Infer multi-file binaries like `src/bin/server/main.rs` by convention

[matklad]

Currently cargo infers binaries from files in src/bin. This works if you binary fits in one file, but if you need more than one file, you have to write custom [[bin]] specification in Cargo.toml.

Looks like a reasonable convention for multifile binary projects is this:

src/
  bin/
    server/
        main.rs
        aux.rs
    client/
        main.rs
        foo.rs

So let's infer src/bin/foo/main.rs as a binary named foo?

This should be mostly backwards compatible change. The only failure case is when someone has src/bin/foo/main.rs which is not a binary, and no [[bin]] sections are present, and this seems unlikely.

A potential edge case is

src/
  bin/
    foo.rs
    foo/
      main.rs

This should be an error.

[alexcrichton]

Sounds great to me!

[matklad]

If anyone wants to fix it, the place to look at is this line

cargo/src/cargo/util/toml.rs

Line 54 in 263548d

try_add_files(&mut bins, root_path.join("src").join("bin"));

and this function

cargo/src/cargo/util/toml.rs

Line 503 in 263548d

fn inferred_bin_targets(name: &str, layout: &Layout) -> Vec<TomlTarget> {

.

The tests should probably go into this file: https://github.com/rust-lang/cargo/blob/master/tests/build.rs

[msehnout]

Is anybody working on this?

[alexcrichton]

@msehnout not that I know of, feel free to take it!

[crumblingstatue]

#4214 enabled this for src/bin, but how about also enabling this pattern for examples (and maybe integration tests)?

[matklad]

@crumblingstatue that sounds plausible! Right now I am refactoring the implementation of this stuff in #4259 though, so, if you'd like to send a PR, it's better to wait for a while :)

[rwakulszowa]

Hi @matklad, I think I could try to work on this one. The PR you mentioned is merged already. Is there anything I should be aware of before I start?

[matklad]

Awesome @rwakulszowa ! I think toml/targets.rs is the only file that should me modified, besides the test.

[rwakulszowa]

Hey, I have a few questions

• the discussion here mentions tests and examples. What about banchmarks?
• is there a nice way to test for existence of test binaries? Examples end up in the examples folder, but tests only produce artifacts in the main folder, decorated with hashes; is there a way to pass a regex / prefix string to the assert_that(..., existing_file())?