--emit=metadata,obj produces confusing error

[DusterTheFirst]

EDIT ehuss:

With an empty file, foo.rs, the command rustc --emit=metadata,obj --crate-type=lib foo.rs returns a confusing error:

error: failed to build archive: No such file or directory

The error message should at least be a little clearer. I do not know why the combination of metadata+obj causes this error. obj by itself is fine, but for some reason adding metadata causes an error.

---

Original bug report below:

Original title: Cargo check fails to build the same package that cargo build can with an unhelpful error

Problem

When running cargo check on my project, it errors out with the following error

a very unhelpful, cryptic error. Running with verbose gives no more info than i can get from this screenshot alone.

I have been able to notice that it only happens when compiling for the target thumbv7em-none-eabihf and not my native target thumbv7em-none-eabihf

Steps
I have made a minimum example git repo
https://github.com/DusterTheFirst/cargo-check-bug-cfg-if

Possible Solution(s)

More descriptive errors than "No such file or directory" such as information about the file that is missing would help in solving the problem.

Notes
Output of cargo version:
cargo 1.48.0-nightly (875e01232 2020-09-08)
and
cargo 1.46.0 (149022b1d 2020-07-17)

rustup show

Default host: x86_64-unknown-linux-gnu
rustup home:  /home/dusterthefirst/.local/share/rustup

installed toolchains
--------------------

stable-x86_64-unknown-linux-gnu (default)
nightly-x86_64-unknown-linux-gnu

installed targets for active toolchain
--------------------------------------

thumbv7em-none-eabi
thumbv7em-none-eabihf
x86_64-unknown-linux-gnu

active toolchain
----------------

nightly-x86_64-unknown-linux-gnu (overridden by '/home/dusterthefirst/Documents/projects/rockets/avionics/viper/rust-toolchain')
rustc 1.48.0-nightly (a1947b3f9 2020-09-10)

[ehuss]

Thanks for the detailed report! I have transferred this to rust-lang/rust, as the issue appears to originate in rustc.

This is caused by the --emit=obj in your config file. I'm uncertain why you have included that, though. Generally, I don't think that should be passed to every compiler invocation. But the compiler also probably shouldn't fail.

[DusterTheFirst]

the specific use case that I have is using the outputted obj file into a c compiler for embedded development. Namely compiling a rust binary and feeding it into platformio so that it can link to the arduino library

[ehuss]

I believe this is now fixed via #81118.