Make metadata a FileDescription operation

src/shims/files.rs

@@ -1,9 +1,9 @@
 use std::any::Any;
 use std::collections::BTreeMap;
-use std::io;
 use std::io::{IsTerminal, Read, SeekFrom, Write};
 use std::ops::Deref;
 use std::rc::{Rc, Weak};
+use std::{fs, io};
 
 use rustc_abi::Size;
 
@@ -62,6 +62,10 @@ pub trait FileDescription: std::fmt::Debug + Any {
         throw_unsup_format!("cannot close {}", self.name());
     }
 
+    fn metadata<'tcx>(&self) -> InterpResult<'tcx, io::Result<fs::Metadata>> {
+        throw_unsup_format!("obtaining metadata is only supported on file-backed file descriptors");
+    }
+
     fn is_tty(&self, _communicate_allowed: bool) -> bool {
         // Most FDs are not tty's and the consequence of a wrong `false` are minor,
         // so we use a default impl here.
@@ -216,7 +220,7 @@ impl Deref for FileDescriptionRef {
 }
 
 impl FileDescriptionRef {
-    fn new(fd: impl FileDescription, id: FdId) -> Self {
+    pub fn new(fd: impl FileDescription, id: FdId) -> Self {
         FileDescriptionRef(Rc::new(FileDescWithId { id, file_description: Box::new(fd) }))
     }
 
@@ -273,8 +277,8 @@ impl VisitProvenance for WeakFileDescriptionRef {
 
 /// A unique id for file descriptions. While we could use the address, considering that
 /// is definitely unique, the address would expose interpreter internal state when used
-/// for sorting things. So instead we generate a unique id per file description that stays
-/// the same even if a file descriptor is duplicated and gets a new integer file descriptor.
+/// for sorting things. So instead we generate a unique id per file description is the name
+/// for all `dup`licates and is never reused.
 #[derive(Debug, Copy, Clone, Default, Eq, PartialEq, Ord, PartialOrd)]
 pub struct FdId(usize);
 

src/shims/unix/fs.rs

@@ -2,7 +2,8 @@
 
 use std::borrow::Cow;
 use std::fs::{
-    DirBuilder, File, FileType, OpenOptions, ReadDir, read_dir, remove_dir, remove_file, rename,
+    DirBuilder, File, FileType, Metadata, OpenOptions, ReadDir, read_dir, remove_dir, remove_file,
+    rename,
 };
 use std::io::{self, ErrorKind, IsTerminal, Read, Seek, SeekFrom, Write};
 use std::path::{Path, PathBuf};
@@ -100,6 +101,10 @@ impl FileDescription for FileHandle {
         }
     }
 
+    fn metadata<'tcx>(&self) -> InterpResult<'tcx, io::Result<Metadata>> {
+        interp_ok(self.file.metadata())
+    }
+
     fn is_tty(&self, communicate_allowed: bool) -> bool {
         communicate_allowed && self.file.is_terminal()
     }
@@ -1698,16 +1703,7 @@ impl FileMetadata {
             return interp_ok(Err(LibcError("EBADF")));
         };
 
-        let file = &fd
-            .downcast::<FileHandle>()
-            .ok_or_else(|| {
-                err_unsup_format!(
-                    "obtaining metadata is only supported on file-backed file descriptors"
-                )
-            })?
-            .file;
-
-        let metadata = file.metadata();
+        let metadata = fd.metadata()?;
         drop(fd);
         FileMetadata::from_meta(ecx, metadata)
     }