Add default extension version to \dx

In an effort to make at least a couple of more people realize they have
to run ALTER EXTENSION UPDATE after they've upgraded an extension,  as
well as make it a bit easier to realize when you have to do it, this
adds the default version of an extension to the output of \dx. We
previously showed the installed version in the schema, but no
indications that a newer one might be installed on the system.

Author: JelteF

src/bin/psql/describe.c

@@ -6188,13 +6188,16 @@ listExtensions(const char *pattern)
 	initPQExpBuffer(&buf);
 	printfPQExpBuffer(&buf,
 					  "SELECT e.extname AS \"%s\", "
-					  "e.extversion AS \"%s\", n.nspname AS \"%s\", c.description AS \"%s\"\n"
+					  "e.extversion AS \"%s\", ae.default_version AS \"%s\","
+					  "n.nspname AS \"%s\", c.description AS \"%s\"\n"
 					  "FROM pg_catalog.pg_extension e "
 					  "LEFT JOIN pg_catalog.pg_namespace n ON n.oid = e.extnamespace "
 					  "LEFT JOIN pg_catalog.pg_description c ON c.objoid = e.oid "
+					  "LEFT JOIN pg_catalog.pg_available_extensions() ae(name, default_version, comment) ON ae.name = e.extname "
 					  "AND c.classoid = 'pg_catalog.pg_extension'::pg_catalog.regclass\n",
 					  gettext_noop("Name"),
 					  gettext_noop("Version"),
+					  gettext_noop("Default version"),
 					  gettext_noop("Schema"),
 					  gettext_noop("Description"));
 

src/test/regress/expected/psql.out

@@ -6460,9 +6460,9 @@ List of schemas
 (0 rows)
 
 \dx "no.such.installed.extension"
-     List of installed extensions
- Name | Version | Schema | Description 
-------+---------+--------+-------------
+              List of installed extensions
+ Name | Version | Default version | Schema | Description 
+------+---------+-----------------+--------+-------------
 (0 rows)
 
 \dX "no.such.extended.statistics"