The condition check unit.getRoot() == node.getRoot() is not needed. I tested #519 snippet without this check, it worked.

For some reason for me it start to fail before in shouldVisitNode the end becomes -1 since the on JDT side the start + length of the node becomes equal to the end of the compilation unit's last position. I will try again without this check.

OK now I found the reason, if you don't have a empty line at the end of the class, that after the last class definitions' brace, then the end getLineNumber becomes -1

I can reproduce it, but i would prefer to modify the implementation shouldVisitNode() to fix the problem.

Since the offset range of the ast node is [node.getStartPosition, node.getStartPosition() + node.getLength() - 1], the ending line should be got from unit.getLineNumber(node.getStartPosition() + node.getLength() - 1).

The fix could be as follow:

    private boolean shouldVisitNode(ASTNode node) {
        int start = unit.getLineNumber(node.getStartPosition());
        int end = unit.getLineNumber(node.getStartPosition() + node.getLength() - 1);

        if (line >= start && line <= end) {
            return true;
        }

        return false;
    }

Look at the caller, actually we took the first parameter as current, the second one as original. So we should change the signature definition to private boolean isSameLocation(Location current, Location original, MethodInvocation targetStepIn).

The last condition check should be (targetStepIn != null && targetStepIn.lineEnd >= current.lineNumber()), which supports multiline expression better.

I can reproduce it, but i would prefer to modify the implementation shouldVisitNode() to fix the problem.

Since the offset range of the ast node is [node.getStartPosition, node.getStartPosition() + node.getLength() - 1], the ending line should be got from unit.getLineNumber(node.getStartPosition() + node.getLength() - 1).

The fix could be as follow:

    private boolean shouldVisitNode(ASTNode node) {
        int start = unit.getLineNumber(node.getStartPosition());
        int end = unit.getLineNumber(node.getStartPosition() + node.getLength() - 1);

        if (line >= start && line <= end) {
            return true;
        }

        return false;
    }

this doesn't work for multiline method invocation. We should use targetStepIn.lineEnd in the last check, e.g. targetStepIn.lineEnd >= current.lineNumber().

For the use case below, step-into target filterMe doesn't work, it stops at the line of "2", "3", .

new ArrayList<>(List.of("1"))
        .subList(0, 1)
        .addAll(filterMe("1", 
            "2", "3", 
            "4"));