Bug#42364 SHOW ERRORS returns empty resultset after dropping non existent table

partial backport of bug43138 fix


mysql-test/r/warnings.result:
  test result
mysql-test/t/warnings.test:
  test case
sql/sql_class.cc:
  partial backport of bug43138 fix
sql/sql_class.h:
  partial backport of bug43138 fix
sql/sql_table.cc:
  partial backport of bug43138 fix

sql/sql_class.cc

@@ -399,6 +399,31 @@ char *thd_security_context(THD *thd, char *buffer, unsigned int length,
   return buffer;
 }
 
+
+/**
+  Implementation of Drop_table_error_handler::handle_error().
+  The reason in having this implementation is to silence technical low-level
+  warnings during DROP TABLE operation. Currently we don't want to expose
+  the following warnings during DROP TABLE:
+    - Some of table files are missed or invalid (the table is going to be
+      deleted anyway, so why bother that something was missed);
+    - A trigger associated with the table does not have DEFINER (One of the
+      MySQL specifics now is that triggers are loaded for the table being
+      dropped. So, we may have a warning that trigger does not have DEFINER
+      attribute during DROP TABLE operation).
+
+  @return TRUE if the condition is handled.
+*/
+bool Drop_table_error_handler::handle_error(uint sql_errno,
+                                            const char *message,
+                                            MYSQL_ERROR::enum_warning_level level,
+                                            THD *thd)
+{
+  return ((sql_errno == EE_DELETE && my_errno == ENOENT) ||
+          sql_errno == ER_TRG_NO_DEFINER);
+}
+
+
 /**
   Clear this diagnostics area.