Share the CommonMark grammar, close the guard's hole, refuse the lists no marker spells

src/adf-document.ts

@@ -1,4 +1,4 @@
-import { isJsonValue, type JsonValue } from './canonical-json.ts'
+import { isJsonValue, type JsonValue } from './json-value.ts'
 
 export type AdfAttributes = { [key: string]: JsonValue }
 
@@ -48,7 +48,7 @@ function isAdfNode(value: unknown): value is AdfNode {
 }
 
 function isArrayOf<T>(value: unknown, guard: (item: unknown) => item is T): value is T[] {
-  return Array.isArray(value) && value.every(guard)
+  return Array.isArray(value) && [...value].every(guard)
 }
 
 function isAttributes(value: unknown): value is AdfAttributes {

src/adf-to-markdown.test.ts

@@ -1,7 +1,7 @@
 import assert from 'node:assert/strict'
 import test from 'node:test'
 
-import type { AdfDocument, AdfNode } from './adf-document.ts'
+import type { AdfDocument, AdfMark, AdfNode } from './adf-document.ts'
 import type { Result } from './result.ts'
 import { adfToMarkdown } from './index.ts'
 
@@ -109,11 +109,17 @@ test('refuses a node whose content model the canonical form cannot emit', () =>
   assert.equal(code(adfToMarkdown(document({ type: 'listItem' }))), 'unsupported-node-shape')
   assert.equal(code(adfToMarkdown(document({ content: [paragraph()], type: 'codeBlock' }))), 'unsupported-node-shape')
   assert.equal(code(adfToMarkdown(document({ content: [paragraph()], type: 'bulletList' }))), 'unsupported-node-shape')
+  assert.equal(code(adfToMarkdown(document({ type: 'bulletList' }))), 'unsupported-node-shape')
+  assert.equal(code(adfToMarkdown(document({ attrs: { order: 2 }, content: [], type: 'orderedList' }))), 'unsupported-node-shape')
 })
 
-test('refuses an ordered list start no marker spells', () => {
-  const items: AdfNode[] = [{ content: [paragraph({ text: 'x', type: 'text' })], type: 'listItem' }]
-  assert.equal(code(adfToMarkdown(document({ attrs: { order: 1.5 }, content: items, type: 'orderedList' }))), 'unsupported-node-shape')
+test('refuses an ordered list no marker spells', () => {
+  const item: AdfNode = { content: [paragraph({ text: 'x', type: 'text' })], type: 'listItem' }
+  const list = (order: number, items: number): AdfDocument =>
+    document({ attrs: { order }, content: Array.from({ length: items }, () => item), type: 'orderedList' })
+  assert.equal(code(adfToMarkdown(list(1.5, 1))), 'unsupported-node-shape')
+  assert.equal(markdown(adfToMarkdown(list(999999999, 1))), '999999999. x\n')
+  assert.equal(code(adfToMarkdown(list(999999999, 2))), 'unspellable-list-marker')
 })
 
 test('refuses a code span over anything but one text node', () => {
@@ -150,6 +156,15 @@ test('escapes a heading closing sequence', () => {
   assert.equal(heading('#tag first'), '## #tag first\n')
 })
 
+test('wraps adjacent nodes carrying one mark once, and a differing mark twice', () => {
+  const marked = (text: string, ...marks: AdfMark[]): AdfNode => ({ marks, text, type: 'text' })
+  const emitted = (...content: AdfNode[]): string => markdown(adfToMarkdown(document(paragraph(...content))))
+  assert.equal(emitted(marked('a', { type: 'strong' }), marked('b', { type: 'strong' }, { type: 'em' })), '**a*b***\n')
+  assert.equal(emitted(marked('a', { type: 'strong' }), marked('b', { type: 'em' })), '**a**_b_\n')
+  const link = (href: string): AdfMark => ({ attrs: { href }, type: 'link' })
+  assert.equal(emitted(marked('a', link('http://x')), marked('b', link('http://y'))), '[a](http://x)[b](http://y)\n')
+})
+
 test('emits an empty list item without trailing whitespace', () => {
   assert.equal(markdown(adfToMarkdown(document({ content: [{ type: 'listItem' }], type: 'bulletList' }))), '-\n')
 })

src/adf-to-markdown.ts

@@ -1,9 +1,11 @@
 import type { AdfDocument, AdfNode } from './adf-document.ts'
+import type { JsonValue } from './json-value.ts'
 import { emitInlineLine } from './markdown-inline.ts'
 import { failure, success, type Result } from './result.ts'
 import { isAdfDocument } from './adf-document.ts'
 import { longestBacktickRun } from './backtick-runs.ts'
 
