Error messages are still displayed despite the "sendCommandFeedback" gamerule being set to "false"

@Marcono1234 when there are no blocks diffrent from before to after, it says error no blocks filled, you can use destroy however, that will always succeed

"Destroy" will physically break the blocks leaving the drops, but it's better than nothing at least.

you can kill the items who are iron bars (or from whatever your gate is made)

I do not think this is intended. Whether the message is an error message or a success message shouldn't affect whether it's displayed. The point of the gamerule is to reduce the number of chat messages being seen, and to prevent players who shouldn't see a message from seeing it. Allowing error messages to be seen defeats the purpose of the gamerule.

That's what I thought.
Finally someone who agrees.

Until the issue is fixed, you could use the setup in the screen shot. The left most command block is empty and the other one would execute the command you want. The command in the book would be '/blockdata <x> <y> <z> {SuccessCount:15}', where x,y,and z are the coordinates of the empty command block.

The problem is that the sendcommandfeedback gamerule might only work on command blocks, which is why messages still appear when using a book or using chat.
My setup also works when a command is too long to be used in a book. I found this out when trying to summon fireworks with a book, and when I got the book, a large portion of the command appeared as written text.

I can't replicate your problem with the book. Can you clarify?

I haven't done much work with commands in books, so I'm not sure on the proper way to enter a long command into the book.
This is the command I used:
give @p written_book 1 0 {title:Wireless Commands,author:,pages:["{text:'Wireless Commands\n\n',extra:[{text:'Fireworks\n',color:dark_purple,clickEvent:{action:run_command,value:'/execute @p ~ ~ ~ summon FireworksRocketEntity ~ ~1 ~ {Motion:[0.0,0.5,0.0],FireworksItem:{id:fireworks,Count:1,tag:{Fireworks:{Flight:0,Explosions:[{Type:1,Flicker:1,FadeColors:[14188952,12801229],Colors:[1973019,8073150],Trail:1}]}}},LifeTime:15}'}}]}"]}

I get this error message:
Data tag parsing failed:Unbalanced brackets: {Motion:[0.0,0.5,0.0],FireworksItem:{id:firewo
Failed to execute '{Motion:[0.0,0.5,0.0],FireworksItem:{id:firewo' as <Player Name>

Oh, you just mean you get an error message. I thought you meant something else.

By the way, you can use http://mcstacker.bimbimma.com/ to generate commands like that.

Confirmed for 1.13.1.

Please, keep the ticket updated.

Confirmed in snapshot 19w13a! Trying to use the gamerule to hide the message "Triggered [objective]" when using a click event command in chat, but it still shows.

Confirmed in 1.15.2 and 1.16 Pre-release 3.

Can confirm in 20w51a.

Can confirm in 21w03a.

Can confirm in 21w05b.

Can confirm in 21w06a.

Can confirm in 21w07a.

Video attached.