Minecraft crashes with IncompatibleClassChangeError

[Failender]

I need the library "reflections" for something I am triing. unfortunately minecraft crashes with an exception, once i add the library to my project.

 

Is there something I can do to prevent the crash?

build.gradle

buildscript {
    repositories {
        jcenter()
        maven { url = "http://files.minecraftforge.net/maven" }
    }
    dependencies {
        classpath 'net.minecraftforge.gradle:ForgeGradle:2.3-SNAPSHOT'
    }
}
apply plugin: 'net.minecraftforge.gradle.forge'
//Only edit below this line, the above code adds and enables the necessary things for Forge to be setup.

version = "1.0"
group = "com.yourname.modid" // http://maven.apache.org/guides/mini/guide-naming-conventions.html
archivesBaseName = "modid"

sourceCompatibility = targetCompatibility = '1.8' // Need this here so eclipse task generates correctly.
compileJava {
    sourceCompatibility = targetCompatibility = '1.8'
}

repositories {
    mavenLocal()
}

minecraft {
    version = "1.12.2-14.23.3.2655"
    runDir = "run"

    // the mappings can be changed at any time, and must be in the following format.
    // snapshot_YYYYMMDD   snapshot are built nightly.
    // stable_#            stables are built at the discretion of the MCP team.
    // Use non-default mappings at your own risk. they may not always work.
    // simply re-run your setup task after changing the mappings to update your workspace.
    mappings = "snapshot_20171003"
    // makeObfSourceJar = false // an Srg named sources jar is made by default. uncomment this to disable.
}

dependencies {
    compile group: 'org.reflections', name: 'reflections', version: '0.9.10'
//    compile project(':easymods')
    // you may put jars on which you depend on in ./libs
    // or you may define them like so..
    //compile "some.group:artifact:version:classifier"
    //compile "some.group:artifact:version"

    // real examples
    //compile 'com.mod-buildcraft:buildcraft:6.0.8:dev'  // adds buildcraft to the dev env
    //compile 'com.googlecode.efficient-java-matrix-library:ejml:0.24' // adds ejml to the dev env

    // the 'provided' configuration is for optional dependencies that exist at compile-time but might not at runtime.
    //provided 'com.mod-buildcraft:buildcraft:6.0.8:dev'

    // the deobf configurations:  'deobfCompile' and 'deobfProvided' are the same as the normal compile and provided,
    // except that these dependencies get remapped to your current MCP mappings
    //deobfCompile 'com.mod-buildcraft:buildcraft:6.0.8:dev'
    //deobfProvided 'com.mod-buildcraft:buildcraft:6.0.8:dev'

    // for more info...
    // http://www.gradle.org/docs/current/userguide/artifact_dependencies_tutorial.html
    // http://www.gradle.org/docs/current/userguide/dependency_management.html

}

processResources {
    // this will ensure that this task is redone when the versions change.
    inputs.property "version", project.version
    inputs.property "mcversion", project.minecraft.version

    // replace stuff in mcmod.info, nothing else
    from(sourceSets.main.resources.srcDirs) {
        include 'mcmod.info'

        // replace version and mcversion
        expand 'version': project.version, 'mcversion': project.minecraft.version
    }

    // copy everything else except the mcmod.info
    from(sourceSets.main.resources.srcDirs) {
        exclude 'mcmod.info'
    }
}

 

Crash:

Exception in thread "main" java.lang.IncompatibleClassChangeError: Class com.google.common.base.Functions$IdentityFunction does not implement the requested interface java.util.function.Function
	at net.minecraftforge.server.console.log4j.TerminalConsoleAppender.formatEvent(TerminalConsoleAppender.java:184)
	at net.minecraftforge.server.console.log4j.TerminalConsoleAppender.append(TerminalConsoleAppender.java:178)
	at org.apache.logging.log4j.core.config.AppenderControl.tryCallAppender(AppenderControl.java:156)
	at org.apache.logging.log4j.core.config.AppenderControl.callAppender0(AppenderControl.java:129)
	at org.apache.logging.log4j.core.config.AppenderControl.callAppenderPreventRecursion(AppenderControl.java:120)
	at org.apache.logging.log4j.core.config.AppenderControl.callAppender(AppenderControl.java:84)
	at org.apache.logging.log4j.core.config.LoggerConfig.callAppenders(LoggerConfig.java:448)
	at org.apache.logging.log4j.core.config.LoggerConfig.processLogEvent(LoggerConfig.java:433)
	at org.apache.logging.log4j.core.config.LoggerConfig.log(LoggerConfig.java:417)
	at org.apache.logging.log4j.core.config.LoggerConfig.log(LoggerConfig.java:403)
	at org.apache.logging.log4j.core.config.AwaitCompletionReliabilityStrategy.log(AwaitCompletionReliabilityStrategy.java:63)
	at org.apache.logging.log4j.core.Logger.logMessage(Logger.java:146)
	at org.apache.logging.log4j.spi.AbstractLogger.logMessageSafely(AbstractLogger.java:2091)
	at org.apache.logging.log4j.spi.AbstractLogger.logMessage(AbstractLogger.java:1988)
	at org.apache.logging.log4j.spi.AbstractLogger.logIfEnabled(AbstractLogger.java:1960)
	at org.apache.logging.log4j.spi.AbstractLogger.info(AbstractLogger.java:1297)
	at net.minecraftforge.gradle.GradleStartCommon.parseArgs(GradleStartCommon.java:176)
	at net.minecraftforge.gradle.GradleStartCommon.launch(GradleStartCommon.java:78)
	at GradleStart.main(GradleStart.java:25)

 

[MDW01]

Your newly packaged library is not backward binary compatible the with the old version. For this reason, some of the library clients that are not recompiled may throw the exception. Pretty much you have made some incompatible binary changes to the library without recompiling the client code. This can mean making changes such as changing non-static non-private fields/methods to be static or vice versa.

[loordgek]

reflections is using Guava 20 MC is using 21

https://github.com/ronmamo/reflections/blob/c95609a4e83e1f3fc71e4b2fc58b17352a16eef7/pom.xml#L57

[HashtagShell]

Heh, I just ran into the same problem today. What a coincidence.

 

Anyway, I tried shading both reflections and guava (and javassist too while I was at it) using forge's reobf task. Reobfuscating them to a unique package should fix this collision as far as I can tell. The jar builds correctly and, while I haven't tested it yet, should work in an obfuscated environment.

In the devenv however, since the reobf task doesn't run (why would it), the collision remains. The reobf task can be run on arbitrary artifacts since FG 2.3ish, but I'm not sure how the devenv runClient task works, there might technically not be any gradle artifacts involved in the process.

 

Just my two cents.

[HashtagShell]

Rebuilding reflections against guava 21 just works out of the box, seems there were no relevant API changes. Minecraft does start loading in the devenv, which means the binary compatibility problem is fixed (thx MDW and diesieben for pointing that out).

It's still a good idea to shadow reflections (and javassist) if it needs to be present in production. Guava doesn't need to be shaded, since v21 comes with forge (thx loordgek).

Since reflections is under the WTFPL, here's the jar (reflections 9.11 against guava 21.0 and javassist 3.21.0-GA). It's literally just a maven build with the version changed in the pom. (Keep in mind that once you're including the library from the filesystem, and not maven, you have to depend on its deps manually somehow)

reflections-0.9.11.jar