Various improvements and fixes to setup-bun (#40)

* Do not save cache on hit
* Support Windows (canary only)
* Support `registry-url` and `scope`

src/bunfig.ts

@@ -0,0 +1,50 @@
+import { EOL } from "node:os";
+import { appendFileSync } from "node:fs";
+import { info } from "@actions/core";
+
+type BunfigOptions = {
+  registryUrl?: string;
+  scope?: string;
+};
+
+export function createBunfig(options: BunfigOptions): string | null {
+  const { registryUrl, scope } = options;
+
+  let url: URL | undefined;
+  if (registryUrl) {
+    try {
+      url = new URL(registryUrl);
+    } catch {
+      throw new Error(`Invalid registry-url: ${registryUrl}`);
+    }
+  }
+
+  let owner: string | undefined;
+  if (scope) {
+    owner = scope.startsWith("@")
+      ? scope.toLocaleLowerCase()
+      : `@${scope.toLocaleLowerCase()}`;
+  }
+
+  if (url && owner) {
+    return `[install.scopes]${EOL}'${owner}' = { token = "$BUN_AUTH_TOKEN", url = "${url}"}${EOL}`;
+  }
+
+  if (url && !owner) {
+    return `[install]${EOL}registry = "${url}"${EOL}`;
+  }
+
+  return null;
+}
+
+export function writeBunfig(path: string, options: BunfigOptions): void {
+  const bunfig = createBunfig(options);
+  if (!bunfig) {
+    return;
+  }
+
+  info(`Writing bunfig.toml to '${path}'.`);
+  appendFileSync(path, bunfig, {
+    encoding: "utf8",
+  });
+}