env!("OUT_DIR") macro

[eupn]

Hello,

This PR is related to the #1964.

@matklad pls give a hint on how do we search for the OUT_DIR in the workspace given that we have a target_path from cargo metadata and can use that.

[matklad]

pls give a hint on how do we search for the OUT_DIR in the workspace given that we have

I don't have any better suggestions here than "look at what Cargo does, and do the same" :)

[CAD97]

"look at what Cargo does, and do the same"

Highly relevant:

https://github.com/rust-lang/cargo/blob/b03182a8ff0117ffa1c426119ae2b5a418776bbd/src/cargo/core/compiler/context/compilation_files.rs#L216-L220
https://github.com/rust-lang/cargo/blob/b03182a8ff0117ffa1c426119ae2b5a418776bbd/src/cargo/core/compiler/context/compilation_files.rs#L197-L204
https://github.com/rust-lang/cargo/blob/b03182a8ff0117ffa1c426119ae2b5a418776bbd/src/cargo/core/compiler/context/compilation_files.rs#L164-L170

    /// Returns the "OUT_DIR" directory for running a build script.
    /// `/path/to/target/{debug,release}/build/PKG-HASH/out`
    pub fn build_script_out_dir(&self, unit: &Unit<'a>) -> PathBuf {
        self.build_script_run_dir(unit).join("out")
    }

    /// Returns the directory where a compiled build script is stored.
    /// `/path/to/target/{debug,release}/build/PKG-HASH`
    pub fn build_script_dir(&self, unit: &Unit<'a>) -> PathBuf {
        assert!(unit.target.is_custom_build());
        assert!(!unit.mode.is_run_custom_build());
        let dir = self.pkg_dir(unit);
        self.layout(CompileKind::Host).build().join(dir)
    }

    pub fn pkg_dir(&self, unit: &Unit<'a>) -> String {
        let name = unit.pkg.package_id().name();
        match self.metas[unit] {
            Some(ref meta) => format!("{}-{}", name, meta),
            None => format!("{}-{}", name, self.target_short_hash(unit)),
        }
    }

cargo metadata's target_directory is just the path to the %workspace/target directory, so it seems the only way to get OUT_DIR would be to guess the package meta disambiguator 😞

If nightly cargo is used, cargo +nightly build -Z unstable-options --build-plan outputs a huge JSON blob that includes

{ "invocations": [
  { "package_name": "this-package",
    "target_kind": [ "custom-build" ],
    "compile_mode": "run-custom-build",
    "env": { "OUT_DIR": "/absolute/path/to/target/debug/build/this-package-hash/out" }
  }
]}

This is present even if the build is fresh and would not be rerun, but does seem to make the build stale and queue a new full rebuild 😞

I think the "best" option would to be adding OUT_DIR to the cargo metadata information, if the package meta is set at that point. cc rust-lang/cargo#7546

[CAD97]

Also related: intellij-rust's implementation of env("OUT_DIR"): intellij-rust/intellij-rust#4542

They use cargo build --build-plan.

[edwin0cheng]

@eupn are you still interested in this patch? I'd be happy to continue to implement it.

[eupn]

@edwin0cheng go ahead!

[CAD97]

Current status:

OUT_DIR for a given build script is reported in the build script's build-script-executed message. rust-lang/cargo#7622

Here's IntelliJ Rust's (currently off-by-default) support for OUT_DIR: intellij-rust/intellij-rust#4734 (unless they've done more recently, ofc).

[edwin0cheng]

@CAD97

Yeah, and the current status of RA part :

We have implemented basic include and concat eager builtin macro. So this is the final puzzle for supporting include!(concat!(env!(“OUT_DIR”), “xxx.rs”))!!

[edwin0cheng]

Another update :

#3549 is landed ! Although it didn't implement fetching OUT_DIR from cargo check yet, but I think it works functionally.

I will close this PR now and feel free to reopen it if needed.
Thanks @eupn.