[Breaking] bring resolve into line with require.resolve, which does not respect trailing slashes on non-directories.

Author: ljharb

lib/async.js

@@ -61,11 +61,17 @@ module.exports = function resolve(x, options, callback) {
     var res;
     function validBasedir() {
         if (/^(?:\.\.?(?:\/|$)|\/|([A-Za-z]:)?[/\\])/.test(x)) {
-            res = path.resolve(basedir, x);
+            res = path.normalize(path.join(basedir, x));
             if (x === '..' || x.slice(-1) === '/') res += '/';
             if (/\/$/.test(x) && res === basedir) {
                 loadAsDirectory(res, opts.package, onfile);
-            } else loadAsFile(res, opts.package, onfile);
+            } else {
+                isFileWithExtensions(res, function (err, resIsFile) {
+                    if (err) { return onfile(err); }
+                    if (resIsFile) { return loadAsFile(res, opts.package, onfile); }
+                    return loadAsDirectory(res, opts.package, onfile);
+                });
+            }
         } else loadNodeModules(x, basedir, function (err, n, pkg) {
             if (err) cb(err);
             else if (core[x]) return cb(null, x);
@@ -78,6 +84,27 @@ module.exports = function resolve(x, options, callback) {
         });
     }
 
+    function isFileWithExtensions(file, cb, extensionIndex) {
+        var newExtensionIndex = 0;
+        var filename = file;
+        if (typeof extensionIndex === 'number') {
+            if (extensionIndex >= extensions.length) {
+                return cb(null, false);
+            }
+
+            newExtensionIndex = extensionIndex + 1;
+            filename = file + extensions[extensionIndex];
+        }
+
+        isFile(filename, function (err, filenameIsFile) {
+            if (err) { return cb(err); }
+            if (filenameIsFile) {
+                return cb(null, filenameIsFile);
+            }
+            isFileWithExtensions(file, cb, newExtensionIndex);
+        });
+    }
+
     function onfile(err, m, pkg) {
         if (err) cb(err);
         else if (m) cb(null, m, pkg);

lib/sync.js

@@ -44,7 +44,7 @@ module.exports = function (x, options) {
     }
 
     if (/^(?:\.\.?(?:\/|$)|\/|([A-Za-z]:)?[/\\])/.test(x)) {
-        var res = path.resolve(basedir, x);
+        var res = path.normalize(path.join(basedir, x));
         if (x === '..' || x.slice(-1) === '/') res += '/';
         var m = loadAsFileSync(res) || loadAsDirectorySync(res);
         if (m) return m;

test/resolver.js

@@ -310,6 +310,23 @@ test('async: #121 - treating an existing file as a dir when no basedir', functio
         });
     });
 
+    t.test('with a trailing slash', function (st) {
+        st.plan(4);
+
+        resolve('./' + testFile + '/', function (err, res, pkg) {
+            st.ok(err, 'there is an error');
+            st.notOk(res, 'no result');
+
+            st.equal(err && err.code, 'MODULE_NOT_FOUND', 'error code matches require.resolve');
+            st.equal(
+                err && err.message,
+                'Cannot find module \'./' + testFile + '/\' from \'' + __dirname + '\'',
+                'can not find nonexistent module'
+            );
+            st.end();
+        });
+    });
+
     t.test('with a fake directory', function (st) {
         st.plan(4);
 

test/resolver_sync.js

@@ -235,6 +235,25 @@ test('sync: #121 - treating an existing file as a dir when no basedir', function
         st.end();
     });
 
+    t.test('with a trailing slash', function (st) {
+        function run() { return resolve.sync('./' + testFile + '/'); }
+
+        st.throws(run, 'throws an error');
+
+        try {
+            run();
+        } catch (e) {
+            st.equal(e.code, 'MODULE_NOT_FOUND', 'error code matches require.resolve');
+            st.equal(
+                e.message,
+                'Cannot find module \'./' + testFile + '/\' from \'' + __dirname + '\'',
+                'can not find nonexistent module'
+            );
+        }
+
+        st.end();
+    });
+
     t.test('with a fake directory', function (st) {
         function run() { return resolve.sync('./' + testFile + '/blah'); }