Environment variable for Cargo Workspace

[Ygg01]

T-cargo notes:

A CARGO_RUSTC_CURRENT_DIR is added as a nightly only environment variable. See #3946 (comment). Seek for feedback.

---

Hi, while working on using workspace in html5ever, I've ran into issue of needing the CARGO_WORKSPACE directory, and being unable, to find it. What I resorted to is essentially, &Path(cargo_manifest).join("..") which feels hacky.

Could CARGO_WORKSPACE be added as environment variable? I'm not sure what it should be when there is no workspace defined, I assume it should either return Err or default it to CARGO_MANIFEST_DIR.

Sidenote I'm willing to work on this issue, if I could get quick pointers, to what I need to do.

[shepmaster]

when there is no workspace defined

I'd expect the environment variable to not be set at all in that case.

[Ygg01]

What would adding the CARGO_WORKSPACE entail. From cursory look, I see custom_build.rs has reference to Context, that has reference to Workspace, but same doesn't exist for compilation.rs.

Would having CARGO_WORKSPACE only for custom builds be ok?

[alexcrichton]

Thanks for the report! I think I may not quite be following what's going on here though? Do you mean accessing the workspace directory from a build script perhaps?

[Ygg01]

@alexcrichton Yes. I was looking for workspace directory in my custom build script. It's related to servo/html5ever#261.

There is a simple workaround of taking CARGO_MANIFEST_DIR and using its parent, but I thought having CARGO_WORKSPACE would be cleaner solution.

[alexcrichton]

Oh yeah definitely makes sense to me! Seems reasonable to basically enhance this section

[Ygg01]

So if I understand correctly, if I expose workspace.root_manifest that would be workspace dir of all projects in workspace, correct? Then I can just:

if let Some(workspace_dir) = cx.ws.root_manifest() { 
    cmd.env("CARGO_WORKSPACE_DIR", workspace_dir);
}

[alexcrichton]

sounds about right! I think you may not want precisely the root_manifest field but rather ws.root().join("Cargo.toml")

[Ygg01]

@alexcrichton I am total newb, but won't adding Cargo.toml to workspace root, return the location of workspace manifest as opposed to directory of the directory in which workspace manifest is?

[alexcrichton]

oh sure yeah, it just depends on the intent of what's being conveyed (the workspace manifest or the directory of the workspace), I'm fine with either.

[Ygg01]

Hm, while writing tests, I've noticed a peculiarity. I assume I'm using this wrong. But I wanted to double check

let p = project("foo")
    .file("Cargo.toml", r#"
        [project]
        name = "foo"
        version = "0.5.0"
        authors = []


        [workspace]
        members = ["a"]
    "#)
    .file("src/lib.rs", "")
    .file("build.rs", r#"
        fn main() {
            //panic!("WILL FAIL");
        }
    "#)
    .file("a/Cargo.toml", r#"
        [project]
        name = "a"
        version = "0.5.0"
        authors = []
        links = "foo"
        build = "build.rs"
    "#)
    .file("a/src/lib.rs", "")
    .file("a/build.rs", r#"
        fn main() {
                panic!("PASSES?");
        }
    "#);
assert_that(p.cargo_process("build").arg("-v"),
                execs().with_status(0));

The panic in a/build.rs never happens, and panic in build.rs always happens, even if workspace doesn't have a build= "build.rs" line.

Idea behind tests was to verify that each member build.rs has appropriate value for environment variables.

[alexcrichton]

@Ygg01 oh cargo build on a workspace doesn't execute all build scripts, and build.rs is inferred to be a build script if otherwise not specified.

[Ygg01]

@alexcrichton Is there an alternative way to test env. variables are properly set in each member build script?

[alexcrichton]

@Ygg01 I think you'd just cargo build in both directories, right? And then have an assert in the build script the env var is correct?

[Ygg01]

Yes, I think that is correct (one call to cargo build in member directory and one call in workspace directory). Are there any examples of such code? I can only see adding files to ProjectBuilder file.

[alexcrichton]

Oh you'll just want to call p.cargo multiple times basically, there's some other tests I believe which run cargo more than once.