feat: add intake method to blockESLint (#2167)

## PR Checklist

- [x] Addresses an existing open issue: fixes #2158
- [x] That issue was marked as [`status: accepting
prs`](https://github.com/JoshuaKGoldberg/create-typescript-app/issues?q=is%3Aopen+is%3Aissue+label%3A%22status%3A+accepting+prs%22)
- [x] Steps in
[CONTRIBUTING.md](https://github.com/JoshuaKGoldberg/create-typescript-app/blob/main/.github/CONTRIBUTING.md)
were taken

## Overview

This is one of the more ridiculous things I've written recently. It:

1. Attempts to parse existing `eslint.config.{js,mjs}` content as a
[`@typescript-eslint/typescript-estree`](https://typescript-eslint.io/packages/typescript-estree)
tree
2. Find the `{ ignores: [...] }` from its first argument
3. Find the next `{ rules: ... }` from its remaining arguments
4. Parse rules groups using
[JSON5.parse](https://www.npmjs.com/package/json5)

...and only if all steps return something looking like what we expect do
we give back some data.

This is really beyond what I'd want folks to have to write in `intake`.
I really wish for this all to be done automatically and reliably:
bingo-js/bingo#128. But that's going to
be a lot more work I don't have time for soon.

🎁

Author: JoshuaKGoldberg

cspell.json

@@ -11,6 +11,7 @@
 	],
 	"words": [
 		"Anson",
+		"TSESTree",
 		"apexskier",
 		"attw",
 		"boop",

package.json

@@ -37,6 +37,7 @@
 		"*": "prettier --ignore-unknown --write"
 	},
 	"dependencies": {
+		"@typescript-eslint/typescript-estree": "^8.29.1",
 		"bingo": "^0.5.14",
 		"bingo-fs": "^0.5.5",
 		"bingo-stratum": "^0.5.11",

pnpm-lock.yaml

@@ -1,9 +1,19 @@
-import { testBlock } from "bingo-stratum-testers";
-import { describe, expect, test } from "vitest";
+import { testBlock, testIntake } from "bingo-stratum-testers";
+import { describe, expect, it, test, vi } from "vitest";
 
 import { blockESLint } from "./blockESLint.js";
 import { optionsBase } from "./options.fakes.js";
 
+const mockIntakeData = { ignores: ["lib"] };
+
+const mockBlockESLintIntake = vi.fn().mockReturnValue(mockIntakeData);
+
+vi.mock("./eslint/blockESLintIntake.js", () => ({
+	get blockESLintIntake() {
+		return mockBlockESLintIntake;
+	},
+}));
+
 describe("blockESLint", () => {
 	test("without addons or mode", () => {
 		const creation = testBlock(blockESLint, {
@@ -1402,4 +1412,40 @@ describe("blockESLint", () => {
 			}
 		`);
 	});
+
+	describe("intake", () => {
+		it("returns undefined when there is no eslint.config file", () => {
+			const actual = testIntake(blockESLint, {
+				files: {},
+			});
+
+			expect(actual).toBeUndefined();
+		});
+
+		it("returns data when there is an eslint.config.js file", () => {
+			const sourceText = "export default ...";
+
+			const actual = testIntake(blockESLint, {
+				files: {
+					"eslint.config.js": [sourceText],
+				},
+			});
+
+			expect(mockBlockESLintIntake).toHaveBeenCalledWith(sourceText);
+			expect(actual).toBe(mockIntakeData);
+		});
+
+		it("returns data when there is an eslint.config.mjs file", () => {
+			const sourceText = "export default ...";
+
+			const actual = testIntake(blockESLint, {
+				files: {
+					"eslint.config.mjs": [sourceText],
+				},
+			});
+
+			expect(mockBlockESLintIntake).toHaveBeenCalledWith(sourceText);
+			expect(actual).toBe(mockIntakeData);
+		});
+	});
 });

src/blocks/blockESLint.test.ts

@@ -12,57 +12,18 @@ import { blockRemoveDependencies } from "./blockRemoveDependencies.js";
 import { blockRemoveFiles } from "./blockRemoveFiles.js";
 import { blockRemoveWorkflows } from "./blockRemoveWorkflows.js";
 import { blockVSCode } from "./blockVSCode.js";
+import { blockESLintIntake } from "./eslint/blockESLintIntake.js";
+import {
+	Extension,
+	ExtensionRuleGroup,
+	ExtensionRules,
+	zExtension,
+	zExtensionRules,
+	zPackageImport,
+} from "./eslint/schemas.js";
+import { intakeFile } from "./intake/intakeFile.js";
 import { CommandPhase } from "./phases.js";
 
-const zRuleOptions = z.union([
-	z.literal("error"),
-	z.literal("off"),
-	z.literal("warn"),
-	z.union([
-		z.tuple([z.union([z.literal("error"), z.literal("warn")]), z.unknown()]),
-		z.tuple([
-			z.union([z.literal("error"), z.literal("warn")]),
-			z.unknown(),
-			z.unknown(),
-		]),
-	]),
-]);
-
-const zExtensionRuleGroup = z.object({
-	comment: z.string().optional(),
-	entries: z.record(z.string(), zRuleOptions),
-});
-
-type ExtensionRuleGroup = z.infer<typeof zExtensionRuleGroup>;
-
-const zExtensionRules = z.union([
-	z.record(z.string(), zRuleOptions),
-	z.array(zExtensionRuleGroup),
-]);
-
-type ExtensionRules = z.infer<typeof zExtensionRules>;
-
-const zExtension = z.object({
-	extends: z.array(z.string()).optional(),
-	files: z.array(z.string()).optional(),
-	languageOptions: z.unknown().optional(),
-	linterOptions: z.unknown().optional(),
-	plugins: z.record(z.string(), z.string()).optional(),
-	rules: zExtensionRules.optional(),
-	settings: z.record(z.string(), z.unknown()).optional(),
-});
-
-type Extension = z.infer<typeof zExtension>;
-
-const zPackageImport = z.object({
-	source: z.union([
-		z.string(),
-		z.object({ packageName: z.string(), version: z.string() }),
-	]),
-	specifier: z.string(),
-	types: z.boolean().optional(),
-});
-
 export const blockESLint = base.createBlock({
 	about: {
 		name: "ESLint",
@@ -76,6 +37,13 @@ export const blockESLint = base.createBlock({
 		rules: zExtensionRules.optional(),
 		settings: z.record(z.string(), z.unknown()).optional(),
 	},
+	intake({ files }) {
+		const eslintConfigRaw = intakeFile(files, [
+			["eslint.config.js", "eslint.config.mjs"],
+		]);
+
+		return eslintConfigRaw ? blockESLintIntake(eslintConfigRaw[0]) : undefined;
+	},
 	produce({ addons, options }) {
 		const { explanations, extensions, ignores, imports, rules, settings } =
 			addons;