fix(xml): use the type system to verify version

Reverts: 78ed4ac

xml/_types.ts

@@ -22,10 +22,12 @@ export type xml_node = {
   [key: string]: unknown
 }
 
+export type v1_x = `1.${number}`
+
 /** XML document. */
-export type xml_document = xml_node & {
+export type xml_document<version extends v1_x = v1_x> = xml_node & {
   /** XML version. */
-  ["@version"]?: string
+  ["@version"]?: version
   /** XML character encoding. */
   ["@encoding"]?: string
   /** XML standalone. */

xml/_types_test.ts

@@ -1 +1,18 @@
 import "./_types.ts"
+import { stringify } from "./mod.ts"
+
+// Verify that the generic type is correctly inferred.
+const _example = stringify({
+  "@version": "1.1",
+  "@encoding": "UTF-8",
+  "@standalone": "yes",
+  "#doctype": {
+    "~name": "html",
+    "~children": [],
+    "#text": "",
+  },
+  "#instructions": {},
+  "~name": "html",
+  "~children": [],
+  "#text": "",
+})

xml/stringify.ts

@@ -1,6 +1,6 @@
 // Imports
 import type { Nullable, record, rw } from "@libs/typing"
-import type { xml_document, xml_node, xml_text } from "./_types.ts"
+import type { v1_x, xml_document, xml_node, xml_text } from "./_types.ts"
 
 // Re-exports
 export type { xml_document, xml_node, xml_text }
@@ -63,15 +63,15 @@ const internal = Symbol("internal")
  * }))
  * ```
  */
-export function stringify(document: Partial<xml_document>, options?: options): string {
+export function stringify<const V extends v1_x>(document: Partial<xml_document<V>>, options?: options): string {
   options ??= {}
   options.format ??= {}
   options.format.indent ??= "  "
   options.format.breakline ??= 128
   const _options = options as _options
   let text = ""
   // Add prolog
-  text += xml_prolog(document as xml_document, _options)
+  text += xml_prolog(document as xml_document<V>, _options)
   // Add processing instructions
   if (document["#instructions"]) {
     for (const nodes of Object.values(document["#instructions"])) {
@@ -86,7 +86,7 @@ export function stringify(document: Partial<xml_document>, options?: options): s
   }
 
   // Add root node
-  const [root, ...garbage] = xml_children(document as xml_document, _options)
+  const [root, ...garbage] = xml_children(document as xml_document<V>, _options)
   if (garbage.length) {
     throw new SyntaxError("Multiple root node detected")
   }
@@ -112,7 +112,7 @@ export function comment(text: string): Omit<xml_text, "~parent"> {
 }
 
 /** Create XML prolog. */
-function xml_prolog(document: xml_document, options: _options): string {
+function xml_prolog<const V extends v1_x>(document: xml_document<V>, options: _options): string {
   ;(document as rw)["~name"] ??= "xml"
   return xml_instruction(document, options)
 }