refactor(tvix/castore): move *Node and Directory to crate root

*Node and Directory are types of the tvix-castore model, not the tvix
DirectoryService model. A DirectoryService only happens to send
Directories.

Move types into individual files in a nodes/ subdirectory, as it's
gotten too cluttered in a single file, and (re-)export all types from
the crate root.

This has the effect that we now cannot poke at private fields directly
from other files inside `crate::directoryservice` (as it's not all in
the same file anymore), but that's a good thing, it now forces us to go
through the proper accessors.

For the same reasons, we currently also need to introduce the `rename`
functions on each *Node directly.

A followup is gonna move the names out of the individual enum kinds, so
we can better represent "unnamed nodes".

Change-Id: Icdb34dcfe454c41c94f2396e8e99973d27db8418
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12199
Reviewed-by: yuka <yuka@yuka.dev>
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

tvix/castore/src/nodes/mod.rs

@@ -0,0 +1,69 @@
+//! This holds types describing nodes in the tvix-castore model.
+mod directory;
+mod directory_node;
+mod file_node;
+mod symlink_node;
+
+use bytes::Bytes;
+pub use directory::Directory;
+pub use directory_node::DirectoryNode;
+pub use file_node::FileNode;
+pub use symlink_node::SymlinkNode;
+
+/// A Node is either a [DirectoryNode], [FileNode] or [SymlinkNode].
+/// While a Node by itself may have any name, only those matching specific requirements
+/// can can be added as entries to a [Directory] (see the documentation on [Directory] for details).
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Node {
+    Directory(DirectoryNode),
+    File(FileNode),
+    Symlink(SymlinkNode),
+}
+
+impl Node {
+    /// Returns the node with a new name.
+    pub fn rename(self, name: Bytes) -> Self {
+        match self {
+            Node::Directory(n) => Node::Directory(n.rename(name)),
+            Node::File(n) => Node::File(n.rename(name)),
+            Node::Symlink(n) => Node::Symlink(n.rename(name)),
+        }
+    }
+}
+
+impl PartialOrd for Node {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for Node {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        self.get_name().cmp(other.get_name())
+    }
+}
+
+/// NamedNode is implemented for [FileNode], [DirectoryNode] and [SymlinkNode]
+/// and [Node], so we can ask all of them for the name easily.
+pub trait NamedNode {
+    fn get_name(&self) -> &Bytes;
+}
+
+impl NamedNode for &Node {
+    fn get_name(&self) -> &Bytes {
+        match self {
+            Node::File(node_file) => node_file.get_name(),
+            Node::Directory(node_directory) => node_directory.get_name(),
+            Node::Symlink(node_symlink) => node_symlink.get_name(),
+        }
+    }
+}
+impl NamedNode for Node {
+    fn get_name(&self) -> &Bytes {
+        match self {
+            Node::File(node_file) => node_file.get_name(),
+            Node::Directory(node_directory) => node_directory.get_name(),
+            Node::Symlink(node_symlink) => node_symlink.get_name(),
+        }
+    }
+}