feat(tidy3d): FXC-4607-autograd-for-clip-operation

Author: marcorudolphflex

CHANGELOG.md

@@ -21,6 +21,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Added flag `remove_fragments` to the base `UnstructuredGrid` to remove fragments in unstructured grids. This can ease meshing by eliminating internal boundaries in overlapping structures.
 - Added deprecation warning for `conformal` in TCAD heat/charge monitors when explicitly set; this option is ignored (treated as `False`) when meshing with `remove_fragments=True`.
 - Added in-memory caching for downloaded batch results, configurable via ``config.batch_data_cache``.
+- Added autograd support for `ClipOperation` geometries like unions or intersections of geometries.
 
 ### Breaking Changes
 - Added optional automatic extrusion of structures at the simulation boundaries into/through PML/Absorber layers via `extrude_structures` field in class `AbsorberSpec`.

tests/test_components/autograd/numerical/conftest.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import hashlib
 import os
 import re
 from pathlib import Path
@@ -9,13 +10,35 @@
 ARTIFACT_ENV_VAR = "TIDY3D_NUMERICAL_ARTIFACT_DIR"
 DEFAULT_RELATIVE_DIR = Path("tests/tmp/autograd_numerical")
 
+# Optional extra cap for the per-test directory name length (in bytes, after fs encoding).
+ARTIFACT_NAME_MAX_ENV_VAR = "TIDY3D_NUMERICAL_ARTIFACT_NAME_MAX"
+
 
 def _sanitize_segment(value: str) -> str:
     sanitized = re.sub(r"[^\w.-]+", "_", value)
     sanitized = sanitized.strip("_")
     return sanitized or "case"
 
 
+def _pathconf_limit(path: Path, key: str, fallback: int) -> int:
+    """Best-effort os.pathconf lookup with a fallback."""
+    try:
+        return int(os.pathconf(str(path), key))
+    except (AttributeError, ValueError, OSError):
+        return fallback
+
+
+def _artifact_name_max_override() -> int | None:
+    """Optional user cap for artifact directory names (bytes)."""
+    raw = os.environ.get(ARTIFACT_NAME_MAX_ENV_VAR)
+    if not raw:
+        return None
+    try:
+        return max(1, int(raw))
+    except ValueError as e:
+        raise ValueError(f"{ARTIFACT_NAME_MAX_ENV_VAR} must be an integer (got {raw!r}).") from e
+
+
 def _resolve_artifact_root() -> Path:
     env_value = os.environ.get(ARTIFACT_ENV_VAR)
     if env_value:
@@ -27,14 +50,60 @@ def _resolve_artifact_root() -> Path:
     return root
 
 
+def _case_dir_name(request, artifact_root: Path) -> str:
+    """Return a filesystem-friendly per-test artifact directory name.
+
+    Uses ``request.node.name``. If truncation is needed to satisfy filesystem
+    path/name limits (and optional ``TIDY3D_NUMERICAL_ARTIFACT_NAME_MAX``), append a
+    short SHA1 digest of the full nodeid. Otherwise, no digest is added, so
+    uniqueness across files is not guaranteed.
+    """
+    raw_nodeid = request.node.nodeid
+    base_name = _sanitize_segment(request.node.name) or "case"
+
+    # Use filesystem-encoded byte lengths to be conservative under multibyte encodings.
+    def _fslen(s: str) -> int:
+        return len(os.fsencode(s))
+
+    root_abs = artifact_root.resolve()
+
+    # Common Linux defaults: NAME_MAX ~255 bytes, PATH_MAX ~4096 bytes (may vary).
+    name_max = _pathconf_limit(root_abs, "PC_NAME_MAX", 255)
+    path_max = _pathconf_limit(root_abs, "PC_PATH_MAX", 4096)
+
+    # Leave room for: <root>/<name> plus NUL (pathconf is in bytes).
+    available = path_max - _fslen(str(root_abs)) - _fslen(os.sep) - 1
+
+    max_len = min(name_max, max(1, available))
+    override = _artifact_name_max_override()
+    if override is not None:
+        max_len = min(max_len, override)
+
+    if _fslen(base_name) <= max_len:
+        return base_name
+
+    digest = hashlib.sha1(raw_nodeid.encode("utf-8")).hexdigest()[:8]
+    suffix = f"-{digest}"
+    max_base = max_len - _fslen(suffix)
+    if max_base < 1:
+        max_base = 1
+
+    # Truncate by bytes (not chars): drop codepoints until it fits.
+    while base_name and _fslen(base_name) > max_base:
+        base_name = base_name[:-1]
+    if not base_name:
+        base_name = "c"
+
+    return f"{base_name}{suffix}"
+
+
 @pytest.fixture(scope="session")
 def numerical_artifact_root() -> Path:
     return _resolve_artifact_root()
 
 
 @pytest.fixture
 def numerical_case_dir(request, numerical_artifact_root: Path) -> Path:
-    safe_nodeid = _sanitize_segment(request.node.nodeid.replace(os.sep, "_"))
-    case_dir = numerical_artifact_root / safe_nodeid
+    case_dir = numerical_artifact_root / _case_dir_name(request, numerical_artifact_root)
     case_dir.mkdir(parents=True, exist_ok=True)
     return case_dir