Add rustc --run

[SiegeLord]

With the removal of the rust tool, there is nothing good to place in the initial hashbang comment in a Rust file (you used to be put rust run in there). rustc --run should be added to fill that gap.

The use case, of course, is some kind support for script-like usage for Rust which will become attractive when the compilation speed improves.

[thestinger]

Also useful would be rustc --test and rustc --bench.

[mletterle]

Is adding all the old rust functionality to rustc really a good idea? Why not have rust resurrected as a separate project?

[thestinger]

I don't think we should have more than one official tool for the same functionality. Either we should commit to moving everything we have now behind a rust command or implement useful functionality for the existing commands.

[SiegeLord]

I was thinking that --run would be composable with other arguments. Since rustc --test already exists, the usage for testing/benchmarking would look like this:

rustc --test --run
rustc --test --run --bench

In the latter case --bench is passed to the test executable (I.e. I'm thinking that all arguments after --run get passed to the executable). Alternatively, --bench could be introduced to rustc and it'd look like this:

rustc --bench --run

[RSully]

Has there been any updates for the compile+execute functionality? Similar to go run?

[japaric]

I got a minimal working implementation here. Feedback welcome.

N.B. I decided to wrap rustc rather than modify it, because that seemed like the fastest way to get a working prototype.

[Ape]

I think we should store the compiled binaries to boost the performance. That way it could easily replace small Python scripts and actually be faster to execute.

When running a rust script (with rustic shebang) called hello.rs, it would check if hello.rsc exists and is modified after hello.rs. If so, it would just execute the binary. Otherwise it would compile, store the binary and then run it.

I would like to see this behaviour merged to the main project.

[thestinger]

It's not that simple. It would need to verify that none of the modules or crates it depends on changed, along with making sure rustc itself wasn't updated.

[steveklabnik]

cargo run serves this purpose.

[SiegeLord]

No, it does not (at least not in its current incarnation). The purpose of rustc --run is to be placed in the hashbang comment. cargo run, on the other hand, currently requires a specific directory structure and Cargo.toml that does not appear to work for this purpose.

[Binero]

I do agree the rust compiler should be able to run rust code.

[japaric]

This issue is a feature request, and needs an approved RFC to be implemented. It should be moved to the rust-lang/rfcs repo. (As per the issues policy)

cc @nick29581

[nrc]

I don't think compiler features (cf language features) need an RFC unless they are very far reaching. Leaving here for now.