Kotlin Jupyter Kernel Dependency Version Conflict Reproducer

Currently, either the Kotlin Jupyter kernel does not perform any conflict resolution when there are multiple versions of a dependency or it's picking a lower version. This can lead to hard-to-diagnose runtime failures. This repository demonstrates a case in which this issue arises.

1. Publish the Example Library to Maven Local

./gradlew -p example-library publishLibraryPublicationToMavenLocal

2. Set Up a Python Virtual Environment and Install Jupyter + Kotlin Kernel

0.14.1.550 is the latest version of the Kotlin Jupyter kernel published to pypi.org and Anaconda.org, as of this commit's author time.

python3 -m venv .venv
source .venv/bin/activate
pip install jupyterlab==4.4.5 kotlin-jupyter-kernel==0.14.1.550

3. Run the Notebook on either commit

• Expected: The notebook succeeds. Ideally, it would succeed by resolving okio to the highest version requested, 3.15.0. That's the most common dependency version conflict resolution strategy experienced by Kotlin users because it's the default in Gradle.
• Actual: The notebook fails with a NoClassDefFoundError for okio.Socket, which is used internally by OkHttp at runtime. Note how this class is not directly used by the notebook or the library, making for a rather confusing failure. The notebook fails on one commit but succeeds on the other, according to the order of dependencies in the example-library's pom. The difference between commits is the order of the dependencies in that pom file (or its build.gradle.kts dependencies, which result in that pom).

# This fails because it uses okio 3.7.0, which does not include okio.Socket
git checkout a4517ae && ./gradlew publishToMavenLocal && jupyter nbconvert --to notebook --execute notebook.ipynb
# This succeeds because it uses okio 3.15.0, which includes okio.Socket
git checkout d2cbe19 && ./gradlew publishToMavenLocal && jupyter nbconvert --to notebook --execute notebook.ipynb

You could also run script.main.kts to see that the Kotlin scripting engine doesn't seem to resolve dependency version conflicts either. However, note that Kotlin scripting has some sort of caching mechanism I couldn't figure out how to disable. I couldn't reproduce the issue reliably while switching commits.

# Edit the @file:Repository value first to use your user home path
# Should fail
git checkout a4517ae && ./gradlew publishToMavenLocal && kotlin -script script.main.kts
# Should succeed
git checkout d2cbe19 && ./gradlew publishToMavenLocal && kotlin -script script.main.kts

Dependencies comparison

pom diff

Output of 'bad pom commit' (a4517ae) vs 'good pom commit' (d2cbe19).

--- build/minimal-bad.pom	2025-07-31 20:39:17
+++ build/minimal-good.pom	2025-07-31 20:39:18
@@ -11,18 +11,18 @@
   <version>SNAPSHOT</version>
   <dependencies>
     <dependency>
-      <groupId>com.squareup.moshi</groupId>
-      <artifactId>moshi</artifactId>
-      <version>1.15.2</version>
-      <scope>compile</scope>
-    </dependency>
-    <dependency>
       <groupId>com.squareup.okhttp3</groupId>
       <artifactId>okhttp-jvm</artifactId>
       <version>5.1.0</version>
       <scope>compile</scope>
     </dependency>
     <dependency>
+      <groupId>com.squareup.moshi</groupId>
+      <artifactId>moshi</artifactId>
+      <version>1.15.2</version>
+      <scope>compile</scope>
+    </dependency>
+    <dependency>
       <groupId>org.jetbrains.kotlin</groupId>
       <artifactId>kotlin-stdlib</artifactId>
       <version>2.1.20</version>

Dependency graphs

Bad pom (a4517ae)

------------------------------------------------------------
Root project 'example-library'
------------------------------------------------------------

runtimeClasspath - Runtime classpath of 'main'.
+--- com.squareup.okhttp3:okhttp:5.1.0
|    \--- com.squareup.okhttp3:okhttp-jvm:5.1.0
|         +--- com.squareup.okio:okio:3.15.0
|         |    \--- com.squareup.okio:okio-jvm:3.15.0
|         |         \--- org.jetbrains.kotlin:kotlin-stdlib:2.1.21 -> 2.2.0
|         |              +--- org.jetbrains:annotations:13.0
|         |              +--- org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.8.0 -> 1.8.21 (c)
|         |              \--- org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.8.0 -> 1.8.21 (c)
|         \--- org.jetbrains.kotlin:kotlin-stdlib:2.2.0 (*)
+--- com.squareup.moshi:moshi:1.15.2
|    +--- com.squareup.okio:okio:3.7.0 -> 3.15.0 (*)
|    \--- org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.8.21
|         +--- org.jetbrains.kotlin:kotlin-stdlib:1.8.21 -> 2.2.0 (*)
|         \--- org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.8.21
|              \--- org.jetbrains.kotlin:kotlin-stdlib:1.8.21 -> 2.2.0 (*)
\--- org.jetbrains.kotlin:kotlin-stdlib:2.1.20 -> 2.2.0 (*)

(c) - A dependency constraint, not a dependency. The dependency affected by the constraint occurs elsewhere in the tree.
(*) - Indicates repeated occurrences of a transitive dependency subtree. Gradle expands transitive dependency subtrees only once per project; repeat occurrences only display the root of the subtree, followed by this annotation.

Good pom (d2cbe19)

------------------------------------------------------------
Root project 'example-library'
------------------------------------------------------------

runtimeClasspath - Runtime classpath of 'main'.
+--- com.squareup.moshi:moshi:1.15.2
|    +--- com.squareup.okio:okio:3.7.0 -> 3.15.0
|    |    \--- com.squareup.okio:okio-jvm:3.15.0
|    |         \--- org.jetbrains.kotlin:kotlin-stdlib:2.1.21 -> 2.2.0
|    |              +--- org.jetbrains:annotations:13.0
|    |              +--- org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.8.0 -> 1.8.21 (c)
|    |              \--- org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.8.0 -> 1.8.21 (c)
|    \--- org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.8.21
|         +--- org.jetbrains.kotlin:kotlin-stdlib:1.8.21 -> 2.2.0 (*)
|         \--- org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.8.21
|              \--- org.jetbrains.kotlin:kotlin-stdlib:1.8.21 -> 2.2.0 (*)
+--- com.squareup.okhttp3:okhttp:5.1.0
|    \--- com.squareup.okhttp3:okhttp-jvm:5.1.0
|         +--- com.squareup.okio:okio:3.15.0 (*)
|         \--- org.jetbrains.kotlin:kotlin-stdlib:2.2.0 (*)
\--- org.jetbrains.kotlin:kotlin-stdlib:2.1.20 -> 2.2.0 (*)

(c) - A dependency constraint, not a dependency. The dependency affected by the constraint occurs elsewhere in the tree.
(*) - Indicates repeated occurrences of a transitive dependency subtree. Gradle expands transitive dependency subtrees only once per project; repeat occurrences only display the root of the subtree, followed by this annotation.