Kotlin unresolved reference in IntelliJ

Intellij Idea Problem Overview

I started off with this tutorial for learning Kotlin in IntelliJ IDEA.
When I tried running the following example,

fun main(args: Array<String>) {
    println("lol")
}

Build fails with the following error:

Error:(5, 5) Kotlin: Unresolved reference: println

This is the first time I am using IntelliJ. I have never worked on a Java project either. Am I missing something?

Edit: I have already seen this other question, though it is not valid for my situation.

Intellij Idea Solutions

Solution 1 - Intellij Idea

Your Intellij IDEA plugin and the Kotlin runtime/compiler that you use in the project need to match. For example if IDE plugin is Beta 1, but your Gradle/Maven project using M12, you'll have issues exactly as you described. So check that everything lines up.

If you still have issues, with some older plugins you need to clear the caches in Intellij IDEA (file menu, Clear Caches and Restart, select option to restart).

Solution 2 - Intellij Idea

UPDATE - 01/2022

The jetbrains thread regarding this issue has moved and is nowhere to be found, so the link below is not valid anymore.

The option, per module, Kotlin -> FIX does not exist anymore and has been that way for years now since this was a temporary patch to deal with integration issues during the early previous releases.

If anyone stumbles across this and NEITHER Invalidate Cache or Update Kotlin's Version work:

First, make sure you can build it from outside the IDE. If you're using gradle, for instance:

gradle clean build

If everything goes well , then your environment is all good to work with Kotlin.

To fix the IDE build, try the following:

>Project Structure -> {Select Module} -> Kotlin -> FIX

As suggested by a JetBrain's member here: https://discuss.kotlinlang.org/t/intellij-kotlin-project-screw-up/597

Solution 3 - Intellij Idea

In my case, it was a misconfigured IntelliJ instance.

> Project Structure -> SDKs -> Remove and add the Java SDK again

Solution 4 - Intellij Idea

Ran into this issue. I had to add the following to my build.grade:

apply plugin: 'kotlin-android'

Solution 5 - Intellij Idea

Ok, i've been here a few times and not entirely sure how or why this happens but reading suggests its a Kotlin/JVM mismatch. I have tried a number of things mentioned on this page but not without complete success. This was the sort of symptom the IDE was displaying in the message panel after trying to run tests via the IDE. However the code panel has no red lines indicating that modules can't be found or imported or anything untoward.

My project (at time of writing this) is a gradle 4.10.2 kotlin 1.3 project in IntelliJ (IntelliJ IDEA 2018.2.5 (Ultimate Edition) Build #IU-182.4892.20, built on October 16, 2018)

For starters though, I invalidated caches and restarted. Then ran a gradle clean build. After rebuilding the project still no joy. I went into the project settings and noticed the compiler versions were not set to java 8, I set the Compiler/Kotlin/Target JVM Version and Compiler/Java/Project Byte Code to 1.8/8 (see below), then ran some tests in the IDE and we are back in business! References resolved in my case.

Solution 6 - Intellij Idea

A possible solution for standalone Kotlin projects is to include Kotlin standard libs explicitliy inside the root project.

To do that in IntelliJ IDEA:

press Ctrl+Shift+A (Search actions or options)
type in "Configure kotlin in project" and let it include standard libs for you

Solution 7 - Intellij Idea

For me, it was due to the project missing Gradle Libraries in its project structure.

Just add in build.gradle:

apply plugin: 'idea'

And then run:

$ gradle idea

After that gradle rebuilds dependencies libraries and the references are recognized!

Solution 8 - Intellij Idea

My problem was solved by adding kotlin as follow

presentation.gradle (app.gradle)

apply plugin: 'com.android.application'

apply plugin: 'kotlin-android' // here

apply plugin: 'kotlin-android-extensions' // and here

android {
    ...
}

dependencies {
    ...
}

domain.gradle (pure kotlin)

> My error was throw here, because Android Studio create my domain > module as pure Java Module and applied plugin as java, and I used it > in the my presentation module that is a Android/Kotlin Module > > The Android Studio finds and import the path of package but the incompatibillity > don't allow the build. > > Just remove apply plugin: 'java' and swith to kotlin as follow

apply plugin: 'kotlin' // here is

dependencies {
    ...
}

...

data.gradle

apply plugin: 'com.android.library'

apply plugin: 'kotlin-android' // here

apply plugin: 'kotlin-android-extensions' // and here 

android {
    ...
}

dependencies {
    ..
}

I think that it will be helpfull

Solution 9 - Intellij Idea

Sometimes this could happen because you are trying to use a project with incompatible versions of Kotlin plugin in Gradle with plugin in your IDE. Check the versions of org.jetbrains.kotlin.jvm and other Kotlin plugins in build.gradle, and version of installed kotlin plugin in your IDE, and try to make it similar:

Solution 10 - Intellij Idea

Check and install Android Studio Updates. This fix the problem.

Solution 11 - Intellij Idea

Had the same with IDEA 14.1.5, Kotlin v.1.0.0-beta-1038-IJ141-17.
Kotlin gets its own list entry (like Java) when creating new project, but the only working config was:

New | Project | Java | "Kotlin (Java)" (make sure you have Project SDK configured, too)
use library: Create, "Copy to: lib".

Solution 12 - Intellij Idea

I tried everything: clean build folders, run gradle clean build, execute AS invalidate cache(x2), reinstall Kotlin plugin, restarting pc.

