rustc --emit=dep-info -Zbinary-dep-depinfo -C prefer-dynamic=yes misses .so input dep

[fangism]

With a command like:

rustc --emit=dep-info=foo.d -Zbinary-dep-depinfo -C prefer-dynamic ...

which uses the rust std library:

libstd-dafa2c58b8297b90.rlib
libstd-dafa2c58b8297b90.so

I expected to see both the .rlib and .so in the generated depfile, however, the .so is missing.

Meta

rustc --version --verbose:

rustc 1.57.0-nightly (af9b508e1 2021-10-15)
binary: rustc
commit-hash: af9b508e1d6c83a8f0e6f5c0b2b75598aa37ed27
commit-date: 2021-10-15
host: x86_64-unknown-linux-gnu
release: 1.57.0-nightly
LLVM version: 13.0.0

Why this is important: We rely on the depfile to know what inputs to upload for remote building. When the .so file is missing we find that rustc still silently and happily builds the crate, but with a different (static?) linking result, which means local output != remote output (but we want perfect reproducibility).

[bjorn3]

You need the unstable -Zbinary-dep-depinfo to get the depinfo for anything other than the source files of the current crate. Cargo internally registers extra file dependencies for all --extern arguments it passes.

Tracking issue: #63012

Edit: Somehow completely overlooked that you passed -Zbinary-dep-depinfo. 🤦 I think #113695 will fix this as side effect for all crates that actually get linked. For rlib crates -Cprefer-dynamic doesn't have any effect and rustc only needs the crate metadata from the rlib (or .rmeta file) anyway.

[bjorn3]

This is still the case even now that #113695 has been merged.