[ty] Fix non-determinism in ConstraintSet.specialize_constrained by dcreager · Pull Request #21744 · astral-sh/ruff (original) (raw)

dcreager added internal

An internal refactor or improvement

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Multi-file analysis & type inference

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Dec 1, 2025

Base automatically changed from dcreager/fire-display to main

December 2, 2025 08:17

• origin/main: [ty] Improve @override, @final and Liskov checks in cases where there are multiple reachable definitions (#21767) [ty] Extend invalid-explicit-override to also cover properties decorated with @override that do not override anything (#21756) [ty] Enable LRU collection for parsed module (#21749) [ty] Support typevar-specialized dynamic types in generic type aliases (#21730) Add token based parenthesized_ranges implementation (#21738) [ty] Default-specialization of generic type aliases (#21765) [ty] Suppress false positives when dataclasses.dataclass(...)(cls) is called imperatively (#21729) [syntax-error] Default type parameter followed by non-default type parameter (#21657) new module for parsing ranged suppressions (#21441) [ty] type[T] is assignable to an inferable typevar (#21766) Fix syntax error false positives for await outside functions (#21763) [ty] Improve diagnostics for unsupported comparison operations (#21737) Move Token, TokenKind and Tokens to ruff-python-ast (#21760) [ty] Don't confuse multiple occurrences of typing.Self when binding bound methods (#21754) Use our org-wide Renovate preset (#21759) Delete my-script.py (#21751) [ty] Move all_members, and related types/routines, out of ide_support.rs (#21695)

dcreager deleted the dcreager/nondeterminism branch

December 3, 2025 15:19

dcreager added a commit that referenced this pull request

Dec 3, 2025

• origin/main: [ty] Reachability constraints: minor documentation fixes (#21774) [ty] Fix non-determinism in ConstraintSet.specialize_constrained (#21744) [ty] Improve @override, @final and Liskov checks in cases where there are multiple reachable definitions (#21767) [ty] Extend invalid-explicit-override to also cover properties decorated with @override that do not override anything (#21756) [ty] Enable LRU collection for parsed module (#21749) [ty] Support typevar-specialized dynamic types in generic type aliases (#21730) Add token based parenthesized_ranges implementation (#21738) [ty] Default-specialization of generic type aliases (#21765) [ty] Suppress false positives when dataclasses.dataclass(...)(cls) is called imperatively (#21729) [syntax-error] Default type parameter followed by non-default type parameter (#21657)

dcreager added a commit that referenced this pull request

Dec 9, 2025

#21744 fixed some non-determinism in our constraint set implementation by switching our BDD representation from being "fully reduced" to being "quasi-reduced". We still deduplicate identical nodes (via salsa interning), but we removed the logic to prune redundant nodes (one with identical outgoing true and false edges). This ensures that the BDD "remembers" all of the individual constraints that it was created with.

However, that comes at the cost of creating larger BDDs, and on #21551 that was causing performance issues. scikit-learn was producing a function signature with dozens of overloads, and we were trying to create a constraint set that would map a return type typevar to any of those overload's return types. This created a combinatorial explosion in the BDD, with by far most of the BDD paths leading to the never terminal.

This change updates the quasi-reduction logic to prune nodes that are redundant because both edges lead to the never terminal. In this case, we don't need to "remember" that constraint, since no assignment to it can lead to a valid specialization. So we keep the "memory" of our quasi-reduced structure, while still pruning large unneeded portions of the BDD structure.

Pulling this out of #21551 for separate review.

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