But in the end after doing all this it still didn't work, but doing also removal from project build.gradle of this line: apply plugin: 'kotlin-android-extensions', gradle sync and then re-adding worked

Solution 13 - Intellij Idea

Top Solution not work for me, after some method tries, remove IDEA caches manully works:

caches directory:

~/Library/Caches/JetBrains/<product><version> on macOS
~/.cache/JetBrains/<product><version> on Linux
%LOCALAPPDATA%\JetBrains\<product><version> on Windows

solution source: KTX issues

Solution 14 - Intellij Idea

In my case all settings were fine and I did Invalidate Cache and restart and still I had the problem. I tried below solution and worked for me.

press crtl + shift + alt + s to enter project structure.
In Project Settings select project.
Then in Project SDK click on your java version and select Kotlin instead.
Run the project.
Do all 1 to 4 but again select your jdk.
Re-Run your project.

Solution 15 - Intellij Idea

After trying a few steps, this is what worked for me.

Right-click on project > Open Module Settings > Project Settings > Modules
I removed other configs and kept just one, ie. "firstmicroservice - Kotlin" https://i.stack.imgur.com/h1uAG.png" width="600" />

From Preferences > Build, Execution, Deployment > Compile > Kotlin Compiler https://i.stack.imgur.com/td1sb.png" width="600" />

From Preferences > Build, Execution, Deployment > Compile > Java Compiler https://i.stack.imgur.com/zPASu.png" width="600" />

From Preferences > Build, Execution, Deployment > Build Tools > Maven > Runner https://i.stack.imgur.com/jvr83.png" width="600" />

Once done RUN:
Maven clean
Maven compile
Maven install

https://i.stack.imgur.com/CdJp1.png" width="200" />

Solution 16 - Intellij Idea

Happened to me today.

My issue was that I had too many tabs open (I didn't know they were open) with source code on them.

If you close all the tabs, maybe you will unconfuse IntelliJ into indexing the dependencies correctly

Solution 17 - Intellij Idea

I had this issue because the linter was printing that my object was an instance of Foo whereas the compiler couldn't define its type and consider it was an Any object like (It was more complex in my case, the linter show error in below code but the idea is here) :

    class Foo {
        val bar: Int = 0
    }

    fun test(): Any {
        return Foo()
    }

    val foo = test()
    foo.bar // <-- Linter consider that foo is an Instance of Foo but not the compiler because it's an Any object so it show the error at compilation.

To fix it I had to cast my object :

val foo = test() as Foo

Solution 18 - Intellij Idea

I was too getting this error, but i have solved this using below concept.

Restart your intellij idea community edition.
After that, go on the right hand corner to set the configuration for java.

choose configuration setting for all module. then re-run the code. It will work.

This error comes because of not configuring java properly.

Solution 19 - Intellij Idea

In my case, I had tried everything to clear cache, Remove dependencies JARs manually and Reload Maven dependencies.

The problem was solved after I enabled all children and Parent POM's for the project:

Goto

> Preferences -> Build,Execution,Deployment -> Build Tool -> Maven -> > Ignored Files

Uncheck all ignored files and then reapply
Sync Maven dependencies
Clear Cache and Restart IntelliJ (if you are still seeing this error)

Solution 20 - Intellij Idea

You have a problem with your root build.gradle file

Check versions of org.jetbrains.kotlin:kotlin-gradle-plugin
check versions of com.android.tools.build:gradle

update those version

Solution 21 - Intellij Idea

What worked for me was right clicking the project > Maven > Reload project.

Solution 22 - Intellij Idea

I was stuck on this IDE bug for half a day. It is certainly a problem related to the compatibility of the integrated Kotlin plugin, but if it is not solved with the various actions explained in the previous answers, the only solution that seems to work is to fully UNINSTALL (remove cache and plugins) and REINSTALL IntelliJ. Probably there are some old plugins that lurking somewhere in the IDE

Solution 23 - Intellij Idea

I ran into the same issue, but it was not an intellij issue, rather than an mapping issue with the new Ktor version, so first you may check if you have to migrate the dependencies from 1.6.* to Ktor 2.0.* on this Site:

https://ktor.io/docs/migrating-2.html

Solution 24 - Intellij Idea

Sometimes in similar situations (I don't think it is your problem because your case is very simple) it's worth to check kotlin file package.

If you have Kotlin file within the same package and put there some classes and missed the package declaration it looks inside the IntelliJ that you have classes in the same package but without definition of package the IntelliJ shows you:

> Error:(5, 5) Kotlin: Unresolved reference: ...

Solution 25 - Intellij Idea

Invalidating caches and updating the Kotlin plugin in Android Studio did the trick for me.

Solution 26 - Intellij Idea

I had this problem because I was trying to set up a multiplatform library configurations.

I had deleted all the source sets with their dependencies from the "build.gradle" file but kept the "common" source set.

Native was working fine but the JVM was not able to build and showed your error.

In the end, the solution was to not delete the Source set of the JVM neither it's dependencies

Solution 27 - Intellij Idea

Another thing I would like to add is that you need to select View -> Tool Windows -> Gradle before you can run the project using the Gradle.

If using the Gradle the project builds and runs normally but using the IntelliJ it doesn't, then this can solve the matter.

Solution 28 - Intellij Idea

Simplest Solution:

Tools->Kotlin->Configure Kotin in Project

Content Type	Original Author	Original Content on Stackoverflow
Question	Anony-mouse	View Question on Stackoverflow
Solution 1 - Intellij Idea	Jayson Minard	View Answer on Stackoverflow
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