chore: share README gate Markdown scanning

scripts/markdown.ts

@@ -5,6 +5,14 @@ import { gfmFromMarkdown } from 'mdast-util-gfm'
 import { gfm } from 'micromark-extension-gfm'
 import type { Nodes } from 'mdast'
 
+/** One authored Markdown line outside fenced code. */
+export interface MarkdownProseLine {
+  /** 1-based source line number. */
+  index: number
+  /** Source text without normalization. */
+  raw: string
+}
+
 /** Parse GitHub-flavored Markdown with the repository's standard extensions. */
 export function parseMarkdown(source: string): Nodes {
   return fromMarkdown(source, { extensions: [gfm()], mdastExtensions: [gfmFromMarkdown()] })
@@ -21,3 +29,27 @@ export function visitMarkdown(node: Nodes, visitor: (node: Nodes) => boolean | v
     for (const child of node.children) visitMarkdown(child, visitor)
   }
 }
+
+/**
+ * Return source lines outside backtick or tilde fences.
+ * @param source - Markdown source whose prose should be retained verbatim.
+ * @returns unfenced lines with their original 1-based locations.
+ */
+export function markdownProseLines(source: string): MarkdownProseLine[] {
+  let fence: { marker: '`' | '~'; length: number } | undefined
+  const kept: MarkdownProseLine[] = []
+  source.split('\n').forEach((raw, i) => {
+    const token = /^ {0,3}(`{3,}|~{3,})/.exec(raw)?.[1]
+    if (token !== undefined) {
+      const marker = token[0] as '`' | '~'
+      if (fence === undefined) {
+        fence = { marker, length: token.length }
+      } else if (marker === fence.marker && token.length >= fence.length) {
+        fence = undefined
+      }
+      return
+    }
+    if (fence === undefined) kept.push({ index: i + 1, raw })
+  })
+  return kept
+}