module: support custom paths to require.resolve()

This commit allows custom lookup paths to be passed to
require.resolve(). It also adds require.resolve.paths()
which retrieves the default resolution paths.

Fixes: nodejs/node#5963
Fixes: nodejs/node#16389
PR-URL: nodejs/node#16397
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Wyatt Preul <wpreul@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>

doc/api/modules.md

@@ -598,14 +598,36 @@ filename scales linearly with the number of registered extensions.
 In other words, adding extensions slows down the module loader and
 should be discouraged.
 
-#### require.resolve()
+#### require.resolve(request[, options])
 <!-- YAML
 added: v0.3.0
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/16397
+    description: The `paths` option is now supported.
 -->
 
+* `request` {string} The module path to resolve.
+* `options` {Object}
+  * `paths` {Array} Paths to resolve module location from. If present, these
+    paths are used instead of the default resolution paths. Note that each of
+    these paths is used as a starting point for the module resolution algorithm,
+    meaning that the `node_modules` hierarchy is checked from this location.
+* Returns: {string}
+
 Use the internal `require()` machinery to look up the location of a module,
 but rather than loading the module, just return the resolved filename.
 
+#### require.resolve.paths(request)
+<!-- YAML
+added: REPLACEME
+-->
+
+* `request` {string} The module path whose lookup paths are being retrieved.
+* Returns: {Array}
+
+Returns an array containing the paths searched during resolution of `request`.
+
 ## The `module` Object
 <!-- YAML
 added: v0.1.16

doc/api/process.md

@@ -1899,7 +1899,7 @@ cases:
 [`promise.catch()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/catch
 [`require()`]: globals.html#globals_require
 [`require.main`]: modules.html#modules_accessing_the_main_module
-[`require.resolve()`]: modules.html#modules_require_resolve
+[`require.resolve()`]: modules.html#modules_require_resolve_request_options
 [`setTimeout(fn, 0)`]: timers.html#timers_settimeout_callback_delay_args
 [Child Process]: child_process.html
 [Cluster]: cluster.html

lib/internal/module.js

@@ -14,12 +14,18 @@ function makeRequireFunction(mod) {
     }
   }
 
-  function resolve(request) {
-    return Module._resolveFilename(request, mod);
+  function resolve(request, options) {
+    return Module._resolveFilename(request, mod, false, options);
   }
 
   require.resolve = resolve;
 
+  function paths(request) {
+    return Module._resolveLookupPaths(request, mod, true);
+  }
+
+  resolve.paths = paths;
+
   require.main = process.mainModule;
 
   // Enable support to add extra extension types.

lib/module.js

@@ -484,12 +484,32 @@ function tryModuleLoad(module, filename) {
   }
 }
 
-Module._resolveFilename = function(request, parent, isMain) {
+Module._resolveFilename = function(request, parent, isMain, options) {
   if (NativeModule.nonInternalExists(request)) {
     return request;
   }
 
-  var paths = Module._resolveLookupPaths(request, parent, true);
+  var paths;
+
+  if (typeof options === 'object' && options !== null &&
+      Array.isArray(options.paths)) {
+    paths = [];
+
+    for (var i = 0; i < options.paths.length; i++) {
+      const path = options.paths[i];
+      const lookupPaths = Module._resolveLookupPaths(path, parent, true);
+
+      if (!paths.includes(path))
+        paths.push(path);
+
+      for (var j = 0; j < lookupPaths.length; j++) {
+        if (!paths.includes(lookupPaths[j]))
+          paths.push(lookupPaths[j]);
+      }
+    }
+  } else {
+    paths = Module._resolveLookupPaths(request, parent, true);
+  }
 
   // look up the filename first, since that's the cache key.
   var filename = Module._findPath(request, paths, isMain);

test/fixtures/require-resolve.js

@@ -0,0 +1,55 @@
+'use strict';
+require('../common');
+const assert = require('assert');
+const path = require('path');
+const nodeModules = path.join(__dirname, 'node_modules');
+const nestedNodeModules = path.join(__dirname, 'node_modules', 'node_modules');
+const nestedIndex = path.join(__dirname, 'nested-index');
+
+// Test the default behavior.
+assert.strictEqual(
+  require.resolve('bar'),
+  path.join(nodeModules, 'bar.js')
+);
+
+// Verify that existing paths are removed.
+assert.throws(() => {
+  require.resolve('bar', { paths: [] })
+}, /^Error: Cannot find module 'bar'$/);
+
+// Verify that resolution path can be overwritten.
+{
+  // three.js cannot be loaded from this file by default.
+  assert.throws(() => {
+    require.resolve('three')
+  }, /^Error: Cannot find module 'three'$/);
+
+  // However, it can be found if resolution contains the nested index directory.
+  assert.strictEqual(
+    require.resolve('three', { paths: [nestedIndex] }),
+    path.join(nestedIndex, 'three.js')
+  );
+
+  // Resolution from nested index directory also checks node_modules.
+  assert.strictEqual(
+    require.resolve('bar', { paths: [nestedIndex] }),
+    path.join(nodeModules, 'bar.js')
+  );
+}
+
+// Verify that the default paths can be used and modified.
+{
+  const paths = require.resolve.paths('bar');
+
+  assert.strictEqual(paths[0], nodeModules);
+  assert.strictEqual(
+    require.resolve('bar', { paths }),
+    path.join(nodeModules, 'bar.js')
+  );
+
+  paths.unshift(nestedNodeModules);
+  assert.strictEqual(
+    require.resolve('bar', { paths }),
+    path.join(nestedNodeModules, 'bar.js')
+  );
+}

test/parallel/test-require-resolve.js

@@ -35,4 +35,5 @@ assert.strictEqual(
   require.resolve(fixtures.path('nested-index', 'one').toLowerCase()));
 assert.strictEqual('path', require.resolve('path'));
 
-console.log('ok');
+// Test configurable resolve() paths.
+require(fixtures.path('require-resolve.js'));