use std::path::{Path, PathBuf}; use crate::fs::Stack; impl Stack {    /// Returns the top-level path of the stack.    pub fn root(&self) -> &Path {        &self.root    }     /// Returns the absolute path the currently set path.    pub fn current(&self) -> &Path {        &self.current    }     /// Returns the currently set path relative to the [`root()`][Stack::root()].    pub fn current_relative(&self) -> &Path {        &self.current_relative    }} /// A delegate for use in a [`Stack`].pub trait Delegate {    /// Called whenever we push a directory on top of the stack, after the fact.    ///    /// It is also called if the currently acted on path is a directory in itself.    /// Use `stack.current()` to see the directory.    fn push_directory(&mut self, stack: &Stack) -> std::io::Result<()>;     /// Called after any component was pushed, with the path available at `stack.current()`.    ///    /// `is_last_component` is true if the path is completely built.    fn push(&mut self, is_last_component: bool, stack: &Stack) -> std::io::Result<()>;     /// Called right after a directory-component was popped off the stack.    ///    /// Use it to pop information off internal data structures.    fn pop_directory(&mut self);} impl Stack {    /// Create a new instance with `root` being the base for all future paths we handle, assuming it to be valid which includes    /// symbolic links to be included in it as well.    pub fn new(root: impl Into<PathBuf>) -> Self {        let root = root.into();        Stack {            current: root.clone(),            current_relative: PathBuf::with_capacity(128),            valid_components: 0,            root,            current_is_directory: true,        }    }     /// Set the current stack to point to the `relative` path and call `push_comp()` each time a new path component is popped    /// along with the stacks state for inspection to perform an operation that produces some data.    ///    /// The full path to `relative` will be returned along with the data returned by push_comp.    /// Note that this only works correctly for the delegate's `push_directory()` and `pop_directory()` methods if    /// `relative` paths are terminal, so point to their designated file or directory.    pub fn make_relative_path_current(        &mut self,        relative: impl AsRef<Path>,        delegate: &mut impl Delegate,    ) -> std::io::Result<()> {        let relative = relative.as_ref();        debug_assert!(            relative.is_relative(),            "only index paths are handled correctly here, must be relative"        );        debug_assert!(!relative.to_string_lossy().is_empty(), "empty paths are not allowed");         if self.valid_components == 0 {            delegate.push_directory(self)?;        }         let mut components = relative.components().peekable();        let mut existing_components = self.current_relative.components();        let mut matching_components = 0;        while let (Some(existing_comp), Some(new_comp)) = (existing_components.next(), components.peek()) {            if existing_comp == *new_comp {                components.next();                matching_components += 1;            } else {                break;            }        }         for _ in 0..self.valid_components - matching_components {            self.current.pop();            self.current_relative.pop();            if self.current_is_directory {                delegate.pop_directory();            }            self.current_is_directory = true;        }        self.valid_components = matching_components;         if !self.current_is_directory && components.peek().is_some() {            delegate.push_directory(self)?;        }         while let Some(comp) = components.next() {            let is_last_component = components.peek().is_none();            self.current_is_directory = !is_last_component;            self.current.push(comp);            self.current_relative.push(comp);            self.valid_components += 1;            let res = delegate.push(is_last_component, self);            if self.current_is_directory {                delegate.push_directory(self)?;            }             if let Err(err) = res {                self.current.pop();                self.current_relative.pop();                self.valid_components -= 1;                return Err(err);            }        }        Ok(())    }}