internal/packing: bug fix: node's links were not synced correctly

Closes #2584

internal/packing/packing.go

@@ -318,7 +318,8 @@ func (p *Page) extend(newWidth int, newHeight int) func() {
 	var rollback func()
 
 	if aborted {
-		origRoot := *p.root
+		origRoot := p.root
+		origRootCloned := *p.root
 
 		// Extend the page in the vertical direction.
 		if newHeight-p.height > 0 {
@@ -366,7 +367,10 @@ func (p *Page) extend(newWidth int, newHeight int) func() {
 		rollback = func() {
 			p.width = origWidth
 			p.height = origHeight
-			p.root = &origRoot
+			// The node address must not be changed, so use the original root node's pointer (#2584).
+			// As the root node might be modified, recover the content from the cloned content.
+			p.root = origRoot
+			*p.root = origRootCloned
 		}
 	} else {
 		origWidth, origHeight := p.width, p.height

internal/packing/packing_test.go

@@ -431,3 +431,23 @@ func TestExtend3(t *testing.T) {
 	p.Free(n1)
 	p.Free(n2)
 }
+
+// Issue #2584
+func TestRemoveAtRootsChild(t *testing.T) {
+	p := packing.NewPage(32, 32, 1024)
+	n0 := p.Alloc(18, 18)
+	n1 := p.Alloc(28, 59)
+	n2 := p.Alloc(18, 18)
+	n3 := p.Alloc(18, 18)
+	n4 := p.Alloc(8, 10)
+	n5 := p.Alloc(322, 242)
+	_ = n5
+	p.Free(n0)
+	p.Free(n2)
+	p.Free(n1)
+	p.Free(n3)
+	p.Free(n4)
+
+	n6 := p.Alloc(18, 18)
+	p.Free(n6)
+}