module: revert #3384 DEP0019 EOL

The original commit was landed without running CITGM. Unfortunately
this change breaks the module `d` which has over 500k downloads a day.

It is worth mentioning that the compatibility hack can be removed
without breaking anything.

We should definitely revisit for the next Semver-Major but shipping
this today will cause non trivial ecosystem breakages.

Refs: nodejs/node#3384

PR-URL: nodejs/node#16634
Refs: nodejs/node#3384
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

doc/api/deprecations.md

@@ -202,7 +202,7 @@ code.
 <a id="DEP0019"></a>
 ### DEP0019: require('.') resolved outside directory
 
-Type: End-of-Life
+Type: Runtime
 
 In certain cases, `require('.')` may resolve outside the package directory.
 This behavior is deprecated and will be removed in a future major Node.js

lib/module.js

@@ -176,6 +176,7 @@ function tryExtensions(p, exts, isMain) {
   return false;
 }
 
+var warned = false;
 Module._findPath = function(request, paths, isMain) {
   if (path.isAbsolute(request)) {
     paths = [''];
@@ -232,6 +233,18 @@ Module._findPath = function(request, paths, isMain) {
     }
 
     if (filename) {
+      // Warn once if '.' resolved outside the module dir
+      if (request === '.' && i > 0) {
+        if (!warned) {
+          warned = true;
+          process.emitWarning(
+            'warning: require(\'.\') resolved outside the package ' +
+            'directory. This functionality is deprecated and will be removed ' +
+            'soon.',
+            'DeprecationWarning', 'DEP0019');
+        }
+      }
+
       Module._pathCache[cacheKey] = filename;
       return filename;
     }
@@ -334,7 +347,8 @@ Module._resolveLookupPaths = function(request, parent, newReturn) {
   }
 
   // Check for relative path
-  if (request.charCodeAt(0) !== 46/*.*/ &&
+  if (request.length < 2 ||
+      request.charCodeAt(0) !== 46/*.*/ ||
       (request.charCodeAt(1) !== 46/*.*/ &&
        request.charCodeAt(1) !== 47/*/*/)) {
     var paths = modulePaths;
@@ -345,6 +359,16 @@ Module._resolveLookupPaths = function(request, parent, newReturn) {
         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.unshift(path.dirname(parent.filename));
+      } else {
+        paths.unshift(path.resolve(request));
+      }
+    }
+
     debug('looking for %j in %j', request, paths);
     return (newReturn ? (paths.length > 0 ? paths : null) : [request, paths]);
   }

test/parallel/test-require-dot.js

@@ -10,7 +10,9 @@ const b = require(fixtures.path('module-require', 'relative', 'dot-slash.js'));
 assert.strictEqual(a.value, 42);
 assert.strictEqual(a, b, 'require(".") should resolve like require("./")');
 
-// require('.') should not lookup in NODE_PATH
 process.env.NODE_PATH = fixtures.path('module-require', 'relative');
 m._initPaths();
-assert.throws(() => { require('.'); }, Error, "Cannot find module '.'");
+
+const c = require('.');
+
+assert.strictEqual(c.value, 42, 'require(".") should honor NODE_PATH');