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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Fix deprecated constant and method usage in `host_env` and `vm` crates.","articleBody":"While compiling RustPython (specifically `rustpython-host_env v0.5.0` and the `vm` crate), several deprecation warnings are emitted. While these do not currently break the build, they introduce technical debt, clutter CI logs, and pose potential stability and portability risks if left unaddressed.\n\n## Context \u0026 Compiler Output\nThe following warnings are generated during compilation:\n\n**1. `libc::RLIM_NLIMITS` deprecation in `host_env`**\n```text\nwarning: use of deprecated constant `libc::RLIM_NLIMITS`: Not stable across OS versions\n  --\u003e crates/host_env/src/resource.rs:11:15\n   |\n11 | pub use libc::RLIM_NLIMITS;\n   |               ^^^^^^^^^^^^\n```\n\n**2. `Atomic::fetch_update` deprecation in `vm`**\n```text\nwarning: use of deprecated method `rustpython_common::atomic::Atomic::\u003cu32\u003e::fetch_update`: renamed to `try_update` for consistency\n  --\u003e crates/vm/src/builtins/function.rs:90:10\n   |\n90 | ...   .fetch_update(Relaxed, Relaxed, |v| (v != 0)...\n   |        ^^^^^^^^^^^^\n\nwarning: use of deprecated method `rustpython_common::atomic::Atomic::\u003cu64\u003e::fetch_update`: renamed to `try_update` for consistency\n  --\u003e crates/vm/src/builtins/type.rs:683:14\n   |\n683| ...   .fetch_update(Ordering::AcqRel, Ordering::A...\n   |        ^^^^^^^^^^^^\n```\n\n## Risks Involved\n\n### 1. Cross-Platform Instability (`RLIM_NLIMITS`)\nThe `libc` crate explicitly marks `RLIM_NLIMITS` as deprecated because **it is not stable across OS versions**. The number of resource limits (`RLIMIT_*`) varies between different operating systems and even across different versions of the same OS (e.g., Linux kernel updates). \n* **Risk:** Relying on this constant as a boundary for iterating over resource limits can lead to out-of-bounds errors, incorrect resource limit calculations, or panics when RustPython is compiled for or run on newer/older OS versions. It severely hinders cross-platform reliability.\n\n### 2. Codebase Confusion and Future Breakage (`fetch_update`)\nThe internal `rustpython_common::atomic::Atomic` wrapper renamed `fetch_update` to `try_update` for API consistency (likely to avoid confusion with the standard library's `std::sync::atomic::Atomic*::fetch_update`).\n* **Risk:** While currently just a warning, keeping deprecated methods in the codebase causes \"warning fatigue\" in CI. If the deprecated `fetch_update` method is eventually removed from `rustpython_common` in a future minor release, it will cause hard compilation failures. Furthermore, it confuses contributors who might look up the standard library's `fetch_update` and expect it to behave identically to the custom wrapper.\n\n## Proposed Solutions\n\n### Fix 1: Replace `RLIM_NLIMITS` in `crates/host_env/src/resource.rs`\nInstead of exporting or using `RLIM_NLIMITS` as a generic upper bound, we should handle resource limits dynamically or use explicit constants.\n* **Action:** Investigate how `RLIM_NLIMITS` is being used in `resource.rs`. If it's used to iterate over all possible limits, refactor the code to use an explicit array of supported `RLIMIT_*` constants for the target OS, or use conditional compilation (`#[cfg(target_os = \"...\")]`) to handle OS-specific maximums safely. Remove the `pub use libc::RLIM_NLIMITS;` export.\n\n### Fix 2: Rename `fetch_update` to `try_update` in `vm`\nThis is a straightforward find-and-replace to align with the updated `rustpython_common` API.\n* **Action:** Update the method calls in the following files:\n  * `crates/vm/src/builtins/function.rs` (Line 90)\n  * `crates/vm/src/builtins/type.rs` (Line 683)\n\n**Example diff for `function.rs`:**\n```diff\n-         .fetch_update(Relaxed, Relaxed, |v| (v != 0).then(|| v.wrapping_add(1)))\n+         .try_update(Relaxed, Relaxed, |v| (v != 0).then(|| v.wrapping_add(1)))\n```\n\n**Example diff for `type.rs`:**\n```diff\n-             .fetch_update(Ordering::AcqRel, Ordering::Acquire, |old| {\n+             .try_update(Ordering::AcqRel, Ordering::Acquire, |old| {\n```\n\n## Action Items\n- [ ] Refactor `crates/host_env/src/resource.rs` to remove reliance on `libc::RLIM_NLIMITS`.\n- [ ] Rename `fetch_update` to `try_update` in `crates/vm/src/builtins/function.rs`.\n- [ ] Rename `fetch_update` to `try_update` in `crates/vm/src/builtins/type.rs`.\n- [ ] Run `cargo build` and `cargo test` to ensure no regressions and verify that the deprecation warnings are gone.","author":{"url":"https://github.com/human-on-vm","@type":"Person","name":"human-on-vm"},"datePublished":"2026-07-17T01:04:42.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/8297/RustPython/issues/8297"}