Add types for JSX support

Closes GH-3.

Reviewed-by: Christian Murphy <christian.murphy.42@gmail.com>
Reviewed-by: Titus Wormer <tituswormer@gmail.com>

Author: remcohaszing

readme.md

@@ -231,6 +231,21 @@ var x = require('xastscript')
 console.log(<music />)
 ```
 
+For [TypeScript][], this can be done by setting `"jsx": "react"`,
+`"jsxFactory": "x"`, and `"jsxFragmentFactory": "null"` in the compiler options.
+For more details on configuring JSX for TypeScript, see the
+[TypeScript JSX handbook page][].
+
+TypeScript also lets you configure this in a script:
+
+```tsx
+/** @jsx x */
+/** @jsxFrag null */
+import * as x from 'xastscript'
+
+console.log(<music />)
+```
+
 ## Security
 
 XML can be a dangerous language: don’t trust user-provided data.
@@ -327,3 +342,7 @@ abide by its terms.
 [babel]: https://github.com/babel/babel
 
 [babel-jsx]: https://github.com/babel/babel/tree/main/packages/babel-plugin-transform-react-jsx
+
+[typescript]: https://www.typescriptlang.org
+
+[typescript jsx handbook page]: https://www.typescriptlang.org/docs/handbook/jsx.html

types/index.d.ts

@@ -1,8 +1,8 @@
-// TypeScript Version: 3.7
+// TypeScript Version: 4.0
 
-import {Element, Node, Root} from 'xast'
+import * as xast from 'xast'
 
-type Children = string | Node | number | Children[]
+type Children = string | xast.Node | number | Children[]
 
 type Primitive = null | undefined | string | number
 
@@ -17,15 +17,15 @@ type Attributes = Record<string, Primitive>
  * @param name Qualified name. Case sensitive and can contain a namespace prefix (such as rdf:RDF).
  * @param children (Lists of) child nodes. When strings are encountered, they are mapped to Text nodes.
  */
-declare function xastscript(name: string, ...children: Children[]): Element
+declare function xastscript(name: string, ...children: Children[]): xast.Element
 
 /**
  * Create XML trees in xast.
  *
  * @param name Qualified name. Case sensitive and can contain a namespace prefix (such as rdf:RDF).
  * @param children (Lists of) child nodes. When strings are encountered, they are mapped to Text nodes.
  */
-declare function xastscript(name: null, ...children: Children[]): Root
+declare function xastscript(name: null, ...children: Children[]): xast.Root
 
 /**
  * Create XML trees in xast.
@@ -38,6 +38,58 @@ declare function xastscript(
   name: string,
   attributes?: Attributes,
   ...children: Children[]
-): Element
+): xast.Element
+
+/**
+ * This unique symbol is declared to specify the key on which JSX children are passed, without conflicting
+ * with the Attributes type.
+ */
+declare const children: unique symbol
+
+/**
+ * This namespace allows to use `xastscript` as a JSX implementation.
+ *
+ * This namespace is only used to support the use as JSX. It’s **not** intended for direct usage.
+ */
+declare namespace xastscript.JSX {
+  /**
+   * This defines the return value of JSX syntax.
+   */
+  type Element = xast.Element | xast.Root
+
+  /**
+   * This disallows the use of functional components.
+   */
+  type IntrinsicAttributes = never
+
+  /**
+   * This defines the prop types for known elements.
+   *
+   * For `xastscript` this defines any string may be used in combination with `xast` `Attributes`.
+   *
+   * This **must** be an interface.
+   */
+  // eslint-disable-next-line @typescript-eslint/consistent-indexed-object-style
+  interface IntrinsicElements {
+    [tagName: string]:
+      | Attributes
+      | {
+          /**
+           * The prop that matches `ElementChildrenAttribute` key defines the type of JSX children, defines the children type.
+           */
+          [children]?: Children
+        }
+  }
+
+  /**
+   * The key of this interface defines as what prop children are passed.
+   */
+  interface ElementChildrenAttribute {
+    /**
+     * Only the key matters, not the value.
+     */
+    [children]?: never
+  }
+}
 
 export = xastscript

types/test-jsx.tsx

@@ -0,0 +1,44 @@
+import {Element, Root} from 'xast'
+import * as x from 'xastscript'
+
+const xmlns = 'http://www.sitemaps.org/schemas/sitemap/0.9'
+
+let jsx: Element | Root
+jsx = <urlset />
+jsx = <urlset xmlns={xmlns} />
+jsx = <urlset>string</urlset>
+jsx = <urlset>{['string', 'string']}</urlset>
+jsx = (
+  <urlset xmlns={xmlns}>
+    <child />
+  </urlset>
+)
+jsx = (
+  <urlset>
+    <loc />
+    string
+  </urlset>
+)
+jsx = (
+  <urlset>
+    <loc />
+  </urlset>
+)
+jsx = (
+  <urlset>
+    <loc />
+    <loc />
+  </urlset>
+)
+jsx = <urlset>{[<loc />, <loc />]}</urlset>
+jsx = <urlset>{[]}</urlset>
+jsx = <></>
+
+jsx = <foo invalid={{}}></foo> // $ExpectError
+jsx = <foo>{{invalid: 'child'}}</foo> // $ExpectError
+
+const element: Element = <foo /> // $ExpectError
+const root: Root = <></> // $ExpectError
+
+declare function Bar(props?: Record<string, unknown>): Element
+const bar = <Bar /> // $ExpectError

types/test.ts

@@ -1,4 +1,4 @@
-import x = require('xastscript')
+import * as x from 'xastscript'
 
 x('urlset') // $ExpectType Element
 x('urlset', 'string') // $ExpectType Element

types/tsconfig.json

@@ -1,6 +1,9 @@
 {
   "compilerOptions": {
     "module": "commonjs",
+    "jsx": "react",
+    "jsxFactory": "x",
+    "jsxFragmentFactory": "null",
     "lib": ["es2015"],
     "noImplicitAny": true,
     "noImplicitThis": true,