Add new 'deps add' command

This makes it easier to add new dependencies, without having to
  manually edit the `aiken.toml` file.

  The command is accessible via two different paths:

  - aiken deps add

  or simply

  - aiken add

  for this is quite common to find at the top-level of the command-line,
  and, we still want to keep commands for managing dependencies grouped
  under a command sub-group and not all at the top-level. So we're
  merely promoting that one for visibility.

crates/aiken/src/cmd/deps/add.rs

@@ -0,0 +1,71 @@
+use aiken_project::{
+    config::{Config, Dependency, Platform},
+    error::Warning,
+    package_name::PackageName,
+    pretty,
+};
+use miette::IntoDiagnostic;
+use owo_colors::OwoColorize;
+use std::{path::PathBuf, process, str::FromStr};
+
+#[derive(clap::Args)]
+/// Add a new project package as dependency
+pub struct Args {
+    /// Package name, in the form of {owner}/{repository}.
+    ///
+    /// For example → 'add aiken-lang/stdlib'
+    ///
+    /// Note that by default, this assumes the package is located
+    /// on Github.
+    package: String,
+    /// The package version, as a git commit hash, a tag or a branch name.
+    #[clap(long)]
+    version: String,
+}
+
+pub fn exec(args: Args) -> miette::Result<()> {
+    let root = PathBuf::from(".");
+
+    let dependency = Dependency {
+        name: PackageName::from_str(&args.package)?,
+        version: args.version,
+        source: Platform::Github,
+    };
+
+    let config = match Config::load(&root) {
+        Ok(config) => config,
+        Err(e) => {
+            e.report();
+            process::exit(1);
+        }
+    };
+
+    println!(
+        "{} {}",
+        pretty::pad_left("Adding".to_string(), 13, " ")
+            .bold()
+            .purple(),
+        dependency.name.bright_blue(),
+    );
+
+    match config.insert(&dependency, false) {
+        Some(config) => {
+            config.save(&root).into_diagnostic()?;
+            println!(
+                "{} version = {}",
+                pretty::pad_left("Added".to_string(), 13, " ")
+                    .bold()
+                    .purple(),
+                dependency.version.yellow()
+            );
+            Ok(())
+        }
+        None => {
+            let warning = Warning::DependencyAlreadyExists {
+                name: dependency.name,
+            };
+            warning.report();
+            process::exit(1)
+        }
+    }
+}

crates/aiken/src/cmd/deps/mod.rs

@@ -1,3 +1,4 @@
+pub mod add;
 pub mod clear_cache;
 
 use clap::Subcommand;
@@ -6,12 +7,16 @@ use clap::Subcommand;
 #[derive(Subcommand)]
 #[clap(setting(clap::AppSettings::DeriveDisplayOrder))]
 pub enum Cmd {
+    /// Add a new dependency
+    Add(add::Args),
+
     /// Clear the system-wide dependencies cache
     ClearCache,
 }
 
 pub fn exec(cmd: Cmd) -> miette::Result<()> {
     match cmd {
+        Cmd::Add(args) => add::exec(args),
         Cmd::ClearCache => clear_cache::exec(),
     }
 }

crates/aiken/src/cmd/new.rs

@@ -29,6 +29,8 @@ pub fn exec(args: Args) -> miette::Result<()> {
 }
 
 fn create_project(args: Args, package_name: &PackageName) -> miette::Result<()> {
+    package_name.restrict().into_diagnostic()?;
+
     let root = PathBuf::from(&package_name.repo);
 
     if root.exists() {

crates/aiken/src/main.rs

@@ -1,4 +1,8 @@
-use aiken::cmd::{build, check, deps, docs, fmt, lsp, new, tx, uplc};
+use aiken::cmd::{
+    build, check,
+    deps::{self, add},
+    docs, fmt, lsp, new, tx, uplc,
+};
 use clap::Parser;
 
 /// Aiken: a smart-contract language and toolchain for Cardano
@@ -12,6 +16,7 @@ pub enum Cmd {
     Build(build::Args),
     Check(check::Args),
     Docs(docs::Args),
+    Add(add::Args),
 
     #[clap(subcommand)]
     Deps(deps::Cmd),
@@ -38,9 +43,10 @@ fn main() -> miette::Result<()> {
         Cmd::New(args) => new::exec(args),
         Cmd::Fmt(args) => fmt::exec(args),
         Cmd::Build(args) => build::exec(args),
-        Cmd::Docs(args) => docs::exec(args),
-        Cmd::Deps(args) => deps::exec(args),
         Cmd::Check(args) => check::exec(args),
+        Cmd::Docs(args) => docs::exec(args),
+        Cmd::Add(args) => add::exec(args),
+        Cmd::Deps(args) => deps::exec(args),
         Cmd::Lsp(args) => lsp::exec(args),
         Cmd::Tx(sub_cmd) => tx::exec(sub_cmd),
         Cmd::Uplc(sub_cmd) => uplc::exec(sub_cmd),