MDEV-18076/MDEV-18077 Crash on AUTO_INCREMENT column after instant DROP

The fix for MDEV-17901 did not cover cases where the AUTO_INCREMENT
column was not dropped, but some other columns before it were.

commit_cache_norebuild(): Revert the MDEV-17901 fix.

dict_index_t::clear_instant_alter(): Update table->persistent_autoinc.

mysql-test/suite/innodb/r/instant_alter.result

@@ -578,6 +578,15 @@ id	f
 1	NULL
 2	NULL
 DROP TABLE t1;
+CREATE TABLE t1(f INT, k INT NOT NULL AUTO_INCREMENT, KEY(k)) ENGINE=InnoDB ROW_FORMAT=REDUNDANT;
+ALTER TABLE t1 DROP COLUMN f;
+INSERT INTO t1 VALUES (1);
+DROP TABLE t1;
+CREATE TABLE t1(pk INT PRIMARY KEY, f INT, k INT AUTO_INCREMENT, KEY(k))
+ENGINE=InnoDB ROW_FORMAT=REDUNDANT;
+ALTER TABLE t1 DROP COLUMN f;
+INSERT INTO t1 (pk) VALUES (1);
+DROP TABLE t1;
 CREATE TABLE t1 (
 pk INT PRIMARY KEY,
 f1 INT,
@@ -1153,6 +1162,15 @@ id	f
 1	NULL
 2	NULL
 DROP TABLE t1;
+CREATE TABLE t1(f INT, k INT NOT NULL AUTO_INCREMENT, KEY(k)) ENGINE=InnoDB ROW_FORMAT=COMPACT;
+ALTER TABLE t1 DROP COLUMN f;
+INSERT INTO t1 VALUES (1);
+DROP TABLE t1;
+CREATE TABLE t1(pk INT PRIMARY KEY, f INT, k INT AUTO_INCREMENT, KEY(k))
+ENGINE=InnoDB ROW_FORMAT=COMPACT;
+ALTER TABLE t1 DROP COLUMN f;
+INSERT INTO t1 (pk) VALUES (1);
+DROP TABLE t1;
 CREATE TABLE t1 (
 pk INT PRIMARY KEY,
 f1 INT,
@@ -1728,6 +1746,15 @@ id	f
 1	NULL
 2	NULL
 DROP TABLE t1;
+CREATE TABLE t1(f INT, k INT NOT NULL AUTO_INCREMENT, KEY(k)) ENGINE=InnoDB ROW_FORMAT=DYNAMIC;
+ALTER TABLE t1 DROP COLUMN f;
+INSERT INTO t1 VALUES (1);
+DROP TABLE t1;
+CREATE TABLE t1(pk INT PRIMARY KEY, f INT, k INT AUTO_INCREMENT, KEY(k))
+ENGINE=InnoDB ROW_FORMAT=DYNAMIC;
+ALTER TABLE t1 DROP COLUMN f;
+INSERT INTO t1 (pk) VALUES (1);
+DROP TABLE t1;
 CREATE TABLE t1 (
 pk INT PRIMARY KEY,
 f1 INT,
@@ -1784,5 +1811,5 @@ SELECT variable_value-@old_instant instants
 FROM information_schema.global_status
 WHERE variable_name = 'innodb_instant_alter_column';
 instants
-125
+131
 SET GLOBAL innodb_purge_rseg_truncate_frequency= @saved_frequency;

mysql-test/suite/innodb/t/instant_alter.test

@@ -447,6 +447,18 @@ ALTER TABLE t1 ADD COLUMN id INT NOT NULL AUTO_INCREMENT FIRST, ADD KEY(id);
 SELECT * FROM t1;
 DROP TABLE t1;
 
+# MDEV-18076/MDEV-18077 Crash on AUTO_INCREMENT column after instant DROP
+eval CREATE TABLE t1(f INT, k INT NOT NULL AUTO_INCREMENT, KEY(k)) $engine;
+ALTER TABLE t1 DROP COLUMN f;
+INSERT INTO t1 VALUES (1);
+DROP TABLE t1;
+
+eval CREATE TABLE t1(pk INT PRIMARY KEY, f INT, k INT AUTO_INCREMENT, KEY(k))
+$engine;
+ALTER TABLE t1 DROP COLUMN f;
+INSERT INTO t1 (pk) VALUES (1);
+DROP TABLE t1;
+
 # MDEV-17763 Assertion `len == 20U' failed in rec_convert_dtuple_to_rec_comp
 # upon DROP COLUMN
 eval CREATE TABLE t1 (

storage/innobase/handler/handler0alter.cc

@@ -10294,14 +10294,6 @@ commit_cache_norebuild(
 						      f->fixed_len);
 				}
 			}
-
-			DBUG_ASSERT(!ctx->instant_table->persistent_autoinc
-				    || ctx->new_table->persistent_autoinc
-				    == ctx->instant_table->persistent_autoinc);
-
-			if (!ctx->instant_table->persistent_autoinc) {
-				ctx->new_table->persistent_autoinc = 0;
-			}
 		}
 	}
 

storage/innobase/include/dict0mem.h

@@ -2218,6 +2218,9 @@ inline void dict_index_t::clear_instant_alter()
 		DBUG_ASSERT(!fields[i].col->is_nullable());
 	}
 #endif
+	const dict_col_t* ai_col = table->persistent_autoinc
+		? fields[table->persistent_autoinc - 1].col
+		: NULL;
 	dict_field_t* const begin = &fields[first_user_field()];
 	dict_field_t* end = &fields[n_fields];
 
@@ -2240,6 +2243,12 @@ inline void dict_index_t::clear_instant_alter()
 	std::sort(begin, end, [](const dict_field_t& a, const dict_field_t& b)
 			      { return a.col->ind < b.col->ind; });
 	table->instant = NULL;
+	if (ai_col) {
+		auto a = std::find_if(begin, end,
+				      [ai_col](const dict_field_t& f)
+				      { return f.col == ai_col; });
+		table->persistent_autoinc = (a == end) ? 0 : 1 + (a - fields);
+	}
 }
 
 /** @return whether the column was instantly dropped