Add no-import-module-exports rule

src/index.js

@@ -30,6 +30,7 @@ export const rules = {
   'no-dynamic-require': require('./rules/no-dynamic-require'),
   'unambiguous': require('./rules/unambiguous'),
   'no-unassigned-import': require('./rules/no-unassigned-import'),
+  'no-import-module-exports': require('./rules/no-import-module-exports'),
 
   // metadata-based
   'no-deprecated': require('./rules/no-deprecated'),

src/rules/no-import-module-exports.js

@@ -0,0 +1,72 @@
+import minimatch from 'minimatch'
+import path from 'path'
+import readPkgUp from 'read-pkg-up'
+
+function getEntryPoint(context) {
+  try {
+    const pkg = readPkgUp.sync({cwd: context.getFilename(), normalize: false})
+    return pkg && pkg.pkg
+      ? path.join(process.cwd(), pkg.pkg.main)
+      : null
+  } catch (e) {
+    return null
+  }
+}
+
+module.exports = {
+  meta: {
+    docs: {
+      description: 'Disallow import statements with module.exports',
+      category: 'Best Practices',
+      recommended: true,
+    },
+    fixable: 'code',
+    schema: [
+      {
+        'type': 'object',
+        'properties': {
+          'exceptions': { 'type': 'array' },
+        },
+        'additionalProperties': false,
+      },
+    ],
+  },
+  create(context) {
+    const importDeclarations = []
+    const entryPoint = getEntryPoint(context)
+    const options = context.options[0] || {}
+    let alreadyReported = false
+
+    function report(node) {
+      const fileName = context.getFilename()
+      const isEntryPoint = entryPoint === fileName
+      const isIdentifier = node.object.type === 'Identifier'
+      const hasKeywords = (/^(module|exports)$/).test(node.object.name)
+      const isException = options.exceptions
+        ? options.exceptions.some(glob => minimatch(fileName, glob))
+        : false
+
+      if (isIdentifier && hasKeywords && !isEntryPoint && !isException) {
+        importDeclarations.forEach(importDeclaration => {
+          context.report({
+            node: importDeclaration,
+            message: `Cannot use import declarations in modules that export using ` +
+              `CommonJS (module.exports = 'foo' or exports.bar = 'hi')`,
+          })
+        })
+        alreadyReported = true
+      }
+    }
+
+    return {
+      ImportDeclaration(node) {
+        importDeclarations.push(node)
+      },
+      MemberExpression(node) {
+        if (!alreadyReported) {
+          report(node)
+        }
+      },
+    }
+  },
+}

tests/files/package.json

@@ -1,5 +1,6 @@
 {
   "dummy": true,
+  "main": "tests/files/lib/main.js",
   "devDependencies": {
     "glob": "1.0.0",
     "eslint": "2.x"

tests/src/rules/no-import-module-exports.js

@@ -0,0 +1,98 @@
+import path from 'path'
+import { RuleTester } from 'eslint'
+
+import { test, testFilePath } from '../utils'
+
+const ruleTester = new RuleTester({
+  parserOptions: { ecmaVersion: 6, sourceType: 'module' }
+})
+const rule = require('rules/no-import-module-exports')
+
+const error = {
+  message: `Cannot use import declarations in modules that export using CommonJS ` +
+    `(module.exports = 'foo' or exports.bar = 'hi')`,
+  type: 'ImportDeclaration',
+}
+
+ruleTester.run('no-import-module-exports', rule, {
+  valid: [
+    test({
+      code: `
+        const thing = require('thing')
+        module.exports = thing
+      `,
+    }),
+    test({
+      code: `
+        import thing from 'otherthing'
+        console.log(thing.module.exports)
+      `,
+    }),
+    test({
+      code: `
+        import thing from 'other-thing'
+        export default thing
+      `,
+    }),
+    test({
+      code: `
+        import foo from 'path';
+        module.exports = foo;
+      `,
+      // When the file matches the entry point defined in package.json
+      // See tests/files/package.json
+      filename: path.join(process.cwd(), 'tests/files/lib/main.js'),
+    }),
+    test({
+      code: `
+        import foo from 'path';
+        module.exports = foo;
+      `,
+      filename: path.join(process.cwd(), 'tests/files/some/other/entry-point.js'),
+      options: [{ exceptions: ['**/*/other/entry-point.js'] }],
+    }),
+  ],
+  invalid: [
+    test({
+      code: `
+        import { stuff } from 'starwars'
+        module.exports = thing
+      `,
+      errors: [error],
+    }),
+    test({
+      code: `
+        import thing from 'starwars'
+        const baz = module.exports = thing
+        console.log(baz)
+      `,
+      errors: [error],
+    }),
+    test({
+      code: `
+        import * as allThings from 'starwars'
+        exports.bar = thing
+      `,
+      errors: [error],
+    }),
+    test({
+      code: `
+        import foo from 'path';
+        module.exports = foo;
+      `,
+      // When the file does not match the entry point defined in package.json
+      // See tests/files/package.json
+      filename: path.join(process.cwd(), 'tests/files/not/lib/main.js'),
+      errors: [error],
+    }),
+    test({
+      code: `
+        import foo from 'path';
+        module.exports = foo;
+      `,
+      filename: path.join(process.cwd(), 'tests/files/some/other/entry-point.js'),
+      options: [{ exceptions: ['**/*/other/file.js'] }],
+      errors: [error],
+    }),
+  ],
+})