In package with binary and library targets, binary can't link to native libs

[mbrubeck]

When a Cargo package contains both a binary crate and a library crate, linker arguments from the build script are used only when building the library crate.

Originally reported at: https://users.rust-lang.org/t/cant-compile-gtk-hello-world-app/44404

Steps to reproduce:

On a system with zlib installed, run cargo new empty to create a new binary project. Add a build.rs file with the following contents:

fn main() { println!("cargo:rustc-link-lib=z"); }

Replace src/main.rs with the following code:

extern "C" { pub fn zlibVersion() -> *const i8; }
fn main() { unsafe { zlibVersion(); } }

This builds successfully. Note that Cargo passes -l z to rustc when compiling src/main.rs:

$ cargo build -v
   Compiling empty v0.1.0 (/Users/mattbrubeck/src/test/empty)
     Running `rustc --crate-name empty --edition=2018 src/main.rs --error-format=json --json=diagnostic-rendered-ansi --crate-type bin --emit=dep-info,link -Cembed-bitcode=no -C debuginfo=2 -C metadata=e0168590142cc8f4 -C extra-filename=-e0168590142cc8f4 --out-dir /Users/mattbrubeck/src/test/empty/target/debug/deps -C incremental=/Users/mattbrubeck/src/test/empty/target/debug/incremental -L dependency=/Users/mattbrubeck/src/test/empty/target/debug/deps -l z`
    Finished dev [unoptimized + debuginfo] target(s) in 0.19s

Next, run touch src/lib.rs to create an empty library crate. Then build again.

This fails with a linker error when linking the binary. Note that Cargo passes -l z to rustc when compiling src/lib.rs but not when compiling src/main.rs:

