Intellij Idea won't compile kotlin but maven does

Question

I have project, which contains mixed kotlin and java code based on maven. If I compile that project by maven (from command line), it is ok

[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 30.830 s
[INFO] Finished at: 2017-05-19T07:42:55+01:00
[INFO] Final Memory: 44M/482M
[INFO] ------------------------------------------------------------------------

Java:

java version "1.8.0_91"
Java(TM) SE Runtime Environment (build 1.8.0_91-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.91-b14, mixed mode)

Idea:

IntelliJ IDEA 2017.1.3
Build #IU-171.4424.56, built on May 12, 2017
JRE: 1.8.0_112-release-736-b21 x86_64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
Mac OS X 10.12.3

Maven:

Apache Maven 3.3.9 (bb52d8502b132ec0a5a3f4c09453c07478323dc5; 2015-11-10T17:41:47+01:00)
Maven home: /Library/apache-maven-3.3.9/apache-maven-3.3.9
Java version: 1.8.0_91, vendor: Oracle Corporation
Java home: /Library/Java/JavaVirtualMachines/jdk1.8.0_91.jdk/Contents/Home/jre
Default locale: cs_CZ, platform encoding: UTF-8
OS name: "mac os x", version: "10.12.3", arch: "x86_64", family: "mac"

Maven configuration:

<project>
    ..
    <properties>
        <kotlin.version>1.1.2-2</kotlin.version>
    </properties>
    ..
    <dependencies>
        ..
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-stdlib-jre8</artifactId>
            <version>${kotlin.version}</version>
        </dependency>
        ..
    </dependencies>
    <build>
        <plugins>
            ..
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.jetbrains.kotlin</groupId>
                <artifactId>kotlin-maven-plugin</artifactId>
                <version>${kotlin.version}</version>
                <configuration>
                    <jvmTarget>1.8</jvmTarget>
                    <languageVersion>1.1</languageVersion>
                    <apiVersion>1.1</apiVersion>
                </configuration>
                <executions>
                    <execution>
                        <id>compile</id>
                        <phase>process-sources</phase>
                        <goals>
                            <goal>compile</goal>
                        </goals>
                        <configuration>
                            <sourceDirs>
                                <source>src/main/java</source>
                            </sourceDirs>
                        </configuration>
                    </execution>
                    <execution>
                        <id>test-compile</id>
                        <phase>process-test-sources</phase>
                        <goals>
                            <goal>test-compile</goal>
                        </goals>
                        <configuration>
                            <sourceDirs>
                                <source>src/test/java</source>
                            </sourceDirs>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
            ..
        <plugins>
    </build>
</project>

The problem is that if I build this project in idea, I get following error and many sub errors related to this one:

Error:Kotlin: Supertypes of the following classes cannot be resolved. Please make sure you have the required dependencies in the classpath:
    class kotlin.reflect.KDeclarationContainer, unresolved supertypes: kotlin.Any
    class kotlin.reflect.KAnnotatedElement, unresolved supertypes: kotlin.Any
    class kotlin.reflect.KClassifier, unresolved supertypes: kotlin.Any

Please, do you have any idea how to make it work in IntelliJ Idea as well?

Answer 1

Sometimes things get set in project settings under .idea and/or in *.iml files and the simplest thing to do is to start the IntelliJ IDEA project over from scratch.

If your project is under source control (e.g. using git-scm) then you can simply delete your local clone, clone it again, and recreate the project.

If you can't do that then you can manually delete the .idea folder and any *.iml files. Note that IML files may be at the root of your project and in sub directories. You need to delete these while the project is not open in IntelliJ IDEA because otherwise when you close the project it may write some of these files back out to the file system.

Recreating the project is usually a last resort but sometimes it is the easiest thing to do when your project isn't working right and you can't figure out why.