feat: current tests pass; I'm sure I'm missing stuff for new things

packages/svelte/src/compiler/phases/1-parse/state/tag.js

@@ -298,7 +298,8 @@ function open(parser) {
 			throw new Error();
 		}
 
-		parser.eat(raw_snippet_declaration);
+		// slice the `{#` off the beginning since it's already been eaten
+		parser.eat(raw_snippet_declaration.slice(2), true);
 
 		const block = parser.append(
 			/** @type {Omit<import('#compiler').SnippetBlock, 'parent'>} */

packages/svelte/src/compiler/phases/3-transform/client/visitors/template.js

@@ -1755,9 +1755,17 @@ export const template_visitors = {
 
 		/** @type {import('estree').Expression[]} */
 		const args = [context.state.node];
-		node.arguments.forEach((arg) =>
-			args.push(b.thunk(/** @type {import('estree').Expression} */ (context.visit(arg))))
-		);
+		node.arguments.forEach((arg) => {
+			if (arg.type === 'SpreadElement') {
+				// this is a spread operation, meaning we need to thunkify all of its members
+				args.push(
+					/** @type {import('estree').Expression} */ (
+						context.visit(b.spread(b.call('$.shallow_thunk', arg.argument)))
+					)
+				);
+			}
+			args.push(b.thunk(/** @type {import('estree').Expression} */ (context.visit(arg))));
+		});
 
 		let snippet_function = /** @type {import('estree').Expression} */ (
 			context.visit(node.expression)

packages/svelte/src/compiler/phases/3-transform/server/transform-server.js

@@ -1127,18 +1127,13 @@ const template_visitors = {
 		const snippet_function = state.options.dev
 			? b.call('$.validate_snippet', node.expression)
 			: node.expression;
+
+		const snippet_args = node.arguments.map((arg) => {
+			return /** @type {import('estree').Expression} */ (context.visit(arg));
+		});
+
 		state.template.push(
-			t_statement(
-				b.stmt(
-					b.call(
-						snippet_function,
-						b.id('$$payload'),
-						...node.arguments.map(
-							(arg) => /** @type {import('estree').Expression} */ (context.visit(arg))
-						)
-					)
-				)
-			)
+			t_statement(b.stmt(b.call(snippet_function, b.id('$$payload'), ...snippet_args)))
 		);
 
 		state.template.push(t_expression(anchor_id));

packages/svelte/src/internal/client/utils.js

@@ -16,3 +16,18 @@ export var get_descriptors = Object.getOwnPropertyDescriptors;
 export function is_function(thing) {
 	return typeof thing === 'function';
 }
+
+/**
+ * TODO: Do the types matter on this? If so, can we improve them so that
+ * `shallow_thunk(['one', 2])` returns a tuple type instead of a union?
+ * @template {unknown} T
+ * @param {Iterable<T>} iterable
+ * @returns {(() => T)[]}
+ */
+function shallow_thunk(iterable) {
+	const thunks = [];
+	for (const item of iterable) {
+		thunks.push(() => item);
+	}
+	return thunks;
+}