MDEV-452 Add full support for auto-initialized/updated timestamp and datetime

Generalized support for auto-updated and/or auto-initialized timestamp
and datetime columns. This patch is a reimplementation of MySQL's
"WL#5874: CURRENT_TIMESTAMP as DEFAULT for DATETIME columns". In order to
ease future merges, this implementation reused few function and variable
names from MySQL's patch, however the implementation is quite different.

TODO:
The only unresolved problem in this patch is the semantics of LOAD DATA for
TIMESTAMP and DATETIME columns in the cases when there are missing or NULL
columns. I couldn't fully comprehend the logic behind MySQL's behavior and
its relationship with their own documentation, so I left the results to be
more consistent with all other LOAD cases.

The problematic test cases can be seen by running the test file function_defaults,
and observing the test case differences. Those were left on purpose for discussion.

1 files changed, 20 insertions, 29 deletions

diff --git a/sql/sql_load.cc b/sql/sql_load.cc
index 98031c96225..18cea96dd92 100644
--- a/sql/sql_load.cc
+++ b/sql/sql_load.cc
@@ -273,7 +273,6 @@ int mysql_load(THD *thd,sql_exchange *ex,TABLE_LIST *table_list,
     for (field=table->field; *field ; field++)
       fields_vars.push_back(new Item_field(*field));
     bitmap_set_all(table->write_set);
-    table->timestamp_field_type= TIMESTAMP_NO_AUTO_SET;
     /*
       Let us also prepare SET clause, altough it is probably empty
       in this case.
@@ -289,21 +288,9 @@ int mysql_load(THD *thd,sql_exchange *ex,TABLE_LIST *table_list,
         setup_fields(thd, 0, set_fields, MARK_COLUMNS_WRITE, 0, 0) ||
         check_that_all_fields_are_given_values(thd, table, table_list))
       DBUG_RETURN(TRUE);
-    /*
-      Check whenever TIMESTAMP field with auto-set feature specified
-      explicitly.
-    */
-    if (table->timestamp_field)
-    {
-      if (bitmap_is_set(table->write_set,
-                        table->timestamp_field->field_index))
-        table->timestamp_field_type= TIMESTAMP_NO_AUTO_SET;
-      else
-      {
-        bitmap_set_bit(table->write_set,
-                       table->timestamp_field->field_index);
-      }
-    }
+    /* Add all fields with default functions to table->write_set. */
+    if (table->default_field)
+      table->mark_default_fields_for_write();
     /* Fix the expressions in SET clause */
     if (setup_fields(thd, 0, set_values, MARK_COLUMNS_READ, 0, 0))
       DBUG_RETURN(TRUE);
@@ -850,7 +837,7 @@ read_fixed_length(THD *thd, COPY_INFO &info, TABLE_LIST *table_list,
                             ER(ER_WARN_TOO_FEW_RECORDS),
                             thd->warning_info->current_row_for_warning());
         if (!field->maybe_null() && field->type() == FIELD_TYPE_TIMESTAMP)
-            ((Field_timestamp*) field)->set_time();
+          field->set_time();
       }
       else
       {
@@ -864,6 +851,7 @@ read_fixed_length(THD *thd, COPY_INFO &info, TABLE_LIST *table_list,
 	pos[length]=save_chr;
 	if ((pos+=length) > read_info.row_end)
 	  pos= read_info.row_end;	/* Fills rest with space */
+        field->set_explicit_default(NULL);
       }
     }
     if (pos != read_info.row_end)
@@ -876,10 +864,10 @@ read_fixed_length(THD *thd, COPY_INFO &info, TABLE_LIST *table_list,
     }
 
     if (thd->killed ||
-        fill_record_n_invoke_before_triggers(thd, set_fields, set_values,
+        fill_record_n_invoke_before_triggers(thd, table, set_fields, set_values,
                                              ignore_check_option_errors,
-                                             table->triggers,
-                                             TRG_EVENT_INSERT))
+                                             TRG_EVENT_INSERT) ||
+        (table->default_field && table->update_default_fields()))
       DBUG_RETURN(1);
 