+const largestListMarker = 999999999
 const listTypes = ['bulletList', 'orderedList']
 
 export function adfToMarkdown(document: AdfDocument): Result<string> {
@@ -16,10 +18,8 @@ export function adfToMarkdown(document: AdfDocument): Result<string> {
 
 function emitBlocks(nodes: readonly AdfNode[], inListItem: boolean): Result<string> {
   let output = ''
-  for (let index = 0; index < nodes.length; index += 1) {
-    const node = nodes[index]
-    if (node === undefined) return failure('unsupported-node-shape', 'the block content holds a hole')
-    const previous = nodes[index - 1]
+  let previous: AdfNode | undefined
+  for (const node of nodes) {
     if (previous !== undefined) {
       if (listTypes.includes(node.type) && previous.type === node.type) {
         return failure('unspellable-adjacent-lists', `two adjacent ${node.type} nodes read back as one list`)
@@ -29,6 +29,7 @@ function emitBlocks(nodes: readonly AdfNode[], inListItem: boolean): Result<stri
     const block = emitBlock(node)
     if (!block.ok) return block
     output += block.value
+    previous = node
   }
   return success(output)
 }
@@ -47,8 +48,8 @@ function emitBlock(node: AdfNode): Result<string> {
 }
 
 function emitBlockquote(node: AdfNode): Result<string> {
-  const invalid = validateBlockNode(node, [])
-  if (!invalid.ok) return invalid
+  const validation = validateBlockNode(node, [])
+  if (!validation.ok) return validation
   const inner = emitBlocks(node.content ?? [], false)
   if (!inner.ok) return inner
   return success(
@@ -60,17 +61,10 @@ function emitBlockquote(node: AdfNode): Result<string> {
 }
 
 function emitCodeBlock(node: AdfNode): Result<string> {
-  const invalid = validateBlockNode(node, ['language'])
-  if (!invalid.ok) return invalid
-  const language = node.attrs?.['language']
-  if (language !== undefined) {
-    if (typeof language !== 'string') return failure('unsupported-node-shape', 'a codeBlock language is no string')
-    if (language === '') return failure('ambiguous-empty-code-block-language', 'an empty codeBlock language and an absent one share one markdown spelling')
-    if (language === 'adf') return failure('reserved-adf-language', 'the adf info string is reserved for the opaque carry')
-    if (/[`\n\r]/.test(language) || language !== language.trim()) {
-      return failure('unspellable-code-block-language', 'a fence info string holds no backtick and no edge whitespace')
-    }
-  }
+  const validation = validateBlockNode(node, ['language'])
+  if (!validation.ok) return validation
+  const info = spellCodeFenceInfo(node.attrs?.['language'])
+  if (!info.ok) return info
   let text = ''
   for (const child of node.content ?? []) {
     if (child.type !== 'text' || typeof child.text !== 'string' || (child.marks ?? []).length > 0 || Object.keys(child.attrs ?? {}).length > 0) {
@@ -79,13 +73,24 @@ function emitCodeBlock(node: AdfNode): Result<string> {
     text += child.text
   }
   const fence = '`'.repeat(Math.max(3, longestBacktickRun(text) + 1))
-  const opening = `${fence}${language ?? ''}`
+  const opening = `${fence}${info.value}`
   return success(text === '' ? `${opening}\n${fence}` : `${opening}\n${text}\n${fence}`)
 }
 
+function spellCodeFenceInfo(language: JsonValue | undefined): Result<string> {
+  if (language === undefined) return success('')
+  if (typeof language !== 'string') return failure('unsupported-node-shape', 'a codeBlock language is no string')
+  if (language === '') return failure('ambiguous-empty-code-block-language', 'an empty codeBlock language and an absent one share one markdown spelling')
+  if (language === 'adf') return failure('reserved-adf-language', 'the adf info string is reserved for the opaque carry')
+  if (/[`\n\r]/.test(language) || language !== language.trim()) {
+    return failure('unspellable-code-block-language', 'a fence info string holds no backtick and no edge whitespace')
+  }
+  return success(language)
+}
+
 function emitHeading(node: AdfNode): Result<string> {
-  const invalid = validateBlockNode(node, ['level'])
-  if (!invalid.ok) return invalid
+  const validation = validateBlockNode(node, ['level'])
+  if (!validation.ok) return validation
   const level = node.attrs?.['level']
   if (typeof level !== 'number' || !Number.isInteger(level) || level < 1 || level > 6) {
     return failure('unsupported-heading-level', `no ATX heading spells level ${JSON.stringify(level ?? null)}`)
@@ -100,49 +105,56 @@ function emitHeading(node: AdfNode): Result<string> {
 
