Support hydrating elements with properties whose getters throw.

packages/svelte/src/internal/client/dom/elements/attributes.js

@@ -136,7 +136,12 @@ export function set_xlink_attribute(dom, attribute, value) {
  */
 export function set_custom_element_data(node, prop, value) {
 	if (prop in node) {
-		var curr_val = node[prop];
+		try {
+			var curr_val = node[prop];
+		} catch {
+			set_attribute(node, prop, value);
+			return;
+		}
 		var next_val = typeof curr_val === 'boolean' && value === '' ? true : value;
 		if (typeof curr_val !== 'object' || curr_val !== next_val) {
 			node[prop] = next_val;

packages/svelte/tests/hydration/samples/custom-element-with-settable-only-property/custom-element-with-settable-only-property.js

@@ -0,0 +1,10 @@
+// Note that custom element names must be unique across tests that can be run at the same time. So we use a verbose element name instead of just `<custom-element>`
+customElements.define("custom-element-with-settable-only-property", class CustomElement extends HTMLElement {
+  set prop(n) {
+    this.value = n;
+  }
+
+  get prop() {
+    throw new Error("This value is not gettable");
+  }
+});

packages/svelte/tests/hydration/samples/custom-element-with-settable-only-property/main.svelte

@@ -0,0 +1,5 @@
+<script>
+  import "./custom-element-with-settable-only-property.js"
+</script>
+
+<custom-element-with-settable-only-property prop="8"></custom-element-with-settable-only-property>