bug#18577: Regexp I-search: [(error Stack overflow in regexp matcher)]

[Alan Mackenzie]

Hi, Emacs.

In the trunk, emacs -Q.  Visit our favourite big file, xdisp.c.

With point at BOB, do C-M-s and enter this regular expression at the
prompt:

/\*\(\([^'*]\|\*[^/']\)*\*?'\([^'*]\|\*[^/']\)*\*?'\)*\([^'*]\|\*[^'/]\)*\*?'\([^'*]\|\*[^/']\)*\*?\*/

Press C-s.  This gives the error message "[(error Stack overflow in
regexp matcher)]".

This feels like a bug.  Regexp searching with this expression (which
finds a block comment containing an odd number of apostrophes) works fine
in the rest of the buffer.  Only in the second (large) comment in xdisp.c
does it trigger this error.  Surely an iterative regexp (which all
regexps are, surely?) shouldn't be triggering unbounded recursive
behaviour in the search engine.

[N.B. the regexp when parsed a bit looks like this:

/\*\(                                              \)*\(     \|       \)*\*?'\( 
    \|       \)*\*?\*/
     \(     \|       \)*\*?'\(     \|       \)*\*?'     [^'*]  \*[^'/]         
[^'*]  \*[^/']
       [^'*]  \*[^/']         [^'*]  \*[^/']

].  

-- 
Alan Mackenzie (Nuremberg, Germany).