 function emitList(node: AdfNode): Result<string> {
   const ordered = node.type === 'orderedList'
-  const invalid = validateBlockNode(node, ordered ? ['order'] : [])
-  if (!invalid.ok) return invalid
+  const validation = validateBlockNode(node, ordered ? ['order'] : [])
+  if (!validation.ok) return validation
+  const items = node.content ?? []
+  if (items.length === 0) return failure('unsupported-node-shape', `a ${node.type} holds at least one listItem`)
   const start = ordered ? node.attrs?.['order'] : 0
   if (ordered && (start === undefined || start === 1)) {
     return failure('ambiguous-ordered-list-start', 'an orderedList starting at 1 and one with no order share one markdown spelling')
   }
-  if (typeof start !== 'number' || !Number.isInteger(start) || start < 0 || start > 999999999) {
+  if (typeof start !== 'number' || !Number.isInteger(start) || start < 0 || start > largestListMarker) {
     return failure('unsupported-node-shape', `no list marker spells the order ${JSON.stringify(start ?? null)}`)
   }
-  const items: string[] = []
-  for (const [offset, item] of (node.content ?? []).entries()) {
-    if (item.type !== 'listItem') return failure('unsupported-node-shape', `a ${node.type} holds listItem nodes only`)
-    const invalidItem = validateBlockNode(item, [])
-    if (!invalidItem.ok) return invalidItem
-    const inner = emitBlocks(item.content ?? [], true)
-    if (!inner.ok) return inner
-    const marker = ordered ? `${start + offset}. ` : '- '
-    if (inner.value === '') {
-      items.push(marker.trimEnd())
-      continue
-    }
-    const indent = ' '.repeat(marker.length)
-    items.push(
-      inner.value
-        .split('\n')
-        .map((line, lineIndex) => (lineIndex === 0 ? `${marker}${line}` : line === '' ? '' : `${indent}${line}`))
-        .join('\n'),
-    )
+  if (start + items.length - 1 > largestListMarker) {
+    return failure('unspellable-list-marker', `no list marker spells the ${items.length} items an orderedList starting at ${start} needs`)
   }
-  return success(items.join('\n'))
+  const lines: string[] = []
+  for (const [offset, item] of items.entries()) {
+    if (item.type !== 'listItem') return failure('unsupported-node-shape', `a ${node.type} holds listItem nodes only`)
+    const emitted = emitListItem(item, ordered ? `${start + offset}. ` : '- ')
+    if (!emitted.ok) return emitted
+    lines.push(emitted.value)
+  }
+  return success(lines.join('\n'))
+}
+
+function emitListItem(item: AdfNode, marker: string): Result<string> {
+  const validation = validateBlockNode(item, [])
+  if (!validation.ok) return validation
+  const inner = emitBlocks(item.content ?? [], true)
+  if (!inner.ok) return inner
+  if (inner.value === '') return success(marker.trimEnd())
+  const indent = ' '.repeat(marker.length)
+  return success(
+    inner.value
+      .split('\n')
+      .map((line, index) => (index === 0 ? `${marker}${line}` : line === '' ? '' : `${indent}${line}`))
+      .join('\n'),
+  )
 }
 
 function emitParagraph(node: AdfNode): Result<string> {
-  const invalid = validateBlockNode(node, [])
-  if (!invalid.ok) return invalid
+  const validation = validateBlockNode(node, [])
+  if (!validation.ok) return validation
   const content = node.content ?? []
   if (content.length === 0) return success('::paragraph')
   return emitInlineLine(content, 'paragraph')
 }
 
 function emitRule(node: AdfNode): Result<string> {
-  const invalid = validateBlockNode(node, [])
-  if (!invalid.ok) return invalid
+  const validation = validateBlockNode(node, [])
+  if (!validation.ok) return validation
   if ((node.content ?? []).length > 0) return failure('unsupported-node-shape', 'a rule holds no content')
   return success('---')
 }

src/canonical-json.ts

@@ -1,16 +1,7 @@
-export type JsonValue = JsonValue[] | boolean | null | number | string | { [key: string]: JsonValue }
+import type { JsonValue } from './json-value.ts'
 
 export type JsonSpelling = 'compact' | 'two-space'
 
