use posix error messages under 127

Author: youknowone

crates/vm/src/stdlib/io.rs

@@ -20,25 +20,33 @@ pub use _io::{OpenArgs, io_open as open};
 impl ToPyException for std::io::Error {
     fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
         let errno = self.posix_errno();
-        let msg = self.to_string();
-        #[allow(clippy::let_and_return)]
-        let exc = vm.new_errno_error(errno, msg);
 
         #[cfg(windows)]
-        {
-            use crate::object::AsObject;
-            let winerror = if let Some(winerror) = self.raw_os_error() {
-                vm.new_pyobj(winerror)
-            } else {
-                vm.ctx.none()
-            };
-
-            // FIXME: manual setup winerror due to lack of OSError.__init__ support
-            exc.as_object()
-                .set_attr("winerror", vm.new_pyobj(winerror), vm)
-                .unwrap();
-        }
-        exc
+        let msg = {
+            // On Windows, use C runtime's strerror for POSIX errno values
+            // For Windows-specific error codes, fall back to FormatMessage
+
+            // UCRT's strerror returns "Unknown error" for invalid errno values
+            // Use strerror for POSIX errno range, fall back to FormatMessage otherwise
+            // Windows UCRT defines errno values 1-42 plus some more up to ~127
+            const MAX_POSIX_ERRNO: i32 = 127;
+            if errno > 0 && errno <= MAX_POSIX_ERRNO {
+                // Safety: strerror returns a valid C string
+                let ptr = unsafe { libc::strerror(errno) };
+                if !ptr.is_null() {
+                    let msg = unsafe { std::ffi::CStr::from_ptr(ptr) }.to_string_lossy();
+                    // Check if strerror returned a valid message (not "Unknown error")
+                    if !msg.starts_with("Unknown error") {
+                        return vm.new_errno_error(errno, msg.into_owned());
+                    }
+                }
+            }
+            // For Windows-specific errors or unknown errno, use FormatMessage
+            self.to_string()
+        };
+        #[cfg(not(windows))]
+        let msg = self.to_string();
+        vm.new_errno_error(errno, msg)
     }
 }