apache/dubbo · error · IllegalArgumentException

non-public delegate class from different packages

Error message

non-public delegate class from different packages

What it means

Thrown by Mixin.mixin when two or more INTERFACE classes (the ics array) are non-public AND reside in different packages. The generated mixin must live in one package to access package-private interfaces; if non-public interfaces span multiple packages, neither package can host the class, so Dubbo aborts with IllegalArgumentException.

Solutions

Make the interfaces public so they can be implemented from any package.
Keep all non-public interfaces in a single shared package.
Split into multiple mixin instances grouped by package.

Example fix

// before
package a.b; interface InternalA {} // package-private
package c.d; interface InternalB {} // package-private
Mixin.mixin(new Class[]{ InternalA.class, InternalB.class }, dc);

// after
package a.b; public interface InternalA {} // promote to public

Defensive patterns

Strategy: validation

Validate before calling

for (Class<?> ic : ics) {
    if (!Modifier.isPublic(ic.getModifiers())) {
        // all non-public interfaces must share a single package
    }
}

Prevention

Make interfaces public whenever they are mixed via Mixin.
Keep package-private interfaces in one package if you must mix them.
Validate interface visibility before calling Mixin.mixin.

When it happens

Trigger: Mixin.mixin(ics, dc) where ics contains package-private interfaces drawn from more than one package.

Common situations: Mixing internal package-private interfaces from different modules; SPI extension interfaces that are not public and come from separate libraries.

Related errors

AI-assisted analysis of apache/dubbo@3a3043227f (2026-08-14). Data as JSON: /api/errors/5f6ec21a8ddc4a93. Report an issue: GitHub.

Appendix: source

Thrown at dubbo-common/src/main/java/org/apache/dubbo/common/bytecode/Mixin.java:129

                        .append("];\n");
                if (MixinAware.class.isAssignableFrom(dcs[i])) {
                    code.append('d').append(i).append(".setMixinInstance(this);\n");
                }
            }
            ccp.addConstructor(Modifier.PUBLIC, new Class<?>[] {Object[].class}, code.toString());

            Class<?> neighbor = null;
            // impl methods.
            Set<String> worked = new HashSet<>();
            for (int i = 0; i < ics.length; i++) {
                if (!Modifier.isPublic(ics[i].getModifiers())) {
                    String npkg = ics[i].getPackage().getName();
                    if (pkg == null) {
                        pkg = npkg;
                        neighbor = ics[i];
                    } else {
                        if (!pkg.equals(npkg)) {
                            throw new IllegalArgumentException("non-public delegate class from different packages");
                        }
                    }
                }

                ccp.addInterface(ics[i]);

                for (Method method : ics[i].getMethods()) {
                    if ("java.lang.Object".equals(method.getDeclaringClass().getName())) {
                        continue;
                    }

                    String desc = ReflectUtils.getDesc(method);
                    if (worked.contains(desc)) {
                        continue;
                    }
                    worked.add(desc);

                    int ix = findMethod(dcs, desc);

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