v0.12.0

kache 0.12.0 — pluggable storage backends, and a cache that knows what things cost

kache is a content-addressed build cache that plugs in as a RUSTC_WRAPPER (and a C/C++ compiler wrapper). 0.12.0 opens up where the cache can live (OpenDAL-backed S3 and filesystem remotes), teaches garbage collection what an entry actually costs to rebuild, and makes "why did this miss?" point at the crate that really changed.

Why

Two of the cache's oldest simplifications were starting to hurt. The remote layer was welded to one S3 SDK, so "put the cache on a plain shared filesystem" or "use a different object store" meant a rewrite. And eviction ranked entries purely by size — but on a real 52k-entry store, size correlates only loosely with rebuild cost (log-log 0.73), and the value-per-byte of an entry spans roughly 48x between crates, so size-only eviction throws away expensive-to-rebuild artifacts to keep cheap ones. 0.12.0 fixes both, and sharpens the diagnostics you reach for when a hit you expected turns into a miss.

What's new

• Pluggable remotes via OpenDAL. New S3 and filesystem remotes built on OpenDAL sit alongside the original backend, so the cache can live on a shared filesystem or a non-AWS object store without a bespoke integration — the payoff of the RemoteBackend trait extracted in 0.11.0.
• Cost-aware eviction. GC now indexes each entry's compile_time_ms (already recorded in its metadata) so eviction can weigh what an artifact costs to rebuild, not just how big it is; it also records post-eviction demand via tombstones to learn from what it dropped.
• why-miss points at the real culprit. When one crate's artifact changes, its extern:<name>=<hash> re-keys every crate above it, and the old report blamed all of them equally. why-miss now walks the extern chain to the crate that actually changed, instead of making you trace forty downstream crates by hand.
• Lossless recovery from a corrupt index. The index is derived state — blobs plus each entry's meta.json are the source of truth — so a corrupt index is now quarantined and rebuilt from the store rather than discarded.
• Executables cached by default on Linux. Linux embeds DWARF in the binary, so a restored executable debugs exactly like a freshly linked one; the old skip-by-default was paying a macOS-specific debuggability tax (Mach-O N_OSO) that doesn't apply on Linux.
• Also: a Nix flake (checks, devShell, formatter, module), more cc flags classified so aws-lc-sys TUs cache, and a fix for RUSTSEC-2026-0213 (ammonia).

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

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What's Changed

• fix(bench): tolerate CRLF-ified patch payloads and pin byte-exact checkouts by @jleni in #571
• fix(remote): enforce max_bytes when Content-Length is unavailable by @Ysh204 in #547
• fix(config): expand bare "~" in shellexpand by @Ysh204 in #545
• Update ammonia to 4.1.4 (RUSTSEC-2026-0213) and drop a stale advisory ignore by @jleni in #574
• Add [cache] storage_layout_advice to mute copy-restore layout advisories by @jleni in #573
• ci(package-publish): trigger Scoop bucket autoupdate on release by @emmanuelm41 in #576
• docs: add Scoop (Windows) install instructions by @emmanuelm41 in #575
• ci(package-publish): publish kache to Chocolatey on release by @emmanuelm41 in #577
• docs: add Chocolatey (Windows) install instructions by @emmanuelm41 in #578
• ci(aur): publish official kache-bin to the AUR by @emmanuelm41 in #579
• fix(wrapper): avoid following symlinks for warning marker files by @Ysh204 in #546
• feat(daemon): prefetch P0.5 measurement closure (#583) by @jleni in #584
• In-flight build observability: heartbeat, ETA, stuck detection, miss diagnostics, monitor panel by @jleni in #585
• feat(daemon): experimental daemon-assisted local hits (#565 milestone 1) by @jleni in #587
• Never gate daemon startup on tmutil addexclusion by @jleni in #589
• perf(local-hit): never wait to fill a pin batch by @jleni in #591
• feat: add OpenDAL S3 and filesystem remotes by @jleni in #593
• refactor(gc): decouple eviction selection from removal mechanism by @jleni in #596
• chore(nix): drop flake-utils input by @meskill in #597
• feat(gc): index compile_time_ms so eviction can see rebuild cost by @jleni in #598
• fix(tests): stop leaking ~2 GB target dirs per test run (#599) by @jleni in #601
• fix(remote): never fail a build on remote config, restore legacy prefixes by @jleni in #600
• feat(nix): flake checks, devShell, formatter, and a standalone module by @jleni in #605
• feat(gc): record post-eviction demand via tombstones by @jleni in #604
• feat(cache): cache executables by default on Linux by @jleni in #603
• chore: bump kache to v0.12.0 by @jleni in #612
• feat(why-miss): walk the extern chain to the crate that actually changed (#609) by @jleni in #611
• fix(daemon): claim prefetch keys at download time, not plan install (#613) by @jleni in #621
• fix(cc): classify --include=, -fwrapv and --param so aws-lc-sys TUs cache (#580) by @jleni in #607
• fix(store): cache units whose .rmeta is legitimately empty (#624) by @jleni in #625
• feat(store): warn when the cache dir is not on host-local storage (#415 Part A) by @jleni in #623
• fix(prefetch): merge planner sources; stop inferring whole-bucket warms (#614, #615) by @jleni in #622
• fix(e2e): enforce gate integrity by @jleni in #628
• feat(store): rebuild the index from the store after corruption (#415) by @jleni in #630
• feat(report): surface compiles that failed to store (#629) by @jleni in #632
• feat(prefetch): bound a plan by keys, bytes, and time (#616 stage 1) by @jleni in #633
• test: add staged mutation testing by @jleni in #634
• perf(restore): avoid redundant create_dir_all on restore hot path by @Ysh204 in #592
• Improve the monitor tui scroll state management by @AzureZee in #636

New Contributors

• @meskill made their first contribution in #597
• @AzureZee made their first contribution in #636

Full Changelog: v0.11.0...v0.12.0