Update Ferric to handle tier 3 targets with build-std instructions

Co-authored-by: kraenhansen <1243959+kraenhansen@users.noreply.github.com>

Author: Copilot

packages/ferric/src/targets.ts

@@ -49,25 +49,68 @@ export type AppleTargetName = (typeof APPLE_TARGETS)[number];
 export const ALL_TARGETS = [...ANDROID_TARGETS, ...APPLE_TARGETS] as const;
 export type TargetName = (typeof ALL_TARGETS)[number];
 
+/**
+ * Tier 3 Rust targets that are not available via `rustup target add` 
+ * and require building the standard library from source using `-Zbuild-std`.
+ * 
+ * @see https://doc.rust-lang.org/rustc/platform-support.html
+ * @see https://doc.rust-lang.org/cargo/reference/unstable.html#build-std
+ */
+export const TIER_3_TARGETS: readonly TargetName[] = [
+  "aarch64-apple-visionos",
+  "aarch64-apple-visionos-sim",
+] as const;
+
+/**
+ * Check if a target is a tier 3 target that requires build-std
+ */
+export function isTier3Target(target: TargetName): boolean {
+  return TIER_3_TARGETS.includes(target);
+}
+
 /**
  * Ensure the targets are installed into the Rust toolchain
  * We do this up-front because the error message and fix is very unclear from the failure when missing.
  */
 export function ensureInstalledTargets(expectedTargets: Set<TargetName>) {
   const installedTargets = getInstalledTargets();
-  const missingTargets = new Set([
-    ...[...expectedTargets].filter((target) => !installedTargets.has(target)),
+  const missingStandardTargets = new Set([
+    ...[...expectedTargets].filter(
+      (target) => !installedTargets.has(target) && !isTier3Target(target),
+    ),
   ]);
-  if (missingTargets.size > 0) {
-    // TODO: Ask the user if they want to run this
+  const tier3Targets = new Set([
+    ...[...expectedTargets].filter((target) => isTier3Target(target)),
+  ]);
+
+  // Handle standard targets that can be installed via rustup
+  if (missingStandardTargets.size > 0) {
     throw new UsageError(
       `You're missing ${
-        missingTargets.size
+        missingStandardTargets.size
       } targets - to fix this, run:\n\n${chalk.italic(
-        `rustup target add ${[...missingTargets].join(" ")}`,
+        `rustup target add ${[...missingStandardTargets].join(" ")}`,
       )}`,
     );
   }
+
+  // Handle tier 3 targets that require build-std setup
+  if (tier3Targets.size > 0) {
+    throw new UsageError(
+      `You're using tier 3 targets (${[...tier3Targets].join(", ")}) that require building the standard library from source.\n\n` +
+        `To set up support for these targets:\n\n` +
+        `1. Install nightly Rust with the rust-src component:\n` +
+        `   ${chalk.italic("rustup toolchain install nightly --component rust-src")}\n\n` +
+        `2. Configure Cargo to use build-std by creating a .cargo/config.toml file:\n` +
+        `   ${chalk.italic("[unstable]")}\n` +
+        `   ${chalk.italic('build-std = ["std", "panic_abort"]')}\n\n` +
+        `3. Set your default toolchain to nightly:\n` +
+        `   ${chalk.italic("rustup default nightly")}\n\n` +
+        `For more information, see:\n` +
+        `- Rust Platform Support: ${chalk.italic("https://doc.rust-lang.org/rustc/platform-support.html")}\n` +
+        `- Cargo build-std: ${chalk.italic("https://doc.rust-lang.org/cargo/reference/unstable.html#build-std")}`,
+    );
+  }
 }
 
 export function isAndroidTarget(