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This commit improves on the results of commit 511ae628f in two ways: 1. It restores the historical behavior that "\set FOO" is interpreted as setting FOO to "on", if FOO is a boolean control variable. We already found one test script that was expecting that behavior, and the psql documentation certainly does nothing to discourage people from assuming that would work, since it often says just "if FOO is set" when describing the effects of a boolean variable. However, now this case will result in actually setting FOO to "on", not an empty string. 2. It arranges for an "\unset" of a control variable to set the value back to its default value, rather than becoming apparently undefined. The control variables are also initialized that way at psql startup. In combination, these things guarantee that a control variable always has a displayable value that reflects what psql is actually doing. That is a pretty substantial usability improvement. The implementation involves adding a second type of variable hook function that is able to replace a proposed new value (including NULL) with another one. We could alternatively have complicated the API of the assign hook, but this way seems better since many variables can share the same substitution hook function. Also document the actual behavior of these variables more fully, including covering assorted behaviors that were there before but never documented. This patch also includes some minor cleanup that should have been in 511ae628f but was missed. Patch by me, but it owes a lot to discussions with Daniel Vérité. Discussion: https://postgr.es/m/9572.1485821620@sss.pgh.pa.us
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. 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/.