12c: one block opener speller beside its reader, the line readers split along the union, and AGENTS.md records the leaf body

src/markdown/directive-syntax.ts

@@ -77,17 +77,7 @@ export function malformedDirective(message: string): ConvertFault {
 
 export function readDirectiveLine(line: string): Read<DirectiveLine> | undefined {
   if (!claimsDirectivePrefix(line, 0)) return undefined
-  const closer = line.charAt(directivePrefix.length) === '/'
-  const start = directivePrefix.length + (closer ? 1 : 0)
-  directiveName.lastIndex = start
-  const name = directiveName.exec(line)?.[0]
-  if (name === undefined) return undefined
-  const rest = line.slice(start + name.length)
-  if (closer) return lineEnd.test(rest) ? { value: { kind: 'closer', name } } : { fault: malformedDirective(closerFault) }
-  if (!rest.startsWith(' ') && !lineEnd.test(rest)) return undefined
-  const opener = readOpenerRest(rest)
-  if (opener.fault !== undefined) return { fault: opener.fault }
-  return { value: { argument: opener.value.argument, attributes: opener.value.attributes, kind: 'opener', name } }
+  return line.charAt(directivePrefix.length) === '/' ? readCloserLine(line) : readOpenerLine(line)
 }
 
 export function readInlineDirective(text: string, index: number): Read<DirectiveSpan> | undefined {
@@ -119,6 +109,10 @@ export function spellDirectiveCloser(name: string): string {
   return `${directivePrefix}/${name}`
 }
 
+export function spellDirectiveOpener(name: string, argument: string | undefined, attributes: string): string {
+  return `${directivePrefix}${name}${argument === undefined ? '' : ` ${argument}`}${attributes === '' ? '' : ` ${attributes}`}`
+}
+
 export function spellJsonAttribute(value: JsonValue): string {
   return quote(serializeCanonicalJson(value, 'compact'))
 }
@@ -173,24 +167,39 @@ function inlineDirectiveName(text: string, index: number): string | undefined {
   return opened === undefined ? undefined : opened.slice(directivePrefix.length, -1)
 }
 
+function readCloserLine(line: string): Read<DirectiveLine> | undefined {
+  const start = directivePrefix.length + 1
+  const name = readDirectiveName(line, start)
+  if (name === undefined) return undefined
+  return lineEnd.test(line.slice(start + name.length)) ? { value: { kind: 'closer', name } } : { fault: malformedDirective(closerFault) }
+}
+
+function readOpenerLine(line: string): Read<DirectiveLine> | undefined {
+  const name = readDirectiveName(line, directivePrefix.length)
+  if (name === undefined) return undefined
+  const rest = line.slice(directivePrefix.length + name.length)
+  if (!rest.startsWith(' ') && !lineEnd.test(rest)) return undefined
+  const opener = readOpenerRest(rest)
+  if (opener.fault !== undefined) return { fault: opener.fault }
+  return { value: { argument: opener.value.argument, attributes: opener.value.attributes, kind: 'opener', name } }
+}
+
+function readDirectiveName(text: string, index: number): string | undefined {
+  directiveName.lastIndex = index
+  return directiveName.exec(text)?.[0]
+}
+
 function readOpenerRest(rest: string): Read<{ argument: string | undefined; attributes: DirectiveAttributes }> {
-  let cursor = 0
-  let argument: string | undefined
-  let attributes = noAttributes
-  if (rest.charAt(0) === ' ' && rest.charAt(1) !== '{' && !lineEnd.test(rest)) {
-    bareRun.lastIndex = 1
-    argument = bareRun.exec(rest)?.[0]
-    if (argument === undefined) return { fault: malformedDirective(openerFault) }
-    cursor = 1 + argument.length
-  }
-  if (rest.charAt(cursor) === ' ' && rest.charAt(cursor + 1) === '{') {
-    const read = readAttributesAt(rest, cursor + 1, false)
-    if (read.fault !== undefined) return { fault: read.fault }
-    attributes = read.value.attributes
-    cursor = read.value.end
-  }
-  if (!lineEnd.test(rest.slice(cursor))) return { fault: malformedDirective(openerFault) }
-  return { value: { argument, attributes } }
+  bareRun.lastIndex = 1
+  const argument = bareRun.exec(rest)?.[0]
+  const attributes = readOpenerAttributes(rest, argument === undefined ? 0 : 1 + argument.length)
+  if (attributes.fault !== undefined) return { fault: attributes.fault }
+  if (!lineEnd.test(rest.slice(attributes.value.end))) return { fault: malformedDirective(openerFault) }
+  return { value: { argument, attributes: attributes.value.attributes } }
+}
+
+function readOpenerAttributes(rest: string, index: number): Read<Attributes> {
+  return rest.charAt(index) === ' ' ? readAttributesAt(rest, index + 1, false) : { value: { attributes: noAttributes, end: index } }
 }
 
 function readNestedDirective(text: string, index: number, depth: number): Read<DirectiveSpan> | undefined {

