[Refactor] node-modules-paths: Change paths function option to receive a thunk for node modules resolution paths

 - this would be a breaking change, but the “paths as function” option has not yet been released.

Author: ljharb

lib/node-modules-paths.js

@@ -2,25 +2,7 @@ var path = require('path');
 var fs = require('fs');
 var parse = path.parse || require('path-parse');
 
-module.exports = function nodeModulesPaths(start, opts, request) {
-    var modules = opts && opts.moduleDirectory
-        ? [].concat(opts.moduleDirectory)
-        : ['node_modules'];
-
-    // ensure that `start` is an absolute path at this point,
-    // resolving against the process' current working directory
-    var absoluteStart = path.resolve(start);
-
-    if (opts && opts.preserveSymlinks === false) {
-        try {
-            absoluteStart = fs.realpathSync(absoluteStart);
-        } catch (err) {
-            if (err.code !== 'ENOENT') {
-                throw err;
-            }
-        }
-    }
-
+var getNodeModulesDirs = function getNodeModulesDirs(absoluteStart, modules) {
     var prefix = '/';
     if ((/^([A-Za-z]:)/).test(absoluteStart)) {
         prefix = '';
@@ -35,17 +17,40 @@ module.exports = function nodeModulesPaths(start, opts, request) {
         parsed = parse(parsed.dir);
     }
 
-    var dirs = paths.reduce(function (dirs, aPath) {
+    return paths.reduce(function (dirs, aPath) {
         return dirs.concat(modules.map(function (moduleDir) {
             return path.join(prefix, aPath, moduleDir);
         }));
     }, []);
+};
 
-    if (!opts || !opts.paths) {
-        return dirs;
+module.exports = function nodeModulesPaths(start, opts, request) {
+    var modules = opts && opts.moduleDirectory
+        ? [].concat(opts.moduleDirectory)
+        : ['node_modules'];
+
+    // ensure that `start` is an absolute path at this point, resolving against the process' current working directory
+    var absoluteStart = path.resolve(start);
+
+    if (opts && opts.preserveSymlinks === false) {
+        try {
+            absoluteStart = fs.realpathSync(absoluteStart);
+        } catch (err) {
+            if (err.code !== 'ENOENT') {
+                throw err;
+            }
+        }
     }
-    if (typeof opts.paths === 'function') {
-        return dirs.concat(opts.paths(request, absoluteStart, opts));
+
+    if (opts && typeof opts.paths === 'function') {
+        return opts.paths(
+            request,
+            absoluteStart,
+            function () { return getNodeModulesDirs(absoluteStart, modules); },
+            opts
+        );
     }
-    return dirs.concat(opts.paths);
+
+    var dirs = getNodeModulesDirs(absoluteStart, modules);
+    return opts && opts.paths ? dirs.concat(opts.paths) : dirs;
 };

readme.markdown

@@ -74,6 +74,7 @@ options are:
   For advanced users, `paths` can also be a `opts.paths(request, start, opts)` function
     * request - the import specifier being resolved
     * start - lookup path
+    * getNodeModulesDirs - a thunk (no-argument function) that returns the paths using standard `node_modules` resolution
     * opts - the resolution options
 
 * opts.moduleDirectory - directory (or directories) in which to recursively look for modules. default: `"node_modules"`

test/node-modules-paths.js

@@ -65,8 +65,8 @@ test('node-modules-paths', function (t) {
     });
 
     t.test('with paths=function option', function (t) {
-        var paths = function paths(request, absoluteStart, opts) {
-            return [path.join(absoluteStart, 'not node modules', request)];
+        var paths = function paths(request, absoluteStart, getNodeModulesDirs, opts) {
+            return getNodeModulesDirs().concat(path.join(absoluteStart, 'not node modules', request));
         };
 
         var start = path.join(__dirname, 'resolver');
@@ -77,6 +77,16 @@ test('node-modules-paths', function (t) {
         t.end();
     });
 
+    t.test('with paths=function skipping node modules resolution', function (t) {
+        var paths = function paths(request, absoluteStart, getNodeModulesDirs, opts) {
+            return [];
+        };
+        var start = path.join(__dirname, 'resolver');
+        var dirs = nodeModulesPaths(start, { paths: paths });
+        t.deepEqual(dirs, [], 'no node_modules was computed');
+        t.end();
+    });
+
     t.test('with moduleDirectory option', function (t) {
         var start = path.join(__dirname, 'resolver');
         var moduleDirectory = 'not node modules';