PaperMC / PaperMC/Paper

BlockPistonExtendEvent doesn't fire when nothing is pushed

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status: needs testing type: bug version: 1.20.4
Dominant language
Java
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Description

Expected behavior

BlockPistonExtendEvent should fire when a piston is activated even if nothing is pushed.

Observed/Actual behavior

The event does not fire when the piston pushes no blocks.

Steps/models to reproduce

Listen for BlockPistonExtendEvent, trigger a piston which is set up to push air & observe nothing even though the piston clearly fires. The event doesn't fire when blocks aren't pushed.

Plugin and Datapack List

No datapacks & no other plugins.

Paper version

Paper version git-Paper-485 (MC: 1.20.4) (Implementing API version 1.20.4-R0.1-SNAPSHOT) (Git: https://github.com/PaperMC/Paper/commit/862299b6a6588ff60db69dbc40e8514f9690d318)

Other

When looking at the paper documentation the described behavior for BlockPistonExtendEvent is "Called when a piston extends" which doesn't seem to be the case if nothing is pushed. BlockPistonRetractEvent has the same issue.

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by tracing where BlockPistonExtendEvent and BlockPistonRetractEvent are dispatched during piston activation, especially when no blocks are pushed. Reproduce the behavior on Paper 1.20.4 with the event listener described in the issue. Done means both events fire consistently when their pistons extend or retract, including empty pushes or pulls, with tests covering the behavior.

Written by the indexing model from the issue text.

Assessment

Tech stack
java
Domain
api
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
42/100

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