slint-ui/slint · error

Dex conversion failed

Error message

Dex conversion failed

What it means

D8 ran but exited with a non-zero status during the .class -> .dex conversion; the build script prints D8's stderr under this message rather than panicking immediately. It means the Java class files produced by the earlier javac step could not be dexed — commonly bytecode level vs. D8 version mismatch, or (as the following JDK>=21 warning shows) a too-new JDK producing classes this D8 cannot process.

Solutions

1. Read the D8 stderr printed with the panic for the real cause: most often multidex/MethodTooLarge issues or invalid class files
2. Follow the built-in hint: the script checks the JDK version and warns when JDK >= 21 is used; downgrade to JDK 17 or a compatible toolchain if that warning appears
3. Confirm android_min_api (20) and the single-dex assumption still hold; if the dex exceeds limits, raise min API or enable multidex
4. Ensure all dependency jars (android.jar, d8 jar) match the build-tools version in use

When it happens

Trigger: Thrown at internal/backends/android-activity/build.rs:82 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of slint-ui/slint@bb937076de (2026-09-16). Data as JSON: /api/errors/bf24a2ac5e53947b. Report an issue: GitHub.

Appendix: source

Thrown at internal/backends/android-activity/build.rs:82

        .android_min_api(20) // disable multidex for single dex file output
        .out_dir(out_dir)
        .command()
        .unwrap_or_else(|e| panic!("Could not generate the D8 command: {e}"))
        .output()
        .unwrap_or_else(|e| panic!("Error running D8: {e}"));

    if !o.status.success() {
        eprintln!("Dex conversion failed: {}", String::from_utf8_lossy(&o.stderr));
        let java_home = android_build::java_home().unwrap();
        let java_ver = android_build::check_javac_version(&java_home).unwrap();
        if java_ver >= 21 {
            eprintln!("WARNING: JDK version 21 is known to cause an error with older android SDK");
            eprintln!("See https://github.com/slint-ui/slint/issues/4973");
            eprintln!(
                "Try downgrading your version of Java to something like JDK 17, or upgrade to the SDK build tools 35"
            );
        }
        panic!("Dex conversion failed");
    }

    println!("cargo:rerun-if-changed={java_src_path}");
}

View on GitHub (pinned to bb937076de)