13b - link takes the directive form where CommonMark cannot spell it, unspellable-link leaves the code list

src/markdown/mark-spellings.ts

@@ -1,15 +1,20 @@
-import type { AdfMark } from '../adf/document.ts'
+import type { AdfAttributes, AdfMark } from '../adf/document.ts'
 import type { AttributeVocabulary } from '../adf/attribute-vocabulary.ts'
 import type { MarkType } from '../adf/mark-attributes.ts'
+import { escapeUnbalanced, spellLinkTarget } from './link-syntax.ts'
+import { holdsDirectivePrefix, spellAttributes, spellVocabulary } from './directive-syntax.ts'
+import { holdsEntityReference } from './entity-references.ts'
+import { isAutolink } from './commonmark-grammar.ts'
 import { isMarkType, markAttributes } from '../adf/mark-attributes.ts'
 import { nodeAttrs } from '../adf/document.ts'
-import { spellAttributes, spellVocabulary } from './directive-syntax.ts'
 import { vocabularyPairs } from '../adf/attribute-vocabulary.ts'
 
 type Spelling = { kind: 'code' | 'directive' | 'link'; spelling?: undefined } | { kind: 'emphasis'; spelling: string }
 
 export type MarkSpelling = Spelling & { attributes: AttributeVocabulary }
 
+export type CommonMarkLink = { form: 'autolink'; target?: undefined } | { form: 'inline'; target: string }
+
 const markSpellings: Readonly<Record<MarkType, Spelling>> = {
   border: { kind: 'directive' },
   code: { kind: 'code' },
@@ -30,6 +35,16 @@ export function markSpelling(type: string): MarkSpelling | undefined {
   return { attributes, kind: spelling.kind }
 }
 
+// spec/flavour.md, Marks. `bare`: one text node reading exactly `href`, the link innermost.
+export function commonMarkLink(attrs: AdfAttributes, href: string, bare: boolean, bracketed: boolean): CommonMarkLink | undefined {
+  if (Object.keys(attrs).some((key) => key !== 'href' && key !== 'title')) return undefined
+  const title = attrs['title']
+  const autolinkHolds = !bracketed || (!href.includes('`') && !holdsDirectivePrefix(href) && escapeUnbalanced(href, '[', ']') === href)
+  if (bare && autolinkHolds && title === undefined && isAutolink(href) && !holdsEntityReference(href)) return { form: 'autolink' }
+  const target = spellLinkTarget(href, typeof title === 'string' ? title : undefined)
+  return target === undefined ? undefined : { form: 'inline', target }
+}
+
 export function spellMarkAttributes(mark: AdfMark, vocabulary: AttributeVocabulary): string | undefined {
   const pairs = vocabularyPairs(nodeAttrs(mark), vocabulary, [])
   return pairs === undefined ? undefined : spellAttributes(spellVocabulary(pairs))