Add ability to extract subset of files from yama

yama/src/bin/yama.rs

@@ -56,8 +56,9 @@ enum PileCommand {
         pointer_name: String,
 
         /// Limited expression(s) of files to retrieve.
+        /// LIMITATION OF CURRENT VERSION: ONLY ONE EXACT PATH ALLOWED, PLEASE.
         #[clap(short, long)]
-        subset: Vec<PathBuf>,
+        subset: Option<String>,
 
         destination: PathBuf,
 
@@ -118,7 +119,7 @@ fn wrapped_main() -> anyhow::Result<i32> {
     match &opts.command {
         PileCommand::Retrieve {
             pointer_name,
-            subset: _,
+            subset,
             destination,
             num_workers: workers,
         } => {
@@ -136,10 +137,25 @@ fn wrapped_main() -> anyhow::Result<i32> {
 
             fully_integrate_pointer_node(&pile, &mut root_tree_node.node, &mut pointer)?;
 
+            let mut node_to_extract = &mut root_tree_node.node;
+
+            if let Some(subset) = subset {
+                for path_to_descend in subset.split('/').filter(|s| ! s.is_empty()) {
+                    match node_to_extract.child(path_to_descend) {
+                        Ok(new_node) => {
+                            node_to_extract = new_node;
+                        }
+                        Err(msg) => {
+                            bail!("Can't descend into {path_to_descend:?}: {msg}");
+                        }
+                    }
+                }
+            }
+
             // todo allow disabling apply metadata
             extracting::extract(
                 destination,
-                &mut root_tree_node.node,
+                node_to_extract,
                 &pile,
                 true,
                 workers.unwrap_or(2),

yama/src/definitions.rs

@@ -270,6 +270,31 @@ impl TreeNode {
             }
         }
     }
+
+    /// Recurses into a child by name, or returns Err with a reason.
+    pub fn child(&mut self, name: &str) -> Result<&mut TreeNode, &'static str> {
+        match self {
+            TreeNode::NormalFile { .. } => {
+                Err("not a directory: normal file")
+            }
+            TreeNode::Directory { children, .. } => {
+                match children.get_mut(name) {
+                    None => {
+                        Err("child not in directory")
+                    }
+                    Some(node) => {
+                        Ok(node)
+                    }
+                }
+            }
+            TreeNode::SymbolicLink { .. } => {
+                Err("not a directory: symlink")
+            }
+            TreeNode::Deleted => {
+                Err("not a directory: deleted")
+            }
+        }
+    }
 }
 
 #[derive(Debug, Copy, Clone, Serialize, Deserialize, PartialEq, Eq)]