Bug 306226 – Fix -Wlifetime-safety-permissive warning in XPathNodeSet::findRootNode()

• Status: RESOLVED
• Resolution: FIXED
• Component: XML

[David Kilzer (:ddkilzer)]

The compiler warning `-Wlifetime-safety-permissive` was triggered in `findRootNode()` when building with upstream clang in Source/WebCore/xml/XPathNodeSet.cpp:

```
OpenSource/Source/WebCore/xml/XPathNodeSet.cpp:191:20: error: object whose reference is captured does not live long enough [-Werror,-Wlifetime-safety-permissive]
  191 |             node = parent.get();
      |                    ^~~~~~
OpenSource/Source/WebCore/xml/XPathNodeSet.cpp:191:31: note: destroyed here
  191 |             node = parent.get();
      |                               ^
OpenSource/Source/WebCore/xml/XPathNodeSet.cpp:190:32: note: later used here
  190 |         while (RefPtr parent = node->parentNode())
      |                                ^~~~
```

The issue is in the while loop where `RefPtr parent` is declared in the condition, causing it to be destroyed and reconstructed on every iteration. After `node = parent.get()` executes, `parent` is destroyed, but then `node->parentNode()` is called in the next iteration with `node` potentially pointing to a destroyed object.

[David Kilzer (:ddkilzer)]

The specific lifetime issue is fixed by changing from a `while` loop to a `for` loop pattern to avoid recreating the `RefPtr parent` variable on each iteration.

Current problematic code:

```
while (RefPtr parent = node->parentNode())
    node = parent.get();
```

Proposed fix:

```
for (RefPtr parent = current->parentNode(); parent; parent = current->parentNode())
    current = WTF::move(parent);
```

Why this works:

The `for` loop declares `parent` once and reuses it via assignment, maintaining object lifetime across iterations. When `current->parentNode()` is called in the increment expression, the previous `parent` value is still alive, preventing the lifetime safety issue.

Additional changes to support this fix:
1. Return `RefPtr<Node>` instead of `Node*` for proper lifetime management
2. Use `RefPtr<Node> current` throughout to maintain object lifetime  
3. Replace `&node->document()` with `current->protectedDocument()` (returns `Ref<Document>`)
4. Properly transfer ownership with `WTF::move(parent)`

[Radar WebKit Bug Importer]

<rdar://problem/168880148>

[David Kilzer (:ddkilzer)]

Pull request: https://github.com/WebKit/WebKit/pull/57221

[EWS]

Committed 306240@main (7a9af69f9b93): <https://commits.webkit.org/306240@main>

Reviewed commits have been landed. Closing PR #57221 and removing active labels.