-export function isJsonValue(value: unknown): value is JsonValue {
-  if (value === null) return true
-  if (typeof value === 'boolean' || typeof value === 'string') return true
-  if (typeof value === 'number') return Number.isFinite(value)
-  if (Array.isArray(value)) return value.every(isJsonValue)
-  if (typeof value === 'object') return Object.values(value).every(isJsonValue)
-  return false
-}
-
 export function serializeCanonicalJson(value: JsonValue, spelling: JsonSpelling): string {
   return serialize(value, spelling === 'compact' ? '' : '  ', 0)
 }

src/commonmark-grammar.ts

@@ -0,0 +1,31 @@
+export type LinePosition = 'first' | 'later'
+
+const entityReferenceSource = '&(?:[A-Za-z][A-Za-z0-9]{1,31}|#\\d{1,7}|#[Xx][A-Fa-f0-9]{1,6});'
+
+const anchoredEntityReference = new RegExp(`^(?:${entityReferenceSource})`)
+const entityReference = new RegExp(entityReferenceSource)
+const firstCharacterOpeners = [/^#{1,6}(?:[ \t]|$)/, /^>/, /^[*+-](?:[ \t]|$)/, /^`{3,}/, /^~{3,}/, /^:{2,}/, /^\|/]
+const orderedListOpener = /^(\d{1,9})[.)](?:[ \t]|$)/
+const setextUnderline = /^=+$/
+const thematicBreak = /^(?:(?:\*[ \t]*){3,}|(?:-[ \t]*){3,}|(?:_[ \t]*){3,})$/
+
+export function claimsLine(line: string, position: LinePosition): boolean {
+  return escapesLineClaim(line, 0, position) || orderedListOpener.test(line)
+}
+
+export function escapesLineClaim(line: string, offset: number, position: LinePosition): boolean {
+  if (offset === 0) {
+    if (firstCharacterOpeners.some((opener) => opener.test(line)) || thematicBreak.test(line)) return true
+    return position === 'later' && setextUnderline.test(line)
+  }
+  const digits = orderedListOpener.exec(line)?.[1]
+  return digits !== undefined && offset === digits.length
+}
+
+export function holdsEntityReference(text: string): boolean {
+  return entityReference.test(text)
+}
+
+export function startsEntityReference(text: string): boolean {
+  return anchoredEntityReference.test(text)
+}

src/corpus.test.ts

@@ -6,7 +6,8 @@ import { fileURLToPath } from 'node:url'
 
 import { adfToMarkdown } from './adf-to-markdown.ts'
 import { isAdfDocument } from './adf-document.ts'
-import { isJsonValue, serializeCanonicalJson } from './canonical-json.ts'
+import { isJsonValue } from './json-value.ts'
+import { serializeCanonicalJson } from './canonical-json.ts'
 
 const corpusRoot = join(dirname(fileURLToPath(import.meta.url)), '..', 'corpus')
 const roundTripRoot = join(corpusRoot, 'round-trip')

src/index.ts

@@ -1,4 +1,5 @@
 export type { AdfAttributes, AdfDocument, AdfMark, AdfNode } from './adf-document.ts'
 export type { ConvertError, ConvertErrorCode, Result } from './result.ts'
+export type { JsonValue } from './json-value.ts'
 export { adfToMarkdown } from './adf-to-markdown.ts'
 export { isAdfDocument } from './adf-document.ts'

src/json-value.ts

@@ -0,0 +1,10 @@
+export type JsonValue = JsonValue[] | boolean | null | number | string | { [key: string]: JsonValue }
+
+export function isJsonValue(value: unknown): value is JsonValue {
+  if (value === null) return true
+  if (typeof value === 'boolean' || typeof value === 'string') return true
+  if (typeof value === 'number') return Number.isFinite(value)
+  if (Array.isArray(value)) return [...value].every(isJsonValue)
+  if (typeof value === 'object') return Object.values(value).every(isJsonValue)
+  return false
+}

