path: fix posix.relative() on Windows

Fixes: #13683

Author: Trott

lib/path.js

@@ -23,6 +23,7 @@
 
 const {
   FunctionPrototypeBind,
+  RegExp,
   StringPrototypeCharCodeAt,
   StringPrototypeLastIndexOf,
   StringPrototypeSlice,
@@ -1014,7 +1015,14 @@ const posix = {
     let resolvedAbsolute = false;
 
     for (let i = args.length - 1; i >= -1 && !resolvedAbsolute; i--) {
-      const path = i >= 0 ? args[i] : process.cwd();
+      const path = i >= 0 ?
+        args[i] :
+        (() => {
+          const _ = process.cwd()
+            .replace(new RegExp(`\\${module.exports.sep}`, 'g'), posix.sep);
+          return _.substr(_.indexOf(posix.sep));
+        })();
+
 
       validateString(path, 'path');
 

test/known_issues/known_issues.status

@@ -15,32 +15,18 @@ test-vm-timeout-escape-queuemicrotask: SKIP
 [$system==win32]
 
 [$system==linux]
-# Windows-specific test
-test-path-posix-relative-on-windows: SKIP
 
 [$system==macos]
-# Windows-specific test
-test-path-posix-relative-on-windows: SKIP
 
 [$system==solaris]
-# Windows-specific test
-test-path-posix-relative-on-windows: SKIP
 
 [$system==freebsd]
-# Windows-specific test
-test-path-posix-relative-on-windows: SKIP
 
 [$system==aix]
-# Windows-specific test
-test-path-posix-relative-on-windows: SKIP
 
 [$arch==arm]
 # The Raspberry Pis are too slow to run this test.
 # See https://github.com/nodejs/build/issues/2227#issuecomment-608334574
 test-crypto-authenticated-stream: SKIP
-# Windows-specific test
-test-path-posix-relative-on-windows: SKIP
 
 [$system==ibmi]
-# Windows-specific test
-test-path-posix-relative-on-windows: SKIP