treat <textarea> children the same as a value attribute

src/generators/dom/visitors/Element/Element.ts

@@ -107,6 +107,20 @@ export default function visitElement ( generator: DomGenerator, block: Block, st
 	}
 
 	if ( node.name !== 'select' ) {
+		if ( node.name === 'textarea' ) {
+			// this is an egregious hack, but it's the easiest way to get <textarea>
+			// children treated the same way as a value attribute
+			if ( node.children.length > 0 ) {
+				node.attributes.push({
+					type: 'Attribute',
+					name: 'value',
+					value: node.children
+				});
+
+				node.children = [];
+			}
+		}
+
 		// <select> value attributes are an annoying special case — it must be handled
 		// *after* its children have been updated
 		visitAttributesAndAddProps();

test/runtime/samples/textarea-children/_config.js

@@ -0,0 +1,17 @@
+export default {
+	'skip-ssr': true, // SSR behaviour is awkwardly different
+
+	data: {
+		foo: 42
+	},
+
+	html: `<textarea></textarea>`,
+
+	test ( assert, component, target ) {
+		const textarea = target.querySelector( 'textarea' );
+		assert.strictEqual( textarea.value, `\n\t<p>not actually an element. 42</p>\n` );
+
+		component.set({ foo: 43 });
+		assert.strictEqual( textarea.value, `\n\t<p>not actually an element. 43</p>\n` );
+	}
+};

test/runtime/samples/textarea-children/main.html

@@ -0,0 +1,3 @@
+<textarea>
+	<p>not actually an element. {{foo}}</p>
+</textarea>