Update background.service_worker message

Fixes #5252

Author: dotproto

docs/rules.md

@@ -142,6 +142,7 @@ Rules are sorted by severity.
 | `NONE_DATA_COLLECTION_IS_EXCLUSIVE`                     | error    | "none" must not be specified with other required data collection permissions                                                                                                                                                                                                                                                                             |
 | `HAS_PREVIOUS_CONSENT_IS_RESERVED`                      | error    | The `/browser_specific_settings/gecko/data_collection_permissions/has_previous_consent` property is reserved and cannot be set to `true`                                                                                                                                                                                                                 |
 | `MISSING_ADDON_ID`                                      | warning  | The `/browser_specific_settings/gecko/id` property (add-on ID) should be specified in the manifest. This property will become mandatory in the future. See [https://mzl.la/3PLZYdo](https://mzl.la/3PLZYdo) for more information.                                                                                                                        |
+| `BACKGROUND_SERVICE_WORKER`                             | error    | The `/background/service_worker` property is not supported by itself. It may only be used in combination with `/background/scripts` or `/background/page`.                                                                                                                                                                                               |
 
 ### Static Theme / manifest.json
 

src/messages/manifestjson.js

@@ -888,3 +888,13 @@ export const MISSING_ADDON_ID = {
     future. See https://mzl.la/3PLZYdo for more information.`),
   file: MANIFEST_JSON,
 };
+
+export const BACKGROUND_SERVICE_WORKER = {
+  code: 'BACKGROUND_SERVICE_WORKER',
+  message: i18n._(`"/background/service_worker" is not supported.`),
+  description: i18n._(`The "background" property must contain either "scripts" 
+    or "page". See 
+    https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/background#browser_support
+    (MDN docs) for more information.`),
+  file: MANIFEST_JSON,
+};

src/parsers/manifestjson.js

@@ -589,13 +589,9 @@ export default class ManifestJSONParser extends JSONParser {
           // service worker support isn't enabled by the addons-linter feature
           // flag.
           if (hasScripts || hasPage) {
-            this.collector.addWarning(
-              messages.manifestFieldUnsupported('/background/service_worker')
-            );
+            this.collector.addWarning(messages.BACKGROUND_SERVICE_WORKER);
           } else {
-            this.collector.addError(
-              messages.manifestFieldUnsupported('/background/service_worker')
-            );
+            this.collector.addError(messages.BACKGROUND_SERVICE_WORKER);
             this.isValid = false;
           }
         } else if (this.parsedJSON.manifest_version >= 3) {

tests/unit/parsers/test.manifestjson.js

@@ -3342,7 +3342,7 @@ describe('ManifestJSONParser', () => {
       expect(linter.collector.errors).toEqual(
         expect.arrayContaining([
           expect.objectContaining({
-            code: 'MANIFEST_FIELD_UNSUPPORTED',
+            code: 'BACKGROUND_SERVICE_WORKER',
             message: expect.stringMatching(
               /"\/background\/service_worker" is not supported/
             ),
@@ -3381,7 +3381,7 @@ describe('ManifestJSONParser', () => {
         expect(linter.collector.warnings).toEqual(
           expect.arrayContaining([
             expect.objectContaining({
-              code: 'MANIFEST_FIELD_UNSUPPORTED',
+              code: 'BACKGROUND_SERVICE_WORKER',
               message: expect.stringMatching(
                 /"\/background\/service_worker" is not supported/
               ),
@@ -3413,7 +3413,7 @@ describe('ManifestJSONParser', () => {
       expect(linter.collector.errors).toEqual(
         expect.arrayContaining([
           expect.objectContaining({
-            code: 'MANIFEST_FIELD_UNSUPPORTED',
+            code: 'BACKGROUND_SERVICE_WORKER',
             message: expect.stringMatching(
               /"\/background\/service_worker" is not supported/
             ),