Add `astro/types` for common prop patterns (#5147)

* wip: add type-utils

* feat: update type-utils

* feat: RequireDefaultSlot => WithChildren

* chore: add changeset

* chore: move types to ./types

* chore: update changeset

* Update dirty-cycles-lick.md

Co-authored-by: Nate Moore <nate@astro.build>

3 files changed, 28 insertions, 0 deletions

diff --git a/.changeset/dirty-cycles-lick.md b/.changeset/dirty-cycles-lick.md
new file mode 100644
index 000000000..e8e39be9b
--- /dev/null
+++ b/.changeset/dirty-cycles-lick.md
@@ -0,0 +1,16 @@
+---
+'astro': minor
+---
+
+Add `astro/types` entrypoint. These utilities can be used for common prop type patterns.
+
+## `HTMLAttributes`
+
+If you would like to extend valid HTML attributes for a given HTML element, you may use the provided `HTMLAttributes` type—it accepts an element name and returns the valid HTML attributes for that element name.
+
+```ts
+import { HTMLAttributes } from 'astro/types';
+interface Props extends HTMLAttributes<'a'> {
+  myProp?: string;
+};
+```
diff --git a/packages/astro/package.json b/packages/astro/package.json
index 527a87e1a..331ef6b27 100644
--- a/packages/astro/package.json
+++ b/packages/astro/package.json
@@ -29,6 +29,7 @@
       "default": "./astro.js"
     },
     "./env": "./env.d.ts",
+    "./types": "./types.d.ts",
     "./client": "./client.d.ts",
     "./client-base": "./client-base.d.ts",
     "./import-meta": "./import-meta.d.ts",
diff --git a/packages/astro/types.d.ts b/packages/astro/types.d.ts
new file mode 100644
index 000000000..ae56cd2dc
--- /dev/null
+++ b/packages/astro/types.d.ts
@@ -0,0 +1,11 @@
+import './astro-jsx';
+import { AstroBuiltinAttributes } from './dist/@types/astro';
+
+/** Any supported HTML or SVG element name, as defined by the HTML specification */
+export type HTMLTag = keyof astroHTML.JSX.DefinedIntrinsicElements;
+/** The built-in attributes for any known HTML or SVG element name */
+export type HTMLAttributes<Tag extends HTMLTag> = Omit<astroHTML.JSX.IntrinsicElements[Tag], keyof AstroBuiltinAttributes>;
+
+// TODO: Enable generic/polymorphic types once compiler output stabilizes in the Language Server
+// type PolymorphicAttributes<P extends { as: HTMLTag }> = Omit<(P & HTMLAttributes<P['as']>), 'as'> & { as?: P['as'] };
+// export type Polymorphic<P extends { as: HTMLTag }> = PolymorphicAttributes<Omit<P, 'as'> & { as: NonNullable<P['as']>}>;