Add a puffin add command (#117)

This needs far better error handling and user-facing feedback, but it
does the basic operation (and includes discovery of the `pyproject.toml`
file, etc.).

crates/puffin-cli/Cargo.toml

@@ -20,6 +20,7 @@ puffin-installer = { path = "../puffin-installer" }
 puffin-interpreter = { path = "../puffin-interpreter" }
 puffin-package = { path = "../puffin-package" }
 puffin-resolver = { path = "../puffin-resolver" }
+puffin-workspace = { path = "../puffin-workspace" }
 
 anyhow = { workspace = true }
 bitflags = { workspace = true }

crates/puffin-cli/src/commands/add.rs

@@ -0,0 +1,29 @@
+use anyhow::Result;
+use tracing::info;
+
+use crate::commands::ExitStatus;
+use crate::printer::Printer;
+
+/// Add a dependency to the workspace.
+pub(crate) fn add(name: &str, _printer: Printer) -> Result<ExitStatus> {
+    // Locate the workspace.
+    let Some(workspace_root) = puffin_workspace::find_pyproject_toml(std::env::current_dir()?)
+    else {
+        return Err(anyhow::anyhow!(
+            "Could not find a `pyproject.toml` file in the current directory or any of its parents"
+        ));
+    };
+
+    info!("Found workspace at: {}", workspace_root.display());
+
+    // Parse the manifest.
+    let mut manifest = puffin_workspace::Workspace::try_from(workspace_root.as_path())?;
+
+    // Add the dependency.
+    manifest.add_dependency(name)?;
+
+    // Write the manifest back to disk.
+    manifest.save(&workspace_root)?;
+
+    Ok(ExitStatus::Success)
+}

crates/puffin-cli/src/commands/mod.rs

@@ -1,6 +1,7 @@
 use std::process::ExitCode;
 use std::time::Duration;
 
+pub(crate) use add::add;
 pub(crate) use clean::clean;
 pub(crate) use compile::compile;
 pub(crate) use freeze::freeze;
@@ -8,6 +9,7 @@ pub(crate) use sync::{sync, SyncFlags};
 pub(crate) use uninstall::uninstall;
 pub(crate) use venv::venv;
 
+mod add;
 mod clean;
 mod compile;
 mod freeze;

crates/puffin-cli/src/main.rs

@@ -45,6 +45,8 @@ enum Commands {
     Uninstall(UninstallArgs),
     /// Create a virtual environment.
     Venv(VenvArgs),
+    /// Add a dependency to the workspace.
+    Add(AddArgs),
 }
 
 #[derive(Args)]
@@ -83,6 +85,12 @@ struct VenvArgs {
     name: PathBuf,
 }
 
+#[derive(Args)]
+struct AddArgs {
+    /// The name of the package to add.
+    name: String,
+}
+
 #[tokio::main]
 async fn main() -> ExitCode {
     let cli = Cli::parse();
@@ -153,6 +161,7 @@ async fn main() -> ExitCode {
             .await
         }
         Commands::Venv(args) => commands::venv(&args.name, args.python.as_deref(), printer).await,
+        Commands::Add(args) => commands::add(&args.name, printer),
     };
 
     match result {