From 1e44bda48ff4982b8ccfeec9c14156ea9e8ae5a2 Mon Sep 17 00:00:00 2001 From: Igor Soarez Date: Tue, 18 Aug 2026 20:04:28 +0100 Subject: [PATCH] fix(langgraph): detect subgraphs from bytecode instead of source (#8569) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Fixes langchain-ai/langgraph#8559 `find_subgraph_pregel` runs once per node at build time and recovers each node function's reachable values with `inspect.getsource` + `ast.parse`; langchain-ai/langgraph#8559 measures that source parsing at 80% of `StateGraph.compile()`. This replaces it with a `dis` walk over `func.__code__`, which reads the same information already in memory. Closure cells and the globals named in `co_names` supply the values directly, and a walk over the instruction stream recovers the attribute paths the function actually takes. The closure alone cannot express those: a captured `holder` whose graph lives at `holder.graph` is reachable only if something records that `graph` is loaded off `holder`. Both implementations over-declare — a node can reference a graph it never invokes — and this one over-declares a different set. It no longer reports a graph named only along an attribute path in code the compiler removed; such a path cannot execute, so that entry was always a phantom. Nothing that can actually run stopped being detected. `find_subgraph_pregel` returns the first `PregelProtocol` it finds, so the remaining extra candidates only widen detection. ## Release note Subgraph auto-detection now reads node functions' bytecode instead of parsing their source. Graph builds with many function-backed nodes are substantially faster, and subgraphs are now detected inside functions with no retrievable source — defined in a REPL or notebook cell, or via `exec` — where detection previously failed silently and returned nothing. ## Performance Against [langgraph-build-bench]() — 713 nodes, 500 state fields, 264 tools; CPython 3.12.8, Apple silicon: ``` before build 1412 ms subgraph detection 1132 ms (80%) after build 286 ms subgraph detection 4 ms (2%) ``` **4.9x on total build, \~266x on detection.** The bench prints whole ms; at full precision detection is 1139 ms -> 4.23 ms. Co-authored-by: Elior Nataf Lackritz --- libs/langgraph/langgraph/pregel/_utils.py | 212 +++++-------- .../tests/test_subgraph_detection.py | 286 ++++++++++++++++++ 2 files changed, 357 insertions(+), 141 deletions(-) create mode 100644 libs/langgraph/tests/test_subgraph_detection.py diff --git a/libs/langgraph/langgraph/pregel/_utils.py b/libs/langgraph/langgraph/pregel/_utils.py index f7f91e08b..dabc309e0 100644 --- a/libs/langgraph/langgraph/pregel/_utils.py +++ b/libs/langgraph/langgraph/pregel/_utils.py @@ -1,11 +1,10 @@ from __future__ import annotations -import ast -import inspect +import dis import re -import textwrap from collections.abc import Callable, Sequence from functools import partial +from types import CodeType, FunctionType from typing import Any from langchain_core.runnables import ( @@ -17,7 +16,6 @@ from langchain_core.runnables import ( from langchain_core.runnables.base import RunnableBindingBase from langchain_core.runnables.config import run_in_executor from langgraph.checkpoint.base import ChannelVersions -from typing_extensions import override from langgraph._internal._runnable import RunnableCallable, RunnableSeq from langgraph._internal._timeout import sync_timeout_unsupported @@ -137,155 +135,87 @@ def validate_timeout_supported(runnable: Runnable, *, name: str) -> None: raise sync_timeout_unsupported(name) +# Values treated as dead ends when deciding whether to walk a function's +# bytecode. A container can hold a graph, but `find_subgraph_pregel` does not +# look inside one, so skipping it costs nothing while that holds. Matched by +# exact type, since a subclass of a builtin can carry attributes. +_LEAF_TYPES = frozenset( + { + int, + float, + complex, + bool, + str, + bytes, + bytearray, + list, + tuple, + dict, + set, + frozenset, + type(None), + } +) + + def get_function_nonlocals(func: Callable) -> list[Any]: - """Get the nonlocal variables accessed by a function. + """Get the values a function reaches from outside its own scope. Args: func: The function to check. Returns: - List[Any]: The nonlocal variables accessed by the function. + Every captured cell value, the globals the function names, and each + value along an attribute path it loads. Over-approximates: a value can + come back without the function reaching it at runtime. """ - try: - code = inspect.getsource(func) - tree = ast.parse(textwrap.dedent(code)) - visitor = FunctionNonLocals() - visitor.visit(tree) - values: list[Any] = [] - closure = ( - inspect.getclosurevars(func.