JetBrains/intellij-community · error · EvaluateException

Unable to set value

Error message

Unable to set value

What it means

Thrown by LocalVariablesUtil when setting a value of a decompiled local variable fails. This path uses reflection to drive the JDI SlotInfo/set protocol for variables with no local-variable table (classes compiled without debug info); any reflective or invocation failure is wrapped in EvaluateException('Unable to set value').

Source

Thrown at java/debugger/impl/src/com/intellij/debugger/jdi/LocalVariablesUtil.java:273

      else {
        final Long frameId = ReflectionUtil.getField(frame.getClass(), frame, long.class, "id");
        final VirtualMachine vm = frame.virtualMachine();
        final Method stateMethod = vm.getClass().getDeclaredMethod("state");
        stateMethod.setAccessible(true);

        Object slotInfoArray = createSlotInfoArraySet(variable.slot(), value);

        Object ps;
        final Object vmState = stateMethod.invoke(vm);
        synchronized (vmState) {
          ps = ourEnqueueMethodSet.invoke(null, vm, frame.thread(), frameId, slotInfoArray);
        }

        ourWaitForReplyMethodSet.invoke(null, vm, ps);
      }
    }
    catch (Exception e) {
      throw new EvaluateException("Unable to set value", e);
    }
  }

  private static Object createSlotInfoArraySet(int slot, Value value)
    throws IllegalAccessException, InvocationTargetException, InstantiationException {
    Object arrayInstance = Array.newInstance(ourSlotInfoClassSet, 1);
    Array.set(arrayInstance, 0, slotInfoConstructorSet.newInstance(slot, value));
    return arrayInstance;
  }

  private static Object createSlotInfoArray(Collection<? extends DecompiledLocalVariable> vars) throws Exception {
    final Object arrayInstance = Array.newInstance(ourSlotInfoClass, vars.size());

    int idx = 0;
    for (DecompiledLocalVariable var : vars) {
      final Object info = slotInfoConstructor.newInstance(var.slot(), (byte)var.signature().charAt(0));
      Array.set(arrayInstance, idx++, info);
    }

View on GitHub (pinned to be881553f2)

Solutions

1. Recompile the debuggee with debug info (-g or gradle/maven debug flag) so real LocalVariables exist instead of decompiled slots
2. Ensure the assigned value's type exactly matches the variable's expected type (no implicit conversions in slot assignment)
3. Update the IDE — reflective JDI internals change between JDK versions and are patched per-JDK

Example fix

# before
javac Main.java  # no -g, decompiled slots

# after
javac -g Main.java

// before assigning to a decompiled variable
if (!(variable instanceof DecompiledLocalVariable)) {
  frame.setValue(variable, value);
} else {
  // ensure value type matches slot type exactly; otherwise wrap/cast first
}

boolean isSafeSlotAssignment(DecompiledLocalVariable v, Value value) {
  return value == null || v.typeName().equals(value.type().name());
}

try {
  LocalVariablesUtil.setValue(frame, variable, value);
} catch (EvaluateException e) {
  // 'Unable to set value': report slot/type mismatch, suggest recompiling with -g
}

When it happens

Trigger: Calling the setValue path for a DecompiledLocalVariable: it reflects into the VM state object, builds a SlotInfo array via createSlotInfoArraySet(variable.slot(), value), invokes the enqueue/WaitForReply JDI internals; ClassNotFoundException/IllegalAccessException/InvocationTargetException from the reflection setup or the reflective call itself is caught by 'catch (Exception e)' and rethrown as EvaluateException.

Common situations: Debugging classes compiled without -g (no local variable table) so the debugger decompiles variables; assigning to such a variable in the Variables view or evaluator while the JDI internals reject the value type for the slot; JDI implementation differences across JDK versions breaking the reflective protocol.

Related errors

• Interface method invocation is not supported in JVM {}. Use
• Cannot construct wrapper object for value of type {}: Unable
• Cannot convert to primitive value of type
• Thread has been collected
• There is no executable code at {0}:{1}

AI-assisted analysis of JetBrains/intellij-community@be881553f2 (2026-08-14). Data as JSON: /api/errors/cdbf616a4b36cda2. Report an issue: GitHub.