Honor live $HOME mutations in os.homedir()

src/js/node/os.ts

@@ -24,6 +24,22 @@ var tmpdir = function () {
   return tmpdir();
 };
 
+// Node reads $HOME on every os.homedir() call, but POSIX process.env writes
+// never reach the C environ, so the live check must happen here in JS. The
+// native binding is the passwd fallback, which userInfo() also calls directly.
+function homedirFactory(bindingHomedir) {
+  if (process.platform === "win32") {
+    // uv_os_homedir already reads USERPROFILE live.
+    return bindingHomedir;
+  }
+  return function homedir() {
+    // Like libuv: HOME="" is returned verbatim; only absent HOME falls through.
+    const home = Bun.env["HOME"];
+    if (home !== undefined) return home;
+    return bindingHomedir();
+  };
+}
+
 // os.cpus() is super expensive
 // Specifically: getting the CPU speed on Linux is very expensive
 // Some packages like FastGlob only bother to read the length of the array
@@ -103,7 +119,7 @@ function bound(binding) {
     },
     freemem: binding.freemem,
     getPriority: binding.getPriority,
-    homedir: binding.homedir,
+    homedir: homedirFactory(binding.homedir),
     hostname: binding.hostname,
     loadavg: binding.loadavg,
     networkInterfaces: binding.networkInterfaces,

src/runtime/node/node_os.rs

@@ -712,7 +712,9 @@ mod _impl {
     }
 
     pub(crate) fn homedir(global: &JSGlobalObject) -> JsResult<BunString> {
-        // In Node.js, this is a wrapper around uv_os_homedir.
+        // In Node.js, this is a wrapper around uv_os_homedir. The live HOME
+        // check lives in `src/js/node/os.ts`; this is the passwd fallback,
+        // which `userInfo()` also calls directly.
         #[cfg(windows)]
         {
             let mut out = PathBuffer::uninit();
@@ -727,14 +729,6 @@ mod _impl {
         }
         #[cfg(not(windows))]
         {
-            // The posix implementation of uv_os_homedir first checks the HOME
-            // environment variable, then falls back to reading the passwd entry.
-            if let Some(home) = env_var::HOME.get() {
-                if !home.is_empty() {
-                    return Ok(BunString::init(home));
-                }
-            }
-
             // From libuv:
             // > Calling sysconf(_SC_GETPW_R_SIZE_MAX) would get the suggested size, but it
             // > is frequently 1024 or 4096, so we can just use that directly. The pwent
@@ -751,6 +745,7 @@ mod _impl {
             let mut result: *mut libc::passwd = core::ptr::null_mut();
 
             let ret: c_int = loop {
+                // Effective uid: libuv's uv_os_get_passwd keys on geteuid().
                 // SAFETY: valid buffers and out-pointer
                 let ret = unsafe {
                     libc::getpwuid_r(

test/js/node/os/os-homedir-env.test.mjs

@@ -0,0 +1,88 @@
+// https://github.com/oven-sh/bun/issues/29244
+// os.homedir() must reflect live process.env.HOME (HOME="" → ""; only absent
+// HOME falls through to passwd); os.userInfo().homedir must NOT honor HOME.
+// Uses node:test so the same file runs under Node.js to verify parity:
+//   node test/js/node/os/os-homedir-env.test.mjs
+// Each check spawns process.execPath so HOME mutations can't leak out.
+import assert from "node:assert";
+import { spawnSync } from "node:child_process";
+import { test } from "node:test";
+
+const isWindows = process.platform === "win32";
+
+function runWithEnv(source, envOverride = {}) {
+  const env = { ...process.env };
+  for (const [key, value] of Object.entries(envOverride)) {
+    if (value === undefined) delete env[key];
+    else env[key] = value;
+  }
+  const { stdout, stderr, status } = spawnSync(process.execPath, ["-e", source], {
+    env,
+    encoding: "utf8",
+  });
+  assert.strictEqual(status, 0, stderr);
+  return JSON.parse(stdout);
+}
+
+test("homedir() reflects HOME mutation after require", { skip: isWindows }, () => {
+  const result = runWithEnv(`
+    const os = require("node:os");
+    const before = os.homedir();
+    process.env.HOME = "/tmp/test-home-29244";
+    console.log(JSON.stringify({ before, after: os.homedir() }));
+  `);
+  assert.strictEqual(result.after, "/tmp/test-home-29244");
+  assert.notStrictEqual(result.before, "/tmp/test-home-29244");
+  assert.ok(result.before.length > 0);
+});
+
+test("homedir() reflects HOME mutation before require", { skip: isWindows }, () => {
+  const result = runWithEnv(`
+    process.env.HOME = "/tmp/before-require-29244";
+    console.log(JSON.stringify(require("node:os").homedir()));
+  `);
+  assert.strictEqual(result, "/tmp/before-require-29244");
+});
+
+test("homedir() honors HOME from parent env", { skip: isWindows }, () => {
+  const result = runWithEnv(`console.log(JSON.stringify(require("node:os").homedir()));`, {
+    HOME: "/tmp/inherited-29244",
+  });
+  assert.strictEqual(result, "/tmp/inherited-29244");
+});
+
+test("homedir() returns '' when HOME is set to empty string", { skip: isWindows }, () => {
+  // uv_os_homedir returns getenv("HOME") verbatim whenever it is non-NULL,
+  // including ""; only an absent HOME falls through to the passwd entry.
+  const result = runWithEnv(`
+    process.env.HOME = "";
+    console.log(JSON.stringify(require("node:os").homedir()));
+  `);
+  assert.strictEqual(result, "");
+});
+
+test("homedir() falls back to passwd when HOME is deleted", { skip: isWindows }, () => {
+  // Seed a sentinel so a silently-ignored delete is detectable, and
+  // cross-check against userInfo().homedir (the passwd entry).
+  const sentinel = "/tmp/sentinel-deleted-29244";
+  const result = runWithEnv(
+    `
+      delete process.env.HOME;
+      const os = require("node:os");
+      console.log(JSON.stringify({ h: os.homedir(), passwd: os.userInfo().homedir }));
+    `,
+    { HOME: sentinel },
+  );
+  assert.notStrictEqual(result.h, sentinel);
+  assert.strictEqual(result.h, result.passwd);
+  assert.ok(result.h.startsWith("/"));
+});
+
+test("userInfo().homedir ignores HOME mutation", { skip: isWindows }, () => {
+  const result = runWithEnv(`
+    process.env.HOME = "/tmp/should-not-appear-29244";
+    console.log(JSON.stringify(require("node:os").userInfo().homedir));
+  `);
+  assert.notStrictEqual(result, "/tmp/should-not-appear-29244");
+  assert.ok(result.length > 0);
+});