Rowan upgrade to 0.16.0 breaks prev_sibling behaviour

[MalteJanz]

Discovered by MalteJanz/ludtwig#122

The failed test pipeline contains a bunch of issues related to the rowan upgrade that might need further investigation. But I think the easiest failing test is the following:

(can be found here)

    #[test]
    fn it_should_not_panic_on_prev_sibling_call() {
        let parse = parse("<div>a<hr/></div>");
        let root = SyntaxNode::new_root(parse.green_node);
        // println!("{}", debug_tree(&root));

        let prev = root.prev_sibling();
        // println!("prev sibling: {:?}", prev);
        assert!(prev.is_none());

        let child: HtmlTag = support::child(&root).unwrap();
        let prev = child.syntax().prev_sibling();
        // println!("{:?} prev sibling: {:?}", child, prev);
        assert!(prev.is_none());

        let child: HtmlTag = support::child(child.body().unwrap().syntax()).unwrap();
        let prev = child.syntax().prev_sibling();
        // println!("{:?} prev sibling: {:?}", child, prev);
        assert!(prev.is_some());
    }

Btw: I wrote this test while fixing my previous rowan contribution, see #143 . It basically came down to a off-by-one error which might regressed with the latest version, see initial issue: #139

Test output:

---- tests::it_should_not_panic_on_prev_sibling_call stdout ----
thread 'tests::it_should_not_panic_on_prev_sibling_call' panicked at crates/ludtwig-parser/src/lib.rs:152:9:
assertion failed: prev.is_some()

Which points to the last assertion and last line of the test above. Seems like the sibling somehow got lost 🤔

Test explaination

The parsing input:

<div>a<hr/></div>

produces the following tree:

[email protected]
  [email protected]
    [email protected]
      [email protected] "<"
      [email protected] "div"
      [email protected]
      [email protected] ">"
    [email protected]
      [email protected]
        [email protected] "a"
      [email protected]
        [email protected]
          [email protected] "<"
          [email protected] "hr"
          [email protected]
          [email protected] "/>"
    [email protected]
      [email protected] "</"
      [email protected] "div"
      [email protected] ">"

Note: remember the HTML_TEXT node with the "a" word token next to the HTML_TAG node ("hr" tag)

The first declaration of child ends up as the following tree (the outer div):

[email protected]
  [email protected]
    [email protected] "<"
    [email protected] "div"
    [email protected]
    [email protected] ">"
  [email protected]
    [email protected]
      [email protected] "a"
    [email protected]
      [email protected]
        [email protected] "<"
        [email protected] "hr"
        [email protected]
        [email protected] "/>"
  [email protected]
    [email protected] "</"
    [email protected] "div"
    [email protected] ">"

And doesn't have a previous sibling as expected.

Next up it get's the body of that div tag (isn't stored in a variable), which also looks like expected:

[email protected]
  [email protected]
    [email protected] "a"
  [email protected]
    [email protected]
      [email protected] "<"
      [email protected] "hr"
      [email protected]
      [email protected] "/>"

And inside that it get's the first tag which ends up in the second declared child variable:

[email protected]
  [email protected]
    [email protected] "<"
    [email protected] "hr"
    [email protected]
    [email protected] "/>"

As expected that's the <hr/> tag. And now comes the previously working call to prev_sibling on that exact node, which surprisingly ends up with none instead of the HTML_TEXT node.

The same test and parser implementation was succeeding in rowan 0.15.16

[MalteJanz]

@milianw Might be related to your PR #171 as it slightly changed the prev_sibling implementation 🤔
https://github.com/rust-analyzer/rowan/pull/171/files#diff-d652bc172cf95622c9c34f43bd6ed9a6c27f042945f710cb9025cae7b12dd579L393