chown: allow setting arbitrary numeric user ID

Update `chown` to allow setting the owner of a file to a numeric user
ID regardless of whether a corresponding username exists on the
system.

For example,

    $ touch f && sudo chown 12345 f

succeeds even though there is no named user with ID 12345.

Fixes #3380.

src/uu/chown/src/chown.rs

@@ -197,10 +197,17 @@ fn parse_spec(spec: &str, sep: char) -> UResult<(Option<u32>, Option<u32>)> {
  // So, try to parse it this way
  return parse_spec(spec, '.');
  } else {
- return Err(USimpleError::new(
- 1,
- format!("invalid user: {}", spec.quote()),
- ));
+ // It's possible that the `user` string contains a
+ // numeric user ID, in which case, we respect that.
+ match user.parse() {
+ Ok(uid) => uid,
+ Err(_) => {
+ return Err(USimpleError::new(
+ 1,
+ format!("invalid user: {}", spec.quote()),
+ ))
+ }
+ }
  }
  }
  })

tests/by-util/test_chown.rs

@@ -418,6 +418,27 @@ fn test_chown_only_user_id() {
  .stderr_contains(&"failed to change");
 }
 
+/// Test for setting the owner to a user ID for a user that does not exist.
+///
+/// For example:
+///
+/// $ touch f && chown 12345 f
+///
+/// succeeds with exit status 0 and outputs nothing. The owner of the
+/// file is set to 12345, even though no user with that ID exists.
+///
+/// This test must be run as root, because only the root user can
+/// transfer ownership of a file.
+#[test]
+fn test_chown_only_user_id_nonexistent_user() {
+ let (at, mut ucmd) = at_and_ucmd!();
+ at.touch("f");
+ ucmd.args(&["12345", "f"])
+ .succeeds()
+ .no_stdout()
+ .no_stderr();
+}
+
 #[test]
 // FixME: stderr = chown: ownership of 'test_chown_file1' retained as cuuser:wheel
 #[cfg(not(target_os = "freebsd"))]