src/markdown-escaping.ts

@@ -1,3 +1,5 @@
+import { escapesLineClaim, startsEntityReference, type LinePosition } from './commonmark-grammar.ts'
+
 export type InlineSegment = {
   kind: 'emphasis-close' | 'emphasis-open' | 'link-text' | 'literal' | 'syntax'
   text: string
@@ -6,33 +8,19 @@ export type InlineSegment = {
 export type LineContainer = 'heading' | 'paragraph'
 
 const asciiPunctuation = /[!"#$%&'()*+,\-./:;<=>?@[\\\]^_`{|}~]/
-const entityReference = /^&(?:[A-Za-z][A-Za-z0-9]{1,31}|#\d{1,7}|#[Xx][A-Fa-f0-9]{1,6});/
 const htmlConstructs = [/^<[!?]/, /^<\/?[A-Za-z][A-Za-z0-9-]*(?:[\s/>]|$)/, /^<[A-Za-z][A-Za-z0-9+.-]{1,31}:[^\s<>]*>/, /^<[^\s<>@]+@[^\s<>@]+>/]
 const inlineDirective = /^:[a-z][A-Za-z0-9]*[[{]/
 const linkOpener = /\](?=[([:])/
-const orderedListMarker = /^\d{1,9}$/
-const setextUnderline = /^=+$/
-const thematicBreak = /^(?:(?:\*[ \t]*){3,}|(?:-[ \t]*){3,}|(?:_[ \t]*){3,})$/
 const unicodePunctuation = /[\p{P}\p{S}]/u
 const unicodeWhitespace = /[\t\n\f\r \p{Zs}]/u
 
-const escapableOpeners = [/^#{1,6}(?:[ \t]|$)/, /^>/, /^[*+-](?:[ \t]|$)/, /^`{3,}/, /^~{3,}/, /^:{2,}/, /^\|/]
-const blockOpeners = [...escapableOpeners, /^\d{1,9}[.)](?:[ \t]|$)/]
-
 export function assembleInlineLine(segments: readonly InlineSegment[], container: LineContainer): string {
   return escape(resolveEmphasis(segments), container)
 }
 
-export function lineOpensBlock(line: string): boolean {
-  return blockOpeners.some((opener) => opener.test(line)) || thematicBreak.test(line)
-}
-
-export function isWordCharacter(character: string): boolean {
-  return character !== '' && !unicodeWhitespace.test(character) && !unicodePunctuation.test(character)
-}
-
 function resolveEmphasis(segments: readonly InlineSegment[]): InlineSegment[] {
   const resolved = segments.map((segment) => ({ ...segment }))
+  // Offsets index the pre-swap text: every emphasis spelling this swaps between is one character wide.
   const scan = resolved.map((segment) => segment.text).join('')
   const offsets: number[] = []
   let offset = 0
@@ -77,19 +65,29 @@ function escape(segments: readonly InlineSegment[], container: LineContainer): s
 }
 
 function opensConstruct(scan: string, index: number, inLinkText: boolean, container: LineContainer, escaped: ReadonlySet<number>): boolean {
+  const claimsLine = container === 'heading' ? closesHeading(scan, index) : claimsLineStart(scan, index)
+  return claimsLine || claimsCharacter(scan, index, inLinkText, escaped)
+}
+
+function claimsLineStart(scan: string, index: number): boolean {
+  const start = scan.lastIndexOf('\n', index - 1) + 1
+  const end = scan.indexOf('\n', index)
+  const line = scan.slice(start, end === -1 ? undefined : end)
+  const position: LinePosition = start === 0 ? 'first' : 'later'
+  return escapesLineClaim(line, index - start, position)
+}
+
+function closesHeading(scan: string, index: number): boolean {
+  if (scan.charAt(index) !== '#' || !/^#+$/.test(scan.slice(index))) return false
+  return index === 0 || /[ \t]/.test(scan.charAt(index - 1))
+}
+
+function claimsCharacter(scan: string, index: number, inLinkText: boolean, escaped: ReadonlySet<number>): boolean {
   const character = scan.charAt(index)
   const rest = scan.slice(index)
-  const line = rest.split('\n')[0] ?? ''
-  if (container === 'paragraph' && (index === 0 || scan.charAt(index - 1) === '\n')) {
-    if (escapableOpeners.some((opener) => opener.test(rest))) return true
-    if (thematicBreak.test(line)) return true
-    if (index > 0 && setextUnderline.test(line)) return true
-  }
-  if (container === 'paragraph' && (character === '.' || character === ')') && closesOrderedListMarker(scan, index)) return true
-  if (container === 'heading' && character === '#' && /^#+$/.test(rest) && (index === 0 || /[ \t]/.test(scan.charAt(index - 1)))) return true
   if (inLinkText && (character === '[' || character === ']')) return true
   if (character === '\\') return asciiPunctuation.test(scan.charAt(index + 1))
-  if (character === '&') return entityReference.test(rest)
+  if (character === '&') return startsEntityReference(rest)
   if (character === '<') return htmlConstructs.some((construct) => construct.test(rest))
   if (character === ':') return inlineDirective.test(rest)
   if (character === '[') return linkOpener.test(rest)
@@ -98,13 +96,6 @@ function opensConstruct(scan: string, index: number, inLinkText: boolean, contai
   return false
 }
 
