Return no siblings for an element with no parent, without warnings

CHANGELOG.md

@@ -58,6 +58,7 @@ QueryPath Changelog
 - Consolidate the sibling and ancestor walks behind `next()`, `prev()`, `nextAll()`, `prevAll()`, `nextUntil()`, `prevUntil()`, `parent()`, `parents()`, `parentsUntil()` and `closest()` into one helper, so a fix to one no longer has to be repeated in its mirror (issue #115). As a side effect, `parentsUntil()` no longer loops forever on an element that is not attached to the document, and `nextUntil('')` and `prevUntil('')` treat an empty selector as no selector, as the other methods already did, instead of throwing `QueryPath\CSS\ParseException`. `closest('')` returns an empty set, as in jQuery. `nextUntil()`, `prevUntil()` and `parentsUntil()` also stop at an element already collected from an earlier starting element, as `nextAll()` and `prevAll()` do, so `nextUntil()` on each of 2000 siblings falls from about 100 ms to 1 ms
 - **Behaviour change.** `prevAll()`, `prevUntil()`, `nextAll()`, `nextUntil()`, `siblings()`, `parent()` and `closest()` now return the results for a multi-element set in jQuery's order, instead of grouped by starting element (issue #117). `prevAll()` and `prevUntil()` return reverse document order, as `parents()` and `parentsUntil()` already did, and the others return document order. `qp($xml, 'c')->add('d')->prevAll()` now returns `c, b, a` rather than `b, a, c`. `next()` and `prev()` keep the order of the starting elements, as in jQuery, and the results for a single starting element are unchanged
 - **Behaviour change.** A positional pseudo-class (`:first`, `:eq()`, `:last`, ...) in the stop selector of `nextUntil()`, `prevUntil()` and `parentsUntil()` now counts across the whole document, as jQuery's does, instead of seeing each sibling or ancestor as a one-element set (issue #118). `nextUntil(':first')` used to stop at once and now walks to the end, and `nextUntil(':eq(3)')` stops at the fourth element in the document. `closest()` no longer matches a positional selector at all, as in jQuery, where `closest(':first')` used to return the element itself. `next()`, `prev()` and `parent()` still test each candidate on its own, which agrees with jQuery for a single starting element
+- Fix `siblings()` raising an "Attempt to read property "childNodes" on null" warning and a `foreach()` warning when the match set contains an element with no parent, such as one made with `createElement()` and not yet inserted (issue #139). Such an element has no siblings, so it now adds nothing to the result, as in jQuery
 
 # 4.2.0
 

src/Helpers/QueryFilters.php

@@ -940,8 +940,10 @@ public function siblings($selector = null): Query
 	{
 		$found = new SplObjectStorage();
 		foreach ($this->matches as $m) {
-			$parent = $m->parentNode;
-			foreach ($parent->childNodes as $n) {
+			if ($m->parentNode === null) {
+				continue;
+			}
+			foreach ($m->parentNode->childNodes as $n) {
 				if ($n->nodeType === XML_ELEMENT_NODE && $n !== $m) {
 					$found->offsetSet($n);
 				}

tests/Issues/Issue139Test.php

@@ -0,0 +1,40 @@
+<?php
+/**
+ * @file
+ *
+ * Regression tests for https://github.com/GravityPDF/querypath/issues/139
+ *
+ * siblings() on an element with no parent.
+ */
+
+namespace QueryPathTests;
+
+class Issue139Test extends TestCase
+{
+	public function testSiblingsOfAParentlessElementIsEmpty()
+	{
+		$doc  = qp('<?xml version="1.0"?><root/>')->get(0)->ownerDocument;
+		$lone = $doc->createElement('lone');
+
+		$this->assertSame(0, qp($lone)->siblings()->count());
+		$this->assertSame(0, qp($lone)->siblings('*')->count());
+	}
+
+	public function testSiblingsSkipsAParentlessElementInASet()
+	{
+		$qp   = qp('<?xml version="1.0"?><r><i id="a"/><i id="b"/><i id="c"/></r>', '#b');
+		$lone = $qp->get(0)->ownerDocument->createElement('lone');
+
+		$this->assertSame('a,c', $this->idList($qp->add($lone)->siblings()));
+	}
+
+	public function testSiblingsInADetachedSubtree()
+	{
+		$doc = qp('<?xml version="1.0"?><root/>')->get(0)->ownerDocument;
+		$div = $doc->createElement('div');
+		$a   = $div->appendChild($doc->createElement('a'));
+		$b   = $div->appendChild($doc->createElement('b'));
+
+		$this->assertSame([$b], qp($a)->siblings()->get());
+	}
+}