Support frozenset literal constants without a VirtualMachine by 1ndahous3 · Pull Request #8823 · RustPython/RustPython · GitHub

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Summary

PyObjBag::make_constant's Frozenset arm was unimplemented!(), panicking any embedder that calls ctx.new_code() directly on a script with a frozenset literal - this adds a VM-free path to build one correctly instead.

String and bytes constants share the process-wide hash secret with runtime objects, including construction before the first interpreter. Slice and code elements use structural hashes and equality, preserving duplicate elimination and membership for nested constants.

Known limitations

When VM-free constant hashing initializes the process hash secret before the first interpreter, the secret is random; later Settings.hash_seed values do not replace it.

AI assistance

Written with Claude Code (claude-sonnet-5): design research, implementation, and testing were AI-assisted end to end, reviewed by a human before submission.

Follow-up changes written with Codex (GPT-6), reviewed by a human before submission.

Summary by CodeRabbit

Bug Fixes
- Improved handling of frozenset constants, including constants containing nested slices and code objects.
- Frozenset constants now use equality and hashing consistent with runtime frozensets, helping avoid mismatches when values collide or are equivalent.
- Hash behavior is consistent when constants are processed before an interpreter is initialized.

Assisted-by: Claude Code:claude-sonnet-5

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Reviewing files that changed from the base of the PR and between cdc9834 and 727d282.

📒 Files selected for processing (5)

crates/vm/src/builtins/code.rs
crates/vm/src/builtins/set.rs
crates/vm/src/builtins/slice.rs
crates/vm/src/vm/interpreter.rs
crates/vm/src/vm/mod.rs

🚧 Files skipped from review as they are similar to previous changes (1)

crates/vm/src/vm/interpreter.rs

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📝 Walkthrough

Walkthrough

Compile-time frozenset constants can now be built without a VirtualMachine. The change adds structural hashing and equality for supported constants, no-VM insertion paths for prehashed set elements, and tests for constant construction and hash agreement with runtime frozensets.

Changes

Context-only frozenset constants

Layer / File(s)	Summary
Constant hashing and equality crates/vm/src/builtins/code.rs, crates/vm/src/builtins/slice.rs, crates/vm/src/vm/mod.rs, crates/vm/src/vm/interpreter.rs	Structural hashing and equality cover supported constants. Code metadata and slice hashing are shared with runtime operations. Hash-secret initialization returns the process-wide secret to VM-free hash callers.
Prehashed set and dictionary storage crates/vm/src/dict_inner.rs, crates/vm/src/builtins/set.rs	Dictionary lookup and insertion accept supplied hashes and equality callbacks. Frozen-set construction inserts prehashed elements through these paths.
Frozenset constant construction and tests crates/vm/src/builtins/code.rs	PyObjBag builds frozenset constants without a VirtualMachine. Tests cover supported values, nested constants, hash agreement with runtime frozensets, and hash-secret initialization order.

Priority: ⬇️ Low

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant PyObjBag
  participant const_hash
  participant PyFrozenSet
  participant PySetInner
  participant Dict
  PyObjBag->>const_hash: Hash recursively created elements
  PyObjBag->>PyFrozenSet: Pass prehashed elements and const_eq
  PyFrozenSet->>PySetInner: Build from constant elements
  PySetInner->>Dict: Insert using hashes and equality callback

Suggested reviewers: youknowone

Merge Risk: ⚪ Minimal · up to 727d2

The reported custom-seed membership mismatch is resolved at this head; no remaining issue identified here blocks merging after normal checks.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 727d2

The reviewed construction path retains normal frozenset storage and runtime behavior, with no demonstrated security bypass. The remaining design risk is that hashing a constant before interpreter creation can choose the process-wide hash seed ahead of the interpreter’s configuration.

Retained concerns

Low · architecture · observed: Context-only hashing of string or bytes frozenset elements can initialize the process-wide hash secret before an interpreter, causing a subsequently configured interpreter hash seed to be ignored. The observed fallback is random; no reduction in secret strength is established.

Security review details

Security Blast Radius

observed — Hash-secret initialization is process-wide: the first VM-free constant hash or interpreter initialization fixes the value used by later interpreters in that process.

Trust Boundaries and Controls

observed — Prehashed insertion is internal to the VM crate and its reviewed caller supplies hashes and structural equality for newly materialized constants. Subsequent frozenset membership and hashing retain VM-aware operations.

