feat(capi): implement slice C-API methods by krosci · Pull Request #8924 · RustPython/RustPython

krosci · 2026-10-01T10:15:56Z

Implement missing Limited API / abi3 slice functions in crates/capi/src/sliceobject.rs:

PySlice_Check
PySlice_GetIndices
PySlice_GetIndicesEx

Resolves parts of #8156 (under Include/sliceobject.h).

Summary by CodeRabbit

New Features
- Added C API support for checking slice objects and retrieving slice indices. Slice indices are adjusted according to the sequence length and step direction, and callers can obtain the resulting slice length. Invalid bounds, zero steps, and conversion errors are reported through the API’s error return behavior. These additions make slice operations available to applications using the C API.

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crates/capi/src/sliceobject.rs

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crates/capi/src/sliceobject.rs

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📝 Walkthrough

Walkthrough

The change adds PySlice_Check, PySlice_GetIndices, and PySlice_GetIndicesEx, with tests for slice construction and index calculations. It also simplifies closure calls and return placement, and removes a lint expectation in four standard-library modules.

Changes

Slice C API

Layer / File(s)	Summary
Slice checks, index APIs, and tests `crates/capi/src/sliceobject.rs`	Adds `PySlice_Check`, `PySlice_GetIndices`, and `PySlice_GetIndicesEx`. Tests cover slice construction, index adjustment, bounds, negative steps, and zero steps.

Standard-library simplifications

Layer / File(s)	Summary
Closure and control-flow simplifications `crates/vm/src/stdlib/_codecs.rs`, `crates/vm/src/stdlib/_ctypes.rs`, `crates/vm/src/stdlib/builtins.rs`, `crates/vm/src/stdlib/posix.rs`	Passes closures directly to `ok_or_else` and `map`, moves the `hr` return outside an `else` branch, and removes a redundant-else lint expectation.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Feature

Merge Risk: ⚪ Minimal · up to 1c638

This change adds slice C-API functions and small standard-library simplifications. No concrete merge-blocking risk was identified in the supplied context.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 59264

The new slice APIs preserve existing object validation and conversion controls. A legacy error-state compatibility difference may disrupt native caller recovery, but no introduced privilege escalation or concrete exploit path was established. External consumer coverage remains incomplete.

Retained concerns

Low · reliability · inferred: The new legacy PySlice_GetIndices zero-step path sets a ValueError while returning -1, unlike the earlier observed CPython status-only failure. Native callers using that legacy recovery convention could leave an unexpected exception pending across subsequent operations. This is a caller-recovery compatibility risk, not an established security exploit.

Security review details

Security Blast Radius

inferred — The demonstrated exposure is the interpreter process using these native APIs. Effects depend on extension or embedding callers supplying slice objects and consuming returned indices; no concrete external consumer or cross-service attack path was established.

Trust Boundaries and Controls

observed — The index APIs downcast the supplied object to PySlice before conversion. Native object and output-pointer validity remain unsafe caller preconditions; the extended API inherits the existing unpacking helper's required writable output pointers.

Resilience and Maintainability Implications

observed — The POSIX spawn edit preserves signal validation and error propagation before the host spawn operation. The changed HRESULT helper likewise retains its pre-existing negative-result todo! behavior; the edit does not itself add that failure path.

Hardening Proposals

proposed — Document the native pointer, sequence-length, callback-mutation, and exception-recovery preconditions alongside the exported contracts. For resizable collections, clarify when callers should unpack first and obtain the current length after callbacks before adjusting indices.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely identifies the main change: implementing slice C API methods.
Docstring Coverage	✅ Passed	Docstring coverage is 96.30% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 27 functions across 6 files.
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.

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Actionable comments posted: 2

🪄 Fix CodeRabbit comments on this PR

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Inline comments:
Review comments at @crates/capi/src/listobject.rs:
- Line 182: Replace the dynamic `vm.call_method` invocation with the concrete
`PyList` extension operation so list subclasses cannot override the behavior;
add a regression test confirming extension still adds items when the subclass’s
`extend` method is a no-op.

