{
  "$type": "site.standard.document",
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  "path": "/t/alternative-to-cargo-new-templates-examples-as-build-target-templates/24047#post_2",
  "publishedAt": "2026-03-02T16:13:39.000Z",
  "site": "https://internals.rust-lang.org",
  "tags": [
    "PackageIdSpec",
    "crates.io",
    "t-cargo > Making alternative registries nicer to use @"
  ],
  "textContent": "One option could be:\n\n\n    $ cargo new --bin --from clap\n    ... list all examples ...\n    $ cargo new --bin --from clap demo\n\n\nwould create\n\n`Cargo.toml`:\n\n\n    ...\n\n    [dependencies]\n    clap = { version = \"4.5.30\", features = [\"derive\" }\n\n\n`src/main.rs`:\n\n\n    use clap::Parser;\n\n    /// Simple program to greet a person\n    #[derive(Parser, Debug)]\n    #[command(version, about, long_about = None)]\n    struct Args {\n        /// Name of the person to greet\n        #[arg(short, long)]\n        name: String,\n\n        /// Number of times to greet\n        #[arg(short, long, default_value_t = 1)]\n        count: u8,\n    }\n\n    fn main() {\n        let args = Args::parse();\n\n        for _ in 0..args.count {\n            println!(\"Hello {}!\", args.name);\n        }\n    }\n\n\nThere are several routes we can take for copying the example:\n\n  * If its `examples/foo.rs`, copy that in. If its a `examples/foo/main.rs` then copy it to `main.rs`, `lib.rs`, or `mod.rs` along with the rest of the directory\n    * Apparently, cargo doesn't discover `examples/foo/lib.rs` though lib examples are supported by setting `crate-types` in `Cargo.toml`\n  * Should we limit lib examples to only being used for mods and `lib.rs`? Or do we auto-append `fn main()`?\n  * Should we limit bin examples to `main.rs`, tests, and build scripts? Or copy them, over and have `main.rs` be dead code?\n\n\n\nFor mods, maybe this would be:\n\n\n    $ cargo new --mod src/foo --from clap demo\n\n\nIf the mod exists, it will be used as the parent for the new mod. If it isn't, then it will be used.\n\nFor Cargo script, it would be:\n\n\n    $ cargo new --file --from clap demo\n\n\nwhere it defaults the filename to the example name if a path isn't given.\n\nThoughts:\n\n  * Not thrilled with multi-valued flags\n  * We could accept a PackageIdSpec for non-dependency packages\n    * Full-form is verbose and hard to write out (`registry+https://github.com/rust-lang/crates.io-index#clap@4.5.56`)\n    * If we support short form (`clap`, `clap@4.5.56`), we could get some dependency confusion going on (thought you were adding an example from a package in a local dependency that points to git or an alt registry but instead get from crates.io. If we support a default registry in `Cargo.toml` as suggested at #t-cargo > Making alternative registries nicer to use @ , then this might limit the impact but not remove it.\n\n",
  "title": "Alternative to `cargo new` templates: examples as build-target templates"
}