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

test/known_issues/test-path-posix-relative-on-windows.js test/parallel/test-path-posix-relative-on-windows.js

@@ -9,6 +9,14 @@ const failures = [];
 const slashRE = /\//g;
 const backslashRE = /\\/g;
 
+const posixyCwd = common.isWindows ?
+  (() => {
+    const _ = process.cwd()
+      .replace(new RegExp(`\\${module.exports.sep}`, 'g'), path.posix.sep);
+    return _.substr(_.indexOf(path.posix.sep));
+  })() :
+  process.cwd();
+
 const resolveTests = [
   [ path.win32.resolve,
     // Arguments                               result
@@ -31,8 +39,8 @@ const resolveTests = [
     // Arguments                    result
     [[['/var/lib', '../', 'file/'], '/var/file'],
      [['/var/lib', '/../', 'file/'], '/file'],
-     [['a/b/c/', '../../..'], process.cwd()],
-     [['.'], process.cwd()],
+     [['a/b/c/', '../../..'], posixyCwd],
+     [['.'], posixyCwd],
      [['/some/dir', '.', '/absolute/'], '/absolute'],
      [['/foo/tmp.3/', '../tmp.3/cycles/root.js'], '/foo/tmp.3/cycles/root.js']
     ]