Java file cannot resolve Kotlin classes in mixed Kotlin/Java Gradle project

[abdulazizzisan]

Relevance Confirmation

• I confirmed that this is not an issue with the Eclipse JDT Language Server itself

What happened?

Environment

• Zed version:
  Zed 1.1.7
  Commit: c17f25cd782edffab64b7c4167abfa44f865b125
  Version: 1.1.7+stable.268.c17f25cd782edffab64b7c4167abfa44f865b125
• OS:
  MacBook Air, Apple M4, macOS Tahoe 26.4.1 (25E253)
• Java version: java 25.0.3 2026-04-21 LTS
• Build tool: Gradle

Extensions Tested

I tested both:

• Java v0.8.17
• Java with Eclipse JDTLS v0.2.5

Both produced the exact same result.

Description

In a mixed Kotlin + Java Gradle project, Java files show unresolved symbol/type errors when referencing Kotlin classes, even though the project builds successfully with Gradle.

Kotlin files appear to work correctly, but Java diagnostics/navigation/completion do not recognize Kotlin classes.

This seems related to Java support being handled by JDTLS while Kotlin support is provided separately.

Example Error

The import com.zisan.payload.DynamicPagedResponse cannot be resolved

The referenced class is a Kotlin class and the Gradle build succeeds without issues.

Steps to Reproduce

1. Create a Gradle project with both Java and Kotlin enabled.

2. Add a Kotlin class:

3. Reference it from Java:

4. Open the project in Zed.

Actual Behavior

• Java files show unresolved symbol/type errors for Kotlin classes.
• Kotlin files appear fine.
• Gradle build succeeds without issues.

Notes

This may be caused by JDTLS not recognizing Kotlin-generated sources/classes in the project model or classpath.

The issue does not affect compilation, only editor diagnostics/intellisense behavior.

What did you expect to happen?

Expected Behavior

• Java files should resolve Kotlin classes correctly.
• No diagnostics/errors should appear for valid Kotlin references.
• Go-to-definition and autocomplete should work across Java ↔ Kotlin.

Environment

• Zed version:
  Zed 1.1.7
  Commit: c17f25cd782edffab64b7c4167abfa44f865b125
  Version: 1.1.7+stable.268.c17f25cd782edffab64b7c4167abfa44f865b125
• OS:
  MacBook Air, Apple M4, macOS Tahoe 26.4.1 (25E253)
• Java version: java 25.0.3 2026-04-21 LTS
• Build tool: Gradle

[tartarughina]

Thanks for reporting this! This is a known limitation of how JDTLS handles mixed Kotlin/Java projects.

Background

JDTLS has a java.jdt.ls.kotlinSupport.enabled setting (defaults to false) that tells it to cooperate with Kotlin sources. You can try enabling it in your Zed settings:

  "lsp": {
    "jdtls": {
      "initialization_options": {
        "settings": {
          "java": {
            "jdt": {
              "ls": {
                "kotlinSupport": {
                  "enabled": true
                }
              }
            }
          }
        }
      }
    }
  }

After adding this, clear the JDTLS cache (from a Java file, run the Clear JDTLS cache task) and restart the language server.

Important caveat

This flag alone may not fully resolve the issue. In VS Code, Kotlin cross-resolution works because additional plugin JARs (like the Kotlin Language Server plugin for JDTLS) are loaded via the bundles initialization option. The Zed Java extension does not currently bundle or configure any Kotlin plugin, so JDTLS may still not be able to resolve Kotlin-compiled symbols even with the flag enabled.

What you can try in the meantime

1. Make sure you've run ./gradlew build at least once so Kotlin sources are compiled to .class files
2. Verify that Gradle import is working correctly in JDTLS (you should see your project's dependencies resolved)
3. Try the setting above and let us know if it makes a difference

Full support for mixed Kotlin/Java projects would likely require bundling a Kotlin plugin JAR with the extension, that's a feature enhancement we can look into.