Understanding the the transitive dependencies of the Kotlin Standard Library with Maven

I'm trying to understand the relationship between different versions of Kotlin libraries the Maven Kotlin plugin. As the configuration below shows, I'm setting my Kotlin version to 1.8.20-RC2, but for reasons I don't understand, it's getting version 1.3.72 of the Kotlin stdlib. There are features in stdlib version 1.5 that I want and I can't understand why I'm only getting version 1.3.

I've got this in my pom.xml:

<properties>
    <kotlin.version>1.8.20-RC2</kotlin.version>
</properties>

and under <depenencies>,

    <dependency>
        <groupId>org.jetbrains.kotlin</groupId>
        <artifactId>kotlin-stdlib-jdk8</artifactId>
        <version>${kotlin.version}</version>
    </dependency>
    <dependency>
        <groupId>org.jetbrains.kotlin</groupId>
        <artifactId>kotlin-test</artifactId>
        <version>${kotlin.version}</version>
        <scope>test</scope>
    </dependency>

and under <build><plugins>...</plugins></build> section:

<plugin>
    <groupId>org.jetbrains.kotlin</groupId>
    <artifactId>kotlin-maven-plugin</artifactId>
    <version>${kotlin.version}</version>

    // lots more stuff here
</plugin>

But then, I ran mvn dependency:tree, and look what it shows:

// lots of other dependencies listed
[INFO] +- org.jetbrains.kotlin:kotlin-stdlib-jdk8:jar:1.8.20-RC2:compile
[INFO] |  +- org.jetbrains.kotlin:kotlin-stdlib:jar:1.3.72:compile
[INFO] |  |  +- org.jetbrains.kotlin:kotlin-stdlib-common:jar:1.3.72:compile
[INFO] |  |  \- org.jetbrains:annotations:jar:13.0:compile
[INFO] |  \- org.jetbrains.kotlin:kotlin-stdlib-jdk7:jar:1.3.72:compile
[INFO] \- org.jetbrains.kotlin:kotlin-test:jar:1.8.20-RC2:test

I'm not an expert at this, but if I understand this right, version 1.8.20-RC2 is bringing in 1.3.72 as a transitive dependency. I confirmed that I am unable to use a function in my code, firstNotNullOfOrNull that is not available in 1.3 but is available on versions 1.5 or later.

Can someone explain what is going on here, and how I can get a later version of the stdlib?

I'm not sure about your specific issue here, because the artifact does depend on the correct stdlib and stdlib-jdk7, as we can see in the pom on Maven Central:
https://repo1.maven.org/maven2/org/jetbrains/kotlin/kotlin-stdlib-jdk8/1.8.20-RC2/kotlin-stdlib-jdk8-1.8.20-RC2.pom

But anyway, note that those kotlin-stdlib-jdk7 and kotlin-stdlib-jdk8 artifacts have been merged with the regular kotlin-stdlib since Kotlin 1.8, so you shouldn't use them anymore.

Instead, just use kotlin-stdlib directly, it might solve the problem altogether.

My pom has this

        <kotlin.version>1.8.10</kotlin.version>
...    
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-stdlib</artifactId>
            <version>${kotlin.version}</version>
            <scope>provided</scope>
        </dependency>

and I get what you might be expecting on the dependency graph

INFO] +- org.jetbrains.kotlin:kotlin-stdlib:jar:1.8.10:provided
[INFO] |  +- org.jetbrains.kotlin:kotlin-stdlib-common:jar:1.8.10:provided
[INFO] |  \- org.jetbrains:annotations:jar:13.0:provided

My guess about what is happening is that some other dependency is forcing the version down.

What IDE are you using. If you are using IntelliJ is has a Maven analyser which will help you find that a transitive dependency is being overriden.

Obviously you should find the source of that, but if you cannot you can just re-declare the kotlin-stdlib-common explicitly at the top level like this:

        <kotlin.version>1.8.10</kotlin.version>
...    
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-stdlib</artifactId>
            <version>${kotlin.version}</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-stdlib-common</artifactId>
            <version>${kotlin.version}</version>
            <scope>provided</scope>
        </dependency>