__wrapped__) - if hasattr(func, "__wrapped__") and callable(func.__wrapped__) - else inspect.getclosurevars(func) - ) - candidates = {**closure.globals, **closure.nonlocals} - for k, v in candidates.items(): - if k in visitor.nonlocals: - values.append(v) - for kk in visitor.nonlocals: - if "." in kk and kk.startswith(k): - vv = v - for part in kk.split(".")[1:]: - if vv is None: - break - else: - try: - vv = getattr(vv, part) - except AttributeError: - break - else: - values.append(vv) - except (SyntaxError, TypeError, OSError, SystemError): + func = getattr(func, "__func__", func) # bound method -> function + wrapped = getattr(func, "__wrapped__", None) + if callable(wrapped): + func = getattr(wrapped, "__func__", wrapped) + if not isinstance(func, FunctionType): return [] + code = func.__code__ + cells: dict[str, Any] = {} + for name, cell in zip(code.co_freevars, func.__closure__ or ()): + try: + cells[name] = cell.cell_contents + except ValueError: + continue # empty cell: a recursive def not yet bound + + # Every captured value counts, referenced or not: over-declaring costs an + # introspection entry, under-declaring drops the subgraph's checkpoints and + # stream events. Checking each cell against the bytecode would cost more and + # only trade the cheap error for the expensive one. + values: list[Any] = list(cells.values()) + global_ns = func.__globals__ + globals_ = {name: global_ns[name] for name in code.co_names if name in global_ns} + if all(type(v) in _LEAF_TYPES for v in (*cells.values(), *globals_.values())): + return values + + # Nested code objects hold the references made by inner defs, lambdas and + # comprehensions, which resolve against the namespaces gathered above. + codes = [code] + for c in codes: + codes.extend(k for k in c.co_consts if isinstance(k, CodeType)) + value: Any = None + for instruction in dis.get_instructions(c): + opname = instruction.opname + if opname == "LOAD_GLOBAL": + value = globals_.get(instruction.argval) + elif opname == "LOAD_DEREF": + value = cells.get(instruction.argval) + elif opname in ("LOAD_ATTR", "LOAD_METHOD"): + value = getattr(value, instruction.argval, None) + else: + value = None # anything else ends the chain: `a, b.c` is not `a.c` + continue + if value is not None: + values.append(value) return values -class FunctionNonLocals(ast.NodeVisitor): - """Get the nonlocal variables accessed of a function.""" - - def __init__(self) -> None: - self.nonlocals: set[str] = set() - - @override - def visit_FunctionDef(self, node: ast.FunctionDef) -> Any: - """Visit a function definition. - - Args: - node: The node to visit. - - Returns: - Any: The result of the visit. - """ - visitor = NonLocals() - visitor.visit(node) - self.nonlocals.update(visitor.loads - visitor.stores) - - @override - def visit_AsyncFunctionDef(self, node: ast.AsyncFunctionDef) -> Any: - """Visit an async function definition. - - Args: - node: The node to visit. - - Returns: - Any: The result of the visit. - """ - visitor = NonLocals() - visitor.visit(node) - self.nonlocals.update(visitor.loads - visitor.stores) - - @override - def visit_Lambda(self, node: ast.Lambda) -> Any: - """Visit a lambda function. - - Args: - node: The node to visit. - - Returns: - Any: The result of the visit. - """ - visitor = NonLocals() - visitor.visit(node) - self.nonlocals.update(visitor.loads - visitor.stores) - - -class NonLocals(ast.NodeVisitor): - """Get nonlocal variables accessed.""" - - def __init__(self) -> None: - self.loads: set[str] = set() - self.stores: set[str] = set() - - @override - def visit_Name(self, node: ast.Name) -> Any: - """Visit a name node. - - Args: - node: The node to visit. - - Returns: - Any: The result of the visit. - """ - if isinstance(node.ctx, ast.Load): - self.loads.add(node.id) - elif isinstance(node.ctx, ast.Store): - self.stores.add(node.id) - - @override - def visit_Attribute(self, node: ast.Attribute) -> Any: - """Visit an attribute node. - - Args: - node: The node to visit. - - Returns: - Any: The result of the visit. - """ - if isinstance(node.ctx, ast.Load): - parent = node.value - attr_expr = node.attr - while isinstance(parent, ast.Attribute): - attr_expr = parent.attr + "." + attr_expr - parent = parent.value - if isinstance(parent, ast.Name): - self.loads.add(parent.id + "." + attr_expr) - self.loads.discard(parent.id) - elif isinstance(parent, ast.Call): - if isinstance(parent.func, ast.Name): - self.loads.add(parent.func.id) - else: - parent = parent.func - attr_expr = "" - while isinstance(parent, ast.Attribute): - if attr_expr: - attr_expr = parent.attr + "." + attr_expr - else: - attr_expr = parent.attr - parent = parent.value - if isinstance(parent, ast.Name): - self.loads.add(parent.id + "." + attr_expr) - - def is_xxh3_128_hexdigest(value: str) -> bool: """Check if the given string matches the format of xxh3_128_hexdigest.""" return bool(re.fullmatch(r"[0-9a-f]{32}", value)) diff --git a/libs/langgraph/tests/test_subgraph_detection.py b/libs/langgraph/tests/test_subgraph_detection.py new file mode 100644 index 000000000..dca56139f --- /dev/null +++ b/libs/langgraph/tests/test_subgraph_detection.py @@ -0,0 +1,286 @@ +"""Tests for subgraph auto-detection (`pregel/_utils.py`). + +Detection failing is silent — the graph still runs, only introspection goes +quiet — so every shape a node can hold a graph in is pinned here. The expected +values are what the source-parsing implementation this replaced produced for +the same shapes, except for `sourceless`, whose source it could not read, +`empty_closure_cell`, on which it raised, and `unreachable_attribute_chain`, +where it reported a graph that dropped code could never invoke. +""" + +import functools +import operator +from typing import Annotated, Any + +import pytest +from typing_extensions import TypedDict + +from langgraph.graph import END, START, StateGraph +from langgraph.pregel._utils import get_function_nonlocals + + +class State(TypedDict): + log: Annotated[list, operator.add] + + +def _leaf(tag: str) -> Any: + """Return a compiled graph that reports itself as `tag`.""" + builder = StateGraph(State) + builder.add_node(tag, lambda s: {"log": [tag]}) + builder.add_edge(START, tag) + builder.add_edge(tag, END) + compiled = builder.compile() + compiled.name = tag + return compiled + + +def _detect(node: Any) -> str | None: + """Return the name of the subgraph detected for `node`, or None.""" + builder = StateGraph(State) + builder.add_node("n", node) + builder.add_edge(START, "n") + builder.add_edge("n", END) + subgraphs = builder.compile().nodes["n"].subgraphs + return getattr(subgraphs[0], "name", "?") if subgraphs else None + + +class _Box: + def __init__(self, payload: Any) -> None: + self.payload = payload + + +class _ListSubclass(list): + pass + + +class _MethodHolder: + def __init__(self) -> None: + self.graph = _leaf("via_self") + + def as_node(self, state: State) -> Any: + return self.graph.invoke(state) + + +MODULE_GRAPH = _leaf("module_global") +CHAIN = _Box(_Box(_leaf("attr_chain"))) +GRAPH_IN_PLAIN_LIST = [_leaf("in_list")] +METHOD_HOLDER = _MethodHolder() + + +def closure_capture() -> Any: + sub = _leaf("closure") + + def node(state: State) -> Any: + return sub.invoke(state) + + return node + + +def module_global() -> Any: + def node(state: State) -> Any: + return MODULE_GRAPH.invoke(state) + + return node + + +def attribute_chain() -> Any: + def node(state: State) -> Any: + return CHAIN.payload.payload.invoke(state) + + return node + + +def nested_def_captured_attribute() -> Any: + """A chain on a captured holder, named only inside a nested code object. + + The captured value is the holder, not the graph, so the chain itself has to + be recovered from the nested scope. + """ + holder = _Box(_leaf("nested_captured")) + + def node(state: State) -> Any: + def inner() -> Any: + return holder.payload.invoke(state) + + return inner() + + return node + + +def unreachable_branch() -> Any: + """A captured graph referenced only from code the compiler removes.""" + sub = _leaf("unreachable") + + def node(state: State) -> Any: + if False: + sub.invoke(state) + return {"log": []} + + return node + + +def unreachable_attribute_chain() -> Any: + """A graph named