Hm, I've tagged this E-mentor, but we haven't really discussed if we want this feature at all. Will bring it up the next cargo team meeting.

We've discussed this on the meeting and we do want this feature, hence feature-accepted label.

We've figured out a better strategy to detect this error than making src readonly. During publish, we can calculate a checksum before and after we run cargo build, and complain if they don't match. That way, we'll be able to give a precise error message, which is much better than build.rs panicking with PermissionDenied.

I think DirectorySource in Cargo calculates checksums of directories, so it might be useful. Alternatively, PathSource::fingerprint method could be used: it computes mtimes and not checksums, but mtimes are probably even better, because we will be able to point which files exactly are modified.

This can be closed now: it's been fixed with #5584.

Hello, I meet a problem due to this:

I'm working on a crate, and need generate code in src only for doc test.

For example, I generate code in src/test_utils/mod.rs, and use it in doc test:

# #[path = "test_utils/mod.rs"]
# mod test_utils;
use test_utils::xxx;

But I cannot publish it recentlty:

error: failed to verify package tarball

Caused by:
  Source directory was modified by build.rs during cargo publish. Build scripts should not modify anything outside of OUT_DIR.
  Changed: /home/louis/rust/.cargo/target/package/fav_utils-0.0.1/src/proto/bili.rs

  To proceed despite this, pass the `--no-verify` flag.

I tried add #[cfg(test)] ahead of Codegen, then it can be published. However, the Codegen can never run during develop.

// build.rs

// This can generate code but cannot be published
fn main() {
    println!("cargo:warning=Generate some code");
}

// This can be published but cannot generate code
fn main() {
    #[cfg(test)]
    println!("cargo:warning=Generate some code");
}

It will be so kind if anyone can give me a suggestion.

Is there a reason you are generating into src/ rather than $OUT_DIR like encouraged at https://doc.rust-lang.org/cargo/reference/build-script-examples.html#code-generation ?