Close nodejs#1348 Remove require.paths

Module.globalPaths is still set to a read-only copy of the global
include paths pulled off of the NODE_PATH environment variable.

It's important to be able to inspect this, but modifying it no longer
has any effect.

doc/api/modules.markdown

@@ -231,77 +231,24 @@ in pseudocode of what require.resolve does:
        c. let I = I - 1
     6. return DIRS
 
-### Loading from the `require.paths` Folders
+### Loading from the global folders
 
-In node, `require.paths` is an array of strings that represent paths to
-be searched for modules when they are not prefixed with `'/'`, `'./'`, or
-`'../'`.  For example, if require.paths were set to:
+If the `NODE_PATH` environment variable is set to a colon-delimited list
+of absolute paths, then node will search those paths for modules if they
+are not found elsewhere.
 
-    [ '/home/micheil/.node_modules',
-      '/usr/local/lib/node_modules' ]
+Additionally, node will search in the following locations:
 
-Then calling `require('bar/baz.js')` would search the following
-locations:
+* 1: `$HOME/.node_modules`
+* 2: `$HOME/.node_libraries`
+* 3: `$PREFIX/lib/node`
 
-* 1: `'/home/micheil/.node_modules/bar/baz.js'`
-* 2: `'/usr/local/lib/node_modules/bar/baz.js'`
+Where `$HOME` is the user's home directory, and `PREFIX` is node's
+configured `installPrefix`.
 
-The `require.paths` array can be mutated at run time to alter this
-behavior.
-
-It is set initially from the `NODE_PATH` environment variable, which is
-a colon-delimited list of absolute paths.  In the previous example,
-the `NODE_PATH` environment variable might have been set to:
-
-    /home/micheil/.node_modules:/usr/local/lib/node_modules
-
-Loading from the `require.paths` locations is only performed if the
-module could not be found using the `node_modules` algorithm above.
-Global modules are lower priority than bundled dependencies.
-
-#### **Note:** Please Avoid Modifying `require.paths`
-
-`require.paths` may disappear in a future release.
-
-While it seemed like a good idea at the time, and enabled a lot of
-useful experimentation, in practice a mutable `require.paths` list is
-often a troublesome source of confusion and headaches.
-
-##### Setting `require.paths` to some other value does nothing.
-
-This does not do what one might expect:
-
-    require.paths = [ '/usr/lib/node' ];
-
-All that does is lose the reference to the *actual* node module lookup
-paths, and create a new reference to some other thing that isn't used
-for anything.
-
-##### Putting relative paths in `require.paths` is... weird.
-
-If you do this:
-
-    require.paths.push('./lib');
-
-then it does *not* add the full resolved path to where `./lib`
-is on the filesystem.  Instead, it literally adds `'./lib'`,
-meaning that if you do `require('y.js')` in `/a/b/x.js`, then it'll look
-in `/a/b/lib/y.js`.  If you then did `require('y.js')` in
-`/l/m/n/o/p.js`, then it'd look in `/l/m/n/o/lib/y.js`.
-
-In practice, people have used this as an ad hoc way to bundle
-dependencies, but this technique is brittle.
-
-##### Zero Isolation
-
-There is (by regrettable design), only one `require.paths` array used by
-all modules.
-
-As a result, if one node program comes to rely on this behavior, it may
-permanently and subtly alter the behavior of all other node programs in
-the same process.  As the application stack grows, we tend to assemble
-functionality, and those parts interact in ways that are difficult to
-predict.
+These are mostly for historic reasons.  You are highly encouraged to
+place your dependencies localy in `node_modules` folders.  They will be
+loaded faster, and more reliably.
 
