Dumping water handled incorrectly

[9caihezi]

Client version: 1.12.2
Server OS: Windows/Linux/macOS/BSD/...
Commit id: 0dd172b

Expected behavior

Dump water as shown in the following picture, the water should be dumped in the hole.

Actual behavior

Water placed on the snow block in front. It seems like the server assumes the snow block shadows the hole.

Steps to reproduce the behavior

Dumping a water bucket with a non-empty but not full-sized block in between (stone_slab, snow_layer, grass).

Bonus bug: sometimes when I trying to retrieve the water, it fails without letting the client know. The client will see the water retrieved back to the bucket, but the water aside doesn't disappear, until the player does something that refreshes the block and/or inventory.

PS: sometimes the server deliberately acts differently from what the client suggests (block placement at least), the server should send the actual updated block and the block that's supposed to be updated and player's inventory.
E.g., the client sends a block (x,y,z) to the upper face, and the server thought the block should be placed at (x+1,y+1,z) instead of (x,y+1,z), the server should send update to both blocks.

[earboxer]

src/Items/ItemBucket.h

PlaceFluid() uses GetPlacementCoordsFromTrace(),

ScoopUpFluid() uses GetBlockFromTrace().

(The former gives EntryFace, which is used for some hooks, minor change would be required). However, switching this isn't a drop in fix.

You can right click through the snow to pick up water (which the client won't show as picked up until relog).

[Pokechu22]

(which the client won't show as picked up until relog).

Perhaps it would also make sense to send a block change packet to the player whenever they pick up/place water, even if it'd normally be redundant. Vanilla doesn't, but vanilla also has the issue of appearing to pick up water when it actually hasn't been.

[tigerw]

Related to #2923, we treat all blocks' bounding boxes as full cubes, so the trace doesn't work correctly. That is, (pic from #4776 (comment))