Consider the following headers:

$ cat a.h

#include "b.h"

struct Foo {
   struct Bar bar;
   int x;
};


$ cat b.h

struct Bar {
  int y;
};


Extract the headers as follows:

jextract a.h -d classes

Then consider the following program:

$ cat TestUnresolved.java

import java.foreign.*;

class TestUnresolved {
   public static void main(String[] args) {
      try (Scope sc = Scope.globalScope().fork()) {
         sc.allocateStruct(a.Foo.class);
      }
   }
}


And run it like this:

java -cp classes TestUnresolved.java

The following exception will be reported:

Exception in thread "main" java.lang.UnsupportedOperationException: bitsSize on Unresolved
at java.base/java.foreign.layout.Unresolved.bitsSize(Unresolved.java:76)
at java.base/java.util.stream.ReferencePipeline$5$1.accept(ReferencePipeline.java:229)
at java.base/java.util.Spliterators$ArraySpliterator.forEachRemaining(Spliterators.java:948)
at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)
at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913)
at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.base/java.util.stream.LongPipeline.reduce(LongPipeline.java:474)
at java.base/java.util.stream.LongPipeline.sum(LongPipeline.java:432)
at java.base/java.foreign.layout.Group.bitsSize(Group.java:119)
at java.base/java.foreign.memory.LayoutType.bytesSize(LayoutType.java:49)
at java.base/jdk.internal.foreign.ScopeImpl.allocateInternal(ScopeImpl.java:130)
at java.base/jdk.internal.foreign.ScopeImpl.allocate(ScopeImpl.java:156)
at java.base/jdk.internal.foreign.ScopeImpl.allocateStruct(ScopeImpl.java:162)
at TestUnresolved.main(TestUnresolved.java:6)


That is, layout resolution fails, because the name "Bar" is defined in an header that is different from the one in which the unresolved reference "${Bar}" occurs.