Backport fix for bug #70066

Given the number of duplicates this bug report had, it seems
worthwhile to fix this on PHP-7.4 as well.

Cherry-pick of 106e7e4.

Author: nikic

NEWS

@@ -36,6 +36,8 @@ PHP                                                                        NEWS
     statements). (Nikita)
   . Fixed bug #78152 (PDO::exec() - Bad error handling with multiple commands).
     (Nikita)
+  . Fixed bug #70066 (Unexpected "Cannot execute queries while other unbuffered
+    queries"). (Nikita)
 
 - Phpdbg:
   . Fixed bug #76813 (Access violation near NULL on source operand). (cmb)

ext/mysqlnd/mysqlnd_libmysql_compat.h

@@ -82,7 +82,7 @@
 #define mysql_stmt_param_count(s)		mysqlnd_stmt_param_count((s))
 #define mysql_stmt_num_rows(s)			mysqlnd_stmt_num_rows((s))
 #define mysql_stmt_insert_id(s)			mysqlnd_stmt_insert_id((s))
-#define mysql_stmt_close(s)				mysqlnd_stmt_close((s))
+#define mysql_stmt_close(s)				mysqlnd_stmt_close((s), 0)
 #define mysql_stmt_bind_param(s,b)		mysqlnd_stmt_bind_param((s), (b))
 #define mysql_stmt_bind_result(s,b)		mysqlnd_stmt_bind_result((s), (b))
 #define mysql_stmt_errno(s)				mysqlnd_stmt_errno((s))

ext/pdo_mysql/mysql_driver.c

@@ -203,18 +203,17 @@ static int mysql_handle_preparer(pdo_dbh_t *dbh, const char *sql, size_t sql_len
 	}
 
 	if (mysql_stmt_prepare(S->stmt, sql, sql_len)) {
+		if (nsql) {
+			efree(nsql);
+		}
 		/* TODO: might need to pull statement specific info here? */
 		/* if the query isn't supported by the protocol, fallback to emulation */
 		if (mysql_errno(H->server) == 1295) {
-			if (nsql) {
-				efree(nsql);
-			}
+			mysql_stmt_close(S->stmt);
+			S->stmt = NULL;
 			goto fallback;
 		}
 		pdo_mysql_error(dbh);
-		if (nsql) {
-			efree(nsql);
-		}
 		PDO_DBG_RETURN(0);
 	}
 	if (nsql) {

ext/pdo_mysql/mysql_statement.c

@@ -33,11 +33,9 @@
 #ifdef PDO_USE_MYSQLND
 #	define pdo_mysql_stmt_execute_prepared(stmt) pdo_mysql_stmt_execute_prepared_mysqlnd(stmt)
 #	define pdo_free_bound_result(res) zval_ptr_dtor(res.zv)
-#	define pdo_mysql_stmt_close(stmt) mysqlnd_stmt_close(stmt, 0)
 #else
 #	define pdo_mysql_stmt_execute_prepared(stmt) pdo_mysql_stmt_execute_prepared_libmysql(stmt)
 #	define pdo_free_bound_result(res) efree(res.buffer)
-#	define pdo_mysql_stmt_close(stmt) mysql_stmt_close(stmt)
 #endif
 
 
@@ -58,7 +56,7 @@ static int pdo_mysql_stmt_dtor(pdo_stmt_t *stmt) /* {{{ */
 		S->einfo.errmsg = NULL;
 	}
 	if (S->stmt) {
-		pdo_mysql_stmt_close(S->stmt);
+		mysql_stmt_close(S->stmt);
 		S->stmt = NULL;
 	}
 
@@ -352,7 +350,7 @@ static int pdo_mysql_stmt_next_rowset(pdo_stmt_t *stmt) /* {{{ */
 	PDO_DBG_INF_FMT("stmt=%p", S->stmt);
 
 #if PDO_USE_MYSQLND
-	if (!H->emulate_prepare) {
+	if (S->stmt) {
 		if (!mysqlnd_stmt_more_results(S->stmt)) {
 			PDO_DBG_RETURN(0);
 		}

ext/pdo_mysql/tests/bug70066.phpt

@@ -0,0 +1,27 @@
+--TEST--
+Bug #70066: Unexpected "Cannot execute queries while other unbuffered queries"
+--SKIPIF--
+<?php
+if (!extension_loaded('pdo') || !extension_loaded('pdo_mysql')) die('skip not loaded');
+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');
+
+$pdo = MySQLPDOTest::factory();
+$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
+$pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, 0);
+
+$db = $pdo->query('SELECT DATABASE()')->fetchColumn(0);
+// USE is not supported in the prepared statement protocol,
+// so this will fall back to emulation.
+$pdo->query('USE ' . $db);
+
+?>
+===DONE===
+--EXPECT--
+===DONE===