Use copy-on-write when normalizing paths (#9710)

crates/uv-distribution/src/metadata/lowering.rs

@@ -317,10 +317,10 @@ impl LoweredRequirement {
                             let source = if let Some(git_member) = &git_member {
                                 // If the workspace comes from a Git dependency, all workspace
                                 // members need to be Git dependencies, too.
-                                let subdirectory = uv_fs::normalize_path(
-                                    &uv_fs::relative_to(member.root(), git_member.fetch_root)
-                                        .expect("Workspace member must be relative"),
-                                );
+                                let subdirectory =
+                                    uv_fs::relative_to(member.root(), git_member.fetch_root)
+                                        .expect("Workspace member must be relative");
+                                let subdirectory = uv_fs::normalize_path_buf(subdirectory);
                                 RequirementSource::Git {
                                     repository: git_member.git_source.git.repository().clone(),
                                     reference: git_member.git_source.git.reference().clone(),
@@ -711,10 +711,9 @@ fn path_source(
     };
     if is_dir {
         if let Some(git_member) = git_member {
-            let subdirectory = uv_fs::normalize_path(
-                &uv_fs::relative_to(install_path, git_member.fetch_root)
-                    .expect("Workspace member must be relative"),
-            );
+            let subdirectory = uv_fs::relative_to(install_path, git_member.fetch_root)
+                .expect("Workspace member must be relative");
+            let subdirectory = uv_fs::normalize_path_buf(subdirectory);
             return Ok(RequirementSource::Git {
                 repository: git_member.git_source.git.repository().clone(),
                 reference: git_member.git_source.git.reference().clone(),

crates/uv-fs/src/path.rs

@@ -199,7 +199,33 @@ pub fn normalize_absolute_path(path: &Path) -> Result<PathBuf, std::io::Error> {
     Ok(ret)
 }
 
-/// Normalize a path, removing things like `.` and `..`.
+/// Normalize a [`Path`], removing things like `.` and `..`.
+pub fn normalize_path(path: &Path) -> Cow<Path> {
+    // Fast path: if the path is already normalized, return it as-is.
+    if path.components().all(|component| match component {
+        Component::Prefix(_) | Component::RootDir | Component::Normal(_) => true,
+        Component::ParentDir | Component::CurDir => false,
+    }) {
+        Cow::Borrowed(path)
+    } else {
+        Cow::Owned(normalized(path))
+    }
+}
+
+/// Normalize a [`PathBuf`], removing things like `.` and `..`.
+pub fn normalize_path_buf(path: PathBuf) -> PathBuf {
+    // Fast path: if the path is already normalized, return it as-is.
+    if path.components().all(|component| match component {
+        Component::Prefix(_) | Component::RootDir | Component::Normal(_) => true,
+        Component::ParentDir | Component::CurDir => false,
+    }) {
+        path
+    } else {
+        normalized(&path)
+    }
+}
+
+/// Normalize a [`Path`].
 ///
 /// Unlike [`normalize_absolute_path`], this works with relative paths and does never error.
 ///
@@ -216,8 +242,7 @@ pub fn normalize_absolute_path(path: &Path) -> Result<PathBuf, std::io::Error> {
 /// Out: `workspace-git-path-dep-test/packages/d`
 ///
 /// In: `./a/../../b`
-/// Out: `../b`
-pub fn normalize_path(path: &Path) -> PathBuf {
+fn normalized(path: &Path) -> PathBuf {
     let mut normalized = PathBuf::new();
     for component in path.components() {
         match component {

crates/uv-resolver/src/lock/mod.rs

@@ -3749,7 +3749,8 @@ fn normalize_requirement(
             ext,
             url: _,
         } => {
-            let install_path = uv_fs::normalize_path(&workspace.install_path().join(&install_path));
+            let install_path =
+                uv_fs::normalize_path_buf(workspace.install_path().join(&install_path));
             let url = VerbatimUrl::from_absolute_path(&install_path)
                 .map_err(LockErrorKind::RequirementVerbatimUrl)?;
 
@@ -3772,7 +3773,8 @@ fn normalize_requirement(
             r#virtual,
             url: _,
         } => {
-            let install_path = uv_fs::normalize_path(&workspace.install_path().join(&install_path));
+            let install_path =
+                uv_fs::normalize_path_buf(workspace.install_path().join(&install_path));
             let url = VerbatimUrl::from_absolute_path(&install_path)
                 .map_err(LockErrorKind::RequirementVerbatimUrl)?;
 

crates/uv/src/lib.rs

@@ -65,8 +65,7 @@ async fn run(mut cli: Cli) -> Result<ExitStatus> {
         .as_deref()
         .map(std::path::absolute)
         .transpose()?
-        .as_deref()
-        .map(uv_fs::normalize_path)
+        .map(uv_fs::normalize_path_buf)
         .map(Cow::Owned)
         .unwrap_or_else(|| Cow::Borrowed(&*CWD));