$ touch src/lib.rs
$ cargo build -v
   Compiling empty v0.1.0 (/Users/mattbrubeck/src/test/empty)
     Running `/Users/mattbrubeck/src/test/empty/target/debug/build/empty-e48820509d59e846/build-script-build`
     Running `rustc --crate-name empty --edition=2018 src/lib.rs --error-format=json --json=diagnostic-rendered-ansi --crate-type lib --emit=dep-info,metadata,link -Cembed-bitcode=no -C debuginfo=2 -C metadata=74a0fcb7e53d7be8 -C extra-filename=-74a0fcb7e53d7be8 --out-dir /Users/mattbrubeck/src/test/empty/target/debug/deps -C incremental=/Users/mattbrubeck/src/test/empty/target/debug/incremental -L dependency=/Users/mattbrubeck/src/test/empty/target/debug/deps -l z`
     Running `rustc --crate-name empty --edition=2018 src/main.rs --error-format=json --json=diagnostic-rendered-ansi --crate-type bin --emit=dep-info,link -Cembed-bitcode=no -C debuginfo=2 -C metadata=8f7bc0d71f260462 -C extra-filename=-8f7bc0d71f260462 --out-dir /Users/mattbrubeck/src/test/empty/target/debug/deps -C incremental=/Users/mattbrubeck/src/test/empty/target/debug/incremental -L dependency=/Users/mattbrubeck/src/test/empty/target/debug/deps --extern empty=/Users/mattbrubeck/src/test/empty/target/debug/deps/libempty-74a0fcb7e53d7be8.rlib`
error: linking with `cc` failed: exit code: 1
  |
  = note: "cc" "-m64" "-L" "/Users/mattbrubeck/.rustup/toolchains/nightly-2020-05-09-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib" "/Users/mattbrubeck/src/test/empty/target/debug/deps/empty-8f7bc0d71f260462.14fgmq3pyd8wbdzy.rcgu.o" "/Users/mattbrubeck/src/test/empty/target/debug/deps/empty-8f7bc0d71f260462.1nmjqwqdeg3fnvtr.rcgu.o" "/Users/mattbrubeck/src/test/empty/target/debug/deps/empty-8f7bc0d71f260462.222cmglc6zpl1h9c.rcgu.o" "/Users/mattbrubeck/src/test/empty/target/debug/deps/empty-8f7bc0d71f260462.47vtrnft28odh9ni.rcgu.o" "/Users/mattbrubeck/src/test/empty/target/debug/deps/empty-8f7bc0d71f260462.4bedw166csntaxsa.rcgu.o" "-o" "/Users/mattbrubeck/src/test/empty/target/debug/deps/empty-8f7bc0d71f260462" "/Users/mattbrubeck/src/test/empty/target/debug/deps/empty-8f7bc0d71f260462.57a1c5asbd3w922o.rcgu.o" "-Wl,-dead_strip" "-nodefaultlibs" "-L" "/Users/mattbrubeck/src/test/empty/target/debug/deps" "-L" "/Users/mattbrubeck/.rustup/toolchains/nightly-2020-05-09-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib" "/Users/mattbrubeck/.rustup/toolchains/nightly-2020-05-09-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libstd-02be9dff15a2e744.rlib" "/Users/mattbrubeck/.rustup/toolchains/nightly-2020-05-09-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libpanic_unwind-a0dbc9da17125acb.rlib" "/Users/mattbrubeck/.rustup/toolchains/nightly-2020-05-09-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libhashbrown-be16c55789af999a.rlib" "/Users/mattbrubeck/.rustup/toolchains/nightly-2020-05-09-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/librustc_std_workspace_alloc-7323f6a9a844a3dc.rlib" "/Users/mattbrubeck/.rustup/toolchains/nightly-2020-05-09-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libbacktrace-9de488196a5a1e00.rlib" "/Users/mattbrubeck/.rustup/toolchains/nightly-2020-05-09-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libbacktrace_sys-8b6a39e8ef70be7d.rlib" "/Users/mattbrubeck/.rustup/toolchains/nightly-2020-05-09-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/librustc_demangle-a4569d4d3725ef76.rlib" "/Users/mattbrubeck/.rustup/toolchains/nightly-2020-05-09-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libunwind-7d1ef8925268e123.rlib" "/Users/mattbrubeck/.rustup/toolchains/nightly-2020-05-09-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libcfg_if-709a2b0cfa362a8d.rlib" "/Users/mattbrubeck/.rustup/toolchains/nightly-2020-05-09-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/liblibc-98194019dd82bdcf.rlib" "/Users/mattbrubeck/.rustup/toolchains/nightly-2020-05-09-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/liballoc-38feed196e113296.rlib" "/Users/mattbrubeck/.rustup/toolchains/nightly-2020-05-09-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/librustc_std_workspace_core-37c2c6822f6e4416.rlib" "/Users/mattbrubeck/.rustup/toolchains/nightly-2020-05-09-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libcore-2e6e530c778a3583.rlib" "/Users/mattbrubeck/.rustup/toolchains/nightly-2020-05-09-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libcompiler_builtins-0d81316630962f56.rlib" "-lSystem" "-lresolv" "-lc" "-lm"
  = note: Undefined symbols for architecture x86_64:
            "_zlibVersion", referenced from:
                empty::main::h4f36ec3104a21c20 in empty-8f7bc0d71f260462.1nmjqwqdeg3fnvtr.rcgu.o
          ld: symbol(s) not found for architecture x86_64
          clang: error: linker command failed with exit code 1 (use -v to see invocation)
          

error: aborting due to previous error

error: could not compile `empty`.

Caused by:
  process didn't exit successfully: `rustc --crate-name empty --edition=2018 src/main.rs --error-format=json --json=diagnostic-rendered-ansi --crate-type bin --emit=dep-info,link -Cembed-bitcode=no -C debuginfo=2 -C metadata=8f7bc0d71f260462 -C extra-filename=-8f7bc0d71f260462 --out-dir /Users/mattbrubeck/src/test/empty/target/debug/deps -C incremental=/Users/mattbrubeck/src/test/empty/target/debug/incremental -L dependency=/Users/mattbrubeck/src/test/empty/target/debug/deps --extern empty=/Users/mattbrubeck/src/test/empty/target/debug/deps/libempty-74a0fcb7e53d7be8.rlib` (exit code: 1)

Proposed solution

Cargo should pass linker arguments from the build script to rustc for all targets of the package.

[mbrubeck]

Oops, this is a duplicate of #7506.