Implement fmt::Display for Pid, Uid, Gid

Closes #1439

Author: rusty-snake

src/pid.rs

@@ -2,7 +2,7 @@
 
 #![allow(unsafe_code)]
 
-use core::num::NonZeroI32;
+use core::{fmt, num::NonZeroI32};
 
 /// A process identifier as a raw integer.
 pub type RawPid = i32;
@@ -87,6 +87,12 @@ impl Pid {
     }
 }
 
+impl fmt::Display for Pid {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

src/ugid.rs

@@ -1,5 +1,7 @@
 //! User and Group ID types.
 
+use core::fmt;
+
 use crate::backend::c;
 use crate::ffi;
 
@@ -86,6 +88,18 @@ impl Gid {
     }
 }
 
+impl fmt::Display for Uid {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
+impl fmt::Display for Gid {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
 // Return the raw value of the IDs. In case of `None` it returns `!0` since it
 // has the same bit pattern as `-1` indicating no change to the owner/group ID.
 pub(crate) fn translate_fchown_args(