Keep an empty doc content in editor-normal ADF, as the schema requires

docs/decisions.md

@@ -42,8 +42,8 @@ adjacent text nodes, an empty `attrs`, `content` or `marks`, and `-0`. Neither s
 CommonMark's spelling stays wherever a document holds none of those shapes. The plain reader builds
 what is written, as `markdownToAdf` does. Only the plain writer is lossy: its reduction reads and
 writes editor-normal ADF — adjacent text nodes of identical marks and no attributes merged, `-0` as
-`0`, and an empty `attrs`, `content` or `marks` the absent key — so two documents the editor holds
-equal write the same plain markdown.
+`0`, and an empty `attrs`, `content` or `marks` the absent key, but the doc's `content` — so two
+documents the editor holds equal write the same plain markdown.
 
 ## `!adf:textBreak{}` parts text CommonMark would join
 

src/markdown/plain/adf-to-plain-markdown.ts

@@ -58,7 +58,7 @@ export function reduceToPlain(document: AdfDocument): Result<AdfDocument> {
     const raw = reduceBlocks(nodeContent(document), { depth: 0, memo: new Map(), path: [] })
     return !raw.ok && raw.error.code === blocks.error.code ? raw : blocks
   }
-  return success({ content: nodeContent(toEditorNormal({ content: blocks.value, type: 'doc', version: 1 })).slice(), type: 'doc', version: 1 })
+  return success(toEditorNormal({ content: blocks.value, type: 'doc', version: 1 }))
 }
 
 function reduceBlocks(nodes: readonly AdfNode[], reduction: Reduction): Result<AdfNode[]> {

src/markdown/plain/editor-normal.test.ts

@@ -50,14 +50,15 @@ test('reads negative zero as zero, as JSON does', () => {
   )
 })
 
-test('reads an empty attrs object, marks array or content array as the absent key', () => {
+test('reads an empty attrs object, marks array or content array as the absent key, but on doc', () => {
   const paragraph: AdfNode = { attrs: {}, content: [{ attrs: {}, marks: [], text: 'a', type: 'text' }, { marks: [{ attrs: {}, type: 'em' }], text: 'b', type: 'text' }], marks: [], type: 'paragraph' }
   assert.deepEqual(toEditorNormal({ content: [paragraph, { content: [], type: 'rule' }], type: 'doc', version: 1 }), {
     content: [{ content: [{ text: 'a', type: 'text' }, { marks: [{ type: 'em' }], text: 'b', type: 'text' }], type: 'paragraph' }, { type: 'rule' }],
     type: 'doc',
     version: 1,
   })
-  assert.deepEqual(toEditorNormal({ content: [], type: 'doc', version: 1 }), { type: 'doc', version: 1 })
+  assert.deepEqual(toEditorNormal({ content: [], type: 'doc', version: 1 }), { content: [], type: 'doc', version: 1 })
+  assert.deepEqual(toEditorNormal({ type: 'doc', version: 1 }), { type: 'doc', version: 1 })
 })
 
 test('normalizes blocks and mark attributes nesting far past the levels a recursive walk survives', () => {

src/markdown/plain/editor-normal.ts

@@ -28,6 +28,8 @@ export function toEditorNormal(document: AdfDocument): AdfDocument {
       return holder
     })
   }
+  // ADF's schema requires content on doc, so an empty one stays.
+  if (document.content !== undefined && normal.content === undefined) normal.content = []
   return normal
 }