From ddbf1ffecbb149442bf73e6c2db8671090bc6771 Mon Sep 17 00:00:00 2001
From: can1357 <me@can.ac>
Date: Thu, 13 Aug 2026 07:18:17 +0200
Subject: [PATCH] feat: fell back to pinned bunx package for bun2nix generation

- Added a fallback to the pinned bunx package when generating Nix bun dependencies without an active Nix environment.
- Updated generator resolution logic and corresponding tests.
---
 README.md                   |  2 +-
 scripts/gen-nix-bun.test.ts | 11 ++++++-----
 scripts/gen-nix-bun.ts      | 20 +++++++++++++++-----
 3 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/README.md b/README.md
index 2f4b8ac4e..1ffb9a58b 100644
--- a/README.md
+++ b/README.md
@@ -620,7 +620,7 @@ Build and smoke-test the distributable Nix package with `nix build .#omp`. Wayla
 bun run gen:nix
 ```
 
-The command uses `bun2nix` from `nix develop` when available, otherwise enters the development shell through Nix. Do not edit `nix/bun.nix` manually.
+The command uses `bun2nix` from `nix develop` when available, otherwise enters the development shell through Nix, then falls back to the pinned `bunx bun2nix@2.1.2`. Do not edit `nix/bun.nix` manually.
 
 For a non-interactive smoke check:
 
diff --git a/scripts/gen-nix-bun.test.ts b/scripts/gen-nix-bun.test.ts
index 2cf1c36a9..359a5d0bd 100644
--- a/scripts/gen-nix-bun.test.ts
+++ b/scripts/gen-nix-bun.test.ts
@@ -1,5 +1,5 @@
 import { describe, expect, test } from "bun:test";
-import { resolveNixBunDepsGenerator } from "./gen-nix-bun";
+import { BUN2NIX_NPM_SPEC, resolveNixBunDepsGenerator } from "./gen-nix-bun";
 
 describe("resolveNixBunDepsGenerator", () => {
 	test("prefers bun2nix from the active development shell", () => {
@@ -17,9 +17,10 @@ describe("resolveNixBunDepsGenerator", () => {
 		expect(generator).toEqual({ kind: "nix", executable: "/usr/bin/nix" });
 	});
 
-	test("fails before a release mutates files when no generator is available", () => {
-		expect(() => resolveNixBunDepsGenerator(() => null)).toThrow(
-			"Generating nix/bun.nix requires bun2nix from `nix develop`, or Nix to enter that shell.",
-		);
+	test("falls back to the pinned portable bunx package", () => {
+		expect(resolveNixBunDepsGenerator(() => null)).toEqual({
+			kind: "bunx",
+			package: BUN2NIX_NPM_SPEC,
+		});
 	});
 });
diff --git a/scripts/gen-nix-bun.ts b/scripts/gen-nix-bun.ts
index 32e68eacd..3760ef924 100755
--- a/scripts/gen-nix-bun.ts
+++ b/scripts/gen-nix-bun.ts
@@ -6,10 +6,16 @@ import { $which } from "../packages/utils/src/which";
 
 const repoRoot = path.join(import.meta.dir, "..");
 
+/** Pinned npm package matching flake.lock's bun2nix revision (`0f2a1f…`). */
+export const BUN2NIX_NPM_SPEC = "bun2nix@2.1.2";
+
 type FindExecutable = (command: string) => string | null;
 
 /** The executable path and invocation mode for the pinned Bun dependency generator. */
-export type NixBunDepsGenerator = { kind: "bun2nix"; executable: string } | { kind: "nix"; executable: string };
+export type NixBunDepsGenerator =
+	| { kind: "bun2nix"; executable: string }
+	| { kind: "nix"; executable: string }
+	| { kind: "bunx"; package: typeof BUN2NIX_NPM_SPEC };
 
 /** Resolve the generator needed by releases before they mutate repository state. */
 export function resolveNixBunDepsGenerator(findExecutable: FindExecutable = $which): NixBunDepsGenerator {
@@ -19,7 +25,7 @@ export function resolveNixBunDepsGenerator(findExecutable: FindExecutable = $whi
 	const nix = findExecutable("nix");
 	if (nix) return { kind: "nix", executable: nix };
 
-	throw new Error("Generating nix/bun.nix requires bun2nix from `nix develop`, or Nix to enter that shell.");
+	return { kind: "bunx", package: BUN2NIX_NPM_SPEC };
 }
 
 /** Regenerate the checked-in Bun dependency expression with the pinned bun2nix input. */
@@ -28,10 +34,14 @@ export async function generateNixBunDeps(generator: NixBunDepsGenerator = resolv
 		await $`${generator.executable} -l bun.lock -c ../ -o nix/bun.nix`.cwd(repoRoot);
 		return;
 	}
+	if (generator.kind === "nix") {
+		await $`${generator.executable} --extra-experimental-features ${"nix-command flakes"} --accept-flake-config develop --command bun2nix -l bun.lock -c ../ -o nix/bun.nix`.cwd(
+			repoRoot,
+		);
+		return;
+	}
 
-	await $`${generator.executable} --extra-experimental-features ${"nix-command flakes"} --accept-flake-config develop --command bun2nix -l bun.lock -c ../ -o nix/bun.nix`.cwd(
-		repoRoot,
-	);
+	await $`bunx ${generator.package} -l bun.lock -c ../ -o nix/bun.nix`.cwd(repoRoot);
 }
 
 if (import.meta.main) await generateNixBunDeps();