MDEV-19819 ALTER from POINT to LINESTRING erroneously preserves POINT values

mysql-test/main/gis.result

@@ -5019,5 +5019,21 @@ ERROR HY000: Illegal parameter data types int and geometry for operation 'in'
 SELECT (1,(0,0)) IN ((1,(POINT(1,1),0)),(0,(0,0)));
 ERROR HY000: Illegal parameter data types int and geometry for operation 'in'
 #
+# MDEV-19819 ALTER from POINT to LINESTRING erroneously preserves POINT values
+#
+CREATE TABLE t1 (a POINT) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (Point(0,0));
+ALTER TABLE t1 MODIFY a LINESTRING;
+ERROR 22007: Incorrect LINESTRING value: 'POINT' for column `test`.`t1`.`a` at row 1
+DROP TABLE t1;
+CREATE TABLE t1 (a LINESTRING);
+CREATE TABLE t2 (a POINT);
+INSERT INTO t2 VALUES (POINT(0,0));
+INSERT INTO t1 SELECT * FROM t2;
+ERROR 22007: Incorrect LINESTRING value: 'POINT' for column `test`.`t1`.`a` at row 1
+SELECT AsText(a) FROM t1;
+AsText(a)
+DROP TABLE t1, t2;
+#
 # End of 10.4 tests
 #

mysql-test/main/gis.test

@@ -3094,6 +3094,25 @@ SELECT (1,0) IN ((POINT(1,1),0),(0,0));
 --error ER_ILLEGAL_PARAMETER_DATA_TYPES2_FOR_OPERATION
 SELECT (1,(0,0)) IN ((1,(POINT(1,1),0)),(0,(0,0)));
 
+--echo #
+--echo # MDEV-19819 ALTER from POINT to LINESTRING erroneously preserves POINT values
+--echo #
+
+CREATE TABLE t1 (a POINT) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (Point(0,0));
+--error ER_TRUNCATED_WRONG_VALUE_FOR_FIELD
+ALTER TABLE t1 MODIFY a LINESTRING;
+DROP TABLE t1;
+
+CREATE TABLE t1 (a LINESTRING);
+CREATE TABLE t2 (a POINT);
+INSERT INTO t2 VALUES (POINT(0,0));
+--error ER_TRUNCATED_WRONG_VALUE_FOR_FIELD
+INSERT INTO t1 SELECT * FROM t2;
+SELECT AsText(a) FROM t1;
+DROP TABLE t1, t2;
+
+
 --echo #
 --echo # End of 10.4 tests
 --echo #

mysql-test/suite/innodb_gis/r/alter_spatial_index.result

@@ -485,8 +485,7 @@ ALTER TABLE tab MODIFY COLUMN c2 GEOMETRY NOT NULL;
 affected rows: 0
 info: Records: 0  Duplicates: 0  Warnings: 0
 ALTER TABLE tab MODIFY COLUMN c3 POLYGON NOT NULL;
-affected rows: 10
-info: Records: 10  Duplicates: 0  Warnings: 0
+ERROR 22007: Incorrect POLYGON value: 'LINESTRING' for column `test`.`tab`.`c3` at row 1
 ALTER TABLE tab add COLUMN c7 POINT NOT NULL;
 affected rows: 0
 info: Records: 0  Duplicates: 0  Warnings: 0
@@ -528,7 +527,7 @@ Table	Create Table
 tab	CREATE TABLE `tab` (
   `c1` int(11) NOT NULL,
   `c2` geometry NOT NULL,
-  `c3` polygon NOT NULL,
+  `c3` linestring NOT NULL,
   `c4` polygon NOT NULL,
   `c5` geometry NOT NULL,
   `c7` point NOT NULL,
@@ -565,7 +564,7 @@ Table	Create Table
 tab	CREATE TABLE `tab` (
   `c1` int(11) NOT NULL,
   `c2` geometry NOT NULL,
-  `c3` polygon NOT NULL,
+  `c3` linestring NOT NULL,
   `c4` geometry NOT NULL,
   `c5` geometry NOT NULL,
   `c7` point NOT NULL,
@@ -614,9 +613,6 @@ SET @g2 = ST_GeomFromText('LINESTRING(1 1,2 2,3 3)');
 ALTER TABLE tab MODIFY COLUMN c2 POINT NOT NULL;
 affected rows: 8
 info: Records: 8  Duplicates: 0  Warnings: 0
-ALTER TABLE tab MODIFY COLUMN c3 LINESTRING NOT NULL;
-affected rows: 8
-info: Records: 8  Duplicates: 0  Warnings: 0
 ALTER TABLE tab MODIFY COLUMN c4 POLYGON NOT NULL;
 affected rows: 8
 info: Records: 8  Duplicates: 0  Warnings: 0

mysql-test/suite/innodb_gis/t/alter_spatial_index.test

@@ -476,6 +476,7 @@ ALTER TABLE tab ADD INDEX idx6(c4(10)) USING BTREE;
 
 ALTER TABLE tab MODIFY COLUMN c2 GEOMETRY NOT NULL;
 
+--error ER_TRUNCATED_WRONG_VALUE_FOR_FIELD
 ALTER TABLE tab MODIFY COLUMN c3 POLYGON NOT NULL;
 
 ALTER TABLE tab add COLUMN c7 POINT NOT NULL;
@@ -552,8 +553,6 @@ SET @g2 = ST_GeomFromText('LINESTRING(1 1,2 2,3 3)');
 --enable_info
 ALTER TABLE tab MODIFY COLUMN c2 POINT NOT NULL;
 
-ALTER TABLE tab MODIFY COLUMN c3 LINESTRING NOT NULL;
-
 ALTER TABLE tab MODIFY COLUMN c4 POLYGON NOT NULL;
 --disable_info
 

sql/field.h

@@ -1528,7 +1528,7 @@ class Field: public Value_source
   {
     return field_length / charset()->mbmaxlen;
   }
-  virtual geometry_type get_geometry_type()
+  virtual geometry_type get_geometry_type() const
   {
     /* shouldn't get here. */
     DBUG_ASSERT(0);
@@ -4138,6 +4138,21 @@ class Field_geom :public Field_blob {
                                   const Item *item,
                                   bool is_eq_func) const;
   void sql_type(String &str) const;
+  Copy_func *get_copy_func(const Field *from) const
+  {
+    if (type_handler() == from->type_handler() &&
+        (geom_type == GEOM_GEOMETRY ||
+         geom_type == static_cast<const Field_geom*>(from)->geom_type))
+      return get_identical_copy_func();
+    return do_conv_blob;
+  }
+  bool memcpy_field_possible(const Field *from) const
+  {
+    return type_handler() == from->type_handler() &&
+           (geom_type == GEOM_GEOMETRY ||
+            geom_type == static_cast<const Field_geom*>(from)->geom_type) &&
+           !table->copy_blobs;
+  }
   uint is_equal(Create_field *new_field);
   int  store(const char *to, size_t length, CHARSET_INFO *charset);
   int  store(double nr);
@@ -4161,7 +4176,7 @@ class Field_geom :public Field_blob {
   bool load_data_set_null(THD *thd);
   bool load_data_set_no_data(THD *thd, bool fixed_format);
 
-  geometry_type get_geometry_type() { return geom_type; };
+  geometry_type get_geometry_type() const { return geom_type; };
   static geometry_type geometry_type_merge(geometry_type, geometry_type);
   uint get_srid() { return srid; }
   void print_key_value(String *out, uint32 length)