cs & regexp: fix incorrect request for extra bytes

When trying to match "\r\n" on an input port, for example, don't
insist on peeking a second byte if the first one already isn't "\r".

Closes #3132

pkgs/racket-test-core/tests/racket/rx.rktl

@@ -1850,6 +1850,25 @@
                                                                 (or y "[y]")
                                                                 (or z "[z]"))))
 
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Don't get stuck waiting for an unneeded byte
+
+(let ()
+  (define-values (i o) (make-pipe))
+  (write-string "1\n" o)
+  (define rx (regexp "^(?:(.*?)(?:\r\n|\n))"))
+  (test '(#"1\n" #"1") regexp-match rx i))
+(let ()
+  (define-values (i o) (make-pipe))
+  (write-string "abc" o)
+  (define rx (regexp "^(ab)*"))
+  (test '(#"ab" #"ab") regexp-match rx i))
+(let ()
+  (define-values (i o) (make-pipe))
+  (write-string "123" o)
+  (define rx (pregexp "^(12)\\1|123"))
+  (test '(#"123" #f) regexp-match rx i))
+
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (report-errs)

racket/src/regexp/demo.rkt

@@ -77,6 +77,23 @@
 (test (regexp-replace* "-" "zero-or-more?" "_")
       "zero_or_more?")
 
+;; Don't get stuck waiting for an unneeded byte:
+(let ()
+  (define-values (i o) (make-pipe))
+  (write-string "1\n" o)
+  (define rx (rx:regexp "^(?:(.*?)(?:\r\n|\n))"))
+  (test (rx:regexp-match rx i) '(#"1\n" #"1")))
+(let ()
+  (define-values (i o) (make-pipe))
+  (write-string "abc" o)
+  (define rx (rx:regexp "^(ab)*"))
+  (test (rx:regexp-match rx i) '(#"ab" #"ab")))
+(let ()
+  (define-values (i o) (make-pipe))
+  (write-string "123" o)
+  (define rx (rx:pregexp "^(12)\\1|123"))
+  (test (rx:regexp-match rx i) '(#"123" #f)))
+
 ;; ----------------------------------------
 
 (define (check rx in N [M (max 1 (quotient N 10))])

racket/src/regexp/match/match.rkt

@@ -89,7 +89,8 @@
 ;; An iterator performs a single match as many times as possible, up
 ;; to a specified max number of times, and it returns the position
 ;; and the number of items; this mode is used only when each match
-;; has a fixed size
+;; has a fixed size, and `ls-tst` must incrementally check for available
+;; lazy bytes if `size` is greater than 1.
 (define-syntax-rule (define-iterate (op-matcher* arg ...)
                       outer-defn ... 
                       (lambda (s pos2 start limit end state)
@@ -116,7 +117,7 @@
             (let loop ([pos2 pos] [n 0])
               (cond
                [(or (and limit ((+ pos2 size) . > . limit))
-                    (not (lazy-bytes-before-end? s (+ pos2 (sub1 size)) limit))
+                    (not (lazy-bytes-before-end? s pos2 limit)) ; only checks for 1 byte
                     (not ls-tst))
                 (values pos2 n size)]
                [else
@@ -172,11 +173,12 @@
              (for/and ([c1 (in-bytes bstr 0 len)]
                        [c2 (in-bytes s pos (+ pos len))])
                (= c1 c2)))
-        (and (lazy-bytes-before-end? s (sub1 (+ pos len)) limit)
         (for/and ([c1 (in-bytes bstr 0 len)]
                   [i (in-naturals pos)])
+          (and (lazy-bytes-before-end? s i limit)
+               (let ()
                  (define c2 (lazy-bytes-ref s i))
-               (= c1 c2))))
+                 (= c1 c2)))))
     (+ pos len)))
 
 (define-iterate (bytes-matcher* bstr)
@@ -188,8 +190,9 @@
                (= c1 c2))
     #:ls-test (for/and ([c1 (in-bytes bstr 0 len)]
                         [i (in-naturals pos)])
-                (define c2 (lazy-bytes-ref s i))
+                (and (lazy-bytes-before-end? s i limit)
-                (= c1 c2))))
+                     (let ([c2 (lazy-bytes-ref s i)])
+                       (= c1 c2))))))
 
 ;; ----------------------------------------
 ;; An always-fail pattern
@@ -456,12 +459,13 @@
                    (for/and ([c1 (in-bytes s (car p) (cdr p))]
                              [c2 (in-bytes s pos (+ pos len))])
                      (chyte=? c1 c2)))
-              (and (lazy-bytes-before-end? s (sub1 (+ pos len)) limit)
               (for/and ([j (in-range (car p) (cdr p))]
                         [i (in-naturals pos)])
+                (and (lazy-bytes-before-end? s i limit)
+                     (let ()
                        (define c1 (lazy-bytes-ref s j))
                        (define c2 (lazy-bytes-ref s i))
-                     (chyte=? c1 c2)))))
+                       (chyte=? c1 c2))))))
         (and matches?
              (next-m s (+ pos len) start limit end state stack))]))))