Crash when "delete BMessage->Previous()"

[ahwayakchih]

Documentation of BMessage::Previous says that caller SHOULD delete resulting BMessage. But when i do that, BLooper crashes soon after return from MessageReceived.

Documentation: ​https://www.haiku-os.org/docs/api/classBMessage.html#a57c84d02e54ef19fd1516d9bf7e3fe45

I'm attaching mini application that shows the problem. I know it's strange to send message to itself, but it's to closely mimick code that discovered the problem.

My Deskbar replicant has to use PostMessage because on Haiku it cannot get Deskbar location otherwise (outside of some ugly hacks): ​https://github.com/haiku/haiku/blob/4824497d01271c34dc86e092f2df96d6352e452c/src/kits/interface/Deskbar.cpp#L121-L124 So it posts message and waits for reply in MessageReceived, where it gets previous message to make sure it's the right reply message.

[ahwayakchih]

test application to run with or without deleting previous BMessage

[ahwayakchih]

same test app, fixed to post message after ready to run, as advised by PulkoMandy

[ahwayakchih]

PulkoMandy said that message should never be deleted, so i checked BeBook (should ahve done that in the first place... sorry) and it looks like it does not mention deleting at all.

So this bug is about invalid description of BMessage::Previous in HaikuBook.

[pulkomandy]

Fixed in hrev52296. Also submitted to Gerrit for inclusion in r1b1 as ​https://review.haiku-os.org/#/c/haiku/+/488/

[ahwayakchih]

Thanks :)