Use astral-sh/versions as primary version provider (#802)

Closes: #777
Closes: #325

src/download/legacy-version-manifest.ts

@@ -0,0 +1,80 @@
+import * as core from "@actions/core";
+
+export interface ManifestEntry {
+  arch: string;
+  platform: string;
+  version: string;
+  downloadUrl: string;
+  checksum?: string;
+  variant?: string;
+  archiveFormat?: string;
+}
+
+interface LegacyManifestEntry {
+  arch: string;
+  platform: string;
+  version: string;
+  downloadUrl: string;
+  checksum?: string;
+}
+
+const warnedLegacyManifestUrls = new Set<string>();
+
+export function parseLegacyManifestEntries(
+  parsedEntries: unknown[],
+  manifestUrl: string,
+): ManifestEntry[] {
+  warnAboutLegacyManifestFormat(manifestUrl);
+
+  return parsedEntries.map((entry, index) => {
+    if (!isLegacyManifestEntry(entry)) {
+      throw new Error(
+        `Invalid legacy manifest-file entry at index ${index} in ${manifestUrl}.`,
+      );
+    }
+
+    return {
+      arch: entry.arch,
+      checksum: entry.checksum,
+      downloadUrl: entry.downloadUrl,
+      platform: entry.platform,
+      version: entry.version,
+    };
+  });
+}
+
+export function clearLegacyManifestWarnings(): void {
+  warnedLegacyManifestUrls.clear();
+}
+
+function warnAboutLegacyManifestFormat(manifestUrl: string): void {
+  if (warnedLegacyManifestUrls.has(manifestUrl)) {
+    return;
+  }
+
+  warnedLegacyManifestUrls.add(manifestUrl);
+  core.warning(
+    `manifest-file ${manifestUrl} uses the legacy JSON array format, which is deprecated. Please migrate to the astral-sh/versions NDJSON format before the next major release.`,
+  );
+}
+
+function isLegacyManifestEntry(value: unknown): value is LegacyManifestEntry {
+  if (!isRecord(value)) {
+    return false;
+  }
+
+  const checksumIsValid =
+    typeof value.checksum === "string" || value.checksum === undefined;
+
+  return (
+    typeof value.arch === "string" &&
+    checksumIsValid &&
+    typeof value.downloadUrl === "string" &&
+    typeof value.platform === "string" &&
+    typeof value.version === "string"
+  );
+}
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+  return typeof value === "object" && value !== null;
+}