Review comments at @crates/capi/src/sliceobject.rs:
- Line 79: Update PySlice_GetIndices to perform its own index conversion and
bounds checks instead of using PySlice_AdjustIndices, which clips out-of-range
values; return -1 when the stop exceeds the sequence length. Add a regression
test for an out-of-range stop.

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crates/capi/src/listobject.rs
crates/capi/src/sliceobject.rs
crates/capi/src/tupleobject.rs

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bschoenmaeckers · 2026-10-01T12:19:57Z

Both PyList_Clear and PyList_Extend are not part of the limited api. Furthermore your AI hallucinated PyTuple_GetItemRef, this function does not exist.

chatgpt-codex-connector · 2026-10-01T15:09:58Z

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Actionable comments posted: 2

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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
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Inline comments:
Review comments at @crates/capi/src/sliceobject.rs:
- Around line 136-141: Update PySlice_GetIndices to return -1 when stop_val
exceeds length or start_val is equal to or greater than length, and remove the
negative-step lower-bound check. Add a regression test for start equal to
length, preserving CPython-compatible results for negative-step slices.
- Around line 68-144: Update the zero-step branch in PySlice_GetIndices to
return -1 without creating or setting a VM exception; keep the existing handling
for other invalid slice values unchanged.

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📒 Files selected for processing (5)

crates/capi/src/sliceobject.rs
crates/vm/src/stdlib/_codecs.rs
crates/vm/src/stdlib/_ctypes.rs
crates/vm/src/stdlib/builtins.rs
crates/vm/src/stdlib/posix.rs

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crates/vm/src/stdlib/builtins.rs

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Assisted-by: Gemini:gemini-3.7-flash

codspeed · 2026-10-01T19:18:46Z

Merging this PR will not alter performance

✅ 62 untouched benchmarks
⏩ 4 skipped benchmarks¹

_{Comparing krosci:feat/capi-container-methods (b009234) with main (112b7ef)}

4 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

krosci · 2026-10-01T21:20:51Z

Both PyList_Clear and PyList_Extend are not part of the limited api. Furthermore your AI hallucinated PyTuple_GetItemRef, this function does not exist.

Yeah, exactly, I redid it by hand, pretty much like all the others.
Definitely wouldn't do it again; at best it's only good for fixing lint errors.

coderabbitai Bot reviewed Oct 1, 2026

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Comment thread crates/capi/src/listobject.rs Outdated

Comment thread crates/capi/src/sliceobject.rs Outdated

krosci mentioned this pull request Oct 1, 2026

Towards C-extension module loading and C-API ABI expansion #8922

Closed

krosci force-pushed the feat/capi-container-methods branch from 7b19a8c to 2365c95 Compare October 1, 2026 12:29

krosci changed the title ~~feat(capi): implement list, slice, and tuple C-API methods~~ feat(capi): implement slice C-API methods Oct 1, 2026

krosci marked this pull request as draft October 1, 2026 12:30

krosci force-pushed the feat/capi-container-methods branch from 2365c95 to dfe2578 Compare October 1, 2026 12:31

krosci marked this pull request as ready for review October 1, 2026 15:09

krosci force-pushed the feat/capi-container-methods branch from dfe2578 to 5926470 Compare October 1, 2026 15:15

coderabbitai Bot reviewed Oct 1, 2026

View reviewed changes

Comment thread crates/capi/src/sliceobject.rs

Comment thread crates/capi/src/sliceobject.rs Outdated

feat(capi): implement slice C-API methods

b009234

Assisted-by: Gemini:gemini-3.7-flash

krosci force-pushed the feat/capi-container-methods branch from 1c63836 to b009234 Compare October 1, 2026 18:13

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feat(capi): implement slice C-API methods - #8924

feat(capi): implement slice C-API methods#8924
krosci wants to merge 1 commit into
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krosci:feat/capi-container-methods

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