simon/jolt

Yogthos d21ab77e7e Run core.memoize's test suite on jolt

Shaking out clojure.core.memoize (207 assertions, 0 fail) cleared several
general gaps:

- deref/@ on a deftype or reify implementing clojure.lang.IDeref dispatches to
  its deref method (RetryingDelay / make-derefable).
- deftype mutable fields (^:unsynchronized-mutable / ^:volatile-mutable) are
  read live: a set! within a method is observed by a later read in the same
  invocation, not the entry-time capture. Needed for double-checked locking.
  Immutable fields stay let-bound. Field reads rewrite to (.-field inst) with
  lexical-shadow tracking.
- def metadata values are evaluated, like Clojure: ^{:k (f)} stores (f)'s
  result and ^{:af some-fn} the fn. :tag stays a literal hint.
- try dispatches catch clauses by class in order via the exception supertype
  hierarchy; a non-matching value re-throws, an untyped host condition is caught
  by a RuntimeException/Exception/Throwable clause. Previously the last clause
  won and the class was ignored.
- locking takes a real per-object monitor (recursive Chez mutex) now that
  futures/agents/threads share one heap; it was a no-op.
- supers/ancestors reflect a small modeled JVM interface hierarchy, so
  (ancestors (class f)) yields Runnable/Callable (core.memoize's arg check).
- AssertionError / Error constructors.

JOLT_FEATURES is gone from the docs: it isn't read anywhere on Chez, and the
reader already includes :clj in its default feature set. RFC 0002's
{:jolt :default} design was reverted in the reader; docs now match the code.

Raises the SCI floor 205 -> 210.

2026-06-25 13:23:05 -04:00

4.6 KiB

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RFC 0002 — Reader-Conditional Feature Set

Status: Superseded (2026-06-25) — jolt now includes :clj in the default set; see the note below.
Created: 2026-06-10
Spec: docs/spec/02-reader.md §2.3 S18

Update (2026-06-25). The default set is now #{:jolt :clj :default} — :clj is satisfied by default. The clj ecosystem's .cljc libraries gate their host code behind #?(:clj …) with no :jolt/:default fallback, so the conformance libraries (core.cache, core.match, tick, malli, …) only load with :clj present; requiring an opt-in for each was friction with no payoff once jolt's clojure.lang.*/java.* emulation was broad enough to run those :clj branches. Matching is still by clause order, so a library can place a :jolt branch first to override. There is no JOLT_FEATURES environment variable; a loading context overrides the set at runtime with reader-features-set!. The rest of this RFC is the original (reverted) design.

Summary

jolt's reader-conditional feature set is #{:jolt :default}, matched in clause order (the first clause whose key the platform satisfies wins). A loading context may opt a foreign, clj-targeted library into :clj compatibility via reader-features-set! (or process-wide via the JOLT_FEATURES environment variable). jolt does not satisfy :clj by default.

Background

#?(:clj … :cljs … :default …) selects a branch by platform feature at read time. Until now jolt satisfied :clj — a compatibility shortcut inheriting the JVM branches of .cljc files, on the theory that the :clj branch is usually the "main" implementation. Each dialect chooses its own policy: ClojureScript satisfies only :cljs; jank uses :jank; babashka includes :clj because it genuinely is JVM-Clojure-compatible to a deep degree.

Two defects forced the decision:

jolt is not JVM-compatible where it matters for :clj branches: they contain interop (java.util.*, deftype over JVM classes) and encode JVM-specific expectations in tests (e.g. parse-uuid's reference permissiveness), both of which jolt fails.
The old implementation also matched by key priority (:clj first, then :default) rather than clause order — #?(:default 5 :clj 6) read as 6, diverging from Clojure on all platforms.

Decision and evidence

Measured A/B over the cross-dialect clojure-test-suite (identical tree, 2026-06-10):

Feature set	Assertions reached	Pass	Fail	Error	Clean files
`clj, default` (old)	4967	4324	524	119	78
`jolt, default` (new)	5069	4470	518	81	86

The portable convention reads more of the suite (:default branches were being shadowed by :clj ones jolt can't satisfy) and improves every metric: +146 passes, −38 errors, +8 clean files. The :clj shortcut was a net liability, not a compatibility win.

The opposing case — loading real-world clj-targeted libraries — is real: SCI's .cljc sources select their implementation via #?(:clj …)/:cljs with no :jolt branches, and fail to load under the portable set. That is a property of the loading context, not of the platform: the resolution is per-context opt-in, exactly how the SCI bootstrap now loads ((reader-features-set! ["jolt" "clj" "default"])).

Specification (normative, mirrored in spec §2.3 S18)

The platform feature set is implementation-defined and MUST be documented. jolt's is #{:jolt :default}.
Matching MUST be by clause order: the first clause whose key is in the feature set wins. :default matches on every platform. #?(:default 5 :clj 6) is 5 everywhere.
An unmatched conditional reads as nothing (no form); an unmatched #?@(…) splices nothing.
Implementations SHOULD provide a per-loading-context override so foreign libraries written for other dialects can be read under a compatibility set; using it is a deliberate, scoped decision (jolt: reader-features-set! / JOLT_FEATURES).

Consequences

Suite baselines re-measured and raised: baseline-pass 4324 → 4470, baseline-clean-files 78 → 86.
Reader tests assert the portable set + clause-order semantics, plus one opt-in round-trip through reader-features-set!.
Loading clj-ecosystem libraries via deps requires deciding their feature set; the deps loader currently inherits the process default — a future refinement is per-dependency feature configuration (filed with the deps work).
.cljc authors targeting jolt can write :jolt branches and rely on :default fallbacks.

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