fuchsia: Don't fail to spawn if no stdin exists

src/libstd/sys/unix/process/process_fuchsia.rs

@@ -52,30 +52,45 @@ impl Command {
             None => ptr::null(),
         };
 
-        let make_action = |local_io: &ChildStdio, target_fd| if let Some(local_fd) = local_io.fd() {
-            fdio_spawn_action_t {
-                action: FDIO_SPAWN_ACTION_TRANSFER_FD,
-                local_fd,
-                target_fd,
-                ..Default::default()
-            }
-        } else {
-            if let ChildStdio::Null = local_io {
-                // acts as no-op
-                return Default::default();
-            }
-            fdio_spawn_action_t {
-                action: FDIO_SPAWN_ACTION_CLONE_FD,
-                local_fd: target_fd,
-                target_fd,
-                ..Default::default()
+        let make_action = |local_io: &ChildStdio, target_fd| -> io::Result<fdio_spawn_action_t> {
+            if let Some(local_fd) = local_io.fd() {
+                Ok(fdio_spawn_action_t {
+                    action: FDIO_SPAWN_ACTION_TRANSFER_FD,
+                    local_fd,
+                    target_fd,
+                    ..Default::default()
+                })
+            } else {
+                if let ChildStdio::Null = local_io {
+                    // acts as no-op
+                    return Ok(Default::default());
+                }
+
+                let mut handle = ZX_HANDLE_INVALID;
+                let status = fdio_fd_clone(target_fd, &mut handle);
+                if status == ERR_INVALID_ARGS || status == ERR_NOT_SUPPORTED {
+                    // This descriptor is closed; skip it rather than generating an
+                    // error.
+                    return Ok(Default::default());
+                }
+                zx_cvt(status)?;
+
+                let mut cloned_fd = 0;
+                zx_cvt(fdio_fd_create(handle, &mut cloned_fd))?;
+
+                Ok(fdio_spawn_action_t {
+                    action: FDIO_SPAWN_ACTION_TRANSFER_FD,
+                    local_fd: cloned_fd as i32,
+                    target_fd,
+                    ..Default::default()
+                })
             }
         };
 
         // Clone stdin, stdout, and stderr
-        let action1 = make_action(&stdio.stdin, 0);
-        let action2 = make_action(&stdio.stdout, 1);
-        let action3 = make_action(&stdio.stderr, 2);
+        let action1 = make_action(&stdio.stdin, 0)?;
+        let action2 = make_action(&stdio.stdout, 1)?;
+        let action3 = make_action(&stdio.stderr, 2)?;
         let actions = [action1, action2, action3];
 
         // We don't want FileDesc::drop to be called on any stdio. fdio_spawn_etc
@@ -88,7 +103,7 @@ impl Command {
 
         let mut process_handle: zx_handle_t = 0;
         zx_cvt(fdio_spawn_etc(
-            0,
+            ZX_HANDLE_INVALID,
             FDIO_SPAWN_CLONE_JOB | FDIO_SPAWN_CLONE_LDSVC | FDIO_SPAWN_CLONE_NAMESPACE,
             self.get_argv()[0], self.get_argv().as_ptr(), envp,
             actions.len() as size_t, actions.as_ptr(),

src/libstd/sys/unix/process/zircon.rs

@@ -2,8 +2,9 @@
 
 use crate::convert::TryInto;
 use crate::io;
-use crate::os::raw::c_char;
 use crate::i64;
+use crate::mem::MaybeUninit;
+use crate::os::raw::c_char;
 
 use libc::{c_int, c_void, size_t};
 
@@ -122,6 +123,9 @@ extern {
                           argv: *const *const c_char, envp: *const *const c_char,
                           action_count: size_t, actions: *const fdio_spawn_action_t,
                           process: *mut zx_handle_t, err_msg: *mut c_char) -> zx_status_t;
+
+    pub fn fdio_fd_clone(fd: c_int, out_handle: *mut zx_handle_t) -> zx_status_t;
+    pub fn fdio_fd_create(handle: zx_handle_t, fd: *mut c_int) -> zx_status_t;
 }
 
 // fdio_spawn_etc flags