add Error to known globals, declare catch block parameter. fixes #3064

src/compiler/compile/utils/scope.ts

@@ -40,6 +40,13 @@ export function create_scopes(expression: Node) {
 				map.set(node, scope);
 			} else if (/(Class|Variable)Declaration/.test(node.type)) {
 				scope.add_declaration(node);
+			} else if (node.type === 'CatchClause') {
+				scope = new Scope(scope, true);
+				map.set(node, scope);
+
+				extract_names(node.param).forEach(name => {
+					scope.declarations.set(name, node.param);
+				});
 			} else if (node.type === 'Identifier' && is_reference(node as ESTreeNode, parent as ESTreeNode)) {
 				if (!scope.has(node.name) && !globals.has(node.name)) {
 					globals.set(node.name, node);

src/compiler/utils/names.ts

@@ -13,6 +13,7 @@ export const globals = new Set([
 	'document',
 	'encodeURI',
 	'encodeURIComponent',
+	'Error',
 	'Infinity',
 	'Intl',
 	'isFinite',

test/validator/samples/catch-declares-error-variable/input.svelte

@@ -0,0 +1,13 @@
+<script>
+	let value = null;
+</script>
+
+<button on:click={event => {
+	try {
+		throw new Error('foo');
+	} catch (error) {
+		value = error;
+	}
+}}>Click to create error</button>
+
+{String(value)}

test/validator/samples/catch-declares-error-variable/warnings.json

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