Bun.spawn/spawnSync, Bun.which: inherit live process.env instead of the startup snapshot

src/jsc/JSGlobalObject.rs

@@ -1167,6 +1167,12 @@ impl JSGlobalObject {
         ZigGlobalObject__makeNapiEnvForFFI(self)
     }
 
+    /// The live `process.env` JS object (forces the lazy init). Mutations made
+    /// via `process.env.X = ...` / `delete process.env.X` are visible here.
+    pub fn process_env_object(&self) -> JsResult<JSValue> {
+        crate::from_js_host_call(self, || ZigGlobalObject__processEnvObject(self))
+    }
+
     #[inline]
     pub fn assert_on_js_thread(&self) {
         if cfg!(debug_assertions) {
@@ -1679,6 +1685,7 @@ unsafe extern "C" {
     -> JSValue;
 
     safe fn ZigGlobalObject__makeNapiEnvForFFI(this: &JSGlobalObject) -> *mut c_void;
+    safe fn ZigGlobalObject__processEnvObject(this: &JSGlobalObject) -> JSValue;
 
     safe fn JSC__JSGlobalObject__bunVM(this: &JSGlobalObject) -> *mut c_void;
     safe fn JSC__JSGlobalObject__vm(this: &JSGlobalObject) -> *mut VM;

src/jsc/bindings/ZigGlobalObject.cpp

@@ -1882,6 +1882,15 @@ extern "C" napi_env ZigGlobalObject__makeNapiEnvForFFI(Zig::GlobalObject* global
     return globalObject->makeNapiEnvForFFI();
 }
 
+extern "C" JSC::EncodedJSValue ZigGlobalObject__processEnvObject(Zig::GlobalObject* globalObject)
+{
+    auto& vm = JSC::getVM(globalObject);
+    auto scope = DECLARE_THROW_SCOPE(vm);
+    JSC::JSObject* object = globalObject->processEnvObject();
+    RETURN_IF_EXCEPTION(scope, {});
+    return JSValue::encode(object);
+}
+
 JSC_DEFINE_HOST_FUNCTION(jsFunctionPerformMicrotaskVariadic, (JSGlobalObject * globalObject, CallFrame* callframe))
 {
     auto& vm = JSC::getVM(globalObject);

src/runtime/api/BunObject.rs

@@ -614,9 +614,10 @@ pub(crate) fn which(global_this: &JSGlobalObject, callframe: &CallFrame) -> JsRe
         return Ok(JSValue::NULL);
     }
 
-    // SAFETY: `transpiler.env` / `.fs` are process-lifetime singletons set during VM init.
-    let mut path_str =
-        ZigStringSlice::from_utf8_never_free(vm.env_loader().get(b"PATH").unwrap_or(b""));
+    let mut path_str = match global_this.process_env_object()?.get(global_this, "PATH")? {
+        Some(v) if !v.is_undefined_or_null() => v.to_slice(global_this)?,
+        _ => ZigStringSlice::from_utf8_never_free(b""),
+    };
     let mut cwd_str = ZigStringSlice::from_utf8_never_free(vm.top_level_dir());
 
     if let Some(arg) = arguments.next_eat() {

src/runtime/api/bun/js_bun_spawn_bindings.rs

@@ -365,7 +365,6 @@
     // drops after `spawn_process` returns, freeing all argv/env allocations.
     let mut cstr_storage: Vec<ZBox> = Vec::new();
 
-    let mut override_env = false;
     let mut env_array: Vec<CStrPtr> = Vec::new();
     // SAFETY: `bun_vm()` returns the live VirtualMachine for this thread; it
     // outlives this call frame.
@@ -383,9 +382,9 @@
     let mut lazy = false;
     let mut on_exit_callback = JSValue::ZERO;
     let mut on_disconnect_callback = JSValue::ZERO;
-    // `env_loader()` is the audited safe accessor for the per-VM DotEnv loader
-    // (process-lifetime; centralised non-null deref in `VirtualMachine`).
-    let mut path: &[u8] = jsc_vm.env_loader().get(b"PATH").unwrap_or(b"");
+    // Populated from the explicit `env:` option or, when absent, the live
+    // `process.env` object; both via `append_envp_from_js` below.
+    let mut path: &[u8] = b"";
     let mut argv: Vec<CStrPtr> = Vec::new();
     let cmd_value: JSValue;
     let mut detached = false;
@@ -601,7 +600,6 @@
                     );
                 };
 
-                override_env = true;
                 // If the env object does not include a $PATH, it must disable path lookup for argv[0]
                 let mut new_path: &[u8] = b"";
                 // `JSObject` is an `opaque_ffi!` ZST handle; `opaque_ref` is the
@@ -614,6 +612,20 @@
                     &mut cstr_storage,
                 )?;
                 path = new_path;
+            } else {
+                // No explicit env: inherit the live `process.env` so runtime
+                // mutations (set/delete/PATH edits) reach the child.
+                let process_env = global_this.process_env_object()?;
+                process_env.ensure_still_alive();
+                if let Some(object) = process_env.get_object() {
+                    append_envp_from_js(
+                        global_this,
+                        JSObject::opaque_ref(object),
+                        &mut env_array,
+                        &mut path,
+                        &mut cstr_storage,
+                    )?;
+                }
             }
 
             get_argv(
@@ -894,6 +906,19 @@
                 }
             }
         } else {
+            // No options object means no explicit env: inherit the live
+            // `process.env` so runtime mutations reach the child.
+            let process_env = global_this.process_env_object()?;
+            process_env.ensure_still_alive();
+            if let Some(object) = process_env.get_object() {
+                append_envp_from_js(
+                    global_this,
+                    JSObject::opaque_ref(object),
+                    &mut env_array,
+                    &mut path,
+                    &mut cstr_storage,
+                )?;
+            }
             get_argv(
                 global_this,
                 cmd_value,
@@ -908,31 +933,6 @@
 
     bun_output::scoped_log!(Subprocess, "spawn maxBuffer: {:?}", max_buffer);
 
