PyTorch Dynamo fixes set() keyword arg bug causing silent errors

PyTorch's Dynamo compiler, which accelerates PyTorch models by tracing and compiling Python code, had a subtle compatibility bug in its handling of set() and frozenset() constructors. In CPython, calling set(a=1) (keyword argument) or set().__init__(a=1) directly raises a TypeError because these constructors do not accept keyword arguments. However, under Dynamo, the keyword argument check was placed inside an early-return block that only executed when no positional arguments were supplied. This meant that set(a=1) with zero positional args bypassed the check entirely and silently created an empty set, breaking Python's language contract. The bug also affected frozenset and subclass constructors, potentially leading to hard-to-debug silent failures in Dynamo-compiled code.

The fix, submitted as PR #189051 by guilhermeleobas, simply moves the keyword argument validation (raising TypeError) before the positional argument count logic in both the call_set and call_frozenset functions. This reuses the existing error handling path already used for the case of more than one positional argument – no new error routing was needed. The change ensures that set() and frozenset() constructors behave identically to CPython in all cases: valid constructions (set(), set(iterable), and the >1-positional-args TypeError) remain unchanged, while invalid keyword arguments now correctly raise TypeError. The fix was tested against CPython 3.13's test_set.py (623 tests passed) and Dynamo's own test_sets.py, all passing with no new issues. Interestingly, the PR was authored with the help of an AI assistant, highlighting the growing role of AI in code maintenance.