Changelog — Undo Mod

[1.0.5-beta] — 2026-06-14

Changed: YACL is now Optional (Recommended)

YACL (Yet Another Config Lib) v3 is no longer required. It is now a recommended dependency:

• If YACL is installed → full config screen (YACL GUI)
• If YACL is not installed → a basic in-game settings screen is shown (mouse side buttons toggle + undo mode toggle)

Dependency type	Before	After
YACL v3	depends (required)	recommends (optional but recommended)

Don't want to install YACL? Download the -bundled JAR — it has YACL built in.

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New: Basic Settings Screen (No YACL required)

Press U in-game to open settings.

• With YACL installed: full YACL config screen (General / HUD / History categories)
• Without YACL: a simple vanilla screen with two toggles:
  • Mouse Side Buttons — ON/OFF
  • Undo Mode — Full / Block Only

Settings are saved to config/undo-client.json in both cases.

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New: Mod Icon

Added a custom icon (assets/undo/icon.png) displayed in the Minecraft mod list and Modrinth.

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Fix: Mixin Crash on MC 26.1.2 (Java 25 Bytecode)

Bug: MC 26.1.2 requires JDK 25 to build, but the previous config compiled classes to Java 25 bytecode (v69). The Mixin library's ASM reader cannot parse Java 25 class files, causing ClassNotFoundException for all mixin classes on startup.

Symptom:

MixinApplyError: Mixin [...] FAILED during PREPARE
Caused by: java.lang.ClassNotFoundException: ServerPlayerInteractionManagerMixin

Fix: The 26.1.2 build now uses JDK 25 toolchain but outputs Java 21 bytecode:

java {
    toolchain { languageVersion = JavaLanguageVersion.of(25) }
    sourceCompatibility = JavaVersion.VERSION_21
    targetCompatibility = JavaVersion.VERSION_21
}
tasks.compileJava { options.release = 21 }

• Runtime requirement: Java 25 ✅ (MC 26.1.2 needs it)
• Compiled bytecode: Java 21 (v65) ✅ (Mixin ASM can read it)

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Fix: Removed withSourcesJar()

All three projects no longer generate -sources.jar. Build output is now release JARs only.

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Build Output

MC Version	Mapping	Obfuscation	Main JAR	Bundled JAR
26.1.2	Mojang (official)	❌ No (jar task)	Undo1.0.5-beta+fabric26.1.2.jar	Undo1.0.5-beta+fabric26.1.2-bundled.jar
1.21.1	Yarn	✅ Yes (remapJar)	Undo1.0.5-beta+fabric1.21.1.jar	Undo1.0.5-beta+fabric1.21.1-bundled.jar
1.21.2	Yarn	✅ Yes (remapJar)	Undo1.0.5-beta+fabric1.21.2.jar	Undo1.0.5-beta+fabric1.21.2-bundled.jar

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For Modrinth Upload

Main version (YACL not bundled):

• MC 26.1.2 → upload Undo1.0.5-beta+fabric26.1.2.jar
  • Recommends: yet_another_config_lib_v3 ≥ 3.9.0
• MC 1.21.1 → upload Undo1.0.5-beta+fabric1.21.1.jar
  • Recommends: yet_another_config_lib_v3 ≥ 3.6.0
• MC 1.21.2 → upload Undo1.0.5-beta+fabric1.21.2.jar
  • Recommends: yet_another_config_lib_v3 ≥ 3.6.0

Bundled version (YACL included, no external dependency):

Same JARs but remove yet_another_config_lib_v3 from the dependency list when uploading to Modrinth.

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[1.0.5-beta] — 2026-06-12 (Previous Release)

New: YACL Config Screen

Press U in-game to open the config screen (replaces the old custom settings screen).

Three categories:

Category	Options
General	mouseSideButtonsEnabled — use mouse side buttons for Undo/Redo
HUD	hudCorner — where the Undo HUD appears (Top-Left / Top-Right / Bottom-Left / Bottom-Right)
History	maxHistoryPerPlayer — how many actions each player can undo

Config is saved to config/undo-client.json automatically.

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New: Dual Build (Main + Bundled)

Every MC version now has two JARs:

File	YACL included?	When to use
Undo1.0.5-beta+fabricX.Y.jar	❌ No	You already have YACL installed
Undo1.0.5-beta+fabricX.Y-bundled.jar	✅ Yes	You don't want to install YACL separately

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Fix: Mixin Compatibility Level (MC 26.1.2)

undo.mixins.json used "compatibilityLevel": "JAVA_25", which is not valid (max JAVA_22). Changed to JAVA_21.

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Fix: MC 1.21.2 API Changes

Class / Method	Old (≤1.21.1)	New (1.21.2)
Return type of use item callback	TypedActionResult<ItemStack>	ActionResult (merged)
EntityType.loadEntityWithPassengers	2 args	3 args (added SpawnReason)

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Fix: Removed Unused undo.client.mixins.json

Deleted from all three projects (empty mixin list with required: true caused potential issues).

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Version History (Modrinth Releases)

Version	MC Versions	Date	Notes
0.9.0	1.21.1	2024-10-03	First release
0.9.1	1.21.1	2024-10-05	Bug fixes
1.0.0	1.21.1	2024-11-20	First stable release
1.0.1	1.21.1	2024-12-01	Minor fixes
1.0.2	1.21.1	2025-01-15	Minor fixes
1.0.3	1.21.1	2025-03-10	Minor fixes
1.0.4	1.21.1, 1.21.2, 26.1	2025-05-20	Multi-MC version support
1.0.5-beta	1.21.1, 1.21.2, 26.1.2	2026-06-14	YACL optional, basic settings screen, icon, Mixin bytecode fix

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This file is from the undo-mod-26.1.2 project.