-    // Owns the `K=V\0` storage when inheriting the parent env; the struct
-    // lives until spawn returns.
-    let mut inherited_env_storage: Option<bun_dotenv::NullDelimitedEnvMap> = None;
-    if !override_env && env_array.is_empty() {
-        // `Transpiler::env_mut()` is the audited safe `&mut Loader` accessor
-        // (per-VM DotEnv loader, valid for VM lifetime; centralised
-        // single-unsafe deref). `.map` is its `&'a mut Map` slot.
-        let envmap = match jsc_vm
-            .transpiler
-            .env_mut()
-            .map
-            .create_null_delimited_env_map()
-        {
-            Ok(m) => m,
-            Err(_) => return Err(global_this.throw_out_of_memory()),
-        };
-        // Note: `as_slice()` *includes* the trailing null, so strip it; the
-        // common tail below re-appends one after the optional NODE_CHANNEL_*
-        // entries.
-        let entries = envmap.as_slice();
-        env_array.extend_from_slice(&entries[..entries.len().saturating_sub(1)]);
-        inherited_env_storage = Some(envmap);
-    }
-    let _ = &inherited_env_storage;
-
     for fd_index in 0..stdio.len() {
         if stdio[fd_index].can_use_memfd() {
             if stdio[fd_index].use_memfd(fd_index as u32) {

test/js/bun/spawn/spawn-env.test.ts

@@ -1,6 +1,69 @@
 import { spawn } from "bun";
-import { test } from "bun:test";
-import { bunExe } from "harness";
+import { describe, expect, test } from "bun:test";
+import { bunEnv, bunExe, isWindows, tempDir } from "harness";
+import { chmodSync } from "node:fs";
+import { join } from "node:path";
+
+// Bun.spawn / Bun.spawnSync with no `env:` option must inherit the *live*
+// process.env, including runtime mutations, not the startup snapshot.
+describe("default env inherits live process.env", () => {
+  const printEnv = isWindows
+    ? `[process.execPath, "-e", "process.stdout.write((process.env.BUN_TEST_SPAWN_ENV_SET ?? '[unset]') + ',' + (process.env.BUN_TEST_SPAWN_ENV_DEL ?? '[unset]'))"]`
+    : `["/bin/sh", "-c", "printf '%s,%s' \\"\${BUN_TEST_SPAWN_ENV_SET-[unset]}\\" \\"\${BUN_TEST_SPAWN_ENV_DEL-[unset]}\\""]`;
+
+  for (const [label, call] of [
+    ["Bun.spawnSync({cmd})", `Bun.spawnSync({ cmd: ${printEnv} }).stdout.toString()`],
+    ["Bun.spawnSync([cmd])", `Bun.spawnSync(${printEnv}).stdout.toString()`],
+    ["Bun.spawn({cmd})", `await (await Bun.spawn({ cmd: ${printEnv} }).stdout).text()`],
+  ] as const) {
+    test.concurrent(label, async () => {
+      await using proc = Bun.spawn({
+        cmd: [
+          bunExe(),
+          "-e",
+          `process.env.BUN_TEST_SPAWN_ENV_SET = "runtime-value";
+           delete process.env.BUN_TEST_SPAWN_ENV_DEL;
+           process.stdout.write(${call});`,
+        ],
+        env: { ...bunEnv, BUN_TEST_SPAWN_ENV_DEL: "startup-value" },
+        stderr: "pipe",
+      });
+      const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+      expect({ stdout, stderr, exitCode }).toEqual({
+        stdout: "runtime-value,[unset]",
+        stderr: "",
+        exitCode: 0,
+      });
+    });
+  }
+
+  test.concurrent.skipIf(isWindows)("PATH mutation is used for argv0 lookup and Bun.which", async () => {
+    using dir = tempDir("spawn-env-path", {
+      "bun_test_spawn_env_tool": "#!/bin/sh\nprintf found-the-tool\n",
+    });
+    const toolDir = String(dir);
+    chmodSync(join(toolDir, "bun_test_spawn_env_tool"), 0o755);
+
+    await using proc = Bun.spawn({
+      cmd: [
+        bunExe(),
+        "-e",
+        `process.env.PATH = ${JSON.stringify(toolDir)} + ":" + process.env.PATH;
+         console.log(Bun.which("bun_test_spawn_env_tool") !== null);
+         console.log(Bun.spawnSync({ cmd: ["bun_test_spawn_env_tool"] }).stdout.toString());
+         console.log(Bun.spawnSync(["bun_test_spawn_env_tool"]).stdout.toString());`,
+      ],
+      env: bunEnv,
+      stderr: "pipe",
+    });
+    const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+    expect({ stdout, stderr, exitCode }).toEqual({
+      stdout: "true\nfound-the-tool\nfound-the-tool\n",
+      stderr: "",
+      exitCode: 0,
+    });
+  });
+});
 
 test("spawn env", async () => {
   const env = {};