     switch (table_list->view_check_option(thd,
@@ -994,10 +982,11 @@ read_sep_field(THD *thd, COPY_INFO &info, TABLE_LIST *table_list,
             DBUG_RETURN(1);
           }
           field->set_null();
+          field->set_explicit_default(NULL);
           if (!field->maybe_null())
           {
             if (field->type() == MYSQL_TYPE_TIMESTAMP)
-              ((Field_timestamp*) field)->set_time();
+              field->set_time();
             else if (field != table->next_number_field)
               field->set_warning(MYSQL_ERROR::WARN_LEVEL_WARN,
                                  ER_WARN_NULL_TO_NOTNULL, 1);
@@ -1025,6 +1014,7 @@ read_sep_field(THD *thd, COPY_INFO &info, TABLE_LIST *table_list,
         if (field == table->next_number_field)
           table->auto_increment_field_not_null= TRUE;
         field->store((char*) pos, length, read_info.read_charset);
+        field->set_explicit_default(NULL);
       }
       else if (item->type() == Item::STRING_ITEM)
       {
@@ -1066,7 +1056,7 @@ read_sep_field(THD *thd, COPY_INFO &info, TABLE_LIST *table_list,
             DBUG_RETURN(1);
           }
           if (!field->maybe_null() && field->type() == FIELD_TYPE_TIMESTAMP)
-              ((Field_timestamp*) field)->set_time();
+            field->set_time();
           /*
             TODO: We probably should not throw warning for each field.
             But how about intention to always have the same number
@@ -1093,10 +1083,10 @@ read_sep_field(THD *thd, COPY_INFO &info, TABLE_LIST *table_list,
     }
 
     if (thd->killed ||
-        fill_record_n_invoke_before_triggers(thd, set_fields, set_values,
+        fill_record_n_invoke_before_triggers(thd, table, set_fields, set_values,
                                              ignore_check_option_errors,
-                                             table->triggers,
-                                             TRG_EVENT_INSERT))
+                                             TRG_EVENT_INSERT) ||
+        (table->default_field && table->update_default_fields()))
       DBUG_RETURN(1);
 
     switch (table_list->view_check_option(thd,
@@ -1206,7 +1196,7 @@ read_xml_field(THD *thd, COPY_INFO &info, TABLE_LIST *table_list,
           if (!field->maybe_null())
           {
             if (field->type() == FIELD_TYPE_TIMESTAMP)
-              ((Field_timestamp *) field)->set_time();
+              field->set_time();
             else if (field != table->next_number_field)
               field->set_warning(MYSQL_ERROR::WARN_LEVEL_WARN,
                                  ER_WARN_NULL_TO_NOTNULL, 1);
@@ -1225,6 +1215,7 @@ read_xml_field(THD *thd, COPY_INFO &info, TABLE_LIST *table_list,
         if (field == table->next_number_field)
           table->auto_increment_field_not_null= TRUE;
         field->store((char *) tag->value.ptr(), tag->value.length(), cs);
+        field->set_explicit_default(NULL);
       }
       else
         ((Item_user_var_as_out_param *) item)->set_value(
@@ -1269,10 +1260,10 @@ read_xml_field(THD *thd, COPY_INFO &info, TABLE_LIST *table_list,
     }
 
     if (thd->killed ||
-        fill_record_n_invoke_before_triggers(thd, set_fields, set_values,
+        fill_record_n_invoke_before_triggers(thd, table, set_fields, set_values,
                                              ignore_check_option_errors,
-                                             table->triggers,
-                                             TRG_EVENT_INSERT))
+                                             TRG_EVENT_INSERT) ||
+        (table->default_field && table->update_default_fields()))
       DBUG_RETURN(1);
 
     switch (table_list->view_check_option(thd,