Restore the behavior of remembering the CWD fd in the parser

This will be important for concurrent execution, because different parsers will
have different working directories.

fish-rust/src/builtins/cd.rs

@@ -90,7 +90,7 @@ pub fn cd(parser: &mut parser_t, streams: &mut io_streams_t, args: &mut [&wstr])
         errno::set_errno(Errno(0));
 
         // We need to keep around the fd for this directory, in the parser.
-        let dir_fd = AutoCloseFd::new(wopen_cloexec(&norm_dir, O_RDONLY, 0));
+        let mut dir_fd = AutoCloseFd::new(wopen_cloexec(&norm_dir, O_RDONLY, 0));
 
         if !(dir_fd.is_valid() && unsafe { fchdir(dir_fd.fd()) } == 0) {
             // Some errors we skip and only report if nothing worked.
@@ -116,11 +116,9 @@ pub fn cd(parser: &mut parser_t, streams: &mut io_streams_t, args: &mut [&wstr])
             break;
         }
 
-        // Port note: sending the AutocloseFd across the FFI interface requires additional work
-        // It's never actually used in the target parser object (perhaps will be after the port to Rust)
-        // Keep this commented until the parser is ported.
+        // Stash the fd for the cwd in the parser.
+        parser.pin().set_cwd_fd(autocxx::c_int(dir_fd.acquire()));
 
-        //parser.libdata().cwd_fd = std::make_shared<const autoclose_fd_t>(std::move(dir_fd));
         parser.pin().set_var_and_fire(
             &L!("PWD").to_ffi(),
             EnvMode::EXPORT.bits() | EnvMode::GLOBAL.bits(),

src/parser.cpp

@@ -210,6 +210,11 @@ completion_list_t parser_t::expand_argument_list(const wcstring &arg_list_src,
     return result;
 }
 
+void parser_t::set_cwd_fd(int fd) {
+    assert(fd >= 0 && "Invalid fd");
+    this->libdata().cwd_fd = std::make_shared<autoclose_fd_t>(fd);
+}
+
 std::shared_ptr<parser_t> parser_t::shared() { return shared_from_this(); }
 
 cancel_checker_t parser_t::cancel_checker() const {

src/parser.h

@@ -487,6 +487,10 @@ class parser_t : public std::enable_shared_from_this<parser_t> {
     /// Mark whether we should sync universal variables.
     void set_syncs_uvars(bool flag) { syncs_uvars_ = flag; }
 
+    /// Set the given file descriptor as the working directory for this parser.
+    /// This acquires ownership.
+    void set_cwd_fd(int fd);
+
     /// \return a shared pointer reference to this parser.
     std::shared_ptr<parser_t> shared();