feat: Print ConstTag (#66)

src/node/tag/const.ts

@@ -0,0 +1,54 @@
+/**
+ * Related to Svelte AST node {@link ConstTag}.
+ * @see {@link https://svelte.dev/docs/special-tags#const}
+ * @module
+ */
+
+import { print } from "esrap";
+
+import { define_printer } from "#printer";
+import type { ConstTag } from "#types";
+import { insert } from "#util";
+
+/**
+ * Print Svelte AST node {@link ConstTag} as string.
+ * @see {@link https://svelte.dev/docs/special-tags#const}
+ *
+ * @example pattern
+ * ```svelte
+ * {@const assignment}
+ * ```
+ */
+export const print_const_tag = define_printer((node: ConstTag, _options) => {
+	const { declaration } = node;
+
+	return insert(
+		"{@",
+		// NOTE: It removes the semicolon
+		print(declaration).code.slice(0, -1),
+		"}",
+	);
+});
+
+if (import.meta.vitest) {
+	const { describe, it } = import.meta.vitest;
+	const [{ parse_and_extract_svelte_node }, { DEFAULT_OPTIONS }] = await Promise.all([
+		import("#test/mod"),
+		import("#options"),
+	]);
+
+	describe("ConstTag", () => {
+		it("prints correctly when used as direct child of allowed tags ", ({ expect }) => {
+			const code = `
+				{#each boxes as box}
+					{@const area = box.width * box.height}
+					{box.width} * {box.height} = {area}
+				{/each}
+			`;
+			const node = parse_and_extract_svelte_node<ConstTag>(code, "ConstTag");
+			expect(print_const_tag(node, DEFAULT_OPTIONS)).toMatchInlineSnapshot(
+				`"{@const area = box.width * box.height}"`,
+			);
+		});
+	});
+}

src/node/tag/mod.ts

@@ -1,11 +1,12 @@
+import { print_const_tag } from "#node/tag/const";
 import { print_expression_tag } from "#node/tag/expression";
 import { define_printer } from "#printer";
 import type { Tag } from "#types";
 
 export const print_tag = define_printer((node: Tag, options) => {
 	// biome-ignore format: Prettier
 	switch (node.type) {
-		case "ConstTag": return "";
+		case "ConstTag": return print_const_tag(node, options);
 		case "DebugTag": return "";
 		case "ExpressionTag": return print_expression_tag(node, options);
 		case "HtmlTag": return ""

src/types.ts

@@ -8,6 +8,7 @@ import type {
 	ClassDirective,
 	Comment,
 	Component,
+	ConstTag,
 	Css,
 	Directive,
 	EachBlock,
@@ -34,6 +35,7 @@ export type {
 	ClassDirective,
 	Comment,
 	Component,
+	ConstTag,
 	Css,
 	Directive,
 	EachBlock,