Cargo Groups Feature Request Discussion Options Passing

This article discusses a feature request for the cargo-groups tool, focusing on the ability to pass additional options through to underlying Cargo commands like build, check, and test. The current implementation has limitations in this area, which this article will explore. A user has encountered a use case where they need to pass options like --release and --timings to cargo build when using cargo groups. However, they've found that this is not directly supported and have proposed a potential solution. This article delves into the problem, the proposed solution, and the broader implications for the usability and flexibility of cargo-groups.

The Problem: Limited Option Passing

The core challenge lies in the inability to seamlessly pass arbitrary options through cargo-groups to the underlying Cargo commands. Currently, cargo-groups doesn't provide a mechanism to forward options like --release, --timings, --target, --target-dir, --jobs, or --profile directly to commands such as cargo build, cargo check, or cargo test. This limitation restricts the flexibility of the tool and forces users to find workarounds or forgo using cargo-groups in certain scenarios.

When users attempt to pass these options, they encounter errors indicating that the options are unexpected. For instance, the error message error: unexpected argument '--timings' found clearly illustrates this issue. The suggested tip, tip: to pass '--timings' as a value, use '-- --timings', does not resolve the problem in this context, as it's not designed for passing options to the underlying Cargo commands.

This limitation stems from the way cargo-groups parses command-line arguments. It defines a specific set of options it recognizes and processes, and any other options are treated as errors. This rigid structure prevents users from leveraging the full range of options available in Cargo commands, hindering their ability to fine-tune builds, tests, and checks according to their specific needs.

The impact of this limitation is significant. Developers often rely on these options to optimize build times, target specific platforms, or generate profiling information. Without the ability to pass these options through cargo-groups, users may need to resort to manually running Cargo commands for each group, negating the benefits of using cargo-groups in the first place. This friction reduces the tool's usability and can discourage its adoption in complex projects.

A Proposed Solution: Modifying CommandOptions

One potential solution involves modifying the CommandOptions struct within the cargo-groups codebase. The user who raised this issue suggested adding fields to the CommandOptions struct for common flags like --release and --timings. Here's the proposed modification:

// Common flags like --release
#[derive(Parser, Debug)]
struct CommandOptions<Specific = DefaultSpecificOptions>
where
    Specific: Parser + ClapArgs,
{
    #[arg(long)]
    release: bool,
    #[arg(long)]
    timings: bool,
    #[command(flatten)]
    specific: Specific,
}

impl<T> Options for CommandOptions<T>
where
    T: Options + Parser + ClapArgs,
{
    fn add_to_command(&self, cmd: &mut process::Command) {
        let Self {
            release,
            specific,
            timings,
        } = self;
        if *release {
            cmd.arg("--release");
        }

        if *timings {
            cmd.arg("--timings");
        }

        specific.add_to_command(cmd);
    }
}

This modification introduces boolean fields for --release and --timings within the CommandOptions struct. The add_to_command method is then updated to include these flags when constructing the Cargo command. While this approach addresses the immediate need to pass --release and --timings, it's not a comprehensive solution. The key limitation is that it requires explicitly adding fields for each option that needs to be supported. This approach is not scalable and would necessitate frequent code changes to accommodate new options.

The user themselves acknowledged that this solution