fix(prefer-observer): separate suggest message (#322)

Fix prefer-observer's suggestion message to be more descriptive instead
of re-stating the error message.

1. Turns on a new eslint-plugin rule to enforce more helpful
suggestions.
- This can be reverted when
eslint-community/eslint-plugin-eslint-plugin#570
is merged.
3. Fixes the one outstanding violation.

Author: JasonWeinzierl

eslint.config.mjs

@@ -71,6 +71,9 @@ export default defineConfig(gitignore(), {
     ],
     'eslint-plugin/prefer-placeholders': 'error',
     'eslint-plugin/require-meta-schema-description': 'error',
+    'eslint-plugin/require-test-case-name': 'error',
+    'eslint-plugin/unique-test-case-names': 'error',
+    'eslint-plugin/no-matching-violation-suggest-message-ids': 'error',
     // TODO(https://github.com/JasonWeinzierl/eslint-plugin-rxjs-x/issues/51):
     // fixing these may require bumping the minimum ESLint version.
     'eslint-plugin/require-meta-default-options': 'off',

src/rules/prefer-observer.ts

@@ -28,6 +28,7 @@ export const preferObserverRule = ruleCreator({
     messages: {
       forbidden:
         'Passing separate handlers is forbidden; pass an observer instead.',
+      suggest: 'Replace with observer object.',
     },
     schema: [
       {
@@ -104,7 +105,7 @@ export const preferObserverRule = ruleCreator({
           fix,
           suggest: [
             {
-              messageId: 'forbidden',
+              messageId: 'suggest',
               fix,
             },
           ],
@@ -122,7 +123,7 @@ export const preferObserverRule = ruleCreator({
             fix,
             suggest: [
               {
-                messageId: 'forbidden',
+                messageId: 'suggest',
                 fix,
               },
             ],