README: document early cutoff, trade-offs, and cache invalidation#19
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README: document early cutoff, trade-offs, and cache invalidation#19
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The "How it works" cache step still described the pre-cutoff drv-path keying. Add the eff-key model, the rmeta/rlib two-tier split, the cases where cutoff doesn't help (rmeta non-determinism, leaf relinks, ambient build.rs inputs), and what `bob clean` actually removes — in particular that tracked units' eff-keyed artifacts aren't addressable by name. Also fix the stale module doc on cache.rs.
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Stacked on #17.
The README's "How it works" still described the pre-#17 drv-path-only cache
key, so the headline behaviour (edit a deep crate → 2 rebuilt instead of
N) wasn't explained anywhere user-facing.
Adds:
eff(c) = H(own_src ‖ dep output hashes)model, the worked 20-revdep example, and why it differs from cargo's
mtime cascade.
early-gated) but link targets key on full rlib bytes (rlibs aren't
reproducible under
-C incremental).determinism (degrades to slow-not-wrong if rustc breaks it); leaf
relinks always fire; the ambient-
build.rs-input gap; not for CI.bob clean(ambientrerun-if-env-changed, non-hermetic cc,-C incrementalcorruption, disk pressure) and a table of what eachcleanvariant removes — including the footnote that tracked units'eff-keyed artifacts aren't addressable by member name.
Also fixes the stale module doc on
crates/core/src/cache.rs.