use proper discriminated unions (TODO replace args with node-specific properties)

Author: Rich-Harris

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

@@ -49,13 +49,13 @@ export function template_to_string(items) {
 			case 'create_element':
 				last_current_element = insert({
 					kind: 'element',
-					element: /** @type {string[]} */ (instruction.args)[0]
+					element: instruction.args[0]
 				});
 				break;
 			case 'create_text':
 				insert({
 					kind: 'text',
-					value: /** @type {string[]} */ (instruction.args)[0]
+					value: instruction.args[0]
 				});
 				break;
 			case 'create_anchor':
@@ -66,7 +66,7 @@ export function template_to_string(items) {
 				break;
 			case 'set_prop': {
 				const el = /** @type {Element} */ (last_current_element);
-				const [prop, value] = /** @type {string[]} */ (instruction.args);
+				const [prop, value] = instruction.args;
 				el.props ??= {};
 				el.props[prop] = escape_html(value, true);
 				break;

packages/svelte/src/compiler/phases/3-transform/client/types.d.ts

@@ -36,18 +36,31 @@ export interface ClientTransformState extends TransformState {
 	>;
 }
 
-type TemplateOperationsKind =
-	| 'create_element'
-	| 'create_text'
-	| 'create_anchor'
-	| 'set_prop'
-	| 'push_element'
-	| 'pop_element';
+type TemplateOperations = Array<
+	| {
+			kind: 'create_element';
+			args: string[];
+	  }
+	| {
+			kind: 'create_text';
+			args: string[];
+	  }
+	| {
+			kind: 'create_anchor';
+			args?: string[];
+	  }
+	| {
+			kind: 'set_prop';
+			args: string[];
+	  }
+	| {
+			kind: 'push_element';
+	  }
+	| {
+			kind: 'pop_element';
+	  }
+>;
 
-type TemplateOperations = Array<{
-	kind: TemplateOperationsKind;
-	args?: Array<string>;
-}>;
 export interface ComponentClientTransformState extends ClientTransformState {
 	readonly analysis: ComponentAnalysis;
 	readonly options: ValidatedCompileOptions;