enhance: backward compatibility with simulated x64 version

src/download-url.ts

@@ -5,7 +5,14 @@ import {
   validateStrict,
 } from "compare-versions";
 import { Input } from "./action";
-import { getArchitecture, getAvx2, getPlatform, request } from "./utils";
+import {
+  getArchitecture,
+  getAvx2,
+  getPlatform,
+  isWindowsArm64Supported,
+  request,
+  warnWindowsArm64,
+} from "./utils";
 
 export async function getDownloadUrl(options: Input): Promise<string> {
   const { customUrl } = options;
@@ -63,13 +70,21 @@ async function getSemverDownloadUrl(options: Input): Promise<string> {
 
   const eversion = encodeURIComponent(tag ?? version);
   const eos = encodeURIComponent(os ?? getPlatform());
-  const earch = encodeURIComponent(
+
-    getArchitecture(arch ?? process.arch),
+  let archValue = arch ?? process.arch;
-  );
+  let avx2Value = avx2;
+
+  if (eos === "windows" && getArchitecture(archValue) === "aarch64") {
+    if (!isWindowsArm64Supported(tag ?? version)) {
+      warnWindowsArm64();
+      archValue = "x64";
+      avx2Value = false;
+    }
+  }
+
+  const earch = encodeURIComponent(getArchitecture(archValue));
   const eavx2 = encodeURIComponent(
-    getAvx2(arch ?? process.arch, avx2) === false
+    getAvx2(archValue, avx2Value) === false ? "-baseline" : "",
-      ? "-baseline"
-      : "",
   );
   const eprofile = encodeURIComponent(profile === true ? "-profile" : "");
 

src/utils.ts

@@ -1,3 +1,4 @@
+import { compareVersions, validate } from "compare-versions";
 import { debug, warning } from "@actions/core";
 import { info } from "node:console";
 import { createHash } from "node:crypto";
@@ -61,6 +62,25 @@ export function getAvx2(arch: string, avx2?: boolean): boolean {
   return avx2 ?? true;
 }
 
+export function isWindowsArm64Supported(tag: string): boolean {
+  if (tag === "canary" || tag === "latest") return true;
+
+  const version = tag.startsWith("bun-v") ? tag.slice(5) : tag;
+
+  return validate(version) && compareVersions(version, "1.3.10") >= 0;
+}
+
+export function warnWindowsArm64(): void {
+  warning(
+    [
+      "⚠️ Bun does not provide native arm64 builds for Windows.",
+      "Using x64 baseline build which will run through Microsoft's x64 emulation layer.",
+      "This may result in reduced performance and potential compatibility issues.",
+      "💡 For best performance, consider using x64 Windows runners or other platforms with native support.",
+    ].join("\n"),
+  );
+}
+
 const FILE_VERSION_READERS = {
   "package.json": (content: string) => {
     const pkg = JSON.parse(content);

tests/download-url.spec.ts

@@ -1,6 +1,7 @@
 import { afterEach, beforeEach, describe, expect, it, spyOn } from "bun:test";
 import { getDownloadUrl } from "../src/download-url";
 import * as utils from "../src/utils";
+import * as core from "@actions/core";
 
 const MOCK_TAGS = [
   { ref: "refs/tags/bun-v0.5.0" },
@@ -158,4 +159,49 @@ describe("getDownloadUrl", () => {
       );
     });
   });
+
+  describe("Windows ARM64 Fallback", () => {
+    it("should fallback to x64-baseline for versions older than 1.3.10 and log a warning", async () => {
+      const warningSpy = spyOn(core, "warning");
+      const url = await getDownloadUrl({
+        version: "1.1.0",
+        os: "windows",
+        arch: "arm64",
+      });
+
+      expect(url).toBe(
+        "https://github.com/oven-sh/bun/releases/download/bun-v1.1.0/bun-windows-x64-baseline.zip",
+      );
+      expect(warningSpy).toHaveBeenCalled();
+      expect(warningSpy.mock.calls[0][0]).toContain(
+        "Bun does not provide native arm64 builds for Windows",
+      );
+      warningSpy.mockRestore();
+    });
+
+    it("should use aarch64 for version 1.3.10", async () => {
+      const url = await getDownloadUrl({
+        version: "1.3.10",
+        os: "windows",
+        arch: "arm64",
+      });
+
+      expect(url).toBe(
+        "https://github.com/oven-sh/bun/releases/download/bun-v1.3.10/bun-windows-aarch64.zip",
+      );
+    });
+
+    it("should use aarch64 for canary", async () => {
+      const url = await getDownloadUrl({
+        version: "canary",
+        os: "windows",
+        arch: "arm64",
+      });
+
+      expect(url).toBe(
+        "https://github.com/oven-sh/bun/releases/download/canary/bun-windows-aarch64.zip",
+      );
+    });
+  });
 });
+