Add sccache (local disk backend) to the CI cache action#15147
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Add sccache (local disk backend) to the CI cache action#15147reaperhulk wants to merge 8 commits into
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…warm PEP 517 build isolation creates a temporary virtualenv with a randomized path for every build, so PYO3_PYTHON changes on each install. Our cryptography-cffi build script registers rerun-if-env-changed=PYO3_PYTHON, so cryptography-cffi and cryptography-rust recompiled on every CI job even with a fully warm Swatinem/rust-cache (and on free-threaded builds the pyo3 crates recompiled too, since the non-abi3 interpreter config also embeds the ephemeral path). See PyO3/pyo3#6113 Install the build requirements into the session venv and pass --no-build-isolation instead: the build backend then runs from the stable .nox/<session> interpreter, making the cargo fingerprints stable across CI runs. Verified locally: with isolation every reinstall recompiles the crates (~30s); without it a warm-cache reinstall compiles nothing. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Lj3BsMN8xmPQQ89d6nzDcZ
rust-cache skips saving on an exact key hit, so without a roll the caches would keep the fingerprints recorded from isolated builds and every job would keep rebuilding once per run. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Lj3BsMN8xmPQQ89d6nzDcZ
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Lj3BsMN8xmPQQ89d6nzDcZ
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Lj3BsMN8xmPQQ89d6nzDcZ
Compiler-level caching to recover the cases Swatinem/rust-cache can't: Cargo.lock bumps (full rust-cache miss) and the workspace crates that rust-cache deliberately prunes from every saved cache. sccache runs with its local disk backend, persisted as a single actions/cache entry per job (~30-40 MB measured for a cold build), so it adds exactly one cache restore and at most one save per job -- no per-object GHA cache API traffic, no rate-limit exposure. The entry key includes the rustc host triple + version and the existing job key; a restore-keys prefix lets an entry carry over across lockfile changes. Jobs on architectures without prebuilt sccache binaries (and the sccache-action failing for any reason) degrade to today's behavior: the wrapper is only enabled if the binary is actually present. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01WYvs2Ppi5y2moJF5uoWbvr
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01WYvs2Ppi5y2moJF5uoWbvr
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…84' into claude/sccache-gha-caching-lfk8qj # Conflicts: # .github/actions/cache/action.yml
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llvm-cov emits warnings to stderr, which session.run(silent=True) captures into the same string as stdout, so any warning ends up written into the .lcov file and crashes merge_rust_coverage.py's strict parser. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01WYvs2Ppi5y2moJF5uoWbvr
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Adds compiler-level caching via sccache to the shared CI cache composite action, layered on top of the existing
Swatinem/rust-cache. The two cover complementary gaps:target/, cargo registry, git deps.Cargo.lockbumps (full rust-cache key miss, e.g. every Dependabot update) and the workspace crates rust-cache deliberately prunes from every saved cache.Design notes:
actions/cacheentry per job — measured ~30–40 MB per cold build flavor (entries are internally compressed). This adds exactly one cache restore and at most one save per job, so no per-object GHA cache API traffic and no rate-limit exposure, unlikeSCCACHE_GHA_ENABLED.sccache-{rustc host triple + version}-{existing job key}-{Cargo.lock hash}with arestore-keysprefix fallback so entries carry across lockfile changes — exactly the moment rust-cache goes cold. Since sccache hashes its real inputs (compiler digest, args, env), a stale entry can only miss, never produce a wrong object.continue-on-error; the wrapper is only enabled after a runtimecommand -v sccachecheck. Jobs without sccache behave exactly as today.SCCACHE_CACHE_SIZE=512Mbounds accretion from restore-keys chains.Expected quota impact: ≤2 GB across the whole matrix, well within the 10 GB free allowance. The sccache-action's post-job hook prints hit/miss stats in each job's logs for verification.
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https://claude.ai/code/session_01WYvs2Ppi5y2moJF5uoWbvr
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