Description:
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There is currently no way to receive PostgreSQL's notices PHP-side.

A PQsetNoticeProcessor has been defined 15 years ago to the empty function _pdo_pgsql_notice, to prevent libpq's default behaviour (fprintfing to stderr)).

Passing notices to PHP could prove useful, allowing e.g. user-defined RAISE NOTICE in PL/pgSQL long-running code to provide feedback.

A user-space callback would give more control on what to do with the message (compared to the exec-then-fetch method of non-PDO pgsql driver's pg_last_notice)… not the least being the live feedback ability.

Test script:
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function disp($message) { echo trim($message)."\n"; }
$db = new PDO('pgsql:host=localhost;port=5432;dbname=…', '', '');
if(method_exists($db, 'pgsqlSetNoticeCallback'))
    $db->pgsqlSetNoticeCallback('disp');
$db->beginTransaction();
$db->exec("create temporary table t (a varchar(3))");
$db->exec("create function hey() returns trigger as \$\$ begin new.a := 'oh'; raise notice 'I tampered your data, did you know?'; return new; end; \$\$ language plpgsql");
$db->exec("create trigger hop before insert on t for each row execute procedure hey()");
$db->exec("insert into t values ('ah')");
print_r($db->query("select * from t")->fetchAll());

Expected result:
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I would like to know that a trigger triggered ("I tampered your data, did you know?").

Actual result:
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Only tcpdump will display my carefully-crafted RAISE NOTICE.