eslint-plugin: add no-relative-monorepo-imports rule

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

packages/eslint-plugin/index.js

@@ -20,12 +20,14 @@ module.exports = {
       plugins: ['@backstage'],
       rules: {
         '@backstage/no-forbidden-package-imports': 'error',
+        '@backstage/no-relative-monorepo-imports': 'error',
         '@backstage/no-undeclared-imports': 'error',
       },
     },
   },
   rules: {
     'no-forbidden-package-imports': require('./rules/no-forbidden-package-imports'),
+    'no-relative-monorepo-imports': require('./rules/no-relative-monorepo-imports'),
     'no-undeclared-imports': require('./rules/no-undeclared-imports'),
   },
 };

packages/eslint-plugin/lib/getPackages.js

@@ -16,7 +16,7 @@
 
 // @ts-check
 
-/** @type {import('@manypkg/get-packages')} */
+const path = require('path');
 const manypkg = require('@manypkg/get-packages');
 
 /**
@@ -31,6 +31,7 @@ const manypkg = require('@manypkg/get-packages');
  * @property {ExtendedPackage} root
  * @property {ExtendedPackage[]} list
  * @property {Map<string, ExtendedPackage>} map
+ * @property {(path: string) => ExtendedPackage | undefined} byPath
  */
 
 // Loads all packages in the monorepo once, and caches the result
@@ -56,6 +57,13 @@ module.exports = (function () {
       map: new Map(packages.packages.map(pkg => [pkg.packageJson.name, pkg])),
       list: packages.packages,
       root: packages.root,
+      byPath(filePath) {
+        return packages.packages.find(pkg => {
+          if (!path.relative(pkg.dir, filePath).startsWith('..')) {
+            return pkg;
+          }
+        });
+      },
     };
     lastLoadAt = Date.now();
     return result;

packages/eslint-plugin/rules/no-relative-monorepo-imports.js

@@ -0,0 +1,80 @@
+/*
+ * 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
+
+const path = require('path');
+const visitImports = require('../lib/visitImports');
+const getPackageMap = require('../lib/getPackages');
+
+/** @type {import('eslint').Rule.RuleModule} */
+module.exports = {
+  meta: {
+    type: 'problem',
+    messages: {
+      outside: 'Import of {{path}} is outside of any known monorepo package',
+      forbidden:
+        "Relative imports of monorepo packages are forbidden, use '{{newImport}}' instead",
+    },
+  },
+  create(context) {
+    const packages = getPackageMap(context.getCwd());
+    if (!packages) {
+      return {};
+    }
+    const filePath = context.getPhysicalFilename
+      ? context.getPhysicalFilename()
+      : context.getFilename();
+
+    const localPkg = packages.byPath(filePath);
+    if (!localPkg) {
+      return {};
+    }
+
+    return visitImports(context, (node, imp) => {
+      if (imp.type !== 'local') {
+        return;
+      }
+
+      const target = path.resolve(path.dirname(filePath), imp.path);
+      if (!path.relative(localPkg.dir, target).startsWith('..')) {
+        return;
+      }
+
+      const targetPkg = packages.byPath(target);
+      if (!targetPkg) {
+        context.report({
+          node: node,
+          messageId: 'outside',
+          data: {
+            path: target,
+          },
+        });
+        return;
+      }
+
+      const targetPath = path.relative(targetPkg.dir, target);
+      const targetName = targetPkg.packageJson.name ?? '<unknown>';
+      context.report({
+        node: node,
+        messageId: 'forbidden',
+        data: {
+          newImport: targetPath ? `${targetName}/${targetPath}` : targetName,
+        },
+      });
+    });
+  },
+};

packages/eslint-plugin/rules/no-undeclared-imports.js

@@ -135,9 +135,7 @@ module.exports = {
       ? context.getPhysicalFilename()
       : context.getFilename();
 
-    const localPkg = packages.list.find(p =>
-      filePath.startsWith(p.dir + path.sep),
-    );
+    const localPkg = packages.byPath(filePath);
     if (!localPkg) {
       return {};
     }