Separate backend and CLI (#25)

Closes #21.

This PR implements the advise given by @sixfold-origami on Discord. It
makes `bevy_cli` is proper library, moving all `clap` logic to
`main.rs`. It also moves `main.rs` and `lint_driver.rs` to the `src/bin`
folder, so they are distinct from library modules.

I also added a few comments to `Cargo.toml` in
7d22ab7 in a drive-by pass.

---------

Co-authored-by: Rose Peck <rosepeck1997@gmail.com>

Cargo.toml

@@ -6,18 +6,28 @@ name = "bevy_cli"
 version = "0.1.0-dev"
 edition = "2021"
 license = "MIT OR Apache-2.0"
+# When no binary is specific, run the main CLI by default.
 default-run = "bevy"
 
+# The main CLI executable
 [[bin]]
 name = "bevy"
-path = "src/main.rs"
+path = "src/bin/main.rs"
 
+# Integrates custom lints with `rustc`
 [[bin]]
 name = "bevy_lint_driver"
-path = "src/lint_driver.rs"
+path = "src/bin/lint_driver.rs"
 
 [dependencies]
+# CLI argument parsing
+clap = { version = "4.5.16", features = ["derive"] }
+
+# Easy error propagation and contexts
 anyhow = "1.0.86"
-bevy_lint = { version = "0.1.0-dev", path = "./bevy_lint" }
+
+# Generates new Bevy projects from templates
 cargo-generate = "0.21.3"
-clap = { version = "4.5.16", features = ["derive"] }
+
+# Bevy-specific lints
+bevy_lint = { version = "0.1.0-dev", path = "./bevy_lint" }

src/args.rs → src/bin/main.rs

@@ -1,6 +1,19 @@
-use cargo_generate::TemplatePath;
+use anyhow::Result;
 use clap::{Args, Parser, Subcommand};
 
+fn main() -> Result<()> {
+    let cli = Cli::parse();
+
+    match cli.subcommand {
+        Subcommands::New(new) => {
+            bevy_cli::template::generate_template(&new.name, new.template.as_deref())?;
+        }
+        Subcommands::Lint => bevy_cli::lint::lint()?,
+    }
+
+    Ok(())
+}
+
 /// Command-line interface for the Bevy Game Engine
 ///
 /// This CLI provides tools for Bevy project management,
@@ -41,21 +54,3 @@ pub struct NewArgs {
     #[arg(short, long)]
     pub template: Option<String>,
 }
-
-impl NewArgs {
-    /// The path to the template to use for generating the project.
-    pub fn template_path(&self) -> TemplatePath {
-        if let Some(template) = &self.template {
-            TemplatePath {
-                git: Some(template.clone()),
-                ..Default::default()
-            }
-        } else {
-            TemplatePath {
-                git: Some("https://github.com/TheBevyFlock/bevy_quickstart.git".to_string()),
-                branch: Some("cargo-generate".to_string()),
-                ..Default::default()
-            }
-        }
-    }
-}

src/lib.rs

@@ -0,0 +1,4 @@
+//! The library backend for the Bevy CLI.
+
+pub mod lint;
+pub mod template;

src/template.rs

@@ -0,0 +1,38 @@
+use cargo_generate::{GenerateArgs, TemplatePath};
+use std::path::PathBuf;
+
+/// Generates a new template to the returned [`PathBuf`] using the given name and Git repository.
+///
+/// If `git` is [`None`], it will default to [TheBevyFlock/bevy_quickstart].
+///
+/// [TheBevyFlock/bevy_quickstart]: https://github.com/TheBevyFlock/bevy_quickstart
+pub fn generate_template(name: &str, git: Option<&str>) -> anyhow::Result<PathBuf> {
+    cargo_generate::generate(GenerateArgs {
+        template_path: template_path(git),
+        name: Some(name.to_string()),
+        // prevent conversion to kebab-case
+        force: true,
+        ..Default::default()
+    })
+}
+
+/// Returns the [`TemplatePath`] for a given Git repository.
+///
+/// If `git` is [`None`], it will default to `bevy_quickstart`.
+fn template_path(git: Option<&str>) -> TemplatePath {
+    const DEFAULT_REPOSITORY: &str = "https://github.com/TheBevyFlock/bevy_quickstart.git";
+    const DEFAULT_BRANCH: &str = "cargo-generate";
+
+    if let Some(template) = git {
+        TemplatePath {
+            git: Some(template.to_string()),
+            ..Default::default()
+        }
+    } else {
+        TemplatePath {
+            git: Some(DEFAULT_REPOSITORY.to_string()),
+            branch: Some(DEFAULT_BRANCH.to_string()),
+            ..Default::default()
+        }
+    }
+}