Review fixes: print fast-path + regex zero-width advance

- with-deeper-print only parameterizes the print depth when *print-level* is
  set, so printing pays no parameterize on the common nil-default path.
- re-find (the matcher) and re-seq advance past a zero-width match relative to
  the match's own start, not the search origin — a zero-width match found past
  the origin (lookahead/boundary) no longer repeats. (re-seq #"a*" "aba") now
  matches the JVM.

host/chez/regex.ss

@@ -205,9 +205,12 @@
             (start (matcher-t-pos m))
             (mm (and (<= start len) (irregex-search (matcher-t-irx m) str start))))
        (if mm
-           (let ((e (irregex-match-end-index mm 0)))
+           (let ((ms (irregex-match-start-index mm 0))
+                 (e (irregex-match-end-index mm 0)))
              (matcher-t-last-set! m mm)
-             (matcher-t-pos-set! m (if (> e start) e (+ start 1)))
+             ;; advance past this match: to its end, or one past a zero-width match
+             ;; (which may sit past the search origin, e.g. a lookahead/boundary).
+             (matcher-t-pos-set! m (if (> e ms) e (+ e 1)))
              (irx-result mm))
            (begin (matcher-t-last-set! m #f) jolt-nil))))))
 
@@ -227,8 +230,11 @@
     (let loop ((start 0) (acc '()))
       (let ((m (and (<= start len) (irregex-search irx s start))))
         (if m
-            (let ((e (irregex-match-end-index m 0)))
+            (let ((ms (irregex-match-start-index m 0))
-              (loop (if (> e start) e (+ start 1)) (cons (irx-result m) acc)))
+                  (e (irregex-match-end-index m 0)))
+              ;; to the match end, or one past a zero-width match (relative to its
+              ;; own start, which may be past the search origin).
+              (loop (if (> e ms) e (+ e 1)) (cons (irx-result m) acc)))
             (list->cseq (reverse acc)))))))
 
 (def-var! "clojure.core" "re-pattern" jolt-re-pattern)

host/chez/rt.ss

@@ -234,10 +234,14 @@
           (cond ((null? s) (reverse acc))
                 ((fx>=? i lim) (reverse (cons "..." acc)))
                 (else (loop (cdr s) (fx+ i 1) (cons (car s) acc))))))))
-;; bump the print depth around a collection's element rendering.
+;; bump the print depth around a collection's element rendering — but only when
+;; *print-level* is set, since depth is consulted only to enforce it. With the
+;; common nil default this is a plain begin, so printing pays no parameterize.
 (define-syntax with-deeper-print
   (syntax-rules ()
-    ((_ body ...) (parameterize ((jolt-print-depth (fx+ (jolt-print-depth) 1))) body ...))))
+    ((_ body ...) (if (jolt-print-level)
+                      (parameterize ((jolt-print-depth (fx+ (jolt-print-depth) 1))) body ...)
+                      (begin body ...)))))
 
 ;; A host shim registers a type's str-style rendering via register-pr-str-arm! (or
 ;; register-pr-arm! in printing.ss for both printers at once) instead of

test/chez/corpus.edn

@@ -3277,4 +3277,5 @@
   {:suite "printer / str vs print" :label "infinity inside a collection prints readably in str" :expected "true" :actual "(= \"[##Inf]\" (str [##Inf]))"}
   {:suite "interop / uri equality" :label "URIs are value-equal and usable as set members" :expected "[true true]" :actual "[(= (java.net.URI. \"/\") (java.net.URI. \"/\")) (= #{(java.net.URI. \"/\")} #{(java.net.URI. \"/\")})]"}
   {:suite "stdlib / clojure.walk" :label "macroexpand-all expands a form" :expected "true" :actual "(do (require (quote clojure.walk)) (seq? (clojure.walk/macroexpand-all (quote (when true 1)))))"}
+  {:suite "regex / re-seq zero-width" :label "a zero-width match advances by one without repeating" :expected "[\"a\" \"\" \"a\" \"\"]" :actual "(vec (re-seq #\"a*\" \"aba\"))"}
 ]