Cache RBS rewrites with bootsnap & add dsl --only-bootsnap-rbs-cache#2617
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Cache RBS rewrites with bootsnap & add dsl --only-bootsnap-rbs-cache#2617
dsl --only-bootsnap-rbs-cache#2617Conversation
KaanOzkan
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Set up bootsnap with a dedicated cache directory and load require-hooks so the RBS-to-sig rewrite is baked into the cached bytecode. The first run is slow (rewrite + compile every file); subsequent runs against the same cache directory skip the rewrite entirely. Cache directory defaults to `tmp/cache/bootsnap-tapioca-rbs` (override with `TAPIOCA_BOOTSNAP_CACHE_DIR`); kept separate from the host app's regular bootsnap cache so rewritten iseqs don't leak into other processes. `BOOTSNAP_READONLY=1` flows through to bootsnap for consumers reading a pre-populated cache. `Bootsnap.log_stats!` prints hit/miss counts at exit so cache effectiveness is visible.
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KaanOzkan
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May 8, 2026
| # | ||
| # The host app must also skip its own Bootsnap.setup under this flag, | ||
| # otherwise it'll override our settings during Rails boot. | ||
| if ENV["TAPIOCA_RBS_CACHE"] == "1" |
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Rewriter is loaded before any CLI parsing so went with a ENV variable.
`--only-bootsnap-rbs-cache` boots the app and loads DSL extensions/compilers (populating the RBS rewrite cache), then exits before any RBI work. Run it once in a CI prime step so downstream jobs read from a warm cache. The flag is mutually exclusive with `--verify`.
`bootsnap` is an optional dependency. `lib/tapioca/rbs/rewriter.rb` only requires it under `TAPIOCA_RBS_CACHE=1`, so it's not in the Gemfile and Sorbet can't resolve `Bootsnap.setup`/`Bootsnap.log_stats!`. Add a minimal shim under `sorbet/rbi/shims/bootsnap.rbi` declaring just the methods we call.
When `TAPIOCA_RBS_CACHE=1`, tapioca configures bootsnap with its own dedicated cache directory before loading the host app. If the host later runs `Bootsnap.setup` itself (Rails apps do this in `config/boot.rb`), the host's call clobbers tapioca's settings and silently breaks the RBS rewrite cache. Prepend `Tapioca::RBS::BootsnapGuard` so any subsequent `Bootsnap.setup` raises `HostBootsnapSetupError` pointing at the fix (gate the host's setup on `TAPIOCA_RBS_CACHE`). Add a CLI test asserting the raise.
Add a `Rewriting RBS comments to Sorbet signatures` section under Usage explaining what the rewrite does and why it exists, plus subsections covering `TAPIOCA_RBS_CACHE=1` for caching rewrites via bootsnap, the `--only-bootsnap-rbs-cache` priming workflow for CI, and how to coordinate a host app's own `Bootsnap.setup`.
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amomchilov
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May 9, 2026
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| readonly_env = ENV["BOOTSNAP_READONLY"] | ||
| readonly = !readonly_env.nil? && !["0", "false"].include?(readonly_env) |
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I suggest copying Bootsnap's logic for this directly: https://github.com/rails/bootsnap/blob/ff7f97c77123113474fea6ae46459fea5c92ec9f/lib/bootsnap.rb#L190-L193
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Motivation
tapioca dslrewrites RBS comments to Sorbetsig {}blocks on every loaded file viarequire-hooks. On Shopify's monolith this dominates wall time (locally ~16 min). Caching the post-rewrite bytecode in bootsnap drops it to ~4 min (4.2x).Implementation
Opt-in via
TAPIOCA_RBS_CACHE=1. The rewriter sets up bootsnap with a dedicated cache directory (defaulttmp/cache/bootsnap-tapioca-rbs, override viaTAPIOCA_BOOTSNAP_CACHE_DIR) and forwardsBOOTSNAP_READONLYto bootsnap'sreadonly:arg. After setup,Tapioca::RBS::BootsnapGuardis prepended onBootsnap.singleton_classso the host's ownBootsnap.setupraises instead of silently clobbering the cache dir.--only-bootsnap-rbs-cachepopulates the cache and exits before any RBI work (CI prime/consumer pattern, mutually exclusive with--verify).bootsnapstays an optional runtime dep; a Sorbet shim covers the static surface.Tests
CLI tests in
spec/tapioca/cli/dsl_spec.rbcover the flag's early-exit, the--verifymutex, and the guard's raise.