4.2: an empty link destination beside a title spells <>

corpus/round-trip/commonmark-subset/link-empty-destination.json

@@ -0,0 +1,24 @@
+{
+  "content": [
+    {
+      "content": [
+        {
+          "marks": [
+            {
+              "attrs": {
+                "href": "",
+                "title": ""
+              },
+              "type": "link"
+            }
+          ],
+          "text": "a",
+          "type": "text"
+        }
+      ],
+      "type": "paragraph"
+    }
+  ],
+  "type": "doc",
+  "version": 1
+}

corpus/round-trip/commonmark-subset/link-empty-destination.md

@@ -0,0 +1 @@
+[a](<> "")

spec/flavour.md

@@ -43,10 +43,11 @@ normalizes to it through the round-trip.
   CommonMark admits no spelling — the end of a block, inside an ATX heading — or where the node
   carries an attribute, it is the inline directive.
 - An empty paragraph — real payloads carry them — is `::paragraph`.
-- Links `[text](url)`; `<…>` around a destination containing spaces; title in double quotes. A
-  backslash escapes a parenthesis the destination leaves unbalanced, and a quote inside the title;
-  a balanced pair stays bare. `<url>` autolink form only when the text equals the destination and
-  the destination is a valid CommonMark autolink (absolute URI).
+- Links `[text](url)`; `<…>` around a destination containing spaces, `<>` an empty one beside a
+  title; title in double quotes. A backslash escapes a parenthesis the destination leaves
+  unbalanced, and a quote inside the title; a balanced pair stays bare. `<url>` autolink form only
+  when the text equals the destination and the destination is a valid CommonMark autolink
+  (absolute URI).
 - Paragraphs on one line — no soft wrapping; a soft line break in input becomes a single space.
 - Entity references in input decode to their characters; output backslash-escapes only where text
   would otherwise parse as syntax, scanning the assembled line rather than each text node: escape

src/markdown/emit/inline-line.ts

@@ -12,7 +12,7 @@ import { markSpelling, spellMarkAttributes } from '../mark-spellings.ts'
 import { nodeAttrs, nodeContent, nodeMarks } from '../../adf/document.ts'
 import { sameMark } from '../../adf/editor-normal.ts'
 import { slotLineEndingFault, spellLeafDirective } from '../directive-syntax.ts'
-import { spellDestination, spellTitle } from '../link-syntax.ts'
+import { spellDestination, spellLinkTarget } from '../link-syntax.ts'
 import { spellInlineNodeAttributes } from './inline-directive-spelling.ts'
 import { spellTextDirective } from '../text-directive.ts'
 
@@ -285,13 +285,11 @@ function emitLink(nodes: readonly AdfNode[], mark: AdfMark, depth: number, range
   const node = nodes[0]
   const bare = nodes.length === 1 && node !== undefined && node.type === 'text' && node.text === href && nodeMarks(node).length === depth + 1
   if (bare && title === undefined && isAutolink(href) && !holdsEntityReference(href)) return success({ segments: [syntax(`<${href}>`)] })
-  const destination = spellDestination(href, path)
-  if (!destination.ok) return destination
-  const spelledTitle = typeof title === 'string' ? spellTitle(title, path) : success('')
-  if (!spelledTitle.ok) return spelledTitle
+  const target = spellLinkTarget(href, typeof title === 'string' ? title : undefined, path)
+  if (!target.ok) return target
   const inner = emitRun(nodes, depth + 1, range.first, { ...context, bracketed: true })
   if (!inner.ok) return inner
   if (inner.value.carry !== undefined) return inner
-  return success({ segments: [syntax('['), ...inner.value.segments, syntax(`](${destination.value}${spelledTitle.value})`)] })
+  return success({ segments: [syntax('['), ...inner.value.segments, syntax(`](${target.value})`)] })
 }
 

src/markdown/link-syntax.ts

@@ -106,7 +106,15 @@ export function spellDestination(href: string, path: ConvertErrorPath): Result<s
   return success(escapeUnbalanced(href))
 }
 
-export function spellTitle(title: string, path: ConvertErrorPath): Result<string> {
+export function spellLinkTarget(href: string, title: string | undefined, path: ConvertErrorPath): Result<string> {
+  const destination = spellDestination(href, path)
+  if (!destination.ok || title === undefined) return destination
+  const spelledTitle = spellTitle(title, path)
+  if (!spelledTitle.ok) return spelledTitle
+  return success(`${destination.value === '' ? '<>' : destination.value}${spelledTitle.value}`)
+}
+
+function spellTitle(title: string, path: ConvertErrorPath): Result<string> {
   if (/[\n\r\\]/.test(title)) {
     return failure('unspellable-link', 'no canonical escape spells a backslash or newline in a link title', path)
   }