feat(core-eslint): atomic-tier-import-direction rule

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/core-eslint/rules/atomic-tier-import-direction.js

@@ -0,0 +1,47 @@
+const TIERS = ["atoms", "molecules", "organisms", "templates", "pages"];
+
+function tierOf(filepath) {
+  for (let i = 0; i < TIERS.length; i++) {
+    const tier = TIERS[i];
+    if (filepath.includes(`/${tier}/`) || filepath.includes(`\\${tier}\\`)) {
+      return { name: tier, index: i };
+    }
+  }
+  return null;
+}
+
+/** @type {import("eslint").Rule.RuleModule} */
+export default {
+  meta: {
+    type: "problem",
+    docs: {
+      description:
+        "Atomic-design tier imports respect direction: atoms ← molecules ← organisms ← templates ← pages.",
+    },
+    schema: [],
+    messages: {
+      wrongDirection:
+        "{{fromTier}} cannot import from {{toTier}} ({{importPath}}). Tier direction: atoms ← molecules ← organisms ← templates ← pages.",
+    },
+  },
+  create(context) {
+    const filename = context.filename;
+    const from = tierOf(filename);
+    if (!from) return {};
+    return {
+      ImportDeclaration(node) {
+        const source = node.source.value;
+        if (typeof source !== "string") return;
+        const to = tierOf(source);
+        if (!to) return;
+        if (to.index > from.index) {
+          context.report({
+            node,
+            messageId: "wrongDirection",
+            data: { fromTier: from.name, toTier: to.name, importPath: source },
+          });
+        }
+      },
+    };
+  },
+};

packages/core-eslint/rules/atomic-tier-import-direction.test.js

@@ -0,0 +1,55 @@
+import { describe, it } from "vitest";
+import { RuleTester } from "eslint";
+import rule from "./atomic-tier-import-direction.js";
+
+const tester = new RuleTester({
+  languageOptions: {
+    parser: await import("@typescript-eslint/parser"),
+    ecmaVersion: "latest",
+    sourceType: "module",
+    parserOptions: { ecmaFeatures: { jsx: true } },
+  },
+});
+
+describe("atomic-tier-import-direction", () => {
+  it("passes when an organism imports from atoms", () => {
+    tester.run("atomic-tier-import-direction", rule, {
+      valid: [{
+        filename: "/repo/packages/core-ui/src/organisms/Card/Card.tsx",
+        code: `import { Button } from "../../atoms/Button/Button";`,
+      }],
+      invalid: [],
+    });
+  });
+
+  it("fires when an atom imports from organisms", () => {
+    tester.run("atomic-tier-import-direction", rule, {
+      valid: [],
+      invalid: [{
+        filename: "/repo/packages/core-ui/src/atoms/Button/Button.tsx",
+        code: `import { Card } from "../../organisms/Card/Card";`,
+        errors: [{ messageId: "wrongDirection", data: { fromTier: "atoms", toTier: "organisms", importPath: "../../organisms/Card/Card" } }],
+      }],
+    });
+  });
+
+  it("is a no-op for files outside any tier folder", () => {
+    tester.run("atomic-tier-import-direction", rule, {
+      valid: [{
+        filename: "/repo/packages/auth/src/application/use-cases/sign-in.use-case.ts",
+        code: `export const x = 1;`,
+      }],
+      invalid: [],
+    });
+  });
+
+  it("passes for same-tier imports", () => {
+    tester.run("atomic-tier-import-direction", rule, {
+      valid: [{
+        filename: "/repo/packages/core-ui/src/molecules/SearchBar/SearchBar.tsx",
+        code: `import { FormField } from "../FormField/FormField";`,
+      }],
+      invalid: [],
+    });
+  });
+});