simplify field writing

Author: LorrensP-2158466

src/shims/unix/fs.rs

@@ -995,36 +995,16 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 
                 // Write common fields
                 let ino_name =
-                    if this.tcx.sess.target.os == "freebsd" { "d_fileno" } else { "d_ino " };
+                    if this.tcx.sess.target.os == "freebsd" { "d_fileno" } else { "d_ino" };
+                let off_name =
+                    if this.tcx.sess.target.os == "macos" { "d_seekoff" } else { "d_off" };
                 this.write_int_fields_named(
-                    &[(ino_name, ino.into()), ("d_reclen", size.into())],
+                    &[(ino_name, ino.into()), (off_name, 0), ("d_reclen", size.into())],
                     entry_place,
                 )?;
 
-                // Hanlde os specific fields
-                match &*this.tcx.sess.target.os {
-                    "macos" => {
-                        this.write_int_fields_named(
-                            &[
-                                ("d_seekoff", 0),
-                                ("d_namlen", (name_len - 1).into()), // Zero Byte not included
-                            ],
-                            entry_place,
-                        )?;
-                    }
-                    "freebsd" => {
-                        this.write_int_fields_named(
-                            &[
-                                ("d_off", 0),
-                                ("d_namlen", (name_len - 1).into()), // Zero Byte not included
-                            ],
-                            entry_place,
-                        )?;
-                    }
-                    "linux" | "solaris" | "illumos" => {
-                        this.write_int_fields_named(&[("d_off", 0)], entry_place)?;
-                    }
-                    _ => unreachable!(),
+                if let Some(d_namlen) = this.try_project_field_named(entry_place, "d_namlen")? {
+                    this.write_int(name_len.strict_sub(1), &d_namlen)?;
                 }
 
                 let file_type = this.file_type_to_d_type(dir_entry.file_type())?;