fix(custom): lazy exec_globals in validate.prepare_global_scope - #12786
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ogabrielluiz merged 5 commits intoMay 6, 2026
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Rewrites prepare_global_scope to build a LazyImportProxy-backed globals mapping instead of eagerly calling importlib.import_module() for every langchain_* name in the prepended DEFAULT_IMPORT_STRING. Components that do not reference a given langchain symbol no longer trigger its import, cutting transformers/torch off the component-instantiation path. Narrowed scope: only langchain / langchain_core / langchain_classic / langchain_text_splitters / langchain_community prefixes are deferred. Everything else (stdlib, pydantic, lfx) resolves eagerly so class-body validators get concrete values.
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- Replace `_resolved = None` cache sentinel with `_UNSET = object()` so a legitimately-resolved `None` is no longer mistaken for an empty cache. - Add `logger.exception` around `_LazyImportProxy._resolve()` so deferred import failures get attributable log context (the traceback otherwise points at the user's first usage site, not the originating import). - Capture `last_error` per candidate in the module-binding fallback loop and re-raise it (mirroring `_eager_import_from`) instead of re-importing the canonical name, so the error names the package that actually failed. - `_LazyExecGlobals.copy()` now returns `_LazyExecGlobals` rather than a plain `dict`, so the marker type survives common dict idioms. - Honor `alias.asname` in `_handle_module_attributes` (`from X import Y as Z` was binding `Y` instead of `Z` on the eager path). - Expand `from X import *` to the module's public surface (`__all__` or non-underscore `dir()`); previously raised `ImportError` because `*` was treated as a literal attribute name. - Strip internal planning vocabulary from comments / docstrings; fix stale claims (sorts-into-three-lists, 3-arg exec example, "pre-populated" on `_LazyExecGlobals.__init__`); add WHY comments on `__mro_entries__`, `object.__setattr__` use, `__repr__` non-resolution, and the explicit- dunders block. Clarify that `__instancecheck__` / `__subclasscheck__` only fire when the proxy is the right-hand side. Tests: add `TestLazyExecGlobalsBinding` (10) + `TestLazyImportProxyResolution` (3) covering prefix-narrowing, asname binding (lazy + eager), star-import expansion, mixed lazy+eager on a single import node, `__repr__` non- resolution, `ModuleNotFoundError` surfacing, and resolution caching. Also revert accidental `langchain_openai` 1.1.13 -> 1.1.12 downgrade in two starter project JSONs (autofix.ci noise unrelated to this PR).
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May 6, 2026 16:59
ogabrielluiz
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Sub-PR #12786 removed DEFAULT_IMPORT_STRING auto-injection and added an actionable NameError hint as compensation. The runtime NameError handler in create_class only fired for class-body references; the common case (symbol referenced inside def build(), def run(), etc.) compiled silently and crashed at runtime with no guidance. Adds a static analysis pass _check_function_body_name_resolution that walks every FunctionDef / AsyncFunctionDef inside every ClassDef in the parsed module and raises ValueError (same actionable hint as the runtime path) when it sees a free Name reference that is not in exec_globals, function locals, or builtins, AND that the legacy / langchain hint tables can map to a known import. Names with no hint entry are passed through silently to avoid false positives on graph-level runtime-injected globals. Refactors the inline hint logic into _resolve_import_module_for_name and _format_undefined_name_message so both the static and runtime paths phrase the fix identically. Adds an except ValueError: raise branch in create_class so deliberately-raised ValueErrors reach the caller unchanged. Refs: LE-1229.
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…ort_graph QA Bug 3 flagged that test_import_graph.py and the TestLazyValidateExecGlobals class were referenced by the original sub-PR descriptions (#12785, #12786) but absent from the consolidation branch, leaving a regression-coverage gap on the two centerpieces of the cold-start refactor. TestLazyValidateExecGlobals (appended to test_import_absence.py): - _LazyExecGlobals is a dict subclass usable as exec globals - .copy() preserves the marker type (the dict.copy() default would silently strip it and break the laziness contract on nested execs) - prepare_global_scope returns _LazyExecGlobals regardless of imports - langchain imports bind _LazyImportProxy and do NOT touch sys.modules - non-langchain imports stay eager and resolve to real module objects test_import_graph.py (new file, mirrors test_import_absence.py subprocess pattern): - Graph class import stays clean of langchain_core, langchain_classic, langchain_text_splitters, langchain_community, transformers, and torch - Graph payload helpers stay clean - Empty Graph instantiation stays clean - Vertex module import stays clean All 5 + 4 tests run green under uv sync inside src/lfx. Refs: LE-1229 QA Bug 3 (2026-05-18).
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Summary
Rewrites
prepare_global_scopeinlfx/custom/validate.pyto deferlangchain_*imports until the component class body actually references them. Components that do not useAgentExecutor(or similar) no longer trigger thelangchain_classic.agents->transformers->torchchain during instantiation.Scope
src/lfx/src/lfx/custom/validate.py:_LazyImportProxy+_LazyExecGlobals(dict)types;prepare_global_scopebuilds the lazy mapping instead of eagerly callingimportlib.import_module()per import nodelangchain_*prefixes so pydantic-validated imports (e.g., string constants) stay eager_MissingModulePlaceholderpath + star-import eager behaviorsrc/lfx/tests/unit/test_import_absence.py:TestLazyValidateExecGlobals— subprocess-isolated asserts thatvalidate.prepare_global_scopedoes not eagerly importlangchain_classic.agentsuntil a name from that module is accessedWhy
Discovered during cold-start snapshot measurement: every
lfx runinvocation was failing withAttributeError: partially initialized module 'torch' has no attribute 'library' (most likely due to a circular import)because the eager langchain_classic chain pulled transformers -> torch and hit a known torch 2.x partial-init bug. The lazy rewrite bypasses the chain entirely for components that do not need it, and makes everylfx runinvocation pay only for what the component actually uses — a structural cold-start win, not just a bug fix.Stacked on
PR #12785 (import-time deferrals) → #12784 (component index) → #12783 (measurement harness)
Test plan
cd src/lfx && uv run pytest tests/unit/test_import_absence.py::TestLazyValidateExecGlobals -vLFX_BENCHMARK_CHECKPOINTS=1 uv run lfx run src/backend/tests/benchmarks/fixtures/noop_flow.json --format text— exits cleanly without the torch AttributeError