add no-useless-path-segments rule Fixes import-js#471

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-useless-path-segments': require('./rules/no-useless-path-segments'),
 
   // metadata-based
   'no-deprecated': require('./rules/no-deprecated'),

src/rules/no-useless-path-segments.js

@@ -0,0 +1,46 @@
+/**
+ * @fileOverview Ensures that there are no useless path segments
+ * @author Thomas Grainger
+ */
+
+import path from 'path'
+import resolve from 'eslint-module-utils/resolve'
+import moduleVisitor from 'eslint-module-utils/moduleVisitor'
+
+function relative(from, to) {
+  const rel = path.relative(from, to)
+  return rel.startsWith('.') ? rel : `.${path.sep}${rel}`
+}
+
+module.exports = {
+  meta: {},
+
+  create: function (context) {
+    const currentDir = path.dirname(context.getFilename())
+
+    function checkSourceValue(source) {
+      const { value } = source
+      if (!value.startsWith('.')) {
+        return
+      }
+
+      const resolvedPath = resolve(value, context)
+      if (resolvedPath === undefined) {
+        return
+      }
+
+      const expected = path.parse(relative(currentDir, resolvedPath))
+      const valueParsed = path.parse(value)
+
+      if (valueParsed.dir !== expected.dir) {
+        const proposed = path.format({ dir: expected.dir, base: valueParsed.base })
+        context.report({
+          node: source,
+          message: `Useless path segments for "${value}", should be "${proposed}"`,
+        })
+      }
+    }
+
+    return moduleVisitor(checkSourceValue, context.options[0])
+  },
+}

tests/src/rules/no-useless-path-segments.js

@@ -0,0 +1,27 @@
+import { test } from '../utils'
+import { RuleTester } from 'eslint'
+
+const ruleTester = new RuleTester()
+const rule = require('rules/no-useless-path-segments')
+
+function runResolverTests(resolver) {
+  ruleTester.run(`no-useless-path-segments (${resolver})`, rule, {
+    valid: [
+      test({ code: 'import "./malformed.js"' }),
+      test({ code: 'import fs from "fs"' }),
+    ],
+
+    invalid: [
+      test({
+        code: 'import "./../files/malformed.js"',
+        errors: [ 'Useless path segments for "./../files/malformed.js", should be "./malformed.js"'],
+      }),
+      test({
+        code: 'import "./../files/malformed"',
+        errors: [ 'Useless path segments for "./../files/malformed", should be "./malformed"'],
+      }),
+     ],
+   })
+}
+
+['node', 'webpack'].forEach(runResolverTests)