Improve README contribution checks (#327)

* Stabilize README link checks

* Enforce README entry ordering

* Ignore CI-blocked lib.rs links

.github/scripts/check-readme-order.mjs

@@ -0,0 +1,96 @@
+#!/usr/bin/env node
+
+import { readFileSync } from "node:fs";
+
+const [basePath, currentPath] = process.argv.slice(2);
+if (!basePath || !currentPath) {
+  console.error("Usage: check-readme-order.mjs BASE_README CURRENT_README");
+  process.exit(2);
+}
+
+const SORTED_SECTION = "Community Extensions";
+const IGNORED_SECTIONS = new Set(["Contents"]);
+
+function headingName(markdown) {
+  const linkedHeading = markdown.match(/^\[([^\]]+)\]\([^)]+\)$/);
+  return linkedHeading ? linkedHeading[1] : markdown;
+}
+
+function parseSections(path) {
+  const sections = new Map();
+  let section = null;
+
+  for (const line of readFileSync(path, "utf8").split("\n")) {
+    const heading = line.match(/^#{2,3}\s+(.+?)\s*$/);
+    if (heading) {
+      section = headingName(heading[1]);
+      if (!sections.has(section)) {
+        sections.set(section, []);
+      }
+      continue;
+    }
+
+    if (!section || !line.startsWith("- [")) {
+      continue;
+    }
+
+    const item = line.match(/^- \[(.*?)\]\(([^)\s]+)(?:\s+[^)]*)?\)/);
+    if (!item) {
+      continue;
+    }
+
+    const label = item[1].replaceAll("`", "").trim();
+    sections.get(section).push({
+      sortKey: label.toLowerCase(),
+      url: item[2],
+    });
+  }
+
+  return sections;
+}
+
+const baseSections = parseSections(basePath);
+const currentSections = parseSections(currentPath);
+let orderingIsValid = true;
+
+const sortedEntries = currentSections.get(SORTED_SECTION) ?? [];
+for (let index = 1; index < sortedEntries.length; index += 1) {
+  if (sortedEntries[index - 1].sortKey > sortedEntries[index].sortKey) {
+    orderingIsValid = false;
+  }
+}
+
+for (const [section, currentEntries] of currentSections) {
+  if (section === SORTED_SECTION || IGNORED_SECTIONS.has(section)) {
+    continue;
+  }
+
+  const baseEntries = baseSections.get(section) ?? [];
+  if (baseEntries.length === 0) {
+    continue;
+  }
+
+  const isExisting = (entry) =>
+    baseEntries.some(
+      (baseEntry) =>
+        baseEntry.url === entry.url || baseEntry.sortKey === entry.sortKey,
+    );
+
+  let foundNewEntry = false;
+  for (const entry of currentEntries) {
+    const entryAlreadyExists = isExisting(entry);
+    if (entryAlreadyExists && foundNewEntry) {
+      orderingIsValid = false;
+    } else if (!entryAlreadyExists) {
+      foundNewEntry = true;
+    }
+  }
+}
+
+if (!orderingIsValid) {
+  const message = "Thanks for contributing! Please move your new entry to follow the ordering rules in CONTRIBUTING.md, then update this pull request.";
+  console.error(`::error file=${currentPath},title=README entry order::${message}`);
+  process.exit(1);
+}
+
+console.log("README entries follow the required ordering.");