PR 13471: Add cycle-detection during lex-abbrev expansion to raise appropriate syntax error.

Also add test cases for lex-abbrev cycle detection.

original commit: 7146289c34c8256e54bda9157fcdc337047ae043

collects/parser-tools/private-lex/error-tests.rkt

@@ -40,6 +40,35 @@
                        (let ()
                          (lexer ((a) 1))))))
 
+;; Detecting mutual recursion cycle:
+(check-regexp-match #rx"regular-expression"
+                    (catch-syn-error 
+                     (let ()
+                       (define-lex-abbrev a b)
+                       (define-lex-abbrev b a)
+                       (let ()
+                         (lexer ((a) 1))))))
+
+(check-regexp-match #rx"regular-expression"
+                    (catch-syn-error 
+                     (let ()
+                       (define-lex-abbrev a (repetition 0 1 b))
+                       (define-lex-abbrev b (repetition 0 1 a))
+                       (let ()
+                         (lexer ((a) 1))))))
+
+;; Detecting cycle within same abbreviation:
+(check-regexp-match #rx"regular-expression"
+                    (catch-syn-error 
+                     (let ()
+                       (define-lex-abbrev balanced 
+                         (union (concatenation "(" balanced ")" balanced)
+                                any-char))
+                       (lexer
+                        [balanced (string-append lexeme (balanced input-port))]
+                        [(eof) ""]))))
+
+
 (check-regexp-match #rx"regular-expression" (catch-syn-error (lexer (1 1))))
 (check-regexp-match #rx"repetition" (catch-syn-error (lexer ((repetition) 1))))
 (check-regexp-match #rx"repetition" (catch-syn-error (lexer ((repetition #\1 #\1 "3") 1))))

collects/parser-tools/private-lex/stx.rkt

@@ -1,6 +1,6 @@
 (module stx mzscheme
-  (require syntax/boundmap
-           "util.rkt")
+  (require "util.rkt"
+           syntax/id-table)
   
   (provide parse)
 
@@ -37,10 +37,18 @@
   ;; checks for errors and generates the plain s-exp form for s
   ;; Expands lex-abbrevs and applies lex-trans.
   (define (parse stx disappeared-uses)
-    (let ((parse
-           (lambda (s)
-             (parse (syntax-rearm s stx)
-                    disappeared-uses))))
+    (let loop ([stx stx]
+               [disappeared-uses disappeared-uses]
+               ;; seen-lex-abbrevs: id-table
+               [seen-lex-abbrevs (make-immutable-free-id-table)])
+      (let ([recur (lambda (s)
+                     (loop (syntax-rearm s stx)
+                           disappeared-uses
+                           seen-lex-abbrevs))]
+            [recur/abbrev (lambda (s id)
+                            (loop (syntax-rearm s stx)
+                                  disappeared-uses
+                                  (free-id-table-set seen-lex-abbrevs id id)))])
         (syntax-case (disarm stx) (repetition union intersection complement concatenation
                                               char-range char-complement)
           (_
@@ -50,8 +58,15 @@
                (raise-syntax-error 'regular-expression
                                    "undefined abbreviation"
                                    stx))
+             ;; Check for cycles.
+             (when (free-id-table-ref seen-lex-abbrevs stx (lambda () #f))
+               (raise-syntax-error 'regular-expression
+                                   "illegal lex-abbrev cycle detected"
+                                   stx
+                                   #f
+                                   (list (free-id-table-ref seen-lex-abbrevs stx))))
              (set-box! disappeared-uses (cons stx (unbox disappeared-uses)))
-         (parse ((lex-abbrev-get-abbrev expansion)))))
+             (recur/abbrev ((lex-abbrev-get-abbrev expansion)) stx)))
           (_
            (or (char? (syntax-e stx)) (string? (syntax-e stx)))
            (syntax-e stx))
@@ -78,18 +93,18 @@
                   #f
                   "the first argument is not less than or equal to the second argument"
                   stx))
-           `(repetition ,low ,high ,(parse re)))))
+               `(repetition ,low ,high ,(recur re)))))
           ((union re ...)
-       `(union ,@(map parse (syntax->list (syntax (re ...))))))
+           `(union ,@(map recur (syntax->list (syntax (re ...))))))
           ((intersection re ...)
-       `(intersection ,@(map parse (syntax->list (syntax (re ...))))))
+           `(intersection ,@(map recur (syntax->list (syntax (re ...))))))
           ((complement re ...)
            (let ((re-list (syntax->list (syntax (re ...)))))
              (unless (= 1 (length re-list))
                (bad-args stx 1))
-         `(complement ,(parse (car re-list)))))
+             `(complement ,(recur (car re-list)))))
           ((concatenation re ...)
-       `(concatenation ,@(map parse (syntax->list (syntax (re ...))))))
+           `(concatenation ,@(map recur (syntax->list (syntax (re ...))))))
           ((char-range arg ...)
            (let ((arg-list (syntax->list (syntax (arg ...)))))
              (unless (= 2 (length arg-list))
@@ -106,7 +121,7 @@
            (let ((arg-list (syntax->list (syntax (arg ...)))))
              (unless (= 1 (length arg-list))
                (bad-args stx 1))
-         (let ((parsed (parse (car arg-list))))
+             (let ((parsed (recur (car arg-list))))
                (unless (char-set? parsed)
                  (raise-syntax-error #f
                                      "not a character set"
@@ -120,7 +135,7 @@
              (set-box! disappeared-uses (cons o (unbox disappeared-uses)))
              (cond
                ((lex-trans? expansion)
-             (parse ((lex-trans-f expansion) (disarm stx))))
+                (recur ((lex-trans-f expansion) (disarm stx))))
                (expansion
                 (raise-syntax-error 'regular-expression
                                     "not a lex-trans"
@@ -133,7 +148,7 @@
            (raise-syntax-error
             'regular-expression
             "not a char, string, identifier, or (op args ...)"
-        stx)))))
+            stx))))))