fix: locate running binary via execPath instead of argv[0] (#16)

In a Bun single-file executable, process.argv[0] is the literal "bun",
not the executable path. `rb update` therefore failed with "cannot
locate current binary at bun", and the macOS quarantine check in
`rb doctor` misresolved the same way.

Resolve the path via process.execPath (the compiled binary) through a
shared getBinPath() helper used by both update and doctor. Verified
end-to-end on a windows-x64 standalone build: update now locates itself,
downloads, checksum-verifies, and swaps successfully.

Author: a-essawy

src/__tests__/bin-path.test.ts

@@ -0,0 +1,18 @@
+import { describe, it, expect } from "bun:test";
+import { getBinPath } from "../lib/bin-path.js";
+
+describe("getBinPath", () => {
+  it("returns process.execPath (the real executable), not argv[0]", () => {
+    // In a compiled Bun binary, process.argv[0] is the literal "bun" while
+    // process.execPath is the actual rb.exe path. We must use execPath.
+    expect(getBinPath()).toBe(process.execPath);
+  });
+
+  it("never returns the bare runtime name 'bun'", () => {
+    expect(getBinPath()).not.toBe("bun");
+  });
+
+  it("returns a non-empty path", () => {
+    expect(getBinPath().length).toBeGreaterThan(0);
+  });
+});

src/commands/doctor.ts

@@ -9,6 +9,7 @@ import { spawnSync } from "node:child_process";
 import { defineCommand } from "citty";
 import { VERSION } from "../generated/version.js";
 import { getConfigDir } from "../lib/auth.js";
+import { getBinPath } from "../lib/bin-path.js";
 
 // Compile-time defines from `bun build --compile --define`. In dev mode they're undefined.
 declare const IS_STANDALONE: boolean | undefined;
@@ -263,7 +264,7 @@ async function checkGhRateLimit(): Promise<Check> {
 }
 
 export async function runDoctor(opts: { json?: boolean; fix?: boolean } = {}): Promise<void> {
-  const binPath = process.argv[0] ?? "";
+  const binPath = getBinPath();
   const checks: Check[] = [
     await checkVersion(),
     checkInstallMethod(),

src/commands/update.ts

@@ -9,6 +9,7 @@ import { spawnSync } from "node:child_process";
 import { createHash } from "node:crypto";
 import { defineCommand } from "citty";
 import { VERSION } from "../generated/version.js";
+import { getBinPath } from "../lib/bin-path.js";
 
 // Compile-time defines from `bun build --compile --define`. In dev mode they're undefined.
 declare const IS_STANDALONE: boolean | undefined;
@@ -102,11 +103,6 @@ function sha256(data: Uint8Array): string {
   return createHash("sha256").update(data).digest("hex");
 }
 
-function getBinPath(): string {
-  // argv[0] in a compiled bun binary is the binary path
-  return process.argv[0] ?? "";
-}
-
 function isSameVersion(latest: string): boolean {
   return parseVersion(latest) === VERSION;
 }

src/lib/bin-path.ts

@@ -0,0 +1,14 @@
+/**
+ * Absolute path to the currently-running `rb` executable.
+ *
+ * In a Bun single-file executable (`bun build --compile`), `process.execPath`
+ * is the compiled binary itself (the `rb` / `rb.exe`). `process.argv[0]` is the
+ * embedded runtime name — the literal string `"bun"` — and must NOT be used:
+ * doing so broke `rb update` ("cannot locate current binary at bun") and the
+ * macOS quarantine check, which both need the real on-disk path.
+ *
+ * Verified on a compiled binary: execPath → "<dir>/rb.exe", argv[0] → "bun".
+ */
+export function getBinPath(): string {
+  return process.execPath || "";
+}