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

@@ -113,13 +113,16 @@ function directivePair(node: AdfNode, opener: string, body: string): EmittedBloc
 
 function emitDirectiveBlock(node: AdfNode, directive: BlockDirective, path: ConvertErrorPath, depth: number): Result<EmittedBlock> {
   if (node.text !== undefined) return failure('unsupported-node-shape', `a ${node.type} carries no text: this one holds text`, path)
-  const content = nodeContent(node)
-  const leaf = blockDirectiveForm(node.type) === 'leaf'
-  if (leaf && content.length > 0) return failure('unsupported-node-shape', `a ${node.type} holds no content: this one holds some`, path)
+  if (blockDirectiveForm(node.type) === 'leaf' && nodeContent(node).length > 0) return failure('unsupported-node-shape', `a ${node.type} holds no content: this one holds some`, path)
   if (directive.contentModel === 'code') return emitCodeDirective(node, directive, path, depth)
   const opener = spellBlockDirectiveOpener(node, directive)
   if (opener === undefined) return commonMarkLine(carriedBlock(node, path, depth))
-  if (leaf) return success({ spelling: 'directive', text: opener })
+  return emitDirectiveBody(node, directive, opener, path, depth)
+}
+
+function emitDirectiveBody(node: AdfNode, directive: BlockDirective, opener: string, path: ConvertErrorPath, depth: number): Result<EmittedBlock> {
+  if (blockDirectiveForm(node.type) === 'leaf') return success({ spelling: 'directive', text: opener })
+  const content = nodeContent(node)
   const body = directive.contentModel === 'inline' ? emitInlineLine(content, 'paragraph', path) : emitBlocks(content, 'directive', path, depth + 1)
   if (!body.ok) return body
   return success(directivePair(node, opener, body.value))

src/markdown/emit/block-directive-spelling.ts

@@ -1,28 +1,27 @@
 import type { AdfNode } from '../../adf/document.ts'
 import type { BlockDirective } from '../../adf/block-directives.ts'
 import { blockArgument } from '../block-directive-arguments.ts'
-import { directivePrefix, isBareToken, spellAttributes, spellJsonAttribute, spellVocabulary } from '../directive-syntax.ts'
+import { isBareToken, spellAttributes, spellDirectiveOpener, spellJsonAttribute, spellVocabulary } from '../directive-syntax.ts'
 import { markValues, marksAttribute } from '../block-directive-marks.ts'
 import { nodeAttrs, nodeMarks } from '../../adf/document.ts'
 import { vocabularyPairs } from '../../adf/attribute-vocabulary.ts'
 
 export function spellBlockDirectiveOpener(node: AdfNode, directive: BlockDirective, spelledByBody: readonly string[] = []): string | undefined {
   const argumentAttribute = blockArgument(node.type)
-  const argument = spellArgument(node, argumentAttribute)
-  if (argument === undefined) return undefined
+  const slot = bareArgument(node, argumentAttribute)
+  if (slot === undefined) return undefined
   const spelled = argumentAttribute === undefined ? spelledByBody : [argumentAttribute, ...spelledByBody]
   const pairs = vocabularyPairs(nodeAttrs(node), directive.attributes, spelled)
   if (pairs === undefined) return undefined
   const spelledPairs = spellVocabulary(pairs)
   const marks = nodeMarks(node)
   if (marks.length > 0) spelledPairs.push([marksAttribute, spellJsonAttribute(markValues(marks))])
-  const attributes = spellAttributes(spelledPairs)
-  return `${directivePrefix}${node.type}${argument}${attributes === '' ? '' : ` ${attributes}`}`
+  return spellDirectiveOpener(node.type, slot.argument, spellAttributes(spelledPairs))
 }
 
-function spellArgument(node: AdfNode, argumentAttribute: string | undefined): string | undefined {
+// `undefined` where the argument slot holds a value no bare token spells.
+function bareArgument(node: AdfNode, argumentAttribute: string | undefined): { argument: string | undefined } | undefined {
   const value = argumentAttribute === undefined ? undefined : nodeAttrs(node)[argumentAttribute]
-  if (value === undefined) return ''
-  if (typeof value !== 'string' || !isBareToken(value)) return undefined
-  return ` ${value}`
+  if (value === undefined) return { argument: undefined }
+  return typeof value === 'string' && isBareToken(value) ? { argument: value } : undefined
 }

src/markdown/list-break.ts

@@ -1,5 +1,5 @@
-import { directivePrefix } from './directive-syntax.ts'
+import { spellDirectiveOpener } from './directive-syntax.ts'
 
 export const listBreakName = 'listBreak'
 
-export const listBreakSpelling = `${directivePrefix}${listBreakName}`
+export const listBreakSpelling = spellDirectiveOpener(listBreakName, undefined, '')