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A bounded quantifier with m = n = 1 might be thought a no-op. But
according to our documentation (which traces back to Henry Spencer's
original man page) it still imposes greediness, or non-greediness in the
case of the non-greedy variant "{1,1}?", on whatever it's attached to.
This turns out not to work though, because parseqatom() optimizes away
the m = n = 1 case without regard for whether it's supposed to change
the greediness of the argument RE.
We can fix this by just not applying the optimization when the greediness
needs to change; the subsequent general cases handle it fine.
The three cases in which we can still apply the optimization are
(a) no quantifier, or quantifier does not impose a preference;
(b) atom has no greediness property, implying it cannot match a
variable amount of text anyway; or
(c) quantifier's greediness is same as atom's.
Note that in most cases where one of these applies, we'd have exited
earlier in the "not a messy case" fast path. I think it's now only
possible to get to the optimization when the atom involves capturing
parentheses or a non-top-level backref.
Back-patch to all supported branches. I'd ordinarily be hesitant to
put a subtle behavioral change into back branches, but in this case
it's very hard to see a reason why somebody would write "{1,1}?" unless
they're trying to get the documented change-of-greediness behavior.
Discussion: https://postgr.es/m/5bb27a41-350d-37bf-901e-9d26f5592dd0@charter.net
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/.