Answer principles round 2: 1 🔴, 1 🟡; bound the collapsed label at 999 too, pinned by a test

CHANGELOG.md

@@ -37,6 +37,8 @@
   20 lines of 40000 tabs under 80000 nested items took 1988 ms.
 - `losslessMarkdownToAdf` takes time linear in the markdown when an inline directive's `[content]`
   holds many unclosed backtick runs: 640000 characters of them took one second, now 100 ms.
+- Every reader leaves `[text]` and `[text][]` literal when the text runs over 999 characters, where
+  it read them as a link to the matching definition: CommonMark caps a link label at 999 characters.
 - The README compares the package with seven other ADF converters, each checked against its
   published version.
 

src/markdown/parse/inline-content.ts

@@ -432,8 +432,9 @@ function resolveTarget(scan: Scan, start: number, index: number): { definition:
   }
   const label = scan.source.charAt(after) === '[' ? readLabel(scan.source, after) : undefined
   // CommonMark: a label holds at most 999 characters, so longer link text names no definition.
-  if (label === undefined && index - start > 999) return undefined
-  const name = label === undefined || label.value === '' ? scan.source.slice(start, index) : label.value
+  const labelIsText = label === undefined || label.value === ''
+  if (labelIsText && index - start > 999) return undefined
+  const name = labelIsText ? scan.source.slice(start, index) : label.value
   const definition = scan.definitions.get(normalizeLabel(name))
   if (definition === undefined) return undefined
   return { definition, length: label?.length ?? 0 }

src/markdown/parse/markdown-to-adf.test.ts

@@ -1076,6 +1076,17 @@ test('reads the reference links a definition resolves, and leaves the rest liter
   assert.deepEqual(content(losslessMarkdownToAdf('[][]\n')), [paragraph('[][]')])
 })
 
+test('reads link text past 999 characters as no label, in every reader', () => {
+  const longest = `foo${' '.repeat(993)}bar`
+  const tooLong = `foo${' '.repeat(1000)}bar`
+  for (const read of [commonMarkToAdf, losslessMarkdownToAdf, portableMarkdownToAdf]) {
+    assert.deepEqual(content(read(`[${longest}]\n\n[foo bar]: /u\n`)), [{ content: [marked(longest, link('/u'))], type: 'paragraph' }])
+    assert.deepEqual(content(read(`[${longest}][]\n\n[foo bar]: /u\n`)), [{ content: [marked(longest, link('/u'))], type: 'paragraph' }])
+    assert.deepEqual(content(read(`[${tooLong}]\n\n[foo bar]: /u\n`)), [paragraph(`[${tooLong}]`)])
+    assert.deepEqual(content(read(`[${tooLong}][]\n\n[foo bar]: /u\n`)), [paragraph(`[${tooLong}][]`)])
+  }
+})
+
 test('reads an autolink, the email form as the mailto link it means', () => {
   assert.deepEqual(content(losslessMarkdownToAdf('<https://example.com/>\n')), [
     { content: [marked('https://example.com/', link('https://example.com/'))], type: 'paragraph' },