feat: add preserveSymlinks option

Add the possibilty to make `resolve` use real paths
during resolution

Close #130

lib/node-modules-paths.js

@@ -1,4 +1,5 @@
 var path = require('path');
+var fs = require('fs');
 var parse = path.parse || require('path-parse');
 
 module.exports = function nodeModulesPaths(start, opts) {
@@ -10,6 +11,16 @@ module.exports = function nodeModulesPaths(start, opts) {
     // 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 prefix = '/';
     if (/^([A-Za-z]:)/.test(absoluteStart)) {
         prefix = '';

readme.markdown

@@ -73,6 +73,11 @@ node_modules recursive walk (probably don't use this)
 
 * opts.moduleDirectory - directory (or directories) in which to recursively look for modules. default: `"node_modules"`
 
+* opts.preserveSymlinks - if true, doesn't resolve `basedir` to real path before resolving.
+This is the way Node resolves dependencies when executed with the [--preserve-symlinks](https://nodejs.org/api/all.html#cli_preserve_symlinks) flag.
+**Note:** this property is currently `true` by default but it will be changed to
+`false` in the next major version because *Node's resolution algorithm does not preserve symlinks by default*.
+
 default `opts` values:
 
 ``` javascript
@@ -88,7 +93,8 @@ default `opts` values:
             else cb(null, stat.isFile())
         });
     },
-    moduleDirectory: 'node_modules'
+    moduleDirectory: 'node_modules',
+    preserveSymlinks: true
 }
 ```
 
@@ -115,6 +121,11 @@ node_modules recursive walk (probably don't use this)
 
 * opts.moduleDirectory - directory (or directories) in which to recursively look for modules. default: `"node_modules"`
 
+* opts.preserveSymlinks - if true, doesn't resolve `basedir` to real path before resolving.
+This is the way Node resolves dependencies when executed with the [--preserve-symlinks](https://nodejs.org/api/all.html#cli_preserve_symlinks) flag.
+**Note:** this property is currently `true` by default but it will be changed to
+`false` in the next major version because *Node's resolution algorithm does not preserve symlinks by default*.
+
 default `opts` values:
 
 ``` javascript
@@ -127,7 +138,8 @@ default `opts` values:
         try { return fs.statSync(file).isFile() }
         catch (e) { return false }
     },
-    moduleDirectory: 'node_modules'
+    moduleDirectory: 'node_modules',
+    preserveSymlinks: true
 }
 ````
 

test/resolver/symlinked/.gitignore

@@ -0,0 +1 @@
+symlink

test/resolver/symlinked/_/.gitignore

@@ -0,0 +1 @@
+!node_modules

test/symlinks.js

@@ -0,0 +1,54 @@
+var path = require('path');
+var fs = require('fs');
+var test = require('tape');
+var resolve = require('../');
+
+var symlinkDir = path.join(__dirname, 'resolver', 'symlinked', 'symlink');
+try {
+    fs.unlinkSync(symlinkDir);
+} catch (err) {}
+try {
+    fs.symlinkSync('./_/symlink_target', symlinkDir, 'dir');
+} catch (err) {
+    // if fails then it is probably on Windows and lets try to create a junction
+    fs.symlinkSync(path.join(__dirname, 'resolver', 'symlinked', '_', 'symlink_target') + '\\', symlinkDir, 'junction');
+}
+
+test('symlink', function (t) {
+    t.plan(1);
+
+    resolve('foo', { basedir: symlinkDir, preserveSymlinks: false }, function (err, res, pkg) {
+        if (err) t.fail(err);
+        t.equal(res, path.join(__dirname, 'resolver', 'symlinked', '_', 'node_modules', 'foo.js'));
+    });
+});
+
+test('sync symlink when preserveSymlinks = true', function (t) {
+    t.plan(4);
+
+    resolve('foo', { basedir: symlinkDir }, function (err, res, pkg) {
+        t.ok(err, 'there is an error');
+        t.notOk(res, 'no result');
+
+        t.equal(err && err.code, 'MODULE_NOT_FOUND', 'error code matches require.resolve');
+        t.equal(
+            err && err.message,
+            'Cannot find module \'foo\' from \'' + symlinkDir + '\'',
+            'can not find nonexistent module'
+        );
+    });
+});
+
+test('sync symlink', function (t) {
+    var start = new Date();
+    t.equal(resolve.sync('foo', { basedir: symlinkDir, preserveSymlinks: false }), path.join(__dirname, 'resolver', 'symlinked', '_', 'node_modules', 'foo.js'));
+    t.ok(new Date() - start < 50, 'resolve.sync timedout');
+    t.end();
+});
+
+test('sync symlink when preserveSymlinks = true', function (t) {
+    t.throws(function () {
+        resolve.sync('foo', { basedir: symlinkDir });
+    }, /Cannot find module 'foo'/);
+    t.end();
+});