MDEV-15553 Assertion failed in dict_table_get_col_name

dict_foreign_qualify_index(): Avoid a redundant and harmful
computation of col_name of a virtual column. This fixes the
assertion failure.

dict_foreign_push_index_error(): Do not call dict_table_get_col_name()
on a virtual column. (It is unclear if this condition is actually
reachable.)

mysql-test/suite/gcol/r/innodb_virtual_fk.result

@@ -688,3 +688,55 @@ SELECT f1, f3 FROM t2;
 f1	f3
 3	2
 DROP TABLE t2, t1;
+#
+# MDEV-15553 Assertion failed in dict_table_get_col_name
+#
+CREATE TABLE t1 (
+c1 TIMESTAMP,
+c2 YEAR,
+c3 TIME,
+c4 CHAR(10),
+v1 TIMESTAMP AS (c1) VIRTUAL,
+v2 YEAR AS (c2) VIRTUAL,
+v3 TIME AS (c3) VIRTUAL,
+v4 CHAR(10) AS (c4) VIRTUAL
+) ENGINE=InnoDB;
+ALTER TABLE t1 ADD CONSTRAINT fk FOREIGN KEY (v4) REFERENCES nosuch(col);
+ERROR HY000: Can't create table `test`.`#sql-temporary` (errno: 150 "Foreign key constraint is incorrectly formed")
+SET foreign_key_checks=0;
+ALTER TABLE t1 ADD CONSTRAINT fk FOREIGN KEY (v4) REFERENCES nosuch(col);
+ERROR HY000: Failed to add the foreign key constaint. Missing index for constraint 'fk' in the foreign table 't1'
+ALTER TABLE t1 ADD INDEX(v4);
+ALTER TABLE t1 ADD CONSTRAINT fk FOREIGN KEY (v4) REFERENCES nosuch(col);
+SET foreign_key_checks=1;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `c1` timestamp NOT NULL DEFAULT current_timestamp() ON UPDATE current_timestamp(),
+  `c2` year(4) DEFAULT NULL,
+  `c3` time DEFAULT NULL,
+  `c4` char(10) DEFAULT NULL,
+  `v1` timestamp GENERATED ALWAYS AS (`c1`) VIRTUAL,
+  `v2` year(4) GENERATED ALWAYS AS (`c2`) VIRTUAL,
+  `v3` time GENERATED ALWAYS AS (`c3`) VIRTUAL,
+  `v4` char(10) GENERATED ALWAYS AS (`c4`) VIRTUAL,
+  KEY `v4` (`v4`),
+  CONSTRAINT `fk` FOREIGN KEY (`v4`) REFERENCES `nosuch` (`col`)
+) ENGINE=InnoDB DEFAULT CHARSET=latin1
+ALTER TABLE t1 DROP FOREIGN KEY fk;
+ALTER TABLE t1 ADD CONSTRAINT fk FOREIGN KEY (v4) REFERENCES nosuch(col);
+ERROR HY000: Can't create table `test`.`#sql-temporary` (errno: 150 "Foreign key constraint is incorrectly formed")
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `c1` timestamp NOT NULL DEFAULT current_timestamp() ON UPDATE current_timestamp(),
+  `c2` year(4) DEFAULT NULL,
+  `c3` time DEFAULT NULL,
+  `c4` char(10) DEFAULT NULL,
+  `v1` timestamp GENERATED ALWAYS AS (`c1`) VIRTUAL,
+  `v2` year(4) GENERATED ALWAYS AS (`c2`) VIRTUAL,
+  `v3` time GENERATED ALWAYS AS (`c3`) VIRTUAL,
+  `v4` char(10) GENERATED ALWAYS AS (`c4`) VIRTUAL,
+  KEY `v4` (`v4`)
+) ENGINE=InnoDB DEFAULT CHARSET=latin1
+DROP TABLE t1;

mysql-test/suite/gcol/t/innodb_virtual_fk.test

@@ -576,3 +576,34 @@ UPDATE t1 SET f1 = 3;
 EXPLAIN SELECT f1, f3 FROM t2;
 SELECT f1, f3 FROM t2;
 DROP TABLE t2, t1;
+
+--echo #
+--echo # MDEV-15553 Assertion failed in dict_table_get_col_name
+--echo #
+CREATE TABLE t1 (
+  c1 TIMESTAMP,
+  c2 YEAR,
+  c3 TIME,
+  c4 CHAR(10),
+  v1 TIMESTAMP AS (c1) VIRTUAL,
+  v2 YEAR AS (c2) VIRTUAL,
+  v3 TIME AS (c3) VIRTUAL,
+  v4 CHAR(10) AS (c4) VIRTUAL
+) ENGINE=InnoDB;
+--replace_regex /#sql-[0-9a-f_]*/#sql-temporary/
+--error ER_CANT_CREATE_TABLE
+ALTER TABLE t1 ADD CONSTRAINT fk FOREIGN KEY (v4) REFERENCES nosuch(col);
+SET foreign_key_checks=0;
+--error ER_FK_NO_INDEX_CHILD
+ALTER TABLE t1 ADD CONSTRAINT fk FOREIGN KEY (v4) REFERENCES nosuch(col);
+ALTER TABLE t1 ADD INDEX(v4);
+ALTER TABLE t1 ADD CONSTRAINT fk FOREIGN KEY (v4) REFERENCES nosuch(col);
+SET foreign_key_checks=1;
+SHOW CREATE TABLE t1;
+ALTER TABLE t1 DROP FOREIGN KEY fk;
+--replace_regex /#sql-[0-9a-f_]*/#sql-temporary/
+--error ER_CANT_CREATE_TABLE
+ALTER TABLE t1 ADD CONSTRAINT fk FOREIGN KEY (v4) REFERENCES nosuch(col);
+SHOW CREATE TABLE t1;
+# Cleanup
+DROP TABLE t1;

storage/innobase/dict/dict0dict.cc

@@ -4401,7 +4401,9 @@ dict_foreign_push_index_error(
 		const char*	col_name;
 		field = dict_index_get_nth_field(err_index, err_col);
 
-		col_name = dict_table_get_col_name(
+		col_name = dict_col_is_virtual(field->col)
+			? "(null)"
+			: dict_table_get_col_name(
 				table, dict_col_get_no(field->col));
 		fprintf(ef,
 			"%s table %s with foreign key constraint"
@@ -6982,10 +6984,6 @@ dict_foreign_qualify_index(
 			return(false);
 		}
 
-		col_name = col_names
-			? col_names[col_no]
-			: dict_table_get_col_name(table, col_no);
-
 		if (dict_col_is_virtual(field->col)) {
 			for (ulint j = 0; j < table->n_v_def; j++) {
 				col_name = dict_table_get_v_col_name(table, j);
@@ -6993,6 +6991,10 @@ dict_foreign_qualify_index(
 					break;
 				}
 			}
+		} else {
+			col_name = col_names
+				? col_names[col_no]
+				: dict_table_get_col_name(table, col_no);
 		}
 
 		if (0 != innobase_strcasecmp(columns[i], col_name)) {