will hopefully come across this and save themselves some head scratching.

If you don't think that this is an ember-cli-addon-guard issue, please feel free to close this bug report.