-function closesOrderedListMarker(scan: string, index: number): boolean {
-  const lineStart = scan.lastIndexOf('\n', index - 1) + 1
-  if (!orderedListMarker.test(scan.slice(lineStart, index))) return false
-  const following = scan.charAt(index + 1)
-  return following === '' || following === ' ' || following === '\t' || following === '\n'
-}
-
 function opensCodeSpan(scan: string, index: number, escaped: ReadonlySet<number>): boolean {
   if (!startsRun(scan, index, escaped)) return false
   const length = runLength(scan, index)
@@ -155,6 +146,10 @@ function isWhitespace(character: string): boolean {
   return character === '' || unicodeWhitespace.test(character)
 }
 
+function isWordCharacter(character: string): boolean {
+  return character !== '' && !unicodeWhitespace.test(character) && !unicodePunctuation.test(character)
+}
+
 function charAt(text: string, index: number): string {
   return index < 0 ? '' : text.charAt(index)
 }

src/markdown-inline.ts

@@ -1,5 +1,6 @@
 import type { AdfMark, AdfNode } from './adf-document.ts'
-import { assembleInlineLine, lineOpensBlock, type InlineSegment, type LineContainer } from './markdown-escaping.ts'
+import { assembleInlineLine, type InlineSegment, type LineContainer } from './markdown-escaping.ts'
+import { claimsLine, holdsEntityReference } from './commonmark-grammar.ts'
 import { failure, success, type Result } from './result.ts'
 import { longestBacktickRun } from './backtick-runs.ts'
 import { serializeCanonicalJson } from './canonical-json.ts'
@@ -10,20 +11,21 @@ type InlineContext = {
   inLinkText: boolean
 }
 
+type InlineRun = { kind: 'marked'; mark: AdfMark; nodes: AdfNode[] } | { kind: 'plain'; node: AdfNode }
+
 const autolink = /^[A-Za-z][A-Za-z0-9+.-]{1,31}:[^\s<>\u0000-\u001f\u007f]*$/
 const controlCharacter = /[\u0000-\u001f\u007f]/
-const entityReference = /&(?:[A-Za-z][A-Za-z0-9]{1,31}|#\d{1,7}|#[Xx][A-Fa-f0-9]{1,6});/
 const linkAttributes = ['href', 'title']
 
 export function emitInlineLine(nodes: readonly AdfNode[], container: LineContainer): Result<string> {
   const segments = emitRun(nodes, 0, { atBlockEnd: true, container, inLinkText: false })
   if (!segments.ok) return segments
   const line = assembleInlineLine(segments.value, container)
-  for (const single of line.split('\n')) {
+  for (const [index, single] of line.split('\n').entries()) {
     if (/^[ \t]|[ \t]$/.test(single)) {
       return failure('unspellable-whitespace', 'a line begins or ends with whitespace CommonMark strips')
     }
-    if (container === 'paragraph' && lineOpensBlock(single)) {
+    if (container === 'paragraph' && claimsLine(single, index === 0 ? 'first' : 'later')) {
       return failure('unspellable-line-start', `block parsing would claim the emitted line ${JSON.stringify(single)}`)
     }
   }
@@ -31,29 +33,32 @@ export function emitInlineLine(nodes: readonly AdfNode[], container: LineContain
 }
 