Resilience and Maintainability Implications

inferred — The constructor builds a fresh set before returning it, so an interrupted construction does not expose a partially populated frozenset through this return path. Storage retries stale probes, and the existing frozen-set hash cache uses atomic publication.

Hardening Proposals

proposed — Document the first-initializer rule for embedders that require a configured hash seed, or provide a way for such hosts to initialize it before context-only constant construction.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 55.88% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 34 functions across 8 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: adding support for constructing frozenset literal constants without a VirtualMachine.

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Actionable comments posted: 2

🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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Inline comments:
In `@crates/vm/src/builtins/code.rs`:
- Around line 340-386: Update const_eq to compare PyComplex values structurally
and numerically against other PyComplex values and zero-imaginary PyInt,
PyFloat, and PyBool values. Include PyBool through the existing integer
comparison path so equal numeric constants are recognized in frozensets.

In `@crates/vm/src/vm/context.rs`:
- Line 430: Update Context construction so its HashSecret matches the
VirtualMachine hash secret used for membership lookups; ensure
PyObjBag::make_constant and Context::new_code use that shared secret when
computing constant hashes.

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📒 Files selected for processing (5)

crates/common/src/hash.rs
crates/vm/src/builtins/code.rs
crates/vm/src/builtins/set.rs
crates/vm/src/dict_inner.rs
crates/vm/src/vm/context.rs

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Actionable comments posted: 1

🪄 Fix CodeRabbit comments on this PR

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Inline comments:
In `@crates/vm/src/builtins/code.rs`:
- Around line 368-388: Update the complex-versus-integer comparison in
`const_eq` to preserve the integer operand and compare it with the complex real
part using `float_ops::eq_int`, rather than converting the integer to `f64`.
Keep float comparisons against `c.re` and return false when the complex
imaginary part is nonzero.

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📒 Files selected for processing (2)

crates/vm/src/builtins/code.rs
crates/vm/src/dict_inner.rs

🚧 Files skipped from review as they are similar to previous changes (1)

crates/vm/src/dict_inner.rs

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i need to look around a few thinigs to review this. it will take time. thank you for your patient

Assisted-by: Codex:GPT-6

Thank you so much for this. I investigated this problem, and concluded #8867 will fit better. This was helpful to understand the situation.

Support frozenset literal constants without a VirtualMachine

de67f1f

Assisted-by: Claude Code:claude-sonnet-5

coderabbitai Bot reviewed Sep 25, 2026

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Comment thread crates/vm/src/builtins/code.rs Outdated

Comment thread crates/vm/src/vm/context.rs Outdated

formatting + fixes

f38d6de

coderabbitai Bot reviewed Sep 25, 2026

View reviewed changes

Comment thread crates/vm/src/builtins/code.rs Outdated

1ndahous3 added 2 commits September 26, 2026 00:06

compute hash secrets lazily with the VM secret

3f6d33c

fix complex-versus-integer comparisons

cdc9834

1ndahous3 added 2 commits September 27, 2026 12:30

Merge main and align frozenset constant hashing

6d23d5a

Assisted-by: Codex:GPT-6

Handle slice and code in VM-free frozenset constants

727d282

Assisted-by: Codex:GPT-6

youknowone mentioned this pull request Sep 27, 2026

Materialize code constants through the VM #8867

Merged

1 task done

youknowone closed this in #8867 Oct 2, 2026

Support frozenset literal constants without a VirtualMachine by 1ndahous3 · Pull Request #8823 · RustPython/RustPython · GitHub

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Support frozenset literal constants without a VirtualMachine - #8823

Support frozenset literal constants without a VirtualMachine#8823
1ndahous3 wants to merge 6 commits into
RustPython:mainfrom
1ndahous3:frozenset_constants

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Support frozenset literal constants without a VirtualMachine by 1ndahous3 · Pull Request #8823 · RustPython/RustPython · GitHub

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Support frozenset literal constants without a VirtualMachine - #8823

Support frozenset literal constants without a VirtualMachine#88231ndahous3 wants to merge 6 commits intoRustPython:mainRustPython/RustPython:mainfrom 1ndahous3:frozenset_constants1ndahous3/RustPython:frozenset_constantsCopy head branch name to clipboard

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Summary

Known limitations

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Sequence Diagram(s)

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Support frozenset literal constants without a VirtualMachine#8823
1ndahous3 wants to merge 6 commits into
RustPython:mainfrom
1ndahous3:frozenset_constants

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