a bit of FileDescriptor trait cleanup

src/tools/miri/src/helpers.rs

@@ -1,5 +1,6 @@
 pub mod convert;
 
+use std::any::Any;
 use std::cmp;
 use std::iter;
 use std::num::NonZeroUsize;
@@ -23,7 +24,23 @@ use rand::RngCore;
 
 use crate::*;
 
-impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriInterpCx<'mir, 'tcx> {}
+/// A trait to work around not having trait object upcasting:
+/// Add `AsAny` as supertrait and your trait objects can be turned into `&dyn Any` on which you can
+/// then call `downcast`.
+pub trait AsAny: Any {
+    fn as_any(&self) -> &dyn Any;
+    fn as_any_mut(&mut self) -> &mut dyn Any;
+}
+impl<T: Any> AsAny for T {
+    #[inline(always)]
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+    #[inline(always)]
+    fn as_any_mut(&mut self) -> &mut dyn Any {
+        self
+    }
+}
 
 // This mapping should match `decode_error_kind` in
 // <https://github.com/rust-lang/rust/blob/master/library/std/src/sys/unix/mod.rs>.
@@ -119,6 +136,7 @@ fn try_resolve_did(tcx: TyCtxt<'_>, path: &[&str], namespace: Option<Namespace>)
     }
 }
 
+impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriInterpCx<'mir, 'tcx> {}
 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     /// Checks if the given crate/module exists.
     fn have_module(&self, path: &[&str]) -> bool {

src/tools/miri/src/shims/unix/fs.rs

@@ -17,7 +17,6 @@ use crate::shims::os_str::bytes_to_os_str;
 use crate::*;
 use shims::os_str::os_str_to_bytes;
 use shims::time::system_time_to_duration;
-use shims::unix::linux::fd::epoll::Epoll;
 
 #[derive(Debug)]
 pub struct FileHandle {
@@ -25,17 +24,13 @@ pub struct FileHandle {
     writable: bool,
 }
 
-pub trait FileDescriptor: std::fmt::Debug {
+pub trait FileDescriptor: std::fmt::Debug + helpers::AsAny {
     fn name(&self) -> &'static str;
 
     fn as_file_handle<'tcx>(&self) -> InterpResult<'tcx, &FileHandle> {
         throw_unsup_format!("{} cannot be used as FileHandle", self.name());
     }
 
-    fn as_epoll_handle<'tcx>(&mut self) -> InterpResult<'tcx, &mut Epoll> {
-        throw_unsup_format!("not an epoll file descriptor");
-    }
-
     fn read<'tcx>(
         &mut self,
         _communicate_allowed: bool,
@@ -69,7 +64,9 @@ pub trait FileDescriptor: std::fmt::Debug {
 
     fn dup(&mut self) -> io::Result<Box<dyn FileDescriptor>>;
 
-    fn is_tty(&self) -> bool;
+    fn is_tty(&self) -> bool {
+        false
+    }
 
     #[cfg(unix)]
     fn as_unix_host_fd(&self) -> Option<i32> {
@@ -271,10 +268,6 @@ impl FileDescriptor for NullOutput {
     fn dup(&mut self) -> io::Result<Box<dyn FileDescriptor>> {
         Ok(Box::new(NullOutput))
     }
-
-    fn is_tty(&self) -> bool {
-        false
-    }
 }
 
 #[derive(Debug)]

src/tools/miri/src/shims/unix/linux/fd.rs

@@ -80,7 +80,10 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
             let event = EpollEvent { events, data };
 
             if let Some(epfd) = this.machine.file_handler.handles.get_mut(&epfd) {
-                let epfd = epfd.as_epoll_handle()?;
+                let epfd = epfd
+                    .as_any_mut()
+                    .downcast_mut::<Epoll>()
+                    .ok_or_else(|| err_unsup_format!("non-epoll FD passed to `epoll_ctl`"))?;
 
                 epfd.file_descriptors.insert(fd, event);
                 Ok(Scalar::from_i32(0))
@@ -89,7 +92,10 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
             }
         } else if op == epoll_ctl_del {
             if let Some(epfd) = this.machine.file_handler.handles.get_mut(&epfd) {
-                let epfd = epfd.as_epoll_handle()?;
+                let epfd = epfd
+                    .as_any_mut()
+                    .downcast_mut::<Epoll>()
+                    .ok_or_else(|| err_unsup_format!("non-epoll FD passed to `epoll_ctl`"))?;
 
                 epfd.file_descriptors.remove(&fd);
                 Ok(Scalar::from_i32(0))
@@ -148,7 +154,10 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
 
         let numevents = 0;
         if let Some(epfd) = this.machine.file_handler.handles.get_mut(&epfd) {
-            let _epfd = epfd.as_epoll_handle()?;
+            let _epfd = epfd
+                .as_any_mut()
+                .downcast_mut::<Epoll>()
+                .ok_or_else(|| err_unsup_format!("non-epoll FD passed to `epoll_wait`"))?;
 
             // FIXME return number of events ready when scheme for marking events ready exists
             Ok(Scalar::from_i32(numevents))

src/tools/miri/src/shims/unix/linux/fd/epoll.rs

@@ -32,18 +32,10 @@ impl FileDescriptor for Epoll {
         "epoll"
     }
 
-    fn as_epoll_handle<'tcx>(&mut self) -> InterpResult<'tcx, &mut Epoll> {
-        Ok(self)
-    }
-
     fn dup(&mut self) -> io::Result<Box<dyn FileDescriptor>> {
         Ok(Box::new(self.clone()))
     }
 
-    fn is_tty(&self) -> bool {
-        false
-    }
-
     fn close<'tcx>(
         self: Box<Self>,
         _communicate_allowed: bool,

src/tools/miri/src/shims/unix/linux/fd/event.rs

@@ -28,10 +28,6 @@ impl FileDescriptor for Event {
         Ok(Box::new(Event { val: self.val.clone() }))
     }
 
-    fn is_tty(&self) -> bool {
-        false
-    }
-
     fn close<'tcx>(
         self: Box<Self>,
         _communicate_allowed: bool,

src/tools/miri/src/shims/unix/linux/fd/socketpair.rs

@@ -19,10 +19,6 @@ impl FileDescriptor for SocketPair {
         Ok(Box::new(SocketPair))
     }
 
-    fn is_tty(&self) -> bool {
-        false
-    }
-
     fn close<'tcx>(
         self: Box<Self>,
         _communicate_allowed: bool,