fix: prevent accidental frontmatter deletion

Fixes #611

src/examples/basics.tsx

@@ -258,6 +258,9 @@ export function Frontmatter() {
   return (
     <MDXEditor
       markdown={frontmatterMarkdown}
+      onChange={(value) => {
+        console.log(`new value: ${value}`)
+      }}
       plugins={[frontmatterPlugin(), toolbarPlugin({ toolbarContents: () => <InsertFrontmatter /> })]}
     />
   )

src/plugins/core/index.ts

@@ -548,7 +548,9 @@ export const createRootEditorSubscription$ = Appender(rootEditorSubscriptions$,
         },
         COMMAND_PRIORITY_CRITICAL
       )
-    },
+    }
+
+    /*
     // Fixes select all when frontmatter is present
     (rootEditor) => {
       return rootEditor.registerCommand<KeyboardEvent>(
@@ -581,7 +583,7 @@ export const createRootEditorSubscription$ = Appender(rootEditorSubscriptions$,
         },
         COMMAND_PRIORITY_CRITICAL
       )
-    }
+    }*/
   ])
 })
 

src/plugins/frontmatter/FrontmatterNode.tsx

@@ -78,6 +78,10 @@ export class FrontmatterNode extends DecoratorNode<JSX.Element> {
       />
     )
   }
+
+  isKeyboardSelectable(): boolean {
+    return false
+  }
 }
 
 /**

src/plugins/frontmatter/index.ts

@@ -10,7 +10,15 @@ import {
   rootEditor$
 } from '../core'
 import { Action, Cell, withLatestFrom } from '@mdxeditor/gurx'
-import { $getRoot } from 'lexical'
+import {
+  $getRoot,
+  $getSelection,
+  $isRangeSelection,
+  $setSelection,
+  COMMAND_PRIORITY_CRITICAL,
+  KEY_DOWN_COMMAND,
+  LexicalEditor
+} from 'lexical'
 import { frontmatterFromMarkdown, frontmatterToMarkdown } from 'mdast-util-frontmatter'
 import { frontmatter } from 'micromark-extension-frontmatter'
 import { $createFrontmatterNode, $isFrontmatterNode, FrontmatterNode } from './FrontmatterNode'
@@ -87,7 +95,47 @@ export const frontmatterPlugin = realmPlugin({
       [addLexicalNode$]: FrontmatterNode,
       [addImportVisitor$]: MdastFrontmatterVisitor,
       [addExportVisitor$]: LexicalFrontmatterVisitor,
-      [addToMarkdownExtension$]: frontmatterToMarkdown('yaml')
+      [addToMarkdownExtension$]: frontmatterToMarkdown('yaml'),
+      [createRootEditorSubscription$]: (editor: LexicalEditor) => {
+        return editor.registerCommand<KeyboardEvent>(
+          KEY_DOWN_COMMAND,
+          (event) => {
+            let shouldPrevent = false
+
+            editor.read(() => {
+              const selection = $getSelection()
+
+              if ($isRangeSelection(selection)) {
+                if (selection.isCollapsed() && selection.anchor.offset === 0 && selection.focus.offset === 0 && event.key === 'Backspace') {
+                  shouldPrevent = true
+                  event.preventDefault()
+                } else {
+                  const firstNode = selection.getNodes()[0]
+                  if ($isFrontmatterNode(firstNode)) {
+                    const yaml = firstNode.getYaml()
+                    setTimeout(() => {
+                      editor.update(
+                        () => {
+                          $getRoot().splice(0, 0, [$createFrontmatterNode(yaml)])
+                        },
+                        { discrete: true }
+                      )
+                    })
+                  }
+                }
+              }
+            })
+
+            // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+            if (shouldPrevent) {
+              return true
+            }
+
+            return false
+          },
+          COMMAND_PRIORITY_CRITICAL
+        )
+      }
     })
   }
 })