How to get the IDE debugger to use the OpenJDK source code instead of the decompiled class files?

[Anil]

I am trying to learn the Streams package of the JDK, and successfully built
the jdk.
I set the IDE (IntelliJ Community Edition) to use the JDK.
I put some dummy output statements in a stream method, peek(), and built
the JDK again.
I was stepping through a toy Java program that uses it, but I see that when
it gets to the core/base libraries, it does not use the Java code, but
rather, the decompiled code.
How to get the IDE to use the Java code?
Here is the code I changed in java.util.stream.ReferencePipeline.java

public final Stream<P_OUT> peek(Consumer<? super P_OUT> action) {
    Objects.requireNonNull(action);
    System.out.println("=========anil 3 ================");
    return new StatelessOp<>(this, StreamShape.REFERENCE,
            0) {
        @Override
        Sink<P_OUT> opWrapSink(int flags, Sink<P_OUT> sink) {
            return new Sink.ChainedReference<>(sink) {
                @Override
                public void accept(P_OUT u) {
                    System.out.println("=========anil 0 ================");
                    action.accept(u);
                    System.out.println("=========anil 1 ================");
                    downstream.accept(u);
                    System.out.println("=========anil 2 ================");
                }
            };
        }
    };
}

thanks,
Anil