Fix bad module resolution (#42) (#43)

* Fixes issue #42

.gitignore

@@ -26,6 +26,8 @@ build/Release
 # Dependency directory
 # https://docs.npmjs.com/misc/faq#should-i-check-my-node-modules-folder-into-git
 node_modules
+# Keep it for test
+!test/custom-rules/relative-to-cwd/node_modules
 
 # Optional npm cache directory
 .npm

markdownlint.js

@@ -4,6 +4,7 @@
 
 var fs = require('fs');
 var path = require('path');
+var Module = require('module');
 var program = require('commander');
 var getStdin = require('get-stdin');
 var jsYaml = require('js-yaml');
@@ -141,8 +142,15 @@ function loadCustomRuleFromFile(filepath) {
 function tryResolvePath(filepath) {
   try {
     if (path.basename(filepath) === filepath && path.extname(filepath) === '') {
-      // Looks like a package name
-      return require.resolve(filepath);
+      // Looks like a package name, resolve it relative to cwd
+      // Get list of directories, where requested module can be.
+      var paths = Module._nodeModulePaths(process.cwd());
+      paths = paths.concat(Module.globalPaths);
+      if (require.resolve.paths) {
+        // Node >= 8.9.0
+        return require.resolve(filepath, {paths: paths});
+      }
+      return Module._resolveFilename(filepath, {paths: paths});
     }
     // Maybe it is a path to package installed locally
     return require.resolve(path.join(process.cwd(), filepath));

test/custom-rules/relative-to-cwd/package.json

@@ -0,0 +1 @@
+{}

test/test.js

@@ -394,6 +394,25 @@ test('Custom rule from node_modules package loaded', async t => {
   }
 });
 
+test('Custom rule from node_modules package loaded relative to cwd', async t => {
+  try {
+    var input = '# Input';
+    await execa(path.resolve('..', 'markdownlint.js'),
+      ['--rules', 'test-rule-package', '--stdin'], {
+        input,
+        cwd: path.join(__dirname, 'custom-rules', 'relative-to-cwd')
+      });
+    t.fail();
+  } catch (err) {
+    const expected = [
+      'stdin: 1: test-rule-package Test rule package relative to cwd broken',
+      ''
+    ].join('\n');
+    t.true(err.stdout === '');
+    t.true(err.stderr === expected);
+  }
+});
+
 test('Custom rule from package loaded', async t => {
   try {
     var input = '# Input';