Check if a figcaption's first element ancestor is a figure

src/compile/nodes/Element.ts

@@ -224,7 +224,21 @@ export default class Element extends Node {
 		}
 
 		if (this.name === 'figcaption') {
-			if (this.parent.name !== 'figure') {
+			let { parent } = this;
+			let is_figure_parent = false;
+
+			while (parent) {
+				if (parent.name === 'figure') {
+					is_figure_parent = true;
+					break;
+				}
+				if (parent.type === 'Element') {
+					break;
+				}
+				parent = parent.parent;
+			}
+
+			if (!is_figure_parent) {
 				this.component.warn(this, {
 					code: `a11y-structure`,
 					message: `A11y: <figcaption> must be an immediate child of <figure>`

test/validator/samples/a11y-figcaption-in-non-element-block/input.svelte

@@ -0,0 +1,10 @@
+<script>
+	let caption = 'a foo in its natural habitat';
+</script>
+
+<figure>
+	<img src='foo.jpg' alt='a picture of a foo'>
+	{#if caption}
+		<figcaption>{caption}</figcaption>
+	{/if}
+</figure>

test/validator/samples/a11y-figcaption-in-non-element-block/warnings.json

@@ -0,0 +1 @@
+[]