FIX resolvePath handling of .. up from fs root

node.parent doesn't actually give us the parent if the node is a FS root.
In that case, instead of using `node.parent` we should start over from the
beginning.

Resolves #23983.

Author: hoodmane

src/lib/libfs.js

@@ -199,7 +199,12 @@ FS.staticInit();
 
           if (parts[i] === '..') {
             current_path = PATH.dirname(current_path);
-            current = current.parent;
+            if (FS.isRoot(current)) {
+              path = current_path + '/' + parts.slice(i + 1).join('/');
+              continue linkloop;
+            } else {
+              current = current.parent;
+            }
             continue;
           }
 

test/other/test_resolve_mountpoint_parent.c

@@ -0,0 +1,15 @@
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <emscripten.h>
+#include "assert.h"
+
+int main(int argc, char **argv) {
+  EM_ASM({
+    FS.mkdir('/working');
+    FS.mkdir('/other');
+    FS.mount(NODEFS, { root: '.' }, '/working');
+  });
+  struct stat statBuf;
+  assert(stat("/working/../other", &statBuf) == 0);
+}

test/other/test_resolve_mountpoint_parent.out

@@ -8164,6 +8164,11 @@ def test_realpath_2(self):
     create_file('Folder/testfile.txt', '')
     self.do_other_test('test_realpath_2.c', emcc_args=['--embed-file', 'testfile.txt', '--embed-file', 'Folder'])
 
+  @requires_node
+  @also_with_wasmfs
+  def test_resolve_mountpoint_parent(self):
+    self.do_other_test('test_resolve_mountpoint_parent.c', emcc_args=['-sFORCE_FILESYSTEM', '-lnodefs.js'])
+
   @with_env_modify({'EMCC_LOGGING': '0'})  # this test assumes no emcc output
   def test_no_warnings(self):
     # build once before to make sure system libs etc. exist