Stack variable ValueDescriptors return null types/values on first debugger suspend

IntelliJ Platform
1

I am developing a plugin that needs to analyze the local variables of the current stack frame when the debugger suspends. I have been able to use com.intellij.debugger.engine.JavaStackFrame#computeChildren to receive the values in an implementation of com.intellij.xdebugger.frame.XCompositeNode, cast those values to com.intellij.debugger.engine.JavaValue and get their descriptors.

The issue I am having is that on the first suspend, com.intellij.debugger.ui.tree.ValueDescriptor#getType() and com.intellij.debugger.ui.impl.watch.ValueDescriptorImpl#getValue() both return null for all values in the frame. On subsequent suspends for further lines of the same class/method, these methods will start returning values. I have also noticed that if I click off the paused frame to a prior one, then click back to the original frame the types/values will be present then as well.

It seems that there is something I need to do to force a lazy evaluation, or an asynchronous operation I need to wait for? I have tried also using com.intellij.debugger.ui.impl.watch.ValueDescriptorImpl#getFullValueDescriptor and com.intellij.xdebugger.evaluation.XInstanceEvaluator#evaluate thinking these might trigger a more thorough evaluation but I get the same result.

An excerpt of the relevant code is below. Thanks in advance for any advice.

    @Override
    public void addChildren(@NotNull XValueChildrenList xValueChildrenList, boolean b) {

        for (int i = 0; i < xValueChildrenList.size(); i++) {

            String name = xValueChildrenList.getName(i);
            JavaValue value = (JavaValue) xValueChildrenList.getValue(i);

            //these are both null on the first suspend
            var type = value.getDescriptor().getType();
            var descriptorValue = value.getDescriptor().getValue();

        }

    }

Using IDEA 2024.3.5

I am unable to link to my plugin source as it is for internal use. Hopefully this question has a simple answer - if not I can try to recreate just the debugger issues in an isolated public project.

3

I found that if I just let the stack frame analysis run without stopping at a breakpoint it eventually throws an exception trying to access the descriptor values, saying they are not yet computed. That error lead me to this post which has the solution (and seems to imply a bug in com.intellij.debugger.engine.JavaValue which is not fixed): https://intellij-support.jetbrains.com/hc/en-us/community/posts/360010693960-Error-when-reading-debugging-variables-during-a-debugging-session-with-a-plugin

4

yes, for now the value inside should be initialized by calling computePresentation