[BUG] Wrong tree path results with custom `is_leaf` condition

[ASEM000]

Required prerequisites

• [X] I have read the documentation https://optree.readthedocs.io.
• [X] I have searched the Issue Tracker that this hasn't already been reported. (comment there if it has.)

What version of OpTree are you using?

0.9.1

System information

import optree as ot
import sys
print(ot.__version__)
# 0.9.1
print(sys.version, sys.platform)
# 3.11.0 | packaged by conda-forge | (main, Jan 14 2023, 12:26:40) [Clang 14.0.6 ] darwin

Problem description

Incorrect path in optree.tree_flatten_with_path.

The following reproduce the problem

Reproducible example code

import optree as ot
import sys
print(ot.__version__)
# 0.9.1
print(sys.version, sys.platform)
# 3.11.0 | packaged by conda-forge | (main, Jan 14 2023, 12:26:40) [Clang 14.0.6 ] darwin

tree = {"a":1, "b":2, "c": [3,4,5]}

leaves,treedef = ot.tree_flatten(tree, is_leaf=lambda x: False if id(tree) ==id(x) else True)
print(leaves) # one level
# [1, 2, [3, 4, 5]]
print(ot.treespec_paths(treedef)) # one level paths
# [('a',), ('b',), ('c',)]

paths,leaves,treedef = ot.tree_flatten_with_path(tree, is_leaf=lambda x: False if id(tree) ==id(x) else True)
print(leaves) # one level
# [1, 2, [3, 4, 5]]
print(paths) # one level paths
# []

Traceback

No response

Expected behavior

Expected output is

# [('a',), ('b',), ('c',)]

Additional context

No response

[XuehaiPan]

Hi @ASEM000, thanks for raising this issue! It's a bug that the paths are always empty when the is_leaf argument is passed. I will open a PR to fix this.