"cannot produce proc-macro for `crate` as the target `x86_64-unknown-linux-gnu` does not support these crate types" with +crt-static

[otavio]

Build error

% RUSTFLAGS="-C target-feature=+crt-static" cargo +nightly check
error: cannot produce proc-macro for `ctor v0.1.16` as the target `x86_64-unknown-linux-gnu` does not support these crate types

Version it worked on

It most recently worked on: rustc 1.48.0-beta.4 (fb94aa5 2020-10-20)

@rustbot modify labels: +regression-from-stable-to-nightly -regression-untriaged

[camelid]

Could you provide a reproduction?

[camelid]

And also the version you're testing with?

[otavio]

And also the version you're testing with?

The nightly of 2020-10-20.

Could you provide a reproduction?

I'm out of computer now, so I can't. It seems to be related to proc macro use. I can try to cook a test case for it.

[tesuji]

@rustbot modify labels: E-needs-mcve

[mati865]

It most recently worked on: rustc 1.48.0-beta.4 (fb94aa5 2020-10-20)

It did not really work but didn't produce the error since +crt-static was no-op for linux-gnu.
Since #77386 +crt-static now properly links statically.

I think I can add workaround for it.

[mati865]

It works with explicit target:

$ RUSTFLAGS='-C target-feature=+crt-static' cargo b
error: cannot produce proc-macro for `ctor v0.1.16 (/tmp/rust-ctor/ctor)` as the target `x86_64-unknown-linux-gnu` does not support these crate types

$ RUSTFLAGS='-C target-feature=+crt-static' cargo b --target x86_64-unknown-linux-gnu
   Compiling libc v0.2.79
   Compiling proc-macro2 v0.4.30
   Compiling unicode-xid v0.1.0
   Compiling proc-macro2 v1.0.23
   Compiling syn v0.15.44
   Compiling unicode-xid v0.2.0
   Compiling syn v1.0.46
   Compiling lazy_static v1.4.0
   Compiling quote v0.6.13
   Compiling quote v1.0.7
   Compiling libc-print v0.1.14
   Compiling dlopen_derive v0.1.4
   Compiling dlopen v0.1.8
   Compiling ctor v0.1.16 (/tmp/rust-ctor/ctor)
   Compiling tests v0.1.0 (/tmp/rust-ctor/tests)
    Finished dev [unoptimized + debuginfo] target(s) in 7.14s

cc @petrochenkov I assume it's expected that #69519 helped only the case with explicit (aka cross-compiled) target?

[petrochenkov]

@mati865
#69519 introduced different defaults for crt-static for executables (yes) and proc-macros (no) (should apply to all dylibs really).
If -C target-feature=+crt-static is specified explicitly, then the compiler respects it and overrides the defaults, that's the compiler's job.

Then cargo comes into play. AFAIK, it applies RUSTFLAGS only to target if --target specified explicitly, and to both target and host otherwise. (I remember people complaining about this inconsistency.)
So it doesn't pass -C target-feature=+crt-static when compiling proc macro dependencies (which is correct in this case).
I think this is a problem that should be solved at the cargo's abstraction level, in general. Cargo should provide a way to set compiler options per-crate-type and per-build-target (per-crate), and may provide its own defaults (e.g. not pass +crt-static to proc macro crates).

[otavio]

My biggest concern here is this looks like a regression from the user point of view; what can we currently do to workaround it until it is handled on the cargo's abtraction level, as suggested by @petrochenkov?