host: scoped reader-feature toggle, clojure.template, java.util.Locale alias

Follow-ups for running reitit alongside default-feature libraries in one app:

- __reader-features / __reader-features-set! exposed to Clojure so a namespace
  can load a clj-targeted lib (reitit, under :clj) WITHOUT forcing the whole
  process to :clj — set features, require, restore. Honeysql/selmer/ring stay
  on the default set they were validated under. (jolt vector args coerced to a
  janet array — janet map over a pvec iterates keys otherwise.)

- clojure.template added to the stdlib (verbatim, pure Clojure over
  clojure.walk) — honeysql's :clj branch requires it.

- java.util.Locale registered as a qualified alias (+ ROOT) for selmer's :clj
  Locale/US use.

src/jolt/clojure/template.clj

@@ -0,0 +1,33 @@
+;; Verbatim from clojure.template (Stuart Sierra) — pure Clojure over
+;; clojure.walk, which jolt ships. Added so honeysql's :clj branch (which
+;; requires clojure.template) loads under JOLT_FEATURES including clj.
+(ns clojure.template
+  "Macros that expand to repeated copies of a template expression."
+  (:require [clojure.walk :as walk]))
+
+(defn apply-template
+  "For use in macros.  argv is an argument list, as in defn.  expr is
+  a quoted expression using the symbols in argv.  values is a sequence
+  of values to be used for the arguments.
+
+  apply-template will recursively replace argument symbols in expr
+  with their corresponding values, returning a modified expr.
+
+  Example: (apply-template '[x] '(+ x x) '[2])
+           ;=> (+ 2 2)"
+  [argv expr values]
+  (assert (vector? argv))
+  (assert (every? symbol? argv))
+  (walk/postwalk-replace (zipmap argv values) expr))
+
+(defmacro do-template
+  "Repeatedly copies expr (in a do block) for each group of arguments
+  in values.  values are automatically partitioned by the number of
+  arguments in argv, an argument vector as in defn.
+
+  Example: (macroexpand '(do-template [x y] (+ y x) 2 4 3 5))
+           ;=> (do (+ 4 2) (+ 5 3))"
+  [argv expr & values]
+  (let [c (count argv)]
+    `(do ~@(map (fn [a] (apply-template argv expr a))
+                (partition c values)))))

src/jolt/evaluator.janet

@@ -1311,6 +1311,20 @@
   # Java class jolt doesn't ship (e.g. reitit.Trie). __register-class-statics!
   # makes (Class/method ...) resolve; __register-class-methods! makes (.method
   # tagged-value ...) dispatch; __register-class-ctor! makes (Class. ...) build.
+  # Reader-conditional feature toggle, exposed to Clojure so a namespace can
+  # load a clj-targeted library (e.g. reitit, under :clj) WITHOUT forcing the
+  # whole process to :clj — set features, require the lib, restore. Returns the
+  # previous feature set (a list of name strings) for restoration.
+  (ns-intern core "__reader-features"
+    (fn [] (tuple ;(map (fn [k] (string k)) (keys reader-features)))))
+  (ns-intern core "__reader-features-set!"
+    (fn [names]
+      # names arrives as a jolt vector (pvec) or list — coerce to a janet array
+      (def arr (cond (pvec? names) (pv->array names)
+                     (or (tuple? names) (array? names)) names
+                     @[names]))
+      (reader-features-set! (map (fn [n] (if (keyword? n) n (string n))) arr))
+      nil))
   (ns-intern core "__register-class-statics!"
     (fn [nm tbl] (register-class-statics! nm tbl) nil))
   (ns-intern core "__register-class-methods!"

src/jolt/javatime.janet

@@ -129,10 +129,12 @@
   (register-class-statics! "LocalDateTime"
     @{"ofInstant" (fn [inst zone] (local-dt (ms-of inst)))
       "now" (fn [] (local-dt (math/floor (* 1000 (os/clock :realtime)))))})
-  (register-class-statics! "Locale"
-    @{"getDefault" (fn [] @{:jolt/type :jolt/locale :id "default"})
-      "ENGLISH" @{:jolt/type :jolt/locale :id "en"}
-      "US" @{:jolt/type :jolt/locale :id "en-US"}})
+  (let [locale-statics @{"getDefault" (fn [] @{:jolt/type :jolt/locale :id "default"})
+                         "ENGLISH" @{:jolt/type :jolt/locale :id "en"}
+                         "US" @{:jolt/type :jolt/locale :id "en-US"}
+                         "ROOT" @{:jolt/type :jolt/locale :id "root"}}]
+    (each nm ["Locale" "java.util.Locale"]
+      (register-class-statics! nm locale-statics)))
   (register-tagged-methods! :jolt/instant
     @{"atZone" (fn [self zone] (zoned (self :ms) zone))
       "toEpochMilli" (fn [self] (self :ms))})

test/spec/host-interop-spec.janet

@@ -212,3 +212,14 @@
    "(let [m (HashMap. {:a 1 :b 2})] (.get m :b))"]
   ["HashMap put + size" "2"
    "(let [m (HashMap. {})] (.put m :x 1) (.put m :y 2) (.size m))"])
+
+# Reader-feature toggle exposed to Clojure (scoped clj-lib loading): a
+# namespace can load a clj-targeted library under :clj without forcing the
+# whole process — set features, require, restore.
+(defspec "host-interop / reader-feature toggle"
+  ["features default to jolt+default" "true"
+   "(contains? (set (__reader-features)) \"jolt\")"]
+  ["set + read back" "true"
+   "(do (def prev (__reader-features)) (__reader-features-set! [\"clj\" \"jolt\" \"default\"]) (def r (contains? (set (__reader-features)) \"clj\")) (__reader-features-set! prev) r)"]
+  ["restore returns to default" "false"
+   "(do (def prev (__reader-features)) (__reader-features-set! [\"clj\"]) (__reader-features-set! prev) (contains? (set (__reader-features)) \"clj\"))"])