v0.13.0

kache 0.13.0 — keying the env vars a proc-macro reads, and calmer prefetch

kache is a content-addressed build cache that plugs in as a RUSTC_WRAPPER (and a C/C++ compiler wrapper). 0.13.0 closes a subtle cache-key soundness hole around proc macros, makes speculative prefetching opt-in and cost-aware, and sharpens a couple of diagnostics.

Why

rustc only records an env var in its dep-info when a crate reads it through env! / option_env!. But a proc macro that calls std::env::var while expanding leaves no trace at all — the command line, the source hashes, and the --extern set are byte-identical whether or not the var is set, yet the emitted artifact differs. So both compiles computed the same key, and the second one restored the first one's expansion: a silent wrong hit. Separately, speculative remote indexing had been eager by default, doing work that wasn't always worth it.

What's new

• Env vars that steer proc-macro expansion are now keyed. kache accounts for the environment a proc macro can read during expansion, so a build that changes such a var no longer restores a stale expansion from a byte-identical command line.
• Speculative remote indexing is opt-in. The prefetch planner no longer indexes the remote speculatively by default; when prefetch does run, it ranks candidates by cost and urgency and caps weak sources rather than warming everything it can see.
• A build-coalescing race is closed, and restored custom-harness test binaries keep their executable bit.
• Clearer diagnostics. why-miss now joins its cascade walk by compilation unit rather than crate name (so it doesn't confuse two units that share a crate name), and clean / gc detect reflinked sharing and explain when an eviction frees no space because the bytes are still shared.
• Packaging. A kache-git AUR package plus config-driven multi-package AUR publishing.

These notes were drafted with LLM assistance and edited by the maintainers (@jleni, @emmanuelm41).

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What's Changed

• feat(aur): add kache-git + config-driven multi-package aur publishing by @emmanuelm41 in #637
• ci(aur): use the real AUR account name (kunobi) as commit author by @emmanuelm41 in #638
• test(core): add planner ordering properties by @jleni in #643
• fix(why-miss): join the cascade walk by compilation unit, not crate name (#627) by @jleni in #642
• feat(prefetch): rank candidates by cost and urgency, cap weak sources (#616, #617) by @jleni in #640
• fix(key): key env vars that steer proc-macro expansion (#635) by @jleni in #639
• fix(clean,gc): detect reflinked sharing and explain empty evictions (#602, #509) by @jleni in #641
• fix: close build coalescing race by @alecthomas in #646
• test(wrapper): mutation-test the coalesced-restore diagnostics replay by @emmanuelm41 in #653
• fix(restore): keep the executable bit on custom-harness test binaries by @glebpom in #648
• feat(prefetch): make speculative remote indexing optional by @jmagar in #649

New Contributors

• @alecthomas made their first contribution in #646
• @glebpom made their first contribution in #648
• @jmagar made their first contribution in #649

Full Changelog: v0.12.0...v0.13.0