MDEV-18408 Assertion `0' failed in Item::val_native_result / Timestamp_or_zero_datetime_native_null::Timestamp_or_zero_datetime_native_null upon mysqld_list_fields after crash recovery

The problem happened because Item_ident_for_show did not implement val_native().

Solution:

- Removing class Item_ident_for_show
- Implementing a new method Protocol::send_list_fields() instead,
  which accepts a List<Field> instead of List<Item> as input.
  Now no any Item creation is done during mysqld_list_fields().

Adding helper methods, to reuse the code easier:
- Moved a part of Protocol::send_result_set_metadata(),
  responsible for sending an individual field metadata,
  into a new method Protocol_text::store_field_metadata().
  Reusing it in both send_list_fields() and send_result_set_metadata().
- Adding Protocol_text::store_field_metadata()
- Adding Protocol_text::store_field_metadata_for_list_fields()

Note, this patch also automatically fixed another bug:

MDEV-18685 mysql_list_fields() returns DEFAULT 0 instead of DEFAULT NULL for view columns

The reason for this bug was that Item_ident_for_show::val_xxx() and get_date()
did not check field->is_null() before calling field->val_xxx()/get_date().
Now the default value is correctly sent by Protocol_text::store(Field*).

1 files changed, 39 insertions, 1 deletions

diff --git a/tests/mysql_client_test.c b/tests/mysql_client_test.c
index 2d238d84d54..6d17fa74005 100644
--- a/tests/mysql_client_test.c
+++ b/tests/mysql_client_test.c
@@ -8467,6 +8467,43 @@ static void test_list_fields_default()
 }
 
 
+/**
+  Note, this test covers MDEV-18408 and MDEV-18685
+*/
+
+static void test_mdev18408()
+{
+  MYSQL_RES *result;
+  int rc;
+  myheader("test_mdev18408s");
+
+  rc= mysql_query(mysql, "DROP TABLE IF EXISTS t1");
+  myquery(rc);
+
+  rc= mysql_query(mysql, "DROP VIEW IF EXISTS v1");
+  myquery(rc);
+
+  rc= mysql_query(mysql, "CREATE TABLE t1 (c1 TIMESTAMP NULL DEFAULT NULL)");
+  myquery(rc);
+
+  rc= mysql_query(mysql, "CREATE VIEW v1 AS SELECT c1 FROM t1");
+  myquery(rc);
+
+  result= mysql_list_fields(mysql, "v1", NULL);
+  mytest(result);
+
+  rc= my_process_result_set(result);
+  DIE_UNLESS(rc == 0);
+
+  verify_prepare_field(result, 0, "c1", "c1", MYSQL_TYPE_TIMESTAMP,
+                       "v1", "v1",  current_db, 19, 0);
+
+  mysql_free_result(result);
+  myquery(mysql_query(mysql, "DROP VIEW v1"));
+  myquery(mysql_query(mysql, "DROP TABLE t1"));
+}
+
+
 static void test_bug19671()
 {
   MYSQL_RES *result;
@@ -8493,7 +8530,7 @@ static void test_bug19671()
   DIE_UNLESS(rc == 0);
 
   verify_prepare_field(result, 0, "f1", "f1", MYSQL_TYPE_LONG,
-                       "v1", "v1", current_db, 11, "0");
+                       "v1", "v1", current_db, 11, NULL);
 
   mysql_free_result(result);
   myquery(mysql_query(mysql, "drop view v1"));
@@ -20977,6 +21014,7 @@ static struct my_tests_st my_tests[]= {
   { "test_bulk_delete", test_bulk_delete },
 #endif
   { "test_explain_meta", test_explain_meta },
+  { "test_mdev18408", test_mdev18408 },
   { 0, 0 }
 };