There will be toooooons of these eventually, yes.

Until this is implemented, cargo cannot be used for cross compilation.

+1 for passing flags to the compiler as a critical feature

-O has to be the default.

FWIW, I've forked cargo to always pass the "-O" flag to rustc.

-O should probably be the default for dependencies since they are compiled rarely, but it would be nice for cargo build to default to the fastest option for the main code (i.e. no -O).

#140 has added cargo build --release to build with optimizations

+1 for passing flags like --opt-level=3, -Z lto and --emit=obj via command line or manifest file.

And -Z no-landing-pads.

@alexchandel you seem to be able to do this, right?

Thankfully, Cargo doesn't crash when passed extra unrecognized flags. For libraries, I partially hack around this issue by calling rustc afterwards on the last thing cargo builds.

Please add some target and emission specifications. The lib.crate-types key is completely ignored, AS IS #![crate_type = "staticlib"].

Cargo isn't the last step in many build cycles, and the inability to output object files or to compile static libraries is a huge inconvenience.

Being able to output object files and such would be super awesome!

I tried hacking together a fix for this at https://github.com/bfops/cargo. If people are willing to test for me, you can add

extra_rustc_args = ["--foo", "bar"]

to your Cargo.toml. No support yet for passing directly from the command line.

👍 to arbitrary rustc flags

+1 for LTO; we're thinking of building small shared objects in rust and deploying them inside Linux containers that have tight memory restrictions.

One can get LTO by customising the relevant profile.

This is very nice, but: erszcz/erlang-rust-nif#3
cargo cannot compile under MacOS X without adding specific flags.

@maxlapshin would cargo rustc suffice for your use case?

Holy cargo....

It should be noted that the design of cargo is currently to explicitly not allow arbitrary flags. It is very easy to have compilations go awry very quickly,

I just want to know,a project like servo,how to use cargo for minimize version using prefer-dynamic args?

I found this bug and got confused, so I thought I'd add a note for the benefit of other visitors. As of November 2016 it's perfectly possible to pass arbitrary flags to rustc. If you want to use dynamic libraries, for example, you can do either:

cargo rustc -- -C prefer-dynamic

or

RUSTFLAGS='-C prefer-dynamic' cargo build

Hope this helps someone!

@PeteX It helped me, thanks!

There also seems to be flags like CARGO_TARGET_{target-triple in all caps and with "-" replaced by "_"}_LINKER which are still needed if, for example, you want to cross-compile the tests.

It should be noted that the design of cargo is currently to explicitly not allow arbitrary flags. It is very easy to have compilations go awry very quickly, and packages specifying flags for themselves is likely a decision that should not be up to the author but rather the builder.

I think this is a good argument for published dependencies, but less so for toplevel Cargo.tomls. We already have profiles for this, and ideally they'd be able to specify more. You can always override things via .cargo/config or editing the Cargo.toml.

This becomes frustrating because IDEs no longer work with projects forced to use RUSTFLAGS as part of their build process (e.g. Servo) since their build process is more than cargo build. At best they don't work, at worst they clobber builds to boot.

Really, even the ability to override this in .cargo/config ONLY would be quite useful. But it sounds very much like a profile thing.

Edit: My bad, it's possible to do this in the config already