`match-data' set improperly

[Matthew Swift <swift@alum.mit.edu>]

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In GNU Emacs 21.2.1 (i386-debian-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2002-11-06 on beth, modified by Debian
configured using `configure  i386-debian-linux-gnu --prefix=/usr/local --sharedstatedir=/var/lib --libexecdir=/usr/local/lib --localstatedir=/var/lib --infodir=/usr/local/share/info --mandir=/usr/local/share/man --with-pop=yes --with-x=yes --with-x-toolkit=athena --without-gif'
Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: nil
  locale-coding-system: nil
  default-enable-multibyte-characters: t

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

Evaluating the following `let' form gives varying results, but the results
should be consistent.  Correct results are always returned when `s' is "The
quick fox...", which matches the regexp `r'.  When `s' is "great grey
green...", which does not match `r', the results in my trials have never been
correct: either an 'args-out-of-range' error is raised, or incorrect data is
given, which appears to be the result of applying match-data from matching a
previous value of `s' ("The quick fox...") to the current value of `s'.  Sample
results are copied below.

My *guess* is that when `string-match' fails, it either fails to set
`match-data' or sets it incorrectly in one of two (or more) ways.

(let ((r "\\(qu\\)\\(ick\\)")
      ;; \C-x\C-t to swap next two lines
      ;; \M-\C-x to evaluate the `let' form
      (s "The quick fox jumped quickly.")
      (s "great grey green greasy Limpopo River")
      )
  (string-match r s)
  (list
   (match-data)
   (match-string 0 s)
   (match-string 1 s)
   (match-string 2 s)
   (match-string 3 s)
   (match-beginning 0)
   (match-beginning 1)
   (match-beginning 2)
   (match-beginning 3)
   ))


Debugger entered--Lisp error: (args-out-of-range "great grey green greasy Limpopo River" 27326 27327)
  match-string(0 "great grey green greasy Limpopo River")
  (list (match-data) (match-string 0 s) (match-string 1 s) (match-string 2 s) (match-string 3 s) (match-beginning 0) (match-beginning 1) (match-beginning 2) (match-beginning 3))
  (let ((r "\\(qu\\)\\(ick\\)") (s "The quick fox jumped quickly.") (s "great grey green greasy Limpopo River")) (string-match r s) (list (match-data) (match-string 0 s) (match-string 1 s) (match-string 2 s) (match-string 3 s) (match-beginning 0) (match-beginning 1) (match-beginning 2) (match-beginning 3)))
  eval((let ((r "\\(qu\\)\\(ick\\)") (s "The quick fox jumped quickly.") (s "great grey green greasy Limpopo River")) (string-match r s) (list (match-data) (match-string 0 s) (match-string 1 s) (match-string 2 s) (match-string 3 s) (match-beginning 0) (match-beginning 1) (match-beginning 2) (match-beginning 3))))
  eval-last-sexp-1(nil)
  eval-last-sexp(nil)
  call-interactively(eval-last-sexp)


Sometimes I get:

((4 9 4 6 6 9) "t gre" "t " "gre" nil 4 4 6 nil)

I get this less often, and I cannot tell you a reliable way to get it.  I
evaluate the `let' form, evaluate one or more individual lines
e.g. (match-beginning 2), swap the `s' strings, and evaluate the `let' form
again.  Then most of the time I still get the error, but sometimes I get these
incorrect results.

Notice that the match-data is the same as for a successful match of the other
string:

((4 9 4 6 6 9) quick qu ick nil 4 4 6 nil)






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<mouse-1> <down-mouse-5> <mouse-5> <double-down-mouse-5> 
<double-mouse-5> <down-mouse-1> <mouse-1> C-a C-n <return> 
M-1 C-n C-n C-n C-n C-n C-n <return> C-n C-n <return> 
M-1 C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n 
C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n 
C-p <return> <help-echo> <help-echo> <down-mouse-1> 
<mouse-1> C-a C-SPC C-n C-n C-n C-n C-n C-n C-n C-SPC 
C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p 
C-p M-w C-x o q g M-x r e p o r t - e m a c s - b u 
g <return>

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