how to turn off mod jar obfuscation?

[xParadoxical_]

(I don't want to bump 4yo thread so I'm creating this one.)
My mod is throwing an exception, but the line the exception is pointing to is an empty line with a } ending the if statement in my source code. Probably mod jar is obfuscated automatically, so I want to turn it off.
Comment above suggests to paste such code to build.gradle after minecraft block:

task deobfJar(type: Jar) { // Generate deobfuscated
    from sourceSets.main.output
    classifier = 'deobf'
}

task sourceJar(type: Jar) { // Generate sources
    from sourceSets.main.allSource
    classifier = 'sources'
}

tasks.build.dependsOn('sourceJar', 'deobfJar')

artifacts {
    archives deobfJar
    archives sourceJar
    archives jar
}

However, IntelliJ shows the error "Cannot infer argument type", and gradlew b throws a MissingPropertyException: Could not find property '?' on task ':deobfJar'.

How to fix it?

 

Edited April 23, 2019 by xParadoxical_

[xParadoxical_]

(removed)

Edited April 23, 2019 by xParadoxical_

[LexManos]

obf does not change line numbers

[Cadiboo]

To compile a MCP named jar (for dev purposes in an environment that doesn’t support mod remapping, like 1.13 currently) just run the jar task instead of the build task. This jar will obviously not work in production or in an environment with different mappings.