path: faster posix path.resolve() without arguments

benchmark/path/join-posix.js

@@ -16,8 +16,8 @@ function main({ n, paths }) {
 
   bench.start();
   for (let i = 0; i < n; i++) {
-    if (i % 3 === 0) {
-      copy[1] = `${orig}${i}`;
+    if (i % 5 === 0) {
+      copy[1] = `${orig}/${i}`;
       posix.join(...copy);
     } else {
       posix.join(...args);

benchmark/path/join-win32.js

@@ -16,8 +16,8 @@ function main({ n, paths }) {
 
   bench.start();
   for (let i = 0; i < n; i++) {
-    if (i % 3 === 0) {
-      copy[1] = `${orig}${i}`;
+    if (i % 5 === 0) {
+      copy[1] = `${orig}\\${i}`;
       win32.join(...copy);
     } else {
       win32.join(...args);

benchmark/path/normalize-posix.js

@@ -17,7 +17,7 @@ const bench = common.createBenchmark(main, {
 function main({ n, path }) {
   bench.start();
   for (let i = 0; i < n; i++) {
-    posix.normalize(i % 3 === 0 ? `${path}${i}` : path);
+    posix.normalize(i % 5 === 0 ? `${path}/${i}` : path);
   }
   bench.end(n);
 }

benchmark/path/normalize-win32.js

@@ -17,7 +17,7 @@ const bench = common.createBenchmark(main, {
 function main({ n, path }) {
   bench.start();
   for (let i = 0; i < n; i++) {
-    win32.normalize(i % 3 === 0 ? `${path}${i}` : path);
+    win32.normalize(i % 5 === 0 ? `${path}\\${i}` : path);
   }
   bench.end(n);
 }

benchmark/path/resolve-posix.js

@@ -4,23 +4,26 @@ const { posix } = require('path');
 
 const bench = common.createBenchmark(main, {
   paths: [
+    'empty',
     '',
+    '.',
     ['', ''].join('|'),
     ['foo/bar', '/tmp/file/', '..', 'a/../subfile'].join('|'),
     ['a/b/c/', '../../..'].join('|'),
+    ['/a/b/c/', 'abc'].join('|'),
   ],
   n: [1e5],
 });
 
 function main({ n, paths }) {
-  const args = paths.split('|');
+  const args = paths === 'empty' ? [] : paths.split('|');
   const copy = [...args];
-  const orig = copy[0];
+  const orig = copy[0] ?? '';
 
   bench.start();
   for (let i = 0; i < n; i++) {
-    if (i % 3 === 0) {
-      copy[0] = `${orig}${i}`;
+    if (i % 5 === 0) {
+      copy[0] = `${orig}/${i}`;
       posix.resolve(...copy);
     } else {
       posix.resolve(...args);

benchmark/path/resolve-win32.js

@@ -4,7 +4,9 @@ const { win32 } = require('path');
 
 const bench = common.createBenchmark(main, {
   paths: [
+    'empty',
     '',
+    '.',
     ['', ''].join('|'),
     ['c:/ignore', 'd:\\a/b\\c/d', '\\e.exe'].join('|'),
     ['c:/blah\\blah', 'd:/games', 'c:../a'].join('|'),
@@ -13,14 +15,14 @@ const bench = common.createBenchmark(main, {
 });
 
 function main({ n, paths }) {
-  const args = paths.split('|');
+  const args = paths === 'empty' ? [] : paths.split('|');
   const copy = [...args];
-  const orig = copy[0];
+  const orig = copy[0] ?? '';
 
   bench.start();
   for (let i = 0; i < n; i++) {
-    if (i % 3 === 0) {
-      copy[0] = `${orig}${i}`;
+    if (i % 5 === 0) {
+      copy[0] = `${orig}\\${i}`;
       win32.resolve(...copy);
     } else {
       win32.resolve(...args);

lib/path.js

@@ -95,7 +95,7 @@ function normalizeString(path, allowAboveRoot, separator, isPathSeparator) {
             StringPrototypeCharCodeAt(res, res.length - 1) !== CHAR_DOT ||
             StringPrototypeCharCodeAt(res, res.length - 2) !== CHAR_DOT) {
           if (res.length > 2) {
-            const lastSlashIndex = StringPrototypeLastIndexOf(res, separator);
+            const lastSlashIndex = res.length - lastSegmentLength - 1;
             if (lastSlashIndex === -1) {
               res = '';
               lastSegmentLength = 0;
@@ -163,6 +163,8 @@ function _format(sep, pathObject) {
   return dir === pathObject.root ? `${dir}${base}` : `${dir}${sep}${base}`;
 }
 
+const forwardSlashRegExp = /\//g;
+
 const win32 = {
   /**
    * path.resolve([from ...], to)
@@ -186,6 +188,14 @@ const win32 = {
         }
       } else if (resolvedDevice.length === 0) {
         path = process.cwd();
+        // Fast path for current directory
+        if (args.length === 0 || ((args.length === 1 && (args[0] === '' || args[0] === '.')) &&
+            isPathSeparator(StringPrototypeCharCodeAt(path, 0)))) {
+          if (!isWindows) {
+            path = StringPrototypeReplace(path, forwardSlashRegExp, '\\');
+          }
+          return path;
+        }
       } else {
         // Windows has the concept of drive-specific current working
         // directories. If we've resolved a drive letter but not yet an
@@ -1171,6 +1181,12 @@ const posix = {
    * @returns {string}
    */
   resolve(...args) {
+    if (args.length === 0 || (args.length === 1 && (args[0] === '' || args[0] === '.'))) {
+      const cwd = posixCwd();
+      if (StringPrototypeCharCodeAt(cwd, 0) === CHAR_FORWARD_SLASH) {
+        return cwd;
+      }
+    }
     let resolvedPath = '';
     let resolvedAbsolute = false;
 

test/parallel/test-path-resolve.js

@@ -24,6 +24,8 @@ const resolveTests = [
      [['c:/ignore', 'd:\\a/b\\c/d', '\\e.exe'], 'd:\\e.exe'],
      [['c:/ignore', 'c:/some/file'], 'c:\\some\\file'],
      [['d:/ignore', 'd:some/dir//'], 'd:\\ignore\\some\\dir'],
+     [[], process.cwd()],
+     [[''], process.cwd()],
      [['.'], process.cwd()],
      [['//server/share', '..', 'relative\\'], '\\\\server\\share\\relative'],
      [['c:/', '//'], 'c:\\'],
@@ -42,6 +44,8 @@ const resolveTests = [
     [[['/var/lib', '../', 'file/'], '/var/file'],
      [['/var/lib', '/../', 'file/'], '/file'],
      [['a/b/c/', '../../..'], posixyCwd],
+     [[], posixyCwd],
+     [[''], posixyCwd],
      [['.'], posixyCwd],
      [['/some/dir', '.', '/absolute/'], '/absolute'],
      [['/foo/tmp.3/', '../tmp.3/cycles/root.js'], '/foo/tmp.3/cycles/root.js'],