module: restore and warn on require('.') usage with NODE_PATH

lib/module.js

@@ -125,6 +125,11 @@ function tryExtensions(p, exts) {
 }
 
 
+const noopDeprecateRequireDot = util.deprecate(function() {},
+  "warning: require('.') resolved outside the package directory. " +
+  "This functionality will be deprecated soon.");
+
+
 Module._findPath = function(request, paths) {
   var exts = Object.keys(Module._extensions);
 
@@ -169,6 +174,8 @@ Module._findPath = function(request, paths) {
     }
 
     if (filename) {
+      // Warn once if '.' resolved outside the module dir
+      if (request === '.' && i > 0) noopDeprecateRequireDot();
       Module._pathCache[cacheKey] = filename;
       return filename;
     }
@@ -205,12 +212,23 @@ Module._resolveLookupPaths = function(request, parent) {
   }
 
   var start = request.substring(0, 2);
-  if (start !== '.' && start !== './' && start !== '..') {
+  if (start !== './' && start !== '..') {
     var paths = modulePaths;
     if (parent) {
       if (!parent.paths) parent.paths = [];
       paths = parent.paths.concat(paths);
     }
+
+    // Maintain backwards compat with certain broken uses of require('.')
+    // by putting the module's directory in front of the lookup paths.
+    if (request === '.') {
+      if (parent && parent.filename) {
+        paths.splice(0, 0, path.dirname(parent.filename));
+      } else {
+        paths.splice(0, 0, path.resolve(request));
+      }
+    }
+
     return [request, paths];
   }
 

test/parallel/test-require-dot.js

@@ -0,0 +1,16 @@
+var common = require('../common');
+var assert = require('assert');
+var module = require('module');
+
+var a = require(common.fixturesDir + '/module-require/relative/dot.js');
+var b = require(common.fixturesDir + '/module-require/relative/dot-slash.js');
+
+assert.equal(a.value, 42);
+assert.equal(a, b, 'require(".") should resolve like require("./")');
+
+process.env.NODE_PATH = common.fixturesDir + '/module-require/relative';
+module._initPaths();
+
+var c = require('.');
+
+assert.equal(c.value, 42, 'require(".") should honor NODE_PATH');

test/parallel/test-require-extensions-main.js

@@ -1,10 +1,4 @@
 var common = require('../common');
 var assert = require('assert');
 
-require(common.fixturesDir + '/require-bin/bin/req.js');
-
-var a = require(common.fixturesDir + '/module-require/relative/dot.js');
-var b = require(common.fixturesDir + '/module-require/relative/dot-slash.js');
-
-assert.equal(a.value, 42);
-assert.equal(a, b, 'require(".") should resolve like require("./")');
+require(common.fixturesDir + '/require-bin/bin/req.js');