added eslint-plugin

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

.changeset/tough-jeans-camp.md

@@ -0,0 +1,5 @@
+---
+'@backstage/eslint-plugin': minor
+---
+
+Added a new ESLint plugin with common rules for Backstage projects.

.github/vale/Vocab/Backstage/accept.txt

@@ -336,6 +336,7 @@ subfolders
 subheader
 subheaders
 subkey
+subpath
 subroutes
 subtree
 superfences
@@ -418,4 +419,4 @@ Dominik
 Henneke
 Kuang
 Frontside
-Kaswell
+Kaswell

packages/eslint-plugin/README.md

@@ -0,0 +1,40 @@
+# @backstage/eslint-plugin
+
+A collection of ESLint rules useful to Backstage projects.
+
+## Usage
+
+This ESLint plugin is part of the default lint configuration provided by the [Backstage CLI](https://www.npmjs.com/package/@backstage/cli), so you generally do not need to install it manually.
+
+If you do wish to install this plugin manually, start by adding it as a development dependency to your project:
+
+```sh
+yarn add --dev @backstage/eslint-plugin
+```
+
+Then add it to your ESLint configuration:
+
+```js
+extends: [
+  'plugin:@backstage/recommended',
+],
+```
+
+Alternatively, if you want to install in individual rules manually:
+
+```js
+plugins: [
+  '@backstage',
+],
+rules: {
+  '@backstage/no-forbidden-package-imports': 'error',
+}
+```
+
+## Rules
+
+The following rules are provided by this plugin:
+
+| Rule                                      | Description                                                                     |
+| ----------------------------------------- | ------------------------------------------------------------------------------- |
+| `@backstage/no-forbidden-package-imports` | Disallow internal monorepo imports from package subpaths that are not exported. |

packages/eslint-plugin/index.js

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2023 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+module.exports = {
+  configs: {
+    recommended: {
+      plugins: ['@backstage'],
+      rules: {
+        '@backstage/no-forbidden-package-imports': 'error',
+      },
+    },
+  },
+  rules: {
+    'no-forbidden-package-imports': require('./rules/no-forbidden-package-imports'),
+  },
+};

packages/eslint-plugin/package.json

@@ -0,0 +1,16 @@
+{
+  "name": "@backstage/eslint-plugin",
+  "description": "Backstage ESLint plugin",
+  "version": "0.0.0",
+  "publishConfig": {
+    "access": "public"
+  },
+  "homepage": "https://backstage.io",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/backstage/backstage",
+    "directory": "packages/eslint-plugin"
+  },
+  "license": "Apache-2.0",
+  "main": "./index.js"
+}

packages/eslint-plugin/rules/no-forbidden-package-imports.js

@@ -0,0 +1,124 @@
+'use strict';
+/*
+ * Copyright 2023 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// @ts-check
+
+// Note: this file is ES5, because we want to avoid having to transpile it for local development
+
+var fs = require('fs');
+var path = require('path');
+/** @type {import('@manypkg/get-packages')} */
+var manypkg = require('@manypkg/get-packages');
+
+// Loads all packages in the monorepo once, and caches the result
+var getPackageMap = (function () {
+  var map = undefined;
+  var lastLoadAt = undefined;
+
+  /** @returns {Record<string, {dir: string, packageJson: unknown}>} */
+  return function (/** @type {string} */ dir) {
+    if (map) {
+      // Only cache for 5 seconds, to avoid the need to reload ESLint servers
+      if (Date.now() - lastLoadAt > 5000) {
+        map = undefined;
+      } else {
+        return map;
+      }
+    }
+    var packages = manypkg.getPackagesSync(dir).packages;
+    if (!packages) {
+      return undefined;
+    }
+    map = {};
+    lastLoadAt = Date.now();
+    packages.forEach(function (pkg) {
+      map[pkg.packageJson.name] = pkg;
+    });
+    return map;
+  };
+})();
+
+module.exports = {
+  meta: {
+    type: 'problem',
+    messages: {
+      forbidden: '{{packageName}} does not export {{subPath}}',
+    },
+  },
+  create: function (/** @type import('eslint').Rule.RuleContext */ context) {
+    var packageMap = getPackageMap(context.getCwd());
+    if (!packageMap) {
+      return;
+    }
+
+    function checkImport(node) {
+      if (!node.source) {
+        return;
+      }
+      var importPath = node.source.value;
+      if (importPath[0] === '.') {
+        return;
+      }
+
+      var pathParts = importPath.split('/');
+
+      // Check for match with plain name, then namespaced name
+      var name = pathParts.shift();
+      if (!packageMap[name]) {
+        name += '/' + pathParts.shift();
+      }
+      if (!packageMap[name]) {
+        return;
+      }
+
+      // Empty subpaths are always allowed
+      var subPath = pathParts.join('/');
+      if (!subPath) {
+        return;
+      }
+
+      var pkg = packageMap[name];
+
+      // If the import is listed in the package.json exports field, we allow it
+      var exp = pkg.packageJson.exports;
+      if (exp && (exp[subPath] || exp['./' + subPath])) {
+        return;
+      }
+
+      // If there's a package.json in the target directory, we allow the import
+      if (fs.existsSync(path.resolve(pkg.dir, subPath, 'package.json'))) {
+        return;
+      }
+
+      context.report({
+        node: node,
+        messageId: 'forbidden',
+        data: {
+          packageName: pkg.packageJson.name || '<unknown-package>',
+          subPath: subPath,
+        },
+      });
+    }
+
+    return {
+      ImportDeclaration: checkImport,
+      ExportAllDeclaration: checkImport,
+      ExportNamedDeclaration: checkImport,
+      ImportExpression: checkImport,
+    };
+  },
+};

yarn.lock

@@ -4095,6 +4095,12 @@ __metadata:
   languageName: unknown
   linkType: soft
 
+"@backstage/eslint-plugin@workspace:packages/eslint-plugin":
+  version: 0.0.0-use.local
+  resolution: "@backstage/eslint-plugin@workspace:packages/eslint-plugin"
+  languageName: unknown
+  linkType: soft
+
 "@backstage/integration-aws-node@workspace:^, @backstage/integration-aws-node@workspace:packages/integration-aws-node":
   version: 0.0.0-use.local
   resolution: "@backstage/integration-aws-node@workspace:packages/integration-aws-node"