fix(sim): report joint_pos_target in sorted order on isaacgym and pybullet

CHANGELOG.md

@@ -35,6 +35,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- IsaacGym and PyBullet reported `joint_pos_target` in native DoF order while `joint_pos` is in sorted-name order; both now use `get_joint_names(sort=True)` (completes #12).
 - MuJoCo: `<size memory="512M">` is reserved by default; humanoid + mesh scenes no longer die with
   `mj_stackAlloc: out of memory` (get_started/10_mount_camera.py).
 - `hf_util`: a symlinked `roboverse_data` is no longer refused as path traversal; concurrent

metasim/sim/isaacgym/isaacgym.py

@@ -834,7 +834,13 @@ def _joint_pos_target_from_cache(self, robot) -> torch.Tensor | None:
         cache = self._actions_cache
         if not cache or isinstance(cache, (torch.Tensor, np.ndarray)):
             return None
-        joint_names = self._joint_info[robot.name]["names"]
+        # Iterate joints in alphabetically-sorted order so the reported
+        # ``joint_pos_target`` aligns with ``joint_pos`` (emitted via
+        # ``_get_joint_ids_reindex``, i.e. sorted-name order). ``_joint_info[...]["names"]``
+        # is native DOF order, so using it produced a target vector misaligned with
+        # ``joint_pos`` whenever the URDF joint order was not already alphabetical.
+        # Values are name-keyed, so only the output ordering changes.
+        joint_names = self._get_joint_names(robot.name, sort=True)
         targets_per_env = []
         for env_idx, env_action in enumerate(cache):
             if env_idx >= self._num_envs:

metasim/sim/pybullet/pybullet.py

@@ -449,8 +449,14 @@ def _get_states(self, env_ids=None) -> TensorState:
             cached_action = (self._actions_cache or {}).get(robot.name)
             if cached_action is not None and cached_action.get("dof_pos_target") is not None:
                 dof_pos_target = cached_action["dof_pos_target"]
+                # Iterate joints in alphabetically-sorted order so the reported
+                # ``joint_pos_target`` aligns with ``joint_pos``/``joint_vel`` (emitted
+                # via ``joint_reindex``, i.e. sorted-name order). ``object_joint_order``
+                # is native URDF order, so using it produced a target vector misaligned
+                # with ``joint_pos`` whenever that order was not already alphabetical.
+                # Values are name-keyed, so only the output ordering changes.
                 joint_pos_target = torch.tensor(
-                    [dof_pos_target[name] for name in self.object_joint_order[robot.name]],
+                    [dof_pos_target[name] for name in self._get_joint_names(robot.name, sort=True)],
                     dtype=torch.float32,
                 ).unsqueeze(0)
             state = RobotState(

metasim/test/test_joint_target_order_general.py

@@ -0,0 +1,91 @@
+"""Regression guard: ``joint_pos_target`` must be reported in the same
+alphabetically-sorted joint order as ``joint_pos``/``joint_vel`` on every
+backend that materializes it from a name-keyed action cache.
+
+Motivation: ``joint_pos``/``joint_vel``/``joint_effort_target`` are emitted in
+sorted-name order (via ``joint_reindex`` / ``_get_joint_ids_reindex``), but
+several backends assembled the reported ``joint_pos_target`` by iterating their
+*native* URDF joint order instead. Whenever a robot's native joint order is not
+already alphabetical (e.g. numeric names ``joint_2``/``joint_10``, or ``A,C,B``),
+``joint_pos_target[i]`` then referred to a different joint than ``joint_pos[i]``
+— a silent index misalignment. Commit 92755f6 fixed this on sapien2/genesis;
+isaacgym and pybullet were the remaining offenders.
+
+The faithful check needs a live backend (GPU/import order), which CI can't run,
+so this is a static AST guard instead: for each backend it pins that the
+``joint_pos_target`` materializer iterates ``_get_joint_names(..., sort=True)``
+and no longer references the native-order joint list. Pure-Python, no sim env,
+no GPU — runs under ``-k general``.
+"""
+
+from __future__ import annotations
+
+import ast
+from pathlib import Path
+
+import pytest
+
+_SIM_ROOT = Path(__file__).resolve().parents[1].joinpath("sim")
+
+
+def _find_function(tree: ast.AST, class_name: str, func_name: str) -> ast.FunctionDef:
+    cls = next(n for n in ast.walk(tree) if isinstance(n, ast.ClassDef) and n.name == class_name)
+    return next(n for n in ast.walk(cls) if isinstance(n, ast.FunctionDef) and n.name == func_name)
+
+
+def _calls_get_joint_names_sorted(fn: ast.FunctionDef) -> bool:
+    """True if ``fn`` calls ``*._get_joint_names(...)`` with ``sort=True``.
+
+    Accepts either the keyword form ``sort=True`` or the positional form
+    ``_get_joint_names(obj_name, True)`` — both mean sorted order.
+    """
+    for node in ast.walk(fn):
+        if not (isinstance(node, ast.Call) and isinstance(node.func, ast.Attribute)):
+            continue
+        if node.func.attr != "_get_joint_names":
+            continue
+        for kw in node.keywords:
+            if kw.arg == "sort" and isinstance(kw.value, ast.Constant) and kw.value.value is True:
+                return True
+        # positional sort is the 2nd arg after obj_name
+        if len(node.args) >= 2 and isinstance(node.args[1], ast.Constant) and node.args[1].value is True:
+            return True
+    return False
+
+
+def _references_attr(fn: ast.FunctionDef, attr: str) -> bool:
+    return any(isinstance(node, ast.Attribute) and node.attr == attr for node in ast.walk(fn))
+
+
+# (source file, class, function that materializes joint_pos_target, native-order
+#  attribute that must NOT be used to build it).
+_CASES = [
+    pytest.param(
+        "isaacgym/isaacgym.py", "IsaacgymHandler", "_joint_pos_target_from_cache", "_joint_info", id="isaacgym"
+    ),
+    pytest.param("pybullet/pybullet.py", "SinglePybulletHandler", "_get_states", "object_joint_order", id="pybullet"),
+]
+
+
+@pytest.mark.general
+@pytest.mark.parametrize("rel_path,class_name,func_name,native_attr", _CASES)
+def test_joint_pos_target_uses_sorted_joint_order(rel_path: str, class_name: str, func_name: str, native_attr: str):
+    """The ``joint_pos_target`` materializer must iterate sorted joint names.
+
+    Fails if a backend reverts to iterating its native joint order, which would
+    re-open the silent ``joint_pos_target``/``joint_pos`` index misalignment
+    fixed for sapien2/genesis in 92755f6 and here for isaacgym/pybullet.
+    """
+    source = _SIM_ROOT.joinpath(rel_path).read_text(encoding="utf-8")
+    fn = _find_function(ast.parse(source), class_name, func_name)
+
+    assert _calls_get_joint_names_sorted(fn), (
+        f"{class_name}.{func_name} must build joint_pos_target from "
+        f"_get_joint_names(..., sort=True) so it aligns with joint_pos "
+        f"(sorted-name order); no such call found."
+    )
+    assert not _references_attr(fn, native_attr), (
+        f"{class_name}.{func_name} still references native joint order "
+        f"({native_attr!r}) — joint_pos_target[i] would refer to a different "
+        f"joint than joint_pos[i] whenever the native order is not alphabetical."
+    )