Bug#36446: Attempt to set @@join_buffer_size to its minimum value produces spurious warning

If a sys-var has a base and a block-size>1, and then a
user-supplied value >= minimum ended up below minimum
thanks to block-size alignment, we threw a warning.
This meant for instance that when getting, then setting
the minimum, we'd see a warning. This was needlessly
confusing. (updated patch)

mysql-test/r/variables.result

@@ -27,6 +27,7 @@ set @my_slow_launch_time          =@@global.slow_launch_time;
 set @my_storage_engine            =@@global.storage_engine;
 set @my_thread_cache_size         =@@global.thread_cache_size;
 set @my_max_allowed_packet        =@@global.max_allowed_packet;
+set @my_join_buffer_size          =@@global.join_buffer_size;
 set @`test`=1;
 select @test, @`test`, @TEST, @`TEST`, @"teSt";
 @test	@`test`	@TEST	@`TEST`	@"teSt"
@@ -1018,6 +1019,11 @@ show variables like 'hostname';
 Variable_name	Value
 hostname	#
 End of 5.0 tests
+set join_buffer_size=1;
+Warnings:
+Warning	1292	Truncated incorrect join_buffer_size value: '1'
+set @save_join_buffer_size=@@join_buffer_size;
+set join_buffer_size=@save_join_buffer_size;
 set global binlog_cache_size         =@my_binlog_cache_size;
 set global connect_timeout           =@my_connect_timeout;
 set global delayed_insert_timeout    =@my_delayed_insert_timeout;
@@ -1048,6 +1054,7 @@ set global slow_launch_time          =@my_slow_launch_time;
 set global storage_engine            =@my_storage_engine;
 set global thread_cache_size         =@my_thread_cache_size;
 set global max_allowed_packet        =@my_max_allowed_packet;
+set global join_buffer_size          =@my_join_buffer_size;
 show global variables where Variable_name='table_definition_cache' or
 Variable_name='table_lock_wait_timeout';
 Variable_name	Value

mysql-test/t/variables.test

@@ -36,6 +36,7 @@ set @my_slow_launch_time          =@@global.slow_launch_time;
 set @my_storage_engine            =@@global.storage_engine;
 set @my_thread_cache_size         =@@global.thread_cache_size;
 set @my_max_allowed_packet        =@@global.max_allowed_packet;
+set @my_join_buffer_size          =@@global.join_buffer_size;
 # case insensitivity tests (new in 5.0)
 set @`test`=1;
 select @test, @`test`, @TEST, @`TEST`, @"teSt";
@@ -780,6 +781,18 @@ show variables like 'hostname';
 
 --echo End of 5.0 tests
 
+#
+# Bug#36446: Attempt to set @@join_buffer_size to its minimum value
+#            produces spurious warning
+#
+
+# set to 1 so mysqld will correct to minimum (+ warn)
+set join_buffer_size=1;
+# save minimum
+set @save_join_buffer_size=@@join_buffer_size;
+# set minimum
+set join_buffer_size=@save_join_buffer_size;
+
 # This is at the very after the versioned tests, since it involves doing
 # cleanup
 #
@@ -816,6 +829,8 @@ set global slow_launch_time          =@my_slow_launch_time;
 set global storage_engine            =@my_storage_engine;
 set global thread_cache_size         =@my_thread_cache_size;
 set global max_allowed_packet        =@my_max_allowed_packet;
+set global join_buffer_size          =@my_join_buffer_size;
+
 #
 # Bug#28580 Repeatation of status variables
 #

mysys/my_getopt.c

@@ -846,7 +846,8 @@ longlong getopt_ll_limit_value(longlong num, const struct my_option *optp,
   if (num < optp->min_value)
   {
     num= optp->min_value;
-    adjusted= TRUE;
+    if (old < optp->min_value)
+      adjusted= TRUE;
   }
 
   if (fix)
@@ -917,7 +918,8 @@ ulonglong getopt_ull_limit_value(ulonglong num, const struct my_option *optp,
   if (num < (ulonglong) optp->min_value)
   {
     num= (ulonglong) optp->min_value;
-    adjusted= TRUE;
+    if (old < optp->min_value)
+      adjusted= TRUE;
   }
 
   if (fix)