fix(shm): drop cfg_aliases macro, hand-roll build.rs cfg logic

[YuanYuYuan]

Summary

commons/zenoh-shm/build.rs used the cfg_aliases! macro (crate cfg_aliases, pinned to 0.2.1, latest on crates.io) to compute a small set of target-platform boolean flags at build time. That macro's expansion trips rustc's semicolon_in_expressions_from_macros lint, which recently became a hard compile error on current nightly. A 3-line upstream fix exists (katharostech/cfg_aliases#15) but is unreleased. This breaks every nightly CI job (Generate documentation, Coverage (ubuntu-latest, nightly)) on main and every open PR.

Checking actual usage shows shm_external_lockfile is the only alias ever read outside build.rs (9 call sites in src/posix_shm/cleanup.rs and src/shm/unix.rs) — every other alias the macro produced was only an intermediate step in its own alias graph, never queried by any code. So this PR drops the cfg_aliases dependency entirely and computes that one boolean directly from CARGO_CFG_TARGET_OS, no macro, no crate dependency needed. The resulting shm_external_lockfile flag is identical to what the macro produced today (the BSD family, including all Apple targets, plus Redox).

Originally discovered as part of #2678, extracted here since it's an unrelated, pre-existing issue affecting the whole repo.

Key Changes

• commons/zenoh-shm/build.rs: replace cfg_aliases! { ... } with a direct CARGO_CFG_TARGET_OS match computing only shm_external_lockfile. Also drops the cargo:rustc-check-cfg=cfg(apple_targets) / cfg(bsd) declarations — cfg_aliases! mechanically emits cargo:rustc-cfg=... for every alias name in its block, including intermediate composite ones like apple_targets/bsd, not just the final shm_external_lockfile, so those two declarations existed only to describe those extra emissions. Neither is ever read via #[cfg(...)] anywhere in the crate (grep -rn "apple_targets\|\bbsd\b" commons/zenoh-shm/src is empty), and the new script no longer emits them as flags at all — they're just local booleans folded directly into the one matches! — so there's nothing left to declare.
• commons/zenoh-shm/Cargo.toml: remove the now-unused cfg_aliases build-dependency.

---

🏷️ Label-Based Checklist

Based on the labels applied to this PR, please complete these additional requirements:

Labels: bug, dependencies

🐛 Bug Fix Requirements

Since this PR is labeled as a bug fix, please ensure:

• Root cause documented - see "Summary" above: cfg_aliases!'s macro expansion trips rustc's semicolon_in_expressions_from_macros lint, now a hard error on current nightly, with no released crate fix available.
• Reproduction test added - no unit test is meaningful for a build-script/toolchain-lint failure; the reproduction is the existing nightly CI jobs (Generate documentation, Coverage (ubuntu-latest, nightly)) themselves, which already fail on main/any PR without this fix (confirmed on fix(liveliness): decouple send_interest replay from calling thread #2678 before this fix was extracted from it) and are expected to pass once this PR merges.
• Test passes with fix - verified via this PR's own CI run; Generate documentation and Coverage (ubuntu-latest, nightly) are the jobs to watch.
• Regression prevention - the same nightly CI jobs will fail again on any future regression of this build script, same as they did before this fix.
• Fix is minimal - touches exactly one file's build-time cfg logic (commons/zenoh-shm/build.rs) plus removing the now-unused dependency line in commons/zenoh-shm/Cargo.toml; no other files changed, no workspace-root manifest changes.
• Related bugs checked - confirmed via grep -rln "cfg_aliases" --include="Cargo.toml" . that commons/zenoh-shm was the only crate in this workspace depending on cfg_aliases directly; no other crate is affected. Also confirmed via grep -rn "shm_external_lockfile\|apple_targets\|\bbsd\b" commons/zenoh-shm/src that shm_external_lockfile is the only one of the macro's aliases ever read outside build.rs.

Why this matters: Bugs without tests often reoccur.

📦 Dependency Updates

Since this PR removes a dependency (not a version bump or a new dependency):

• Changelog reviewed - N/A, the dependency (cfg_aliases) is removed entirely, not upgraded; there's no new changelog to review.
• Security advisories checked - N/A, removing a dependency only shrinks the attack/advisory surface, never adds to it.
• License compatible - N/A, no new dependency is introduced.
• Tests pass - verified via GitHub Actions CI on this PR; no local toolchain was available to run cargo build/test directly in this session, so CI is the sole verification mechanism.
• Transitive deps reviewed - N/A, no new transitive dependencies are introduced; Cargo.lock's existing cfg_aliases 0.1.1 entry is an unrelated transitive build-dependency of a different external crate, untouched by this change.
• Version pinned appropriately - N/A, no version to pin; the dependency is removed, not versioned.
• Update scope limited - yes, this PR touches exactly one dependency (cfg_aliases, dropped) in exactly one crate (commons/zenoh-shm).

Best practice: Keep dependency updates focused and test thoroughly.

Instructions:

1. Check off items as you complete them (change - [ ] to - [x])
2. The PR checklist CI will verify these are completed

This checklist updates automatically when labels change, but preserves your checked boxes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.30%. Comparing base (e946e58) to head (93d122a).
⚠️ Report is 4 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2680      +/-   ##
==========================================
+ Coverage   74.09%   74.30%   +0.21%     
==========================================
  Files         414      414              
  Lines       62296    62301       +5     
==========================================
+ Hits        46157    46292     +135     
+ Misses      16139    16009     -130     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

[Copilot]

Pull request overview

Removes the cfg_aliases build-dependency from commons/zenoh-shm and replaces the cfg_aliases! { ... } build-time alias graph with a small, direct CARGO_CFG_TARGET_OS-based computation to emit only the shm_external_lockfile cfg flag. This unblocks nightly builds affected by the macro expansion lint becoming a hard error.

Changes:

• Replaced cfg_aliases! usage in commons/zenoh-shm/build.rs with a direct CARGO_CFG_TARGET_OS match to compute and emit shm_external_lockfile.
• Removed the cfg_aliases = "0.2.1" build-dependency from commons/zenoh-shm/Cargo.toml.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
commons/zenoh-shm/build.rs	Hand-rolls build-time cfg emission for shm_external_lockfile without cfg_aliases.
commons/zenoh-shm/Cargo.toml	Drops the now-unused cfg_aliases build-dependency section.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[fuzzypixelz]

@YuanYuYuan this is a fair comment, even if CARGO_CFG_TARGET_OS should be present.

[YuanYuYuan]

Sorry, I missed this since it doesn't show up in the GitHub mobile app. I will address it.