Predicate Caching Impl - #268
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nikomatsakis merged 5 commits intoAug 4, 2026
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This looks good. Two minor suggestions.
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| /// Persist the disk cache back to `cache_path`. No-op if this context | ||
| /// was not built with `with_disk_cache` or the cache was not modified. | ||
| pub fn persist_disk_cache(&mut self, cache_path: &Path) -> Result<()> { |
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Nit: Hmm, should we do this in the Drop impl?
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discussed here - #general > predicate-caching @ 💬
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Adds Watch{File,Env,Time} events on a non_exhaustive enum plus SDK emitter and consumer parser.
Unions Watch events into a set with a CacheTtl and captures mtime+size / env-value fingerprints.
at <cache_dir>/predicates/<sha256(workspace)>.json with schema-version invalidation.
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Thin wrappers that emit WatchEnv/WatchFile before delegating to std, so predicates cache correctly.
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Arc change squashed into the wiring commit, also rebased onto mainline. Wiring commit: f2703d0 |
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What does this PR do?
Implements the predicate-caching RFD (#262). Custom predicates now emit
Watch{File,Env,Time}JSONL events on stdout. Symposium caches their exit-coderesult in~/.symposium/cache/predicates/<workspace-hash>.jsonand skipsre-evaluation until a watched file, env var, or TTL becomes stale.
Three granular events on a
#[non_exhaustive]CustomPredicateEventenumWatchFile(PathBuf)result depends on this file'smtime + size.WatchEnv(String)result depends on this env var's current value.WatchTime(u64)result becomes stale after this many milliseconds.WatchTime(0)disables caching.Exit status still determines pass/fail. Events only control cache lifetime.
Cache layout
Per-workspace cache file at
<SymposiumDirs::cache_dir>/predicates/<sha256(canonical workspace_root)>.jsonI think isolating by workspace prevents two projects on the same machine that emit the same predicate string from stepping on each other's cached answers. Schema version tag invalidates on Symposium upgrade.
Note
path_existsis one stat, env is one hashmap lookup and the cache check would cost the same as just running them, so caching them doesn't buy anything. If it's useful to route them through the cache for observability, happy to add.Disclosure questions
AI disclosure.
Questions for reviewers.