reader: feature set #{:jolt :default}, clause-order matching (RFC 0002)

jolt no longer satisfies :clj in reader conditionals. The shortcut was a
measured net liability: :clj branches carry JVM interop and JVM-specific
test expectations jolt fails, and they shadowed :default branches jolt
passes. A/B over the suite: clj,default = 4967 assertions / 4324 pass / 119
errors; jolt,default = 5069 / 4470 / 81 (+146 pass, -38 errors, +8 clean
files). Baselines raised to 4470/86.

Matching is now by CLAUSE order like Clojure — the first clause whose key is
in the feature set wins (#?(:default 5 :clj 6) is 5 everywhere); the old code
scanned for :clj first, then :default, regardless of position.

Foreign clj-targeted libraries are a property of the LOADING CONTEXT, not the
platform: reader-features-set! opts a load into a compatibility set, and the
SCI bootstrap/runtime tests load SCI under ["jolt" "clj" "default"] (its
.cljc selects implementations via :clj with no :jolt branches).
JOLT_FEATURES remains the process-wide override.

RFC 0002 records the decision with the measured data; spec 02-reader S18 is
now normative (clause order, documented feature set, per-context override).
Reader tests updated to the portable set + an opt-in round-trip.

test/integration/clojure-test-suite-test.janet

@@ -43,9 +43,9 @@
 # Raised 4004 -> 4034 / clean 66 -> 67 porting partition-all + repeatedly to the
 # overlay, which required fixing two leniencies (a char is not callable; take
 # validates its count) — correct beyond those fns, so the suite rose broadly.
-(def baseline-pass 4324)
+(def baseline-pass 4470)
 # A file is "clean" when it ran with zero failures AND zero errors.
-(def baseline-clean-files 78)
+(def baseline-clean-files 86)
 # Per-file wall-clock budget (seconds). Normal files finish in well under 1s, so
 # this normally only fires on genuinely-infinite-sequence hangs. It's an env var
 # (JOLT_SUITE_TIMEOUT) so CI — whose runners are slower than a dev machine — can

test/integration/sci-bootstrap-test.janet

@@ -2,6 +2,12 @@
 (use ../../src/jolt/types)
 (use ../../src/jolt/reader)
 (use ../../src/jolt/api)
+(use ../../src/jolt/reader)
+# SCI is a clj/cljs-targeted library: its .cljc sources select implementation
+# via #?(:clj ...) and have no :jolt branches — load it under clj-compat
+# features (spec 02-reader S18: feature sets are a property of the loading
+# context; the portable default is #{:jolt :default}).
+(reader-features-set! ["jolt" "clj" "default"])
 
 (def ctx (init))
 

test/integration/sci-runtime-test.janet

@@ -2,6 +2,12 @@
 (use ../../src/jolt/types)
 (use ../../src/jolt/reader)
 (use ../../src/jolt/api)
+(use ../../src/jolt/reader)
+# SCI is a clj/cljs-targeted library: its .cljc sources select implementation
+# via #?(:clj ...) and have no :jolt branches — load it under clj-compat
+# features (spec 02-reader S18: feature sets are a property of the loading
+# context; the portable default is #{:jolt :default}).
+(reader-features-set! ["jolt" "clj" "default"])
 
 (defn- load-stubs [ctx filepath]
   (var s (slurp filepath))

test/spec/reader-syntax-spec.janet

@@ -45,8 +45,14 @@
   ["anon fn %&"         "[2 3]"     "(#(vec %&) 2 3)"]
   ["discard #_"         "[1 3]"     "[1 #_2 3]"]
   ["regex literal"      "true"      "(= \"abc\" (re-find #\"abc\" \"xabcx\"))"]
-  ["reader conditional" "1"         "#?(:clj 1 :cljs 2 :default 3)"]
-  ["reader cond splice" "[1 2 3]"   "[#?@(:clj [1 2 3] :cljs [4 5])]"]
+  # Feature set is #{:jolt :default} (spec 02-reader S18; RFC 0002) — :clj
+  # branches are NOT taken; matching is by clause order.
+  ["reader conditional" "3"         "#?(:clj 1 :cljs 2 :default 3)"]
+  ["reader cond :jolt"  "4"         "#?(:clj 1 :jolt 4 :default 3)"]
+  ["reader cond clause order" "5"   "#?(:default 5 :jolt 6)"]
+  ["reader cond no match" "[]"      "[#?(:clj 1 :cljs 2)]"]
+  ["reader cond splice" "[1 2 3]"   "[#?@(:jolt [1 2 3] :cljs [4 5])]"]
+  ["reader cond splice no match" "[]" "[#?@(:clj [1 2 3] :cljs [4 5])]"]
   ["inst literal reads" "true"      "(some? #inst \"2020-01-01T00:00:00Z\")"]
   ["uuid literal"       "\"550e8400-e29b-41d4-a716-446655440000\"" "(str #uuid \"550e8400-e29b-41d4-a716-446655440000\")"]
   ["tagged literal var" "true"      "(var? #'+)"]

test/unit/reader-test.janet

@@ -123,18 +123,23 @@
   (let [[form2 _] (parse-next rest-str)]
     (assert (deep= [3 4] form2) "second form is vector")))
 
-# Reader conditional — resolves :clj branch at read time
-(assert (= 1 (parse-string "#?(:clj 1 :cljs 2)"))
-        "#?(:clj) picks :clj branch")
+# Reader conditional — feature set is #{:jolt :default} (spec 02-reader S18,
+# RFC 0002); matching is by clause order. reader-features-set! lets a loading
+# context opt a clj-targeted library into :clj compat (restored below).
+(assert (= 3 (parse-string "#?(:clj 1 :jolt 3 :cljs 2)"))
+        "#?(...) picks :jolt branch")
 (assert (= nil (parse-string "#?(:cljs 999)"))
-        "#?(:cljs) returns nil on CLJ")
-(assert (= 42 (parse-string "#?(:clj 42)"))
-        "#?(:clj) with single branch")
-(assert (deep= (sym "clj-only") (parse-string "#?(:clj clj-only :cljs cljs-only)"))
-        "#?(:clj) picks :clj symbol")
-# Nested inside a list — :clj branch is evaluated at read time
-(assert (deep= @[(sym "+") 1 3] (parse-string "(+ 1 #?(:clj 3 :cljs 4))"))
-        "#? inside list picks :clj")
+        "unmatched conditional reads as nothing")
+(assert (= 7 (parse-string "#?(:clj 1 :default 7)"))
+        ":default reached when :clj not in feature set")
+(assert (= 5 (parse-string "#?(:default 5 :jolt 6)"))
+        "clause order wins, not key priority")
+(assert (deep= @[(sym "+") 1 3] (parse-string "(+ 1 #?(:jolt 3 :cljs 4))"))
+        "#? inside list picks :jolt")
+(let [prev (reader-features-set! ["jolt" "clj" "default"])]
+  (assert (= 1 (parse-string "#?(:clj 1 :cljs 2)"))
+          "clj-compat opt-in picks :clj")
+  (reader-features-set! (keys prev)))
 
 # Characters — the reader now produces char values {:jolt/type :jolt/char :ch N}
 (let [form (parse-string "\\newline")]