rustc hides linker warnings

[ahl]

I encountered an issue with the linkme crate on illumos (OpenSolaris/OmniOS/Helios) demonstrated with this repo. Of note, the build executes without error or warning, but in fact the linker is emitting an error:

$ cargo run
   Compiling cmd v0.1.0 (/home/ahl/linkme-test/cmd)
    Finished dev [unoptimized + debuginfo] target(s) in 0.28s
     Running `target/debug/cmd`
$ cargo rustc
    Finished dev [unoptimized + debuginfo] target(s) in 0.01s

I can make the linker fail on warnings:

$ cargo rustc -- -C link-arg=-Wl,-zfatal-warnings
   Compiling cmd v0.1.0 (/home/ahl/linkme-test/cmd)
error: linking with `gcc` failed: exit code: 1
  |
  = note: "gcc" "-m64" "-std=c99" "-L" "/opt/ooce/rust/lib/rustlib/x86_64-unknown-illumos/lib" "/home/ahl/linkme-test/cmd/target/debug/deps/cmd-26e8351dc3f3fb69.1m65hci6o5zni2mr.rcgu.o" "/home/ahl/linkme-test/cmd/target/debug/deps/cmd-26e8351dc3f3fb69.1r2sofzghiioxykg.rcgu.o" "/home/ahl/linkme-test/cmd/target/debug/deps/cmd-26e8351dc3f3fb69.2i3xjlynwxgqlmzu.rcgu.o" "/home/ahl/linkme-test/cmd/target/debug/deps/cmd-26e8351dc3f3fb69.3hvsf4zj59kihrhf.rcgu.o" "/home/ahl/linkme-test/cmd/target/debug/deps/cmd-26e8351dc3f3fb69.3lsh1pzemq0xblzm.rcgu.o" "/home/ahl/linkme-test/cmd/target/debug/deps/cmd-26e8351dc3f3fb69.3zpatajw7m7uqqns.rcgu.o" "/home/ahl/linkme-test/cmd/target/debug/deps/cmd-26e8351dc3f3fb69.4yxic0y84aboqmeb.rcgu.o" "/home/ahl/linkme-test/cmd/target/debug/deps/cmd-26e8351dc3f3fb69.a1lfmxsp6lqzsbn.rcgu.o" "-o" "/home/ahl/linkme-test/cmd/target/debug/deps/cmd-26e8351dc3f3fb69" "/home/ahl/linkme-test/cmd/target/debug/deps/cmd-26e8351dc3f3fb69.3n70o9wfzqm9tbsh.rcgu.o" "-Wl,-zignore" "-nodefaultlibs" "-L" "/home/ahl/linkme-test/cmd/target/debug/deps" "-L" "/opt/ooce/rust/lib/rustlib/x86_64-unknown-illumos/lib" "-Wl,-Bstatic" "/home/ahl/linkme-test/cmd/target/debug/deps/liblib-3d689bd64c3873d5.rlib" "/home/ahl/linkme-test/cmd/target/debug/deps/liblinkme-21c998585e123796.rlib" "-Wl,--start-group" "/opt/ooce/rust/lib/rustlib/x86_64-unknown-illumos/lib/libstd-cd23cc7e75a2851c.rlib" "/opt/ooce/rust/lib/rustlib/x86_64-unknown-illumos/lib/libpanic_unwind-566bad254d0594e5.rlib" "/opt/ooce/rust/lib/rustlib/x86_64-unknown-illumos/lib/libminiz_oxide-96e54319d1590148.rlib" "/opt/ooce/rust/lib/rustlib/x86_64-unknown-illumos/lib/libadler-4dbe2335326bb316.rlib" "/opt/ooce/rust/lib/rustlib/x86_64-unknown-illumos/lib/libobject-b0fd875741b20fc0.rlib" "/opt/ooce/rust/lib/rustlib/x86_64-unknown-illumos/lib/libaddr2line-089ce7b4c263282a.rlib" "/opt/ooce/rust/lib/rustlib/x86_64-unknown-illumos/lib/libgimli-ca92a564b7883a12.rlib" "/opt/ooce/rust/lib/rustlib/x86_64-unknown-illumos/lib/librustc_demangle-ce8ee413f3ea18b6.rlib" "/opt/ooce/rust/lib/rustlib/x86_64-unknown-illumos/lib/libhashbrown-17e15682bef35ec2.rlib" "/opt/ooce/rust/lib/rustlib/x86_64-unknown-illumos/lib/librustc_std_workspace_alloc-2dc950a425ee77d8.rlib" "/opt/ooce/rust/lib/rustlib/x86_64-unknown-illumos/lib/libunwind-50867a64287c1bd2.rlib" "/opt/ooce/rust/lib/rustlib/x86_64-unknown-illumos/lib/libcfg_if-129bada4e936c5a0.rlib" "/opt/ooce/rust/lib/rustlib/x86_64-unknown-illumos/lib/liblibc-a98e4fa0f203a39a.rlib" "/opt/ooce/rust/lib/rustlib/x86_64-unknown-illumos/lib/liballoc-35c480f88f8f320a.rlib" "/opt/ooce/rust/lib/rustlib/x86_64-unknown-illumos/lib/librustc_std_workspace_core-86dc76527c7e216a.rlib" "/opt/ooce/rust/lib/rustlib/x86_64-unknown-illumos/lib/libcore-093275d7382c1a2f.rlib" "-Wl,--end-group" "/opt/ooce/rust/lib/rustlib/x86_64-unknown-illumos/lib/libcompiler_builtins-358913705748e96c.rlib" "-Wl,-Bdynamic" "-lsocket" "-lposix4" "-lpthread" "-lresolv" "-lnsl" "-lumem" "-lgcc_s" "-lc" "-lm" "-lrt" "-lpthread" "-Wl,-zfatal-warnings" "-lssp"
  = note: ld: warning: reserved symbol '__start_set_linkme_DOERS' already defined in file /home/ahl/linkme-test/cmd/target/debug/deps/liblib-3d689bd64c3873d5.rlib(lib-3d689bd64c3873d5.2vwi8dtk7ky9hvmq.rcgu.o)
          ld: warning: reserved symbol '__stop_set_linkme_DOERS' already defined in file /home/ahl/linkme-test/cmd/target/debug/deps/liblib-3d689bd64c3873d5.rlib(lib-3d689bd64c3873d5.2vwi8dtk7ky9hvmq.rcgu.o)
          collect2: error: ld returned 1 exit status
          

error: aborting due to previous error

error: could not compile `cmd`.

To learn more, run the command again with --verbose.

These linker warnings need not have been fatal, but I think it would be reasonable for cargo build / cargo run / cargo rustc to display these warnings. In this case those warnings would have helped determine the underlying issues much earlier. Indeed, it seems rare that linker warnings would truly be specious.

Meta

rustc --version --verbose:

$ rustc --version --verbose
rustc 1.47.0
binary: rustc
commit-hash: unknown
commit-date: unknown
host: x86_64-unknown-illumos
release: 1.47.0
LLVM version: 11.0