lib: simplify Module._resolveLookupPaths

This commit consists of two changes:

* Avoids returning request/id *just* for the debug() output
* Returns `null` instead of an empty array for the list of paths

PR-URL: https://github.com/nodejs/node/pull/10789
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

lib/module.js

@@ -326,14 +326,14 @@ if (process.platform === 'win32') {
 // 'index.' character codes
 var indexChars = [ 105, 110, 100, 101, 120, 46 ];
 var indexLen = indexChars.length;
-Module._resolveLookupPaths = function(request, parent) {
+Module._resolveLookupPaths = function(request, parent, newReturn) {
   if (NativeModule.nonInternalExists(request)) {
-    return [request, []];
+    debug('looking for %j in []', request);
+    return (newReturn ? null : [request, []]);
   }
 
-  var reqLen = request.length;
   // Check for relative path
-  if (reqLen < 2 ||
+  if (request.length < 2 ||
       request.charCodeAt(0) !== 46/*.*/ ||
       (request.charCodeAt(1) !== 46/*.*/ &&
        request.charCodeAt(1) !== 47/*/*/)) {
@@ -355,7 +355,8 @@ Module._resolveLookupPaths = function(request, parent) {
       }
     }
 
-    return [request, paths];
+    debug('looking for %j in %j', request, paths);
+    return (newReturn ? (paths.length > 0 ? paths : null) : [request, paths]);
   }
 
   // with --eval, parent.id is not set and parent.filename is null
@@ -363,7 +364,9 @@ Module._resolveLookupPaths = function(request, parent) {
     // 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._nodeModulePaths('.'), modulePaths);
-    return [request, mainPaths];
+
+    debug('looking for %j in %j', request, mainPaths);
+    return (newReturn ? mainPaths : [request, mainPaths]);
   }
 
   // Is the parent an index module?
@@ -413,7 +416,9 @@ Module._resolveLookupPaths = function(request, parent) {
   debug('RELATIVE: requested: %s set ID to: %s from %s', request, id,
         parent.id);
 
-  return [id, [path.dirname(parent.filename)]];
+  var parentDir = [path.dirname(parent.filename)];
+  debug('looking for %j in %j', id, parentDir);
+  return (newReturn ? parentDir : [id, parentDir]);
 };
 
 
@@ -472,16 +477,12 @@ Module._resolveFilename = function(request, parent, isMain) {
     return request;
   }
 
-  var resolvedModule = Module._resolveLookupPaths(request, parent);
+  var paths = Module._resolveLookupPaths(request, parent, true);
-  var id = resolvedModule[0];
-  var paths = resolvedModule[1];
 
   // look up the filename first, since that's the cache key.
-  debug('looking for %j in %j', id, paths);
-
   var filename = Module._findPath(request, paths, isMain);
   if (!filename) {
-    var err = new Error("Cannot find module '" + request + "'");
+    var err = new Error(`Cannot find module '${request}'`);
     err.code = 'MODULE_NOT_FOUND';
     throw err;
   }
@@ -564,7 +565,7 @@ Module.prototype._compile = function(content, filename) {
     if (!resolvedArgv) {
       // we enter the repl if we're not given a filename argument.
       if (process.argv[1]) {
-        resolvedArgv = Module._resolveFilename(process.argv[1], null);
+        resolvedArgv = Module._resolveFilename(process.argv[1], null, false);
       } else {
         resolvedArgv = 'repl';
       }

lib/repl.js

@@ -712,7 +712,7 @@ REPLServer.prototype.createContext = function() {
   }
 
   const module = new Module('<repl>');
-  module.paths = Module._resolveLookupPaths('<repl>', parentModule)[1];
+  module.paths = Module._resolveLookupPaths('<repl>', parentModule, true) || [];
 
   const require = internalModule.makeRequireFunction(module);
   context.module = module;

test/parallel/test-module-relative-lookup.js

@@ -4,7 +4,12 @@ require('../common');
 const assert = require('assert');
 const _module = require('module'); // avoid collision with global.module
 const lookupResults = _module._resolveLookupPaths('./lodash');
-const paths = lookupResults[1];
+let paths = lookupResults[1];
 
 assert.strictEqual(paths[0], '.',
                    'Current directory gets highest priority for local modules');
+
+paths = _module._resolveLookupPaths('./lodash', null, true);
+
+assert.strictEqual(paths && paths[0], '.',
+                   'Current directory gets highest priority for local modules');