cp commands fails if process is in deleted directory

[original-birdman]

If the current directory of a process is deleted and the process runs the Rust cp command it will fail with:

/usr/lib/cargo/bin/coreutils/cp: failed to get current directory No such file or directory (os error 2)

The GNU version of cp does not have this issue.
(This is on Kubuntu 25.10.)

As a result, some automated build processes (which arrive at this situation) now fail to run.

You can see the error by using this simple shell script:

#!/bin/sh
#

echo Rust core-utils

cd $HOME
mkdir -p cu-test-base
touch cu-test-base/file1 cu-test-base/file2
mkdir -p cu-test
cd cu-test
rm -rf $HOME/cu-test
/usr/lib/cargo/bin/coreutils/cp -r $HOME/cu-test-base $HOME/cu-test
ls $HOME/cu-test

#####################

echo GNU core-utils

cd $HOME
mkdir -p cu-test-base
touch cu-test-base/file1 cu-test-base/file2
mkdir -p cu-test
cd cu-test
rm -rf $HOME/cu-test
/usr/bin/gnucp -r $HOME/cu-test-base $HOME/cu-test
ls $HOME/cu-test

The Rust version runs a series of statx() calls (3 in succession for each entry) then calls getcwd() and fails.
It has no reason to be calling getcwd().

[Originally reported at https://bugs.launchpad.net/ubuntu/+source/rust-coreutils/+bug/2130465]

[original-birdman]

The call to getcwd() comes from the env::current_dir() call here, in copydir.rs:`

/// Paths that are invariant throughout the traversal when copying a directory.
struct Context<'a> {
    /// The current working directory at the time of starting the traversal.
    current_dir: PathBuf,

    /// The path to the parent of the source directory, if any.
    root_parent: Option<PathBuf>,

    /// The target path to which the directory will be copied.
    target: &'a Path,

    /// The source path from which the directory will be copied.
    root: &'a Path,
}

impl<'a> Context<'a> {
    fn new(root: &'a Path, target: &'a Path) -> io::Result<Self> {
        let current_dir = env::current_dir()?;
        let root_path = current_dir.join(root);
        let root_parent = if target.exists() && !root.to_str().unwrap().ends_with("/.") {
            root_path.parent().map(|p| p.to_path_buf())
        } else if root == Path::new(".") && target.is_dir() {
            // Special case: when copying current directory (.) to an existing directory,
            // we don't want to use the parent path as root_parent because we want to
            // copy the contents of the current directory directly into the target directory,
            // not create a subdirectory with the current directory's name.
            None
        } else {
            Some(root_path)
        };
        Ok(Self {
            current_dir,
            root_parent,
            target,
            root,
        })
    }
}

The env::current_dir() is a wrapper for getcwd().

I can't think of any reason why cp should need to know the current` directory.
It should just use either full or relative paths, but should never need to convert the latter to the former.

In GNU coreutils the ONLY command to call getcwd() was pwd.