feat: add opt-in projectStructure config for co-located tests

README.md

@@ -890,6 +890,49 @@ otherwise, you can install them manually:
 pnpm i -D eslint-plugin-eslint-plugin
 ```
 
+#### Co-located Tests
+
+`projectStructure` requires every source file to sit next to its test file,
+through
+[eslint-plugin-project-structure](https://github.com/Igorkowalski94/eslint-plugin-project-structure).
+`src/place-service.ts` then has to be joined by `src/place-service.spec.ts`.
+Only `enforceExistence` is driven here, so the rule never enforces naming:
+
+```ts
+// eslint.config.ts
+import isentinel from "@isentinel/eslint-config";
+
+export default isentinel({
+	projectStructure: {
+		// The plugin's name placeholders, plus `{ext}` for the extension of the
+		// file that matched. Default: ["{node-name}.spec.{ext}"]
+		enforceExistence: "__tests__/{node-name}.test.{ext}",
+		// Default: every source file the preset lints
+		files: ["src/**/*.{ts,tsx}"],
+		// Default: tests, `.d.ts` files and build configs
+		ignores: ["**/index.ts"],
+		// Default: `process.cwd()`
+		projectRoot: import.meta.dirname,
+		// Restricts the check to one subtree. Default: all of `projectRoot`
+		structureRoot: "src",
+	},
+});
+```
+
+```bash
+pnpm i -D eslint-plugin-project-structure
+```
+
+`{node-name}` matches the kebab-case filenames the preset enforces; the others
+are `{nodeName}`, `{NodeName}`, `{node_name}` and `{NODE_NAME}`. A file already
+matching a template is exempt from it. A source file with no test disables the
+rule at the source.
+
+Two caveats. Deleting `foo.spec.ts` does not change `foo.ts`, so a cached run
+replays the old clean result — the check is only sound uncached. And the plugin
+writes `projectStructure.cache.json` into `projectRoot` while it has something
+to report, so gitignore it.
+
 ### Git hooks
 
 If you want to apply lint and auto-fix before every commit, use

package.json

@@ -150,6 +150,7 @@
 		"eslint-plugin-jest": "catalog:peer",
 		"eslint-plugin-jest-extended": "catalog:peer",
 		"eslint-plugin-n": "catalog:peer",
+		"eslint-plugin-project-structure": "catalog:peer",
 		"eslint-plugin-react-jsx": "catalog:peer",
 		"eslint-plugin-react-naming-convention": "catalog:peer",
 		"eslint-plugin-react-x": "catalog:peer",
@@ -174,6 +175,7 @@
 		"eslint-plugin-jest": "^29.15.0",
 		"eslint-plugin-jest-extended": "^3.0.0",
 		"eslint-plugin-n": "^17.0.0 || ^18.0.0",
+		"eslint-plugin-project-structure": "^3.14.0",
 		"eslint-plugin-react-jsx": "^5.10.0",
 		"eslint-plugin-react-naming-convention": "^5.10.0",
 		"eslint-plugin-react-x": "^5.10.0",
@@ -197,6 +199,9 @@
 		"eslint-plugin-n": {
 			"optional": true
 		},
+		"eslint-plugin-project-structure": {
+			"optional": true
+		},
 		"eslint-plugin-react-jsx": {
 			"optional": true
 		},

pnpm-workspace.yaml

@@ -60,6 +60,7 @@ catalogs:
     eslint-plugin-jest: 29.16.0
     eslint-plugin-jest-extended: 3.0.1
     eslint-plugin-n: 18.2.2
+    eslint-plugin-project-structure: 3.14.3
     eslint-plugin-react-jsx: 5.17.3
     eslint-plugin-react-naming-convention: 5.17.3
     eslint-plugin-react-x: 5.17.3

scripts/config-factories.ts

@@ -16,6 +16,7 @@ import {
 	packageJson,
 	perfectionist,
 	pnpm,
+	projectStructure,
 	promise,
 	react,
 	roblox,
@@ -74,6 +75,7 @@ export const PRESET_CONFIGS: Array<Awaitable<Array<TypedFlatConfigItem>>> = [
 	packageJson(),
 	perfectionist(),
 	pnpm({ isInEditor: false }),
+	projectStructure(),
 	promise(),
 	react({ testing: true }),
 	roblox(),

src/cli/constants-generated.ts

@@ -1,5 +1,5 @@
 export const versionsMap = {
-  "eslint": "10.7.0",
+  "eslint": "10.8.1",
   "eslint-plugin-jest": "29.16.0",
   "eslint-plugin-react-jsx": "5.17.3",
   "eslint-plugin-react-naming-convention": "5.17.3",

src/eslint/configs/index.ts

@@ -16,6 +16,7 @@ export * from "./oxfmt.ts";
 export * from "./package-json.ts";
 export * from "./perfectionist.ts";
 export * from "./pnpm.ts";
+export * from "./project-structure.ts";
 export * from "./promise.ts";
 export * from "./react.ts";
 export * from "./roblox.ts";