this.parsedJSON.content_scripts.forEach is not a function

[Rob--W]

Describe the problem and steps to reproduce it:

While looking into #4645, I noticed that the underlying issue is that one cannot make any assumptions on this.parsedJSON, other than it being JSON. There are multiple instances where this assumption is violated:

addons-linter/src/parsers/manifestjson.js

Lines 533 to 537 in e1f8902

	if (
	this.parsedJSON.content_scripts &&
	this.parsedJSON.content_scripts.length
	) {
	this.parsedJSON.content_scripts.forEach((scriptRule) => {

addons-linter/src/parsers/manifestjson.js

Lines 884 to 888 in e1f8902

	if (
	this.parsedJSON.browser_action &&
	this.parsedJSON.browser_action.theme_icons
	) {
	this.parsedJSON.browser_action.theme_icons.forEach((icon) => {

Test case, create manifest.json with the following content and run the linter on it:

{
  "content_scripts": {
    "length": true
  }
}

Similarly,

{
  "browser_action": {
    "theme_icons": true
  }
}

What happened?

TypeError: this.parsedJSON.content_scripts.forEach is not a function

TypeError: this.parsedJSON.browser_action.theme_icons.forEach is not a function

What did you expect to happen?

Validation errors for the manifest being invalid, including MANIFEST_FIELD_INVALID with message "/content_scripts" must be an array.
And for the second test case, "/browser_action/theme_icons" must be an array

┆Issue is synchronized with this Jira Task