Under --direct-link a top-level def binds jv$<fqn> and app->app calls bound directly
to it. emit-invoke raw-applied that binding for any var callee, but only a fn-valued
def is a Scheme procedure: (def cfg {...}) then (cfg :a) emitted (jv$cfg :a), applying
a pmap -> "attempt to apply non-procedure". Maps/sets/keywords are invokable in Clojure
via jolt-invoke, which the indirect path used, so this only bit closed-world builds.
Track which direct-linked vars hold fn literals (direct-link-fns, registered at the def
site when the init op is :fn) and only raw-apply those. A non-fn callee falls through to
the jolt-invoke branch, which still uses the direct jv$ binding as the invoke target —
so the var-deref is still skipped, just not the dispatch.
Seed source: re-minted. Regression in directlink-test.ss (jolt-cw1o).
A release/optimized `jolt build` is a closed world: every app def is final, so
an app->app call can bind to the def's Scheme binding directly instead of going
through (jolt-invoke (var-deref ns name)).
The emitter gains a direct-link mode (off for the seed mint, runtime -e/repl, and
dev builds). With it on, a top-level app def also emits a binding jv$<ns>$<name>
that def-var! aliases; an app->app call or value-ref to a name already emitted in
the unit lowers to that binding, skipping both the var-table lookup and the
generic IFn dispatch. ^:dynamic/^:redef defs and nested defs (a defonce's inner
def) opt out and stay indirect. Off direct-link mode, emit-top-form is exactly
emit, so the seed and runtime eval are byte-unchanged (selfhost holds).
build.ss turns it on for release + optimized; the defined-set accumulates across
the dependency-ordered namespaces so a dep's defs are linkable by the time the
entry that calls them is emitted. App->core calls stay indirect for now (core is
the baked seed); that's a later stage.
~1.74x on a hot cross-namespace call loop (26.5s -> 15.2s).
