https://minecraft.net/en-us/article/minecraft-112-pre-release-1
We're so close to 1.12 now that we feel like it's time for a pre-release! We
expect to have at least another pre-release next week, but if all goes well
and no critical bugs are found then a full release is fairly imminent!
Changes in 1.12 pre-release 1
Added new advancements: "A furious cocktail", "Postmortal", "Subspace
Bubble", "Uneasy Alliance"
Advancement trees are now centered in the UI
Technical: Optimized the recipe book
Technical: Items & entities in advancements have an extra "nbt" field
(string nbt, like in commands)
Technical: Entities in advancements have an extra "effects" and
"location" field
Technical: Added new "effects_changed", "used_totem", "nether_travel"
advancements triggers
Technical: Removed "commands" from advancement rewards
Technical: Removed "arbitrary_player_tick" advancement trigger
Technical: Added "function" to advancement rewards
Technical: Added new "function" system, plaintext files in
world/data/functions/namespace/file.txt
Technical: Functions are a list of commands, one line per command, with
//comment (or #comment) support
Technical: Added new "/function namespace:file" command
Technical: Added new gamerule "gameLoopFunction", a function to be
executed once per tick
Technical: Added "hidden" field to advancement display info, defaults to
false
Fixed bug MC-11240 - Ignited TNT can be set on fire by a Flame Bow.
Fixed bug MC-50166 - Game states that "The block couldn't be placed" when
using /setblock to place air in a space occupied by a tile entity, despite
working
Fixed bug MC-95367 - Tamed dog, cat or parrot in a minecart teleports to
a player (not visually)
Fixed bug MC-96555 - Wolves, ocelots and parrots can teleport in all
non-full cube blocks near owner including path, lava, fire...
Fixed bug MC-100468 - Dogs, cats and parrots teleport to player despite
being in a boat (yet not visually)
Fixed bug MC-111699 - Can't rename stacked items
Fixed bug MC-111744 - Anvil outputs only 1 item when renaming
Fixed bug MC-113380 - Concrete powder won't turn into concrete when
replacing water
Fixed bug MC-113434 - The color of white wool sheep is light grey
Fixed bug MC-114235 - Concrete powder texture is not randomly rotated
Fixed bug MC-114534 - Beacon beam is darker than it should be
Fixed bug MC-115070 - Issue with crafting table UI on non-16:9 instances
Fixed bug MC-115206 - Parrots stare at bats over 30 blocks away, through
the ground
Fixed bug MC-115460 - Recipe advancements for yellow dye have reversed
unlock conditions
Fixed bug MC-115813 - Old (non-dyed) beds are invisible
Fixed bug MC-116024 - Pre-17w15a beds become red if in-world but white in
chests
Fixed bug MC-116459 - Parrots suffocate when getting in a bed with a
solid block behind it
Fixed bug MC-116760 - @a selector doesn't work with the /recipe command
in multiplayer
Fixed bug MC-116945 - Knowledge book gives recipe before removing itself
from inventory causing unexpected advancement behavior
Fixed bug MC-116957 - Advancement doesn't get revoked when /reload is
quickly executed afterwards
Fixed bug MC-116963 - Changing dimension prints debug message in log
Fixed bug MC-116964 - Parrots sometimes run in circles instead of
pathfinding normally.
Fixed bug MC-117001 - Serious dedication challenge is granted when
breaking any tool
Fixed bug MC-117007 - milk_bucket can't trigger consume_item of
advancements
Fixed bug MC-117008 - Vines under trapdoors block them
Fixed bug MC-117015 - Glass panes & iron bars no longer connect to glass
Fixed bug MC-117019 - Tripwire hooks break off of backs and sides of
stairs upon receiving a block update
Fixed bug MC-117036 - 17w18b Crafting book glitch
Fixed bug MC-117063 - Snow layers on barriers
Fixed bug MC-117069 - Door in Recipe Book when hold click shows the
trapdoor recipe
Fixed bug MC-117118 - Levers / buttons placed on the trapdoor are dropped
if pressed
Fixed bug MC-117160 - Parrots follow and watch invisible mobs
Fixed bug MC-117161 - Parrots imitate silent mobs
Fixed bug MC-117167 - Error message for player advancement data
containing only "null" calls advancements "achievements"
Added some new bugs!