Rebuild/emit new object file if it has been removed but the source has not changed

[micouy]

I compile my project to an object file I then want to link with non-Rust files:

cargo rustc --release -Z build-std=core -- --emit obj=my-project.o

But sometimes I remove all object files in my project dir. I then want to rebuild my project without changing the source but cargo doesn't emit the object file.

cargo clean -p my-project && cargo rustc ...

Cleaning and building again by running the command above doesn't work. It only emits a new binary file (to the target dir) if I remove it. It may be related to the fact that I build the core library. That's because the binary is emitted to target/target/release not target/release as usual.

What can I do to force cargo to rebuild the project? I don't want to clean the whole target dir since I'd have to rebuild the core crate each time.

[ehuss]

Hm, I'm having a bit of a hard time understanding the exact issue here. It looks like there might be some misconfiguration by the presence of directories like target/target/release. Also, I'm uncertain when you mention "binary file", is my-project a library project or an executable or both? It might help to put together a full reproduction to demonstrate what is going on.

cargo clean -p foo should clean the foo project. Since it looks like you are using -Zbuild-std, but you don't mention passing --target, I'm guessing you have build.target set in a config file? If so, it looks like there is maybe a confusing interaction because cargo clean does not read that. You can clean the project with cargo clean -p my-project --target $TARGET.

[micouy]

1. By my-project I mean the ELF executable, usually located in target/release or target/debug.
2. You are correct, I use a custom target specified in .cargo/config. Sorry, I forgot to mention it.

I solved the issue by running:

cargo clean -p my-project --target $TARGET --release

The flags passed to the clean command must match the ones passed to rustc so I just had to add the --release flag. Thanks for the hint with the --target flag.

However, I wonder why the --target flag is necessary. In the clean command specification it says:

--target TRIPLE
[...]
This may also be specified with the build.target config value.

I ran cargo clean -p my-project --release --verbose first without and then with the --target flag and despite the build.target value being set in the config, without the flag it did nothing.

$ cargo clean -p my-project --release --verbose # doesn't do anything
$ cargo clean -p my-project --release --target $TARGET --verbose
    Removing [...]

[ehuss]

However, I wonder why the --target flag is necessary.

I think it's probably just an oversight. It seems reasonable to me for cargo clean to use build.target by default.