Answer the stability review: a code or HTML block swallows the marker line too

src/markdown/commonmark-grammar.ts

@@ -16,10 +16,11 @@ const atxHeadingOpener = /^(#{1,6})(?:[ \t]|$)/
 const codeFenceOpener = /^(`{3,}|~{3,})/
 const directiveClaim = /^:{2,}(?:[A-Za-z0-9]|[ \t]*$)/
 const pipeClaim = /^\|/
+const bulletListOpener = /^[*+-](?:[ \t]|$)/
 // A superset of what the parser claims: over-escaping a line is safe, under-escaping one breaks the round-trip.
-const firstCharacterOpeners = [atxHeadingOpener, /^>/, /^[*+-](?:[ \t]|$)/, codeFenceOpener, /^:{2,}/, pipeClaim]
+const firstCharacterOpeners = [atxHeadingOpener, /^>/, bulletListOpener, codeFenceOpener, /^:{2,}/, pipeClaim]
 const htmlConstructs = [/^<[!?]/, /^<\/?[A-Za-z][A-Za-z0-9-]*(?:[\s/>]|$)/, /^<[^\s<>@]+@[^\s<>@]+>/]
-const orderedListOpener = /^(\d{1,9})[.)](?:[ \t]|$)/
+const orderedListOpener = /^(\d{1,9})([.)])(?:[ \t]|$)/
 const setextUnderline = /^(=+|-+)[ \t]*$/
 const thematicBreak = /^(?:(?:\*[ \t]*){3,}|(?:-[ \t]*){3,}|(?:_[ \t]*){3,})$/
 const unicodeWhitespace = /[\t\n\f\r \p{Zs}]/u
@@ -86,8 +87,16 @@ export function isUnicodeWhitespace(character: string): boolean {
   return unicodeWhitespace.test(character)
 }
 
-// The first marker of a list, `undefined` for a bullet: one answer both directions read, or the emitter
-// spells a list the parser folds into the paragraph above it.
+// `start` is the list's first number, `undefined` for a bullet.
+export function listMarker(line: string): { delimiter: string; start: number | undefined; width: number } | undefined {
+  const ordered = orderedListOpener.exec(line)
+  if (ordered !== null) {
+    const digits = ordered[1] ?? ''
+    return { delimiter: ordered[2] ?? '', start: Number(digits), width: digits.length + 1 }
+  }
+  return bulletListOpener.test(line) ? { delimiter: line.charAt(0), start: undefined, width: 1 } : undefined
+}
+
 export function markerInterruptsParagraph(start: number | undefined, empty: boolean): boolean {
   return !empty && (start === undefined || start === 1)
 }