GeezerVison is showing github.com — Replace `once_cell` with `std::sync::OnceLock`/`core::cell::OnceCell` by youknowone · Pull Request #7077 · RustPython/RustPython
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youknowone
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Feb 11, 2026
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edited by coderabbitai
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- Replace
once_cell::sync::{Lazy, OnceCell} with std::sync::{LazyLock, OnceLock}
- Replace
once_cell::unsync::{Lazy, OnceCell} with core::cell::{LazyCell, OnceCell}
- Inline
get_or_try_init at call sites (unstable in std as of 1.93)
- Replace
OnceCell::with_value() with OnceCell::from() in codecs.rs
- Remove
once_cell direct dependency from common and vm crates
Summary by CodeRabbit
- Chores
- Removed an external dependency and refactored internal lazy initialization patterns throughout the codebase.
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- Replace `once_cell::sync::{Lazy, OnceCell}` with
`std::sync::{LazyLock, OnceLock}`
- Replace `once_cell::unsync::{Lazy, OnceCell}` with
`core::cell::{LazyCell, OnceCell}`
- Inline `get_or_try_init` at call sites (unstable in std as of 1.93)
- Replace `OnceCell::with_value()` with `OnceCell::from()` in codecs.rs
- Remove `once_cell` direct dependency from common and vm crates
coderabbitai
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commented
Feb 11, 2026
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edited
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📝 Walkthrough
Walkthrough
The PR removes the once_cell crate dependency from the project by migrating to standard library equivalents: std::sync::LazyLock/OnceLock for threading contexts and core::cell::LazyCell/OnceCell for non-threaded contexts. Implementation details across multiple VM and common modules are updated to use explicit lazy initialization patterns.
Changes
| Cohort / File(s) |
Summary |
Dependency Removals
Cargo.toml, crates/common/Cargo.toml, crates/vm/Cargo.toml |
Removed once_cell dependencies from workspace and crate manifests. |
Lock Module Reexports
crates/common/src/lock.rs |
Updated public re-exports to alias stdlib types: LazyLock as Lazy and OnceLock as OnceCell (threaded), or LazyCell as Lazy and OnceCell (non-threaded), replacing once_cell crate references. |
Static Cell Implementation
crates/common/src/static_cell.rs |
Replaced get_or_try_init delegation with explicit initialization: check for existing value via get(), compute if absent, store via set(), and return reference. |
VM Lazy Initialization
crates/vm/src/builtins/function.rs, crates/vm/src/builtins/memory.rs, crates/vm/src/codecs.rs, crates/vm/src/stdlib/os.rs |
Replaced get_or_try_init closures with explicit check-compute-cache patterns using get() and set() calls. Updated initialization of exception cells to use From-based construction instead of with_value. |
Estimated code review effort
🎯 3 (Moderate) | ⏱️ ~25 minutes
Possibly related PRs
Poem
🐰 The once\_cell is gone, hooray, hooray!
We've swapped the crate for stdlib's way
LazyLock and OnceLock now take the stage
Explicit get and set fill every page
Built-in types, no external cage! ✨
🚥 Pre-merge checks | ✅ 2 | ❌ 1
❌ Failed checks (1 warning)
| Check name |
Status |
Explanation |
Resolution |
| Docstring Coverage |
⚠️ Warning |
Docstring coverage is 45.45% which is insufficient. The required threshold is 80.00%. |
Write docstrings for the functions missing them to satisfy the coverage threshold. |
✅ Passed checks (2 passed)
| Check name |
Status |
Explanation |
| Description Check |
✅ Passed |
Check skipped - CodeRabbit’s high-level summary is enabled. |
| Title check |
✅ Passed |
The title accurately summarizes the main change: replacing the once_cell crate with standard library equivalents (std::sync::OnceLock and core::cell::OnceCell). |
✏️ Tip: You can configure your own custom pre-merge checks in the settings.
✨ Finishing touches
🧪 Generate unit tests (beta)
- Create PR with unit tests
- Post copyable unit tests in a comment
No actionable comments were generated in the recent review. 🎉
🧹 Recent nitpick comments
crates/common/src/static_cell.rs (1)
30-40: Threading variant: f() may be invoked concurrently by multiple threads.
Unlike OnceLock::get_or_try_init (which blocks competing callers), this manual get/set pattern allows multiple threads to evaluate f() simultaneously, discarding all but the winner's result. This is functionally safe but differs from the previous once_cell behavior which serialized initialization. If f() is expensive or has side effects, callers should be aware.
Given this is an accepted trade-off for avoiding unstable APIs, just flagging for awareness.
Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.
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Code has been automatically formatted
The code in this PR has been formatted using:
cargo fmt --all
Please pull the latest changes before pushing again:
git pull origin once-cell |
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youknowone
added a commit
to youknowone/RustPython
that referenced
this pull request
Mar 22, 2026
…RustPython#7077)
* Replace `once_cell` with `std::sync::OnceLock`/`core::cell::OnceCell`
- Replace `once_cell::sync::{Lazy, OnceCell}` with
`std::sync::{LazyLock, OnceLock}`
- Replace `once_cell::unsync::{Lazy, OnceCell}` with
`core::cell::{LazyCell, OnceCell}`
- Inline `get_or_try_init` at call sites (unstable in std as of 1.93)
- Replace `OnceCell::with_value()` with `OnceCell::from()` in codecs.rs
- Remove `once_cell` direct dependency from common and vm crates
* Auto-format: cargo fmt --all
---------
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
youknowone
added a commit
that referenced
this pull request
Sep 16, 2026
…#7077)
* Replace `once_cell` with `std::sync::OnceLock`/`core::cell::OnceCell`
- Replace `once_cell::sync::{Lazy, OnceCell}` with
`std::sync::{LazyLock, OnceLock}`
- Replace `once_cell::unsync::{Lazy, OnceCell}` with
`core::cell::{LazyCell, OnceCell}`
- Inline `get_or_try_init` at call sites (unstable in std as of 1.93)
- Replace `OnceCell::with_value()` with `OnceCell::from()` in codecs.rs
- Remove `once_cell` direct dependency from common and vm crates
* Auto-format: cargo fmt --all
---------
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
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