perf: use custom canonicalize impl to avoid usless syscall (#220)

Reduce one redundant fs::symlink_metadata system call.

Author: Brooooooklyn

src/cache.rs

@@ -134,7 +134,6 @@ pub struct CachedPathImpl {
     path: Box<Path>,
     parent: Option<CachedPath>,
     meta: OnceLock<Option<FileMetadata>>,
-    symlink: OnceLock<Option<PathBuf>>,
     canonicalized: OnceLock<Option<PathBuf>>,
     node_modules: OnceLock<Option<CachedPath>>,
     package_json: OnceLock<Option<Arc<PackageJson>>>,
@@ -147,7 +146,6 @@ impl CachedPathImpl {
             path,
             parent,
             meta: OnceLock::new(),
-            symlink: OnceLock::new(),
             canonicalized: OnceLock::new(),
             node_modules: OnceLock::new(),
             package_json: OnceLock::new(),
@@ -190,24 +188,11 @@ impl CachedPathImpl {
         )
     }
 
-    fn symlink<Fs: FileSystem>(&self, fs: &Fs) -> io::Result<Option<PathBuf>> {
-        self.symlink
-            .get_or_try_init(|| {
-                if let Ok(symlink_metadata) = fs.symlink_metadata(&self.path) {
-                    if symlink_metadata.is_symlink {
-                        return fs.canonicalize(self.path()).map(Some);
-                    }
-                }
-                Ok(None)
-            })
-            .cloned()
-    }
-
     pub fn realpath<Fs: FileSystem>(&self, fs: &Fs) -> io::Result<PathBuf> {
         self.canonicalized
             .get_or_try_init(|| {
-                if let Some(link) = self.symlink(fs)? {
-                    return Ok(Some(link));
+                if fs.symlink_metadata(&self.path).is_ok_and(|m| m.is_symlink) {
+                    return fs.canonicalize(&self.path).map(Some);
                 }
                 if let Some(parent) = self.parent() {
                     let parent_path = parent.realpath(fs)?;

src/file_system.rs

@@ -1,6 +1,6 @@
 use std::{
     fs, io,
-    path::{Path, PathBuf},
+    path::{Component, Path, PathBuf},
 };
 
 /// File System abstraction used for `ResolverGeneric`
@@ -91,33 +91,51 @@ impl FileSystem for FileSystemOs {
     }
 
     fn canonicalize(&self, path: &Path) -> io::Result<PathBuf> {
-        #[cfg(not(target_os = "wasi"))]
+        #[cfg(target_os = "windows")]
         {
             dunce::canonicalize(path)
         }
-        #[cfg(target_os = "wasi")]
+        #[cfg(not(target_os = "windows"))]
         {
-            let meta = fs::symlink_metadata(path)?;
-            if meta.file_type().is_symlink() {
-                let link = fs::read_link(path)?;
-                let mut path_buf = path.to_path_buf();
+            let mut path_buf = path.to_path_buf();
+            loop {
+                let link = fs::read_link(&path_buf)?;
                 path_buf.pop();
-                for segment in link.iter() {
-                    match segment.to_str() {
-                        Some("..") => {
+                for component in link.components() {
+                    match component {
+                        Component::ParentDir => {
                             path_buf.pop();
                         }
-                        Some(".") | None => {}
-                        Some(seg) => {
-                            // Need to trim the extra \0 introduces by rust std rust-lang/rust#123727
-                            path_buf.push(seg.trim_end_matches('\0'));
+                        Component::Normal(seg) => {
+                            #[cfg(target_family = "wasm")]
+                            // Need to trim the extra \0 introduces by https://github.com/nodejs/uvwasi/issues/262
+                            {
+                                path_buf.push(seg.to_string_lossy().trim_end_matches('\0'));
+                            }
+                            #[cfg(not(target_family = "wasm"))]
+                            {
+                                path_buf.push(seg);
+                            }
                         }
+                        Component::RootDir => {
+                            #[cfg(target_os = "windows")]
+                            {
+                                path_buf.push("\\");
+                            }
+                            #[cfg(not(target_os = "windows"))]
+                            {
+                                #[allow(clippy::path_buf_push_overwrite)]
+                                path_buf.push("/");
+                            }
+                        }
+                        Component::CurDir | Component::Prefix(_) => {}
                     }
                 }
-                Ok(path_buf)
-            } else {
-                Ok(path.to_path_buf())
+                if !fs::symlink_metadata(&path_buf)?.is_symlink() {
+                    break;
+                }
             }
+            Ok(path_buf)
         }
     }
 }