 ### Accessing the main module
 

lib/module.js

@@ -43,7 +43,8 @@ Module._contextLoad = (+process.env['NODE_MODULE_CONTEXTS'] > 0);
 Module._cache = {};
 Module._pathCache = {};
 Module._extensions = {};
-Module._paths = [];
+var modulePaths = [];
+Module.globalPaths = [];
 
 Module.wrapper = NativeModule.wrapper;
 Module.wrap = NativeModule.wrap;
@@ -217,7 +218,7 @@ Module._resolveLookupPaths = function(request, parent) {
 
   var start = request.substring(0, 2);
   if (start !== './' && start !== '..') {
-    var paths = Module._paths;
+    var paths = modulePaths;
     if (parent) {
       if (!parent.paths) parent.paths = [];
       paths = parent.paths.concat(paths);
@@ -229,7 +230,7 @@ Module._resolveLookupPaths = function(request, parent) {
   if (!parent || !parent.id || !parent.filename) {
     // make require('./path/to/foo') work - normally the path is taken
     // from realpath(__filename) but with eval there is no filename
-    var mainPaths = ['.'].concat(Module._paths);
+    var mainPaths = ['.'].concat(modulePaths);
     mainPaths = Module._nodeModulePaths('.').concat(mainPaths);
     return [request, mainPaths];
   }
@@ -353,15 +354,23 @@ Module.prototype._compile = function(content, filename) {
 
   require.resolve = function(request) {
     return Module._resolveFilename(request, self)[1];
-  }
-  require.paths = Module._paths;
+  };
+
+  Object.defineProperty(require, 'paths', { get: function() {
+    throw new Error('require.paths is removed. Use ' +
+                    'node_modules folders, or the NODE_PATH '+
+                    'environment variable instead.');
+  }});
+
   require.main = process.mainModule;
+
   // Enable support to add extra extension types
   require.extensions = Module._extensions;
   require.registerExtension = function() {
     throw new Error('require.registerExtension() removed. Use ' +
                     'require.extensions instead.');
-  }
+  };
+
   require.cache = Module._cache;
 
   var dirname = path.dirname(filename);
@@ -475,7 +484,10 @@ Module._initPaths = function() {
     paths = process.env['NODE_PATH'].split(':').concat(paths);
   }
 
-  Module._paths = paths;
+  modulePaths = paths;
+
+  // clone as a read-only copy, for introspection.
+  Module.globalPaths = modulePaths.slice(0);
 };
 
 // bootstrap repl

test/simple/test-module-loading.js

@@ -143,15 +143,14 @@ require.extensions['.test'] = function(module, filename) {
 };
 
 assert.equal(require('../fixtures/registerExt2').custom, 'passed');
-common.debug('load modules by absolute id, then change require.paths, ' +
-             'and load another module with the same absolute id.');
-// this will throw if it fails.
-var foo = require('../fixtures/require-path/p1/foo');
-assert.ok(foo.bar.expect === foo.bar.actual);
 
 assert.equal(require('../fixtures/foo').foo, 'ok',
              'require module with no extension');
 
+assert.throws(function() {
+  require.paths;
+}, /removed/, 'Accessing require.paths should throw.');
+
 // Should not attempt to load a directory
 try {
   require('../fixtures/empty');

test/simple/test-require-cache-without-stat.js

@@ -45,17 +45,20 @@ fs.stat = function() {
 };
 
 // Load the module 'a' and 'http' once. It should become cached.
-require.paths.push(common.fixturesDir);
-require('a');
+require(common.fixturesDir + '/a');
+require('../fixtures/a.js');
+require('./../fixtures/a.js');
 require('http');
 
 console.log("counterBefore = %d", counter);
 var counterBefore = counter;
 
-// Now load the module a bunch of times.
+// Now load the module a bunch of times with equivalent paths.
 // stat should not be called.
 for (var i = 0; i < 100; i++) {
-  require('a');
+  require(common.fixturesDir + '/a');
+  require('../fixtures/a.js');
+  require('./../fixtures/a.js');
 }
 
 // Do the same with a built-in module
@@ -67,4 +70,3 @@ console.log("counterAfter = %d", counter);
 var counterAfter = counter;
 
 assert.equal(counterBefore, counterAfter);
-