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

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

@@ -0,0 +1,61 @@
+/**
+ * @fileOverview Ensures that there are no redundant path segments
+ * @author Thomas Grainger
+ */
+
+import path from 'path';
+import _ from 'lodash/fp';
+import resolve from 'eslint-module-utils/resolve'
+import moduleVisitor from 'eslint-module-utils/moduleVisitor'
+
+function stripExtname(fn) {
+  const { dir, name } = path.parse(fn);
+  return path.format({ dir, name });
+}
+
+const cartesianProduct =
+  _.reduce((a, b) =>
+    _.flatMap(x =>
+      _.map(y =>
+        x.concat([y])
+      )(b)
+    )(a)
+)([[]]);
+
+
+const anyMatch = _.flow(
+  cartesianProduct,
+  _.some(([a, b]) => a === b)
+);
+
+module.exports = {
+  meta: {},
+
+  create: function (context) {
+    const currentPath = context.getFilename();
+    const currentPathStripped = stripExtname(currentPath);
+
+    function checkSourceValue(source) {
+      const { value } = source;
+      const resolvedPath = resolve(source, context)
+      if (resolvedPath === undefined) {
+        return;
+      }
+
+      const expected = path.relative(currentPath, resolvedPath);
+      const matched = anyMatch([
+        [value, stripExtname(value)],
+        [expected, stripExtname(expected)]
+      ]);
+
+      if (!matched) {
+        context.report({
+          node: source,
+          message: `Redundant paths for "${value}", should be ${expected}`
+        })
+      }
+    }
+
+    return moduleVisitor(checkSourceValue, context.options[0])
+  },
+}