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Commit cebc1d34e taught parseqatom() to optimize cases where a branch contains only one, "messy", atom by getting rid of excess subRE nodes. The way we really should do that is to keep the subRE built for the "messy" child atom; but to avoid changing parseqatom's nominal API, I made it delete that node after copying its fields to the outer subRE made by parsebranch(). It seems that that actually worked at the time; but it became dangerous after ea1268f63, because that later commit allowed the lower invocation of parse() to return a subRE that was also pointed to by some v->subs[] entry. This meant we could wind up with a dangling pointer in v->subs[], allowing a later backref to misbehave, but only if that subRE struct had been reused in between. So the damage seems confined to cases like '((...))...(...\2'. To fix, do what I should have done before and modify parseqatom's API to make it possible for it to remove the caller's subRE instead of the callee's. That's safer because we know that subRE isn't complete yet, so noplace else will have a pointer to it. Per report from Mark Dilger. Back-patch to v14 where the problematic patches came in. Discussion: https://postgr.es/m/0203588E-E609-43AF-9F4F-902854231EE7@enterprisedb.com
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: https://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. 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 https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.