Compiling crate serde-derive with "-Z sanitizer=leak" fails

[djg]

Compiling my crate that uses serde with RUSTFLAGS="-Z sanitizer=leak" results in:

error: Only executables, staticlibs, cdylibs, dylibs and rlibs can be compiled with `-Z sanitizer`

Verbose output shows:

     Running `rustc --crate-name cubeb_core cubeb-core/src/lib.rs --crate-type lib --emit=dep-info,link -C debuginfo=2 -C metadata=61d1a8a7b2e564d0 -C extra-filename=-61d1a8a7b2e564d0 --out-dir /home/djg/Mozilla/cubeb-rs/target/debug/deps -C incremental=/home/djg/Mozilla/cubeb-rs/target/debug/incremental -L dependency=/home/djg/Mozilla/cubeb-rs/target/debug/deps --extern cubeb_sys=/home/djg/Mozilla/cubeb-rs/target/debug/deps/libcubeb_sys-f4b7e696cf674255.rlib --extern foreign_types=/home/djg/Mozilla/cubeb-rs/target/debug/deps/libforeign_types-9d464a343a654ec3.rlib --extern bitflags=/home/djg/Mozilla/cubeb-rs/target/debug/deps/libbitflags-709a54b1053b84e9.rlib -Z sanitizer=leak -L native=/home/djg/Mozilla/cubeb-rs/target/debug/build/cubeb-sys-52b952c542113788/out/lib -L native=/usr/lib64 -L native=/usr/lib64 -L native=/usr/lib64`
error: aborting due to previous error

error: Could not compile `serde_derive`.

Caused by:
  process didn't exit successfully: `rustc --crate-name serde_derive /home/djg/.cargo/registry/src/github.com-1ecc6299db9ec823/serde_derive-1.0.27/src/lib.rs --crate-type proc-macro --emit=dep-info,link -C prefer-dynamic -C debuginfo=2 --cfg feature="default" -C metadata=8e2449096591e6bb -C extra-filename=-8e2449096591e6bb --out-dir /home/djg/Mozilla/cubeb-rs/target/debug/deps -L dependency=/home/djg/Mozilla/cubeb-rs/target/debug/deps --extern syn=/home/djg/Mozilla/cubeb-rs/target/debug/deps/libsyn-b487ac40d22b413a.rlib --extern quote=/home/djg/Mozilla/cubeb-rs/target/debug/deps/libquote-2902a853682299e0.rlib --extern serde_derive_internals=/home/djg/Mozilla/cubeb-rs/target/debug/deps/libserde_derive_internals-dcd3ff49aa5d175c.rlib --cap-lints warn -Z sanitizer=leak` (exit code: 101)

[djg]

Talking to @Firstyear, proc-macro crates should be ignored by sanitizer.

[RazrFalcon]

Is there a workaround for this bug?

[ishitatsuyuki]

IIRC you need a --target: https://users.rust-lang.org/t/howto-sanitize-your-rust-code/9378

[frewsxcv]

Regarding a fix for this (#63986) we'd need a way to conditionally check whether --target was passed from the command line. Where does the value of this flag get passed through the compiler?

[tmiasko]

What --target does, is to change behavior of cargo so that in no longer uses RUSTFLAGS for builds scripts and procedural macros. In this case it is desirable, since otherwise those instrumented procedural macros are loaded into rustc (which to work would require either instrumented rustc or at least pre-loading the sanitizer runtime).

I think there is little that can be done on rustc side (at best it could generate a warning or an error when building procedural macro crates). I think that improving the user experience here would most likely require implementing sanitizer options in cargo.