 function emitRun(nodes: readonly AdfNode[], depth: number, context: InlineContext): Result<InlineSegment[]> {
+  const runs = inlineRuns(nodes, depth)
   const segments: InlineSegment[] = []
-  let index = 0
-  while (index < nodes.length) {
-    const node = nodes[index]
-    if (node === undefined) return failure('unsupported-node-shape', 'the inline content holds a hole')
-    const mark = (node.marks ?? [])[depth]
-    if (mark === undefined) {
-      const leaf = emitLeaf(node, { ...context, atBlockEnd: context.atBlockEnd && index === nodes.length - 1 })
-      if (!leaf.ok) return leaf
-      segments.push(...leaf.value)
-      index += 1
-      continue
-    }
-    let end = index + 1
-    while (end < nodes.length && sameMark((nodes[end]?.marks ?? [])[depth], mark)) end += 1
-    const wrapped = emitMarkedRun(nodes.slice(index, end), mark, depth, { ...context, atBlockEnd: context.atBlockEnd && end === nodes.length })
-    if (!wrapped.ok) return wrapped
-    segments.push(...wrapped.value)
-    index = end
+  for (const [index, run] of runs.entries()) {
+    const runContext = { ...context, atBlockEnd: context.atBlockEnd && index === runs.length - 1 }
+    const emitted = run.kind === 'plain' ? emitLeaf(run.node, runContext) : emitMarkedRun(run.nodes, run.mark, depth, runContext)
+    if (!emitted.ok) return emitted
+    segments.push(...emitted.value)
   }
   return success(segments)
 }
 
+function inlineRuns(nodes: readonly AdfNode[], depth: number): InlineRun[] {
+  const runs: InlineRun[] = []
+  for (const node of nodes) {
+    const mark = (node.marks ?? [])[depth]
+    if (mark === undefined) {
+      runs.push({ kind: 'plain', node })
+      continue
+    }
+    const previous = runs[runs.length - 1]
+    if (previous?.kind === 'marked' && sameMark(previous.mark, mark)) previous.nodes.push(node)
+    else runs.push({ kind: 'marked', mark, nodes: [node] })
+  }
+  return runs
+}
+
 function emitLeaf(node: AdfNode, context: InlineContext): Result<InlineSegment[]> {
   if (node.type !== 'hardBreak' && node.type !== 'text') {
     return failure('unsupported-node-type', `the canonical form spells no inline node of type ${node.type}`)
@@ -127,7 +132,7 @@ function emitLink(nodes: readonly AdfNode[], mark: AdfMark, depth: number, conte
 function spellDestination(href: string): Result<string> {
   if (controlCharacter.test(href)) return failure('unspellable-link-destination', 'a link destination holds a control character')
   if (href.includes('\\')) return failure('unspellable-link-destination', 'no canonical escape spells a backslash in a link destination')
-  if (entityReference.test(href)) {
+  if (holdsEntityReference(href)) {
     return failure('unspellable-link-destination', 'a link destination shaped like an entity reference decodes on the way back')
   }
   if (href.includes(' ')) {
@@ -143,7 +148,7 @@ function spellDestination(href: string): Result<string> {
 
 function spellTitle(title: string): Result<string> {
   if (/["\n\r\\]/.test(title)) return failure('unspellable-link-title', 'no canonical escape spells a quote, backslash or newline in a link title')
-  if (entityReference.test(title)) return failure('unspellable-link-title', 'a link title shaped like an entity reference decodes on the way back')
+  if (holdsEntityReference(title)) return failure('unspellable-link-title', 'a link title shaped like an entity reference decodes on the way back')
   return success(` "${title}"`)
 }
 
@@ -157,7 +162,7 @@ function balanced(href: string): boolean {
   return depth === 0
 }
 
-function sameMark(candidate: AdfMark | undefined, mark: AdfMark): boolean {
-  if (candidate === undefined || candidate.type !== mark.type) return false
+function sameMark(candidate: AdfMark, mark: AdfMark): boolean {
+  if (candidate.type !== mark.type) return false
   return serializeCanonicalJson(candidate.attrs ?? {}, 'compact') === serializeCanonicalJson(mark.attrs ?? {}, 'compact')
 }

src/result.ts

@@ -8,6 +8,7 @@ export type ConvertErrorCode =
   | 'unspellable-line-start'
   | 'unspellable-link-destination'
   | 'unspellable-link-title'
+  | 'unspellable-list-marker'
   | 'unspellable-mark'
   | 'unspellable-whitespace'
   | 'unspelled-block-marks'