bugfix: copy timestamps correctly in INSERT...SELECT

don't do it via MYSQL_TIME, that conversion is lossy
around DST change dates.

mysql-test/r/old-mode.result

@@ -149,4 +149,26 @@ a	unix_timestamp(a)
 2010-10-31 02:25:26	1288477526
 2010-10-31 02:25:26	1288481126
 drop table t1;
+set global mysql56_temporal_format=false;
+create table t1 (a timestamp);
+set timestamp=1288477526;
+insert t1 values (null);
+set timestamp=1288481126;
+insert t1 values (null);
+select a, unix_timestamp(a) from t1;
+a	unix_timestamp(a)
+2010-10-31 02:25:26	1288477526
+2010-10-31 02:25:26	1288481126
+set global mysql56_temporal_format=true;
+select a, unix_timestamp(a) from t1;
+a	unix_timestamp(a)
+2010-10-31 02:25:26	1288477526
+2010-10-31 02:25:26	1288481126
+create table t2 (a timestamp);
+insert t2 select a from t1;
+select a, unix_timestamp(a) from t2;
+a	unix_timestamp(a)
+2010-10-31 02:25:26	1288477526
+2010-10-31 02:25:26	1288481126
+drop table t1, t2;
 set time_zone=DEFAULT;

mysql-test/t/old-mode.test

@@ -86,6 +86,8 @@ SET @@global.mysql56_temporal_format=DEFAULT;
 #
 # MDEV-12672 Replicated TIMESTAMP fields given wrong value near DST change
 #
+
+# Copy_field
 set time_zone='Europe/Moscow';
 set global mysql56_temporal_format=false;
 create table t1 (a timestamp);
@@ -99,4 +101,19 @@ select a, unix_timestamp(a) from t1;
 alter table t1 modify a timestamp;
 select a, unix_timestamp(a) from t1;
 drop table t1;
+
+# field_conv_incompatible()
+set global mysql56_temporal_format=false;
+create table t1 (a timestamp);
+set timestamp=1288477526;
+insert t1 values (null);
+set timestamp=1288481126;
+insert t1 values (null);
+select a, unix_timestamp(a) from t1;
+set global mysql56_temporal_format=true;
+select a, unix_timestamp(a) from t1;
+create table t2 (a timestamp);
+insert t2 select a from t1;
+select a, unix_timestamp(a) from t2;
+drop table t1, t2;
 set time_zone=DEFAULT;

sql/field.cc

@@ -5064,6 +5064,23 @@ int Field_timestamp::store(longlong nr, bool unsigned_val)
 }
 
 
+int Field_timestamp::store_timestamp(Field_timestamp *from)
+{
+  ulong sec_part;
+  my_time_t ts= from->get_timestamp(&sec_part);
+  store_TIME(ts, sec_part);
+  if (!ts && !sec_part && get_thd()->variables.sql_mode & MODE_NO_ZERO_DATE)
+  {
+    ErrConvString s(
+      STRING_WITH_LEN("0000-00-00 00:00:00.000000") - (decimals() ? 6 - decimals() : 7),
+      system_charset_info);
+    set_datetime_warning(WARN_DATA_TRUNCATED, &s, MYSQL_TIMESTAMP_DATETIME, 1);
+    return 1;
+  }
+  return 0;
+}
+
+
 double Field_timestamp::val_real(void)
 {
   return (double) Field_timestamp::val_int();

sql/field.h

@@ -2186,6 +2186,7 @@ class Field_timestamp :public Field_temporal {
   int  store(longlong nr, bool unsigned_val);
   int  store_time_dec(MYSQL_TIME *ltime, uint dec);
   int  store_decimal(const my_decimal *);
+  int  store_timestamp(Field_timestamp *from);
   double val_real(void);
   longlong val_int(void);
   String *val_str(String*,String *);

sql/field_conv.cc

@@ -219,6 +219,13 @@ set_field_to_null_with_conversions(Field *field, bool no_conversions)
 }
 
 
+static int copy_timestamp_fields(Field *from, Field *to)
+{
+  DBUG_ASSERT(from->type() == MYSQL_TYPE_TIMESTAMP);
+  DBUG_ASSERT(to->type() == MYSQL_TYPE_TIMESTAMP);
+  return ((Field_timestamp*)to)->store_timestamp((Field_timestamp*)from);
+}
+
 static void do_skip(Copy_field *copy __attribute__((unused)))
 {
 }
@@ -419,13 +426,7 @@ static void do_field_decimal(Copy_field *copy)
 
 static void do_field_timestamp(Copy_field *copy)
 {
-  DBUG_ASSERT(copy->from_field->type() == MYSQL_TYPE_TIMESTAMP);
-  DBUG_ASSERT(copy->to_field->type() == MYSQL_TYPE_TIMESTAMP);
-  ulong sec_part;
-  Field_timestamp *f= static_cast<Field_timestamp*>(copy->from_field);
-  Field_timestamp *t= static_cast<Field_timestamp*>(copy->to_field);
-  my_time_t ts= f->get_timestamp(&sec_part);
-  t->store_TIME(ts, sec_part);
+  copy_timestamp_fields(copy->from_field, copy->to_field);
 }
 
 
@@ -938,6 +939,10 @@ int field_conv_incompatible(Field *to, Field *from)
     my_decimal buff;
     return to->store_decimal(from->val_decimal(&buff));
   }
+  if (from->type() == MYSQL_TYPE_TIMESTAMP && to->type() == MYSQL_TYPE_TIMESTAMP)
+  {
+    return copy_timestamp_fields(from, to);
+  }
   if (from->cmp_type() == TIME_RESULT)
   {
     MYSQL_TIME ltime;