feat: basic support for mdx file extension (#964)

packages/core/.editorconfig

@@ -17,3 +17,6 @@ quote_type = single
 
 [*.md]
 trim_trailing_whitespace = false
+
+[*.mdx]
+trim_trailing_whitespace = false

packages/core/dev-test/backends/proxy/_data/navigation.mdx

@@ -0,0 +1,26 @@
+---
+main_menu:
+  - label: News
+    href: /news
+  - label: Features
+    href: '#features'
+  - label: About
+    href: '#about'
+  - label: Contact
+    href: '#contact'
+footer_menus:
+  - label: Company
+    links:
+      - label: Home
+        href: /
+      - label: 'Privacy Policy '
+        href: '#'
+      - label: About us
+        href: '#'
+  - label: Documentation
+    links:
+      - label: Docs
+        href: '#'
+      - label: Blog
+        href: '#'
+---

packages/core/dev-test/backends/proxy/config.yml

@@ -176,6 +176,45 @@ collections:
               - label: Description
                 name: description
                 widget: text
+
+      - name: navigation
+        label: Navigation
+        file: packages/core/dev-test/backends/proxy/_data/navigation.mdx
+        extension: mdx
+        format: yaml-frontmatter
+        fields:
+          - name: main_menu
+            label: Main Menu
+            widget: list
+            collapsed: true
+            fields:
+              - name: label
+                label: Label
+                widget: string
+              - name: href
+                label: Href
+                widget: string
+          - name: footer_menus
+            label: Footer Menus
+            widget: list
+            collapsed: true
+            reuired: false
+            fields:
+              - name: label
+                label: Label
+                widget: string
+              - name: links
+                label: Links
+                widget: list
+                collapsed: true
+                fields:
+                  - name: label
+                    label: Label
+                    widget: string
+                  - name: href
+                    label: Href
+                    widget: string
+
   - name: kitchenSink
     label: Kitchen Sink
     folder: packages/core/dev-test/backends/proxy/_sink

packages/core/src/formats/formats.ts

@@ -26,6 +26,7 @@ export const extensionFormatters: Record<string, FileFormatter> = {
   toml: TomlFormatter,
   json: JsonFormatter,
   md: FrontmatterInfer,
+  mdx: FrontmatterInfer,
   markdown: FrontmatterInfer,
   html: FrontmatterInfer,
 };