Split crates and clean up structure of codebase (#294)

Co-authored-by: Jiahao XU <Jiahao_XU@outlook.com>

crates/normalize-path/src/lib.rs

@@ -0,0 +1,81 @@
+//! Normalizes paths similarly to canonicalize, but without performing I/O.
+//!
+//! This is like Python's `os.path.normpath`.
+//!
+//! Initially adapted from [Cargo's implementation][cargo-paths].
+//!
+//! [cargo-paths]: https://github.com/rust-lang/cargo/blob/fede83ccf973457de319ba6fa0e36ead454d2e20/src/cargo/util/paths.rs#L61
+//!
+//! # Example
+//!
+//! ```
+//! use normalize_path::NormalizePath;
+//! use std::path::Path;
+//!
+//! assert_eq!(
+//!     Path::new("/A/foo/../B/./").normalize(),
+//!     Path::new("/A/B")
+//! );
+//! ```
+
+use std::{
+    borrow::Cow,
+    path::{Component, Path, PathBuf},
+};
+
+/// Extension trait to add `normalize_path` to std's [`Path`].
+pub trait NormalizePath {
+    /// Normalize a path without performing I/O.
+    ///
+    /// All redundant separator and up-level references are collapsed.
+    ///
+    /// However, this does not resolve links.
+    fn normalize(&self) -> Cow<'_, Path>;
+}
+
+fn is_normalized(path: &Path) -> bool {
+    for component in path.components() {
+        match component {
+            Component::CurDir | Component::ParentDir => {
+                return false;
+            }
+            _ => continue,
+        }
+    }
+
+    true
+}
+
+impl NormalizePath for Path {
+    fn normalize(&self) -> Cow<'_, Path> {
+        if is_normalized(self) {
+            return Cow::Borrowed(self);
+        }
+
+        let mut components = self.components().peekable();
+        let mut ret = if let Some(c @ Component::Prefix(..)) = components.peek() {
+            let buf = PathBuf::from(c.as_os_str());
+            components.next();
+            buf
+        } else {
+            PathBuf::new()
+        };
+
+        for component in components {
+            match component {
+                Component::Prefix(..) => unreachable!(),
+                Component::RootDir => {
+                    ret.push(component.as_os_str());
+                }
+                Component::CurDir => {}
+                Component::ParentDir => {
+                    ret.pop();
+                }
+                Component::Normal(c) => {
+                    ret.push(c);
+                }
+            }
+        }
+        Cow::Owned(ret)
+    }
+}