Avoid removing local wheels when unzipping (#560)

## Summary

When installing a local wheel, we need to avoid removing the zipped
wheel (since it lives outside of the cache), _and_ need to ensure that
we unzip the wheel into the cache (rather than replacing the zipped
wheel, which may even live outside of the project).

Closes https://github.com/astral-sh/puffin/issues/553.

crates/puffin-fs/src/lib.rs

@@ -46,47 +46,55 @@ pub fn write_atomic_sync(path: impl AsRef<Path>, data: impl AsRef<[u8]>) -> std:
 
 /// Rename `from` to `to` atomically using a temporary file and atomic rename.
 ///
-/// Returns `false` if the `to` path already existed and thus was removed before performing the
+/// Returns a [`Target`] if the `to` path already existed and thus was removed before performing the
 /// rename.
-pub fn rename_atomic_sync(from: impl AsRef<Path>, to: impl AsRef<Path>) -> std::io::Result<bool> {
-    // Remove the destination if it exists.
-    let safe = if let Ok(metadata) = fs_err::metadata(&to) {
-        if metadata.is_dir() {
+pub fn rename_atomic_sync(
+    from: impl AsRef<Path>,
+    to: impl AsRef<Path>,
+) -> std::io::Result<Option<Target>> {
+    // Remove the destination, if it exists.
+    let target = if let Ok(metadata) = fs_err::metadata(&to) {
+        Some(if metadata.is_dir() {
             fs_err::remove_dir_all(&to)?;
+            Target::Directory
         } else {
             fs_err::remove_file(&to)?;
-        }
-        false
+            Target::File
+        })
     } else {
-        true
+        None
     };
 
     // Move the source file to the destination.
     fs_err::rename(from, to)?;
 
-    Ok(safe)
+    Ok(target)
 }
 
 /// Copy `from` to `to` atomically using a temporary file and atomic rename.
 ///
-/// Returns `false` if the `to` path already existed and thus was removed before performing the
-/// rename.
-pub fn copy_atomic_sync(from: impl AsRef<Path>, to: impl AsRef<Path>) -> std::io::Result<bool> {
+/// Returns a [`Target`] if the `to` path already existed and thus was removed before performing the
+/// copy.
+pub fn copy_atomic_sync(
+    from: impl AsRef<Path>,
+    to: impl AsRef<Path>,
+) -> std::io::Result<Option<Target>> {
     // Copy to a temporary file.
     let temp_file =
         NamedTempFile::new_in(to.as_ref().parent().expect("Write path must have a parent"))?;
     fs_err::copy(from, &temp_file)?;
 
-    // Remove the destination if it exists.
-    let safe = if let Ok(metadata) = fs_err::metadata(&to) {
-        if metadata.is_dir() {
+    // Remove the destination, if it exists.
+    let target = if let Ok(metadata) = fs_err::metadata(&to) {
+        Some(if metadata.is_dir() {
             fs_err::remove_dir_all(&to)?;
+            Target::Directory
         } else {
             fs_err::remove_file(&to)?;
-        }
-        false
+            Target::File
+        })
     } else {
-        true
+        None
     };
 
     // Move the temporary file to the destination.
@@ -101,5 +109,25 @@ pub fn copy_atomic_sync(from: impl AsRef<Path>, to: impl AsRef<Path>) -> std::io
         )
     })?;
 
-    Ok(safe)
+    Ok(target)
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Target {
+    /// The target path was an existing file.
+    File,
+    /// The target path was an existing directory.
+    Directory,
+    /// The target path did not exist.
+    NotFound,
+}
+
+impl Target {
+    pub fn is_file(self) -> bool {
+        matches!(self, Self::File)
+    }
+
+    pub fn is_directory(self) -> bool {
+        matches!(self, Self::Directory)
+    }
 }