only along an attribute path the compiler dropped. + + The closure keeps `holder`, but the `.payload` load is gone. The source + parser reported this one; dropped code cannot invoke anything, so that was + a phantom rather than a detection. + """ + holder = _Box(_leaf("unreachable_attr")) + + def node(state: State) -> Any: + if False: + holder.payload.invoke(state) + return {"log": []} + + return node + + +def wrapper_referencing_nothing() -> Any: + """A wrapper whose own scope holds nothing, so only `__wrapped__` leads on. + + `functools.wraps` would leave the wrapper closing over the inner function; + setting the attribute by hand does not. + """ + sub = _leaf("via_wrapped") + + def inner(state: State) -> Any: + return sub.invoke(state) + + def wrapper(state: State) -> Any: + return {"log": []} + + wrapper.__wrapped__ = inner + return wrapper + + +def captured_list_subclass() -> Any: + """A `list` subclass is not a leaf: it can carry a graph as an attribute.""" + holder = _ListSubclass() + holder.payload = _leaf("list_subclass") + + def node(state: State) -> Any: + return holder.payload.invoke(state) + + return node + + +def empty_closure_cell() -> Any: + """An unassigned closure variable leaves a cell that cannot be read.""" + sub = _leaf("beside_empty_cell") + + def node(state: State) -> Any: + return unassigned, sub.invoke(state) + + return node + unassigned = 1 # never runs, so the cell it creates is never filled + + +def sourceless() -> Any: + """A node compiled without a source file, which `getsource` could not read.""" + namespace: dict[str, Any] = {"SOURCELESS": _leaf("sourceless")} + exec( + compile( + "def node(state):\n return SOURCELESS.invoke(state)", "", "exec" + ), + namespace, + ) + return namespace["node"] + + +async def _async_node(state: State) -> Any: + return await MODULE_GRAPH.ainvoke(state) + + +def async_node() -> Any: + return _async_node + + +def no_subgraph() -> Any: + """Nothing but leaf values in reach, so the bytecode walk is skipped.""" + + def node(state: State) -> Any: + return {"log": [len("abc") + 1]} + + return node + + +def recombined_names() -> Any: + """Loads `CHAIN.payload` and `local.payload`, never `CHAIN.payload.payload`.""" + + def node(state: State) -> Any: + local = _Box("not a graph") + return {"log": [CHAIN.payload, local.payload]} + + return node + + +def broken_attribute_chain() -> Any: + holder = _Box("a string, so `.payload.missing` cannot resolve") + + def node(state: State) -> Any: + return holder.payload.missing.invoke(state) + + return node + + +def nested_def_global() -> Any: + """A global named only in a nested code object: out of reach, as before.""" + + def node(state: State) -> Any: + def inner() -> Any: + return MODULE_GRAPH.invoke(state) + + return inner() + + return node + + +def graph_in_plain_list() -> Any: + def node(state: State) -> Any: + return GRAPH_IN_PLAIN_LIST[0].invoke(state) + + return node + + +def bound_method_self() -> Any: + return METHOD_HOLDER.as_node + + +@pytest.mark.parametrize( + ("factory", "expected"), + [ + (closure_capture, "closure"), + (module_global, "module_global"), + (attribute_chain, "attr_chain"), + (nested_def_captured_attribute, "nested_captured"), + (unreachable_branch, "unreachable"), + (wrapper_referencing_nothing, "via_wrapped"), + (captured_list_subclass, "list_subclass"), + (empty_closure_cell, "beside_empty_cell"), + (sourceless, "sourceless"), + (async_node, "module_global"), + # Shapes no reference chain reaches: a subscript, an instance attribute + # of `self`, a global named only in a nested scope, and an attribute + # path the compiler dropped. + (no_subgraph, None), + (recombined_names, None), + (broken_attribute_chain, None), + (nested_def_global, None), + (graph_in_plain_list, None), + (bound_method_self, None), + (unreachable_attribute_chain, None), + ], + ids=lambda value: value.__name__ if callable(value) else str(value), +) +def test_subgraph_detection(factory: Any, expected: str | None) -> None: + assert _detect(factory()) == expected + + +@pytest.mark.parametrize( + "candidate", + [functools.partial(lambda state, extra: {"log": [extra]}, extra="x"), len], + ids=["partial", "builtin"], +) +def test_callables_without_a_code_object_are_handled(candidate: Any) -> None: + assert get_function_nonlocals(candidate) == []