replace no-never-initialized-let with upstreamed no-unassigned-vars (#59)

### Changelog
Removed `@foxglove/no-never-initialized-let` rule from #55. This rule
has been upstreamed to eslint core and is now available in eslint v9.27+
as
[no-unassigned-vars](https://eslint.org/docs/latest/rules/no-unassigned-vars).

Author: jtbandes

configs/base.js

@@ -75,7 +75,6 @@ module.exports = [
 
       // require double equal for null and undefined, triple equal everywhere else
       "@foxglove/strict-equality": "error",
-      "@foxglove/no-never-initialized-let": "error",
       "@foxglove/no-return-promise-resolve": "error",
       "@foxglove/prefer-hash-private": "error",
 
@@ -87,6 +86,7 @@ module.exports = [
       "no-implied-eval": "error",
       "no-new-func": "error",
 
+      "no-unassigned-vars": "error",
       // unused vars must have `_` prefix
       "no-unused-vars": [
         "error",

configs/typescript.example.tsx

@@ -30,6 +30,9 @@ void (async () => {
 
 void undefined; // eslint-disable-line @typescript-eslint/no-meaningless-void-operator
 
+let x: string | undefined; // eslint-disable-line no-unassigned-vars
+console.log(x);
+
 /* eslint-enable @typescript-eslint/no-unused-expressions */
 42; // eslint-disable-line @typescript-eslint/no-unused-expressions
 <></>; // eslint-disable-line @typescript-eslint/no-unused-expressions

package-lock.json

@@ -29,14 +29,14 @@
     "eslint-plugin-filenames": "^1",
     "eslint-plugin-import": "^2",
     "eslint-plugin-jest": "^28",
+    "eslint-plugin-prettier": "^5",
     "eslint-plugin-react": "^7",
     "eslint-plugin-react-hooks": "^5",
-    "eslint-plugin-prettier": "^5",
     "tsutils": "^3",
     "typescript-eslint": "^8"
   },
   "peerDependencies": {
-    "eslint": "^9"
+    "eslint": "^9.27.0"
   },
   "devDependencies": {
     "@foxglove/eslint-plugin": "file:.",
@@ -45,8 +45,8 @@
     "@swc/jest": "0.2.36",
     "@types/eslint__js": "8.42.3",
     "@types/jest": "29.5.14",
-    "@typescript-eslint/rule-tester": "8.10.0",
-    "eslint": "9.13.0",
+    "@typescript-eslint/rule-tester": "8.32.1",
+    "eslint": "9.27.0",
     "globals": "15.11.0",
     "jest": "29.7.0",
     "prettier": "3.3.3",

package.json

@@ -2,7 +2,6 @@
 module.exports = {
   rules: {
     "no-boolean-parameters": require("./rules/no-boolean-parameters"),
-    "no-never-initialized-let": require("./rules/no-never-initialized-let"),
     "no-restricted-imports": require("./rules/no-restricted-imports"),
     "no-return-promise-resolve": require("./rules/no-return-promise-resolve"),
     "prefer-hash-private": require("./rules/prefer-hash-private"),

plugin.js

@@ -40,38 +40,6 @@ This rule accepts a single object option with the following default configuratio
 
 - `allowLoneParameter: true` will not report an error if a boolean parameter is the **only** parameter to a function.
 
-### [`@foxglove/no-never-initialized-let`](./no-never-initialized-let.js)
-
-Disallow variable declarations that use `let` but have no intitial value and are never assigned. These variables will always be `undefined` and are likely a programmer error.
-
-The builtin [prefer-const](https://eslint.org/docs/latest/rules/prefer-const) rule doesn't flag these because they lack an initializer. Otherwise, they could be flagged by [init-declarations](https://eslint.org/docs/latest/rules/init-declarations), but this rule is mostly stylistic and has some implications for TypeScript type inference & refinement. (See [eslint/eslint#19581](https://github.com/eslint/eslint/issues/19581) & [microsoft/TypeScript#61496](https://github.com/microsoft/TypeScript/issues/61496) for more discussion.)
-
-Examples of **incorrect** code for this rule:
-
-```ts
-let prevX;
-let prevY;
-if (x !== prevX) {
-  prevX = x;
-}
-if (y !== prevY) {
-  prevX = x; // typo, should have been Y
-}
-```
-
-Examples of **correct** code for this rule:
-
-```ts
-let prevX;
-let prevY;
-if (x !== prevX) {
-  prevX = x;
-}
-if (y !== prevY) {
-  prevY = y;
-}
-```
-
 ### [`@foxglove/no-return-promise-resolve`](./no-return-promise-resolve.js) 🔧
 
 Disallow returning `Promise.resolve(...)` or `Promise.reject(...)` inside an async function. This is redundant since an async function will always return a Promise — use `return` or `throw` directly instead.