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The syntax "\n*", that is a backref with a * quantifier directly applied to it, has never worked correctly in Spencer's library. This has been an open bug in the Tcl bug tracker since 2005: https://sourceforge.net/tracker/index.php?func=detail&aid=1115587&group_id=10894&atid=110894 The core of the problem is in parseqatom(), which first changes "\n*" to "\n+|" and then applies repeat() to the NFA representing the backref atom. repeat() thinks that any arc leading into its "rp" argument is part of the sub-NFA to be repeated. Unfortunately, since parseqatom() already created the arc that was intended to represent the empty bypass around "\n+", this arc gets moved too, so that it now leads into the state loop created by repeat(). Thus, what was supposed to be an "empty" bypass gets turned into something that represents zero or more repetitions of the NFA representing the backref atom. In the original example, in place of ^([bc])\1*$ we now have something that acts like ^([bc])(\1+|[bc]*)$ At runtime, the branch involving the actual backref fails, as it's supposed to, but then the other branch succeeds anyway. We could no doubt fix this by some rearrangement of the operations in parseqatom(), but that code is plenty ugly already, and what's more the whole business of converting "x*" to "x+|" probably needs to go away to fix another problem I'll mention in a moment. Instead, this patch suppresses the *-conversion when the target is a simple backref atom, leaving the case of m == 0 to be handled at runtime. This makes the patch in regcomp.c a one-liner, at the cost of having to tweak cbrdissect() a little. In the event I went a bit further than that and rewrote cbrdissect() to check all the string-length-related conditions before it starts comparing characters. It seems a bit stupid to possibly iterate through many copies of an n-character backreference, only to fail at the end because the target string's length isn't a multiple of n --- we could have found that out before starting. The existing coding could only be a win if integer division is hugely expensive compared to character comparison, but I don't know of any modern machine where that might be true. This does not fix all the problems with quantified back-references. In particular, the code is still broken for back-references that appear within a larger expression that is quantified (so that direct insertion of the quantification limits into the BACKREF node doesn't apply). I think fixing that will take some major surgery on the NFA code, specifically introducing an explicit iteration node type instead of trying to transform iteration into concatenation of modified regexps. Back-patch to all supported branches. In HEAD, also add a regression test case for this. (It may seem a bit silly to create a regression test file for just one test case; but I'm expecting that we will soon import a whole bunch of regex regression tests from Tcl, so might as well create the infrastructure now.) |
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PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. PostgreSQL has many language interfaces, many of which are listed here: http://www.postgresql.org/download See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Changes between all PostgreSQL releases are recorded in the file HISTORY. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.