A followup for MDEV-29672 Add MTR tests covering key and key segment flags and types

Adding debug output for key and keyseg flags at ha_myisam::open() time.
So now there are three points of debug output:

1. In the very end of mysql_prepare_create_table()
2. In ha_myisam::create(), after the table2myisam() call
3. In ha_myisan::open(), after the mi_open() call

mi_create(), which is is called between 2 and 3, modifies flags for
some data types, so the output in 2 and 3 is different.

mysql-test/main/myisam_debug_keys.test

@@ -53,6 +53,8 @@ BEGIN NOT ATOMIC
       SELECT tabledef AS ``;
       EXECUTE IMMEDIATE tabledef;
       SHOW WARNINGS;
+      SELECT * FROM t1;
+      SHOW WARNINGS;
       SHOW CREATE TABLE t1;
       DROP TABLE t1;
     END;

sql/sql_debug.h

@@ -63,23 +63,23 @@ class Debug_key: public String
   {
     static const char *names[17]=
     {
-      "HA_NOSAME",
-      "HA_PACK_KEY",
-      "HA_SPACE_PACK_USED",
-      "HA_VAR_LENGTH_KEY",
-      "HA_AUTO_KEY",
-      "HA_BINARY_PACK_KEY",
-      "HA_NULL_PART_KEY",
-      "HA_FULLTEXT",
-      "HA_UNIQUE_CHECK",
-      "HA_SORT_ALLOWS_SAME",
-      "HA_SPATIAL",
-      "HA_NULL_ARE_EQUAL",
-      "HA_GENERATED_KEY",
-      "HA_USES_COMMENT",
-      "HA_USES_PARSER",
-      "HA_USES_BLOCK_SIZE",
-      "HA_KEY_HAS_PART_KEY_SEG"
+      "HA_NOSAME",               // 1
+      "HA_PACK_KEY",             // 2 - used in both HA_KEYSEG and KEY/MI_KEYDEF
+      "HA_SPACE_PACK_USED",      // 4
+      "HA_VAR_LENGTH_KEY",       // 8
+      "HA_AUTO_KEY",             // 16
+      "HA_BINARY_PACK_KEY",      // 32
+      "HA_NULL_PART_KEY",        // 64
+      "HA_FULLTEXT",             // 128
+      "HA_UNIQUE_CHECK",         // 256
+      "HA_SORT_ALLOWS_SAME",     // 512
+      "HA_SPATIAL",              // 1024
+      "HA_NULL_ARE_EQUAL",       // 2048
+      "HA_USES_COMMENT",         // 4096
+      "HA_GENERATED_KEY",        // 8192
+      "HA_USES_PARSER",          // 16384
+      "HA_USES_BLOCK_SIZE",      // 32768
+      "HA_KEY_HAS_PART_KEY_SEG"  // 65536
     };
     return append_flag32_names((uint) flags, names, array_elements(names));
   }
@@ -89,7 +89,7 @@ class Debug_key: public String
     static const char *names[]=
     {
       "HA_SPACE_PACK",      // 1
-      "??? 2 ???",          // 2
+      "HA_PACK_KEY",        // 2 - used in both HA_KEYSEG and KEY/MI_KEYDEF
       "HA_PART_KEY_SEG",    // 4
       "HA_VAR_LENGTH_PART", // 8
       "HA_NULL_PART",       // 16

storage/myisam/ha_myisam.cc

@@ -860,6 +860,13 @@ int ha_myisam::open(const char *name, int mode, uint test_if_locked)
       /* purecov: end */
     }
   }
+
+  DBUG_EXECUTE_IF("key",
+    Debug_key_myisam::print_keys_myisam(table->in_use,
+                                        "ha_myisam::open: ",
+                                        table, file->s->keyinfo,
+                                        file->s->base.keys);
+  );
   
   if (test_if_locked & (HA_OPEN_IGNORE_IF_LOCKED | HA_OPEN_TMP_TABLE))
     (void) mi_extra(file, HA_EXTRA_NO_WAIT_LOCK, 0);