fix: Flush stdout on shutdown matching CPython behavior (#7503)

* fix: flush stdout on interpreter shutdown matching CPython behavior

When stdout flush fails during shutdown, report the error via
run_unraisable and exit with code 120 (matching CPython's
Py_FinalizeEx). Skip flushing already-closed or None streams.
Stderr flush errors remain silently ignored per CPython behavior.

Fixes #5521

Signed-off-by: majiayu000 <1835304752@qq.com>

* refactor: replace magic number 120 with named constant EXITCODE_FLUSH_FAILURE

Address review feedback on PR #7503: improve readability by extracting
the CPython-compat exit code into a named constant.

Signed-off-by: majiayu000 <1835304752@qq.com>

---------

Signed-off-by: majiayu000 <1835304752@qq.com>

Lib/test/test_cmd_line.py

@@ -475,8 +475,6 @@ class CmdLineTest(unittest.TestCase):
         self.assertRegex(err.decode('ascii', 'ignore'), 'SyntaxError')
         self.assertEqual(b'', out)
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     def test_stdout_flush_at_shutdown(self):
         # Issue #5319: if stdout.flush() fails at shutdown, an error should
         # be printed out.

crates/vm/src/vm/interpreter.rs

@@ -10,6 +10,10 @@ use core::sync::atomic::Ordering;
 
 type InitFunc = Box<dyn FnOnce(&mut VirtualMachine)>;
 
+/// Exit code used when stdout/stderr flush fails during interpreter shutdown.
+/// Matches CPython's behavior (see cpython/Python/pylifecycle.c).
+const EXITCODE_FLUSH_FAILURE: u32 = 120;
+
 /// Configuration builder for constructing an Interpreter.
 ///
 /// This is the preferred way to configure and create an interpreter with custom modules.
@@ -401,7 +405,7 @@ impl Interpreter {
     /// Note that calling `finalize` is not necessary by purpose though.
     pub fn finalize(self, exc: Option<PyBaseExceptionRef>) -> u32 {
         self.enter(|vm| {
-            vm.flush_std();
+            let mut flush_status = vm.flush_std();
 
             // See if any exception leaked out:
             let exit_code = if let Some(exc) = exc {
@@ -439,9 +443,16 @@ impl Interpreter {
             // (while builtins is still available for __del__), then clear module dicts.
             vm.finalize_modules();
 
-            vm.flush_std();
+            if vm.flush_std() < 0 && flush_status == 0 {
+                flush_status = -1;
+            }
 
-            exit_code
+            // Match CPython: if exit_code is 0 and stdout flush failed, exit 120
+            if exit_code == 0 && flush_status < 0 {
+                EXITCODE_FLUSH_FAILURE
+            } else {
+                exit_code
+            }
         })
     }
 }

crates/vm/src/vm/vm_object.rs

@@ -52,14 +52,31 @@ impl VirtualMachine {
         }
     }
 
-    pub(crate) fn flush_std(&self) {
+    /// Returns true if the file object's `closed` attribute is truthy.
+    fn file_is_closed(&self, file: &PyObject) -> bool {
+        file.get_attr("closed", self)
+            .ok()
+            .is_some_and(|v| v.try_to_bool(self).unwrap_or(false))
+    }
+
+    pub(crate) fn flush_std(&self) -> i32 {
         let vm = self;
-        if let Ok(stdout) = sys::get_stdout(vm) {
-            let _ = vm.call_method(&stdout, identifier!(vm, flush).as_str(), ());
+        let mut status = 0;
+        if let Ok(stdout) = sys::get_stdout(vm)
+            && !vm.is_none(&stdout)
+            && !vm.file_is_closed(&stdout)
+            && let Err(e) = vm.call_method(&stdout, identifier!(vm, flush).as_str(), ())
+        {
+            vm.run_unraisable(e, None, stdout);
+            status = -1;
         }
-        if let Ok(stderr) = sys::get_stderr(vm) {
+        if let Ok(stderr) = sys::get_stderr(vm)
+            && !vm.is_none(&stderr)
+            && !vm.file_is_closed(&stderr)
+        {
             let _ = vm.call_method(&stderr, identifier!(vm, flush).as_str(), ());
         }
+        status
     }
 
     #[track_caller]