login: temporary spawn diagnostics to pinpoint shell-start hang

src/lib.rs

@@ -80,13 +80,27 @@ pub fn spawn_shell<T: Default>(user: &User<T>) -> IoResult<i32> {
     // the CWD fd (including the child's exec) then hang. Point the CWD at the
     // user's home (falling back to `/`), both of which live on the `file`
     // scheme that is always present in the login namespace.
-    if std::env::set_current_dir(&user.home).is_err() {
-        let _ = std::env::set_current_dir("/");
-    }
+    let chdir_ok = std::env::set_current_dir(&user.home).is_ok()
+        || std::env::set_current_dir("/").is_ok();
+    eprintln!(
+        "spawn-diag: chdir_ok={} cwd={:?}; about to spawn {:?}",
+        chdir_ok,
+        std::env::current_dir().ok(),
+        user.shell
+    );
 
     let mut command = user.shell_cmd();
 
-    let mut child = command.spawn()?;
+    let mut child = match command.spawn() {
+        Ok(c) => {
+            eprintln!("spawn-diag: command.spawn() returned Ok (child created)");
+            c
+        }
+        Err(e) => {
+            eprintln!("spawn-diag: command.spawn() FAILED: {} ({:?})", e, e.raw_os_error());
+            return Err(e);
+        }
+    };
     match child.wait()?.code() {
         Some(code) => Ok(code),
         None => Ok(1),