shell(exit): propagate last status on no-arg, fix negative/invalid arg codes

src/runtime/shell/builtin/exit.rs

@@ -19,28 +19,30 @@
     pub(crate) fn start(interp: &Interpreter, cmd: NodeId) -> Yield {
         let bltn = Builtin::of(interp, cmd);
         let code: crate::shell::ExitCode = match bltn.args_slice().len() {
-            0 => 0,
+            // POSIX: "the exit status shall be that of the last command
+            // executed, or zero if no command was executed."
+            0 => interp.as_cmd(cmd).base.shell().last_exit_code,
             1 => {
                 let s = bltn.arg_bytes(0);
                 match parse_exit_code(s) {
                     Some(c) => c,
                     None => {
-                        return Self::fail(interp, cmd, b"exit: numeric argument required\n");
+                        return Self::fail(interp, cmd, b"exit: numeric argument required\n", 2);
                     }
                 }
             }
             _ => {
-                return Self::fail(interp, cmd, b"exit: too many arguments\n");
+                return Self::fail(interp, cmd, b"exit: too many arguments\n", 1);
             }
         };
         // Intentional divergence from bash: this completes only the current
         // Cmd rather than unwinding the whole script.
         Builtin::done(interp, cmd, code)
     }
 
-    fn fail(interp: &Interpreter, cmd: NodeId, msg: &[u8]) -> Yield {
+    fn fail(interp: &Interpreter, cmd: NodeId, msg: &[u8], code: crate::shell::ExitCode) -> Yield {
         Self::state_mut(interp, cmd).state = State::WaitingIo;
-        Builtin::write_failing_error(interp, cmd, msg, 1)
+        Builtin::write_failing_error(interp, cmd, msg, code)
     }
 
     pub(crate) fn on_io_writer_chunk(
@@ -50,11 +52,13 @@
         _err: Option<bun_sys::SystemError>,
     ) -> Yield {
         Self::state_mut(interp, cmd).state = State::Done;
-        Builtin::done(interp, cmd, 1)
+        let code = Builtin::of(interp, cmd).exit_code.unwrap_or(1);
+        Builtin::done(interp, cmd, code)
     }
 }
 
 fn parse_exit_code(s: &[u8]) -> Option<crate::shell::ExitCode> {
-    // %256 is bash semantics — keep wrapper fn.
-    bun_core::fmt::parse_decimal::<u64>(s).map(|n| (n % 256) as crate::shell::ExitCode)
+    // bash semantics: parse as a signed integer and keep the low 8 bits
+    // (`exit -1` → 255, `exit 300` → 44, `exit -300` → 212).
+    bun_core::fmt::parse_decimal::<i64>(s).map(|n| crate::shell::ExitCode::from(n as u8))
 }

src/runtime/shell/interpreter.rs

@@ -588,6 +588,7 @@ impl Interpreter {
                 __cwd: cwd_arr,
                 cwd_fd,
                 async_pids: SmolList::default(),
+                last_exit_code: 0,
             }),
             root_io: JsCell::new(IO {
                 stdin: crate::shell::io::InKind::Fd(stdin_reader),
@@ -1793,6 +1794,10 @@ pub struct ShellExecEnv {
     pub __cwd: Vec<u8>,
     pub cwd_fd: Fd,
     pub async_pids: SmolList<PidT, 4>,
+    /// Exit status of the most recently completed command in this execution
+    /// context (POSIX `$?`). Read by the `exit` builtin when called with no
+    /// argument. Updated by `Stmt::child_done` and `Binary::child_done`.
+    pub last_exit_code: ExitCode,
 }
 
 pub enum Bufio {
@@ -1958,6 +1963,9 @@ impl ShellExecEnv {
             __cwd: self.__cwd.clone(),
             cwd_fd: dupedfd,
             async_pids: SmolList::default(),
+            // Inherited so a subshell/command-substitution sees the parent's
+            // value; writes never propagate back (POSIX behavior).
+            last_exit_code: self.last_exit_code,
         });
         Ok(bun_core::heap::into_raw(duped))
     }

src/runtime/shell/states/Binary.rs

@@ -80,6 +80,7 @@ impl Binary {
         {
             let me = interp.as_binary_mut(this);
             me.currently_executing = None;
+            me.base.shell_mut().last_exit_code = exit_code;
             if me.left.is_none() {
                 me.left = Some(exit_code);
             } else {

src/runtime/shell/states/Stmt.rs

@@ -78,6 +78,7 @@ impl Stmt {
         {
             let me = interp.as_stmt_mut(this);
             me.last_exit_code = Some(exit_code);
+            me.base.shell_mut().last_exit_code = exit_code;
             me.idx += 1;
             me.currently_executing = None;
         }

test/js/bun/shell/commands/exit.test.ts

@@ -1,6 +1,7 @@
 import { describe } from "bun:test";
-import { createTestBuilder } from "../test_builder";
+import { bunExe, createTestBuilder } from "../test_builder";
 const TestBuilder = createTestBuilder(import.meta.path);
+const BUN = bunExe();
 
 describe("exit", async () => {
   TestBuilder.command`exit`.exitCode(0).runAsTest("works");
@@ -16,5 +17,22 @@ describe("exit", async () => {
   TestBuilder.command`exit 62757836`.exitCode(204).runAsTest("exit code wraps u8");
 
   // prettier-ignore
-  TestBuilder.command`exit abc`.exitCode(1).stderr("exit: numeric argument required\n").runAsTest("numeric argument required");
+  TestBuilder.command`exit abc`.exitCode(2).stderr("exit: numeric argument required\n").runAsTest("numeric argument required");
+
+  describe("no argument propagates the last command's status", async () => {
+    TestBuilder.command`false; exit`.exitCode(1).runAsTest("false; exit");
+    TestBuilder.command`true; exit`.exitCode(0).runAsTest("true; exit");
+    TestBuilder.command`false || exit`.exitCode(1).runAsTest("false || exit");
+    TestBuilder.command`true | false; exit`.exitCode(1).runAsTest("pipeline; exit");
+    TestBuilder.command`${{ raw: "(exit 42); exit" }}`.exitCode(42).runAsTest("subshell; exit");
+    TestBuilder.command`${{ raw: "false; (exit)" }}`.exitCode(1).runAsTest("inherited by subshell");
+    TestBuilder.command`${BUN} -e ${"process.exit(7)"}; exit`.exitCode(7).runAsTest("subprocess; exit");
+    TestBuilder.command`${{ raw: "false\nexit" }}`.exitCode(1).runAsTest("across statements");
+    TestBuilder.command`false; exit 3`.exitCode(3).runAsTest("explicit arg wins");
+  });
+
+  describe("negative argument wraps mod 256", async () => {
+    TestBuilder.command`exit -1`.exitCode(255).runAsTest("-1");
+    TestBuilder.command`exit -300`.exitCode(212).runAsTest("-300");
+  });
 });

test/js/bun/shell/exec.test.ts

@@ -55,7 +55,7 @@ describe("bun exec", () => {
       ["rm",     1, "rm: illegal option -- -\n", ""],
       ["mv",     1, "mv: illegal option -- -\n", ""],
       ["ls",     1, "ls: illegal option -- -\n", ""],
-      ["exit",   1, "exit: numeric argument required\n", ""],
+      ["exit",   2, "exit: numeric argument required\n", ""],
       ["true",   0, "", ""],
       ["false",  1, "", ""],
       // ["yes",    1, "", ""],