docs, more tests

packages/svelte/src/compiler/utils/ast.js

@@ -306,6 +306,9 @@ export function unwrap_ts_expression(node) {
 }
 
 /**
+ * Like `path.at(x)`, but skips over `TSNonNullExpression` and `TSAsExpression` nodes and eases assertions a bit
+ * by removing the `| undefined` from the resulting type.
+ *
  * @template {import('#compiler').SvelteNode} T
  * @param {T[]} path
  * @param {number} at

packages/svelte/tests/runtime-runes/samples/typescript-as-expression/main.svelte

@@ -1,6 +1,6 @@
 <script lang="ts">
 	let count = $state(1) as number;
-	let double = $derived(count * 2) as number;
+	let double = $derived(count as number * 2) as number;
 </script>
 
-{count} {double}
+{count as number} {double as number}

packages/svelte/tests/runtime-runes/samples/typescript-non-null-expression/main.svelte

@@ -1,6 +1,6 @@
 <script lang="ts">
 	let count = $state(1)!;
-	let double = $derived(count * 2)!;
+	let double = $derived(count! * 2)!;
 </script>
 
-{count} {double}
+{count!} {double!}