PDO: add mysql-specific warning count function

MySQL supplies the count of warnings along with the result set and
provides a handy function to retrieve it.

Without this, the only way to discover if there has been warnings
in the last query is to run *another* query: "SHOW WARNINGS" OR
"SELECT @@warning_count". This requires another round-trip across
the network which makes warning discovery or reporting a drag on
performance.

Instead, we use the existing get_driver_methods function that others
(postgres, sqlite) use to provide custom functionality outside the
standard PDO interface.

Thinking about the PDO interface, I looked into several other PDO
drivers but couldn't find an analog for mysql_warning_count(). Thus I
determined that this may well stay mysql-specific.

Fixes php bug: #51499 (https://bugs.php.net/bug.php?id=51499)

Author: danielbeardsley

ext/pdo_mysql/mysql_driver.c

@@ -533,6 +533,36 @@ static int pdo_mysql_check_liveness(pdo_dbh_t *dbh)
 }
 /* }}} */
 
+/* {{{ proto string PDO::mysqlGetWarningCount()
+   Returns the number of SQL warnings during the execution of the last statement */
+static PHP_METHOD(PDO, mysqlGetWarningCount)
+{
+	pdo_dbh_t *dbh;
+	pdo_mysql_db_handle *H;
+
+	dbh = Z_PDO_DBH_P(ZEND_THIS);
+	PDO_CONSTRUCT_CHECK;
+
+	H = (pdo_mysql_db_handle *)dbh->driver_data;
+	RETURN_LONG(mysql_warning_count(H->server));
+}
+/* }}} */
+
+static const zend_function_entry dbh_methods[] = {
+	PHP_ME(PDO, mysqlGetWarningCount, NULL, ZEND_ACC_PUBLIC)
+	PHP_FE_END
+};
+
+static const zend_function_entry *pdo_mysql_get_driver_methods(pdo_dbh_t *dbh, int kind)
+{
+	switch (kind) {
+		case PDO_DBH_DRIVER_METHOD_KIND_DBH:
+			return dbh_methods;
+		default:
+			return NULL;
+	}
+}
+
 /* {{{ pdo_mysql_request_shutdown */
 static void pdo_mysql_request_shutdown(pdo_dbh_t *dbh)
 {
@@ -562,7 +592,7 @@ static const struct pdo_dbh_methods mysql_methods = {
 	pdo_mysql_fetch_error_func,
 	pdo_mysql_get_attribute,
 	pdo_mysql_check_liveness,
-	NULL,
+	pdo_mysql_get_driver_methods,
 	pdo_mysql_request_shutdown,
 	NULL
 };

ext/pdo_mysql/tests/pdo_mysql_get_warning_count.phpt

@@ -0,0 +1,22 @@
+--TEST--
+MySQL PDO->mysqlGetWarningCount()
+--SKIPIF--
+<?php
+require_once(__DIR__ . DIRECTORY_SEPARATOR . 'skipif.inc');
+require_once(__DIR__ . DIRECTORY_SEPARATOR . 'mysql_pdo_test.inc');
+MySQLPDOTest::skip();
+?>
+--FILE--
+<?php
+	require_once(__DIR__ . DIRECTORY_SEPARATOR . 'mysql_pdo_test.inc');
+	$db = MySQLPDOTest::factory();
+	$assertWarnings = function ($db, $q, $count) {
+		$db->query($q);
+		printf("Query %s produced %d warnings\n", $q, $db->mysqlGetWarningCount());
+	};
+	$assertWarnings($db, 'SELECT 1 = 1', 0);
+	$assertWarnings($db, 'SELECT 1 = "A"', 1);
+?>
+--EXPECT--
+Query SELECT 1 = 1 produced 0 warnings
+Query SELECT 1 = "A" produced 1 warnings