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Include rustc version in crate disambiguator #85142

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@bjorn3

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@bjorn3

Otherwise with -Zsymbol-mangling-version=v0 and no -Cmetadata, symbols from the same crate compiled with different versions of rustc are named the same. This makes it possible to replace a rust dylib compiled with one version of rustc with one compiled by another version of rustc even if the ABI doesn't match.

The crate disambiguator is calculated at

pub(crate) fn compute_crate_disambiguator(session: &Session) -> CrateDisambiguator {
use std::hash::Hasher;
// The crate_disambiguator is a 128 bit hash. The disambiguator is fed
// into various other hashes quite a bit (symbol hashes, incr. comp. hashes,
// debuginfo type IDs, etc), so we don't want it to be too wide. 128 bits
// should still be safe enough to avoid collisions in practice.
let mut hasher = StableHasher::new();
let mut metadata = session.opts.cg.metadata.clone();
// We don't want the crate_disambiguator to dependent on the order
// -C metadata arguments, so sort them:
metadata.sort();
// Every distinct -C metadata value is only incorporated once:
metadata.dedup();
hasher.write(b"metadata");
for s in &metadata {
// Also incorporate the length of a metadata string, so that we generate
// different values for `-Cmetadata=ab -Cmetadata=c` and
// `-Cmetadata=a -Cmetadata=bc`
hasher.write_usize(s.len());
hasher.write(s.as_bytes());
}
// Also incorporate crate type, so that we don't get symbol conflicts when
// linking against a library of the same name, if this is an executable.
let is_exe = session.crate_types().contains(&CrateType::Executable);
hasher.write(if is_exe { b"exe" } else { b"lib" });
CrateDisambiguator::from(hasher.finish::<Fingerprint>())
}
This should include something like option_env!("CFG_VERSION").unwrap_or("unknown version") in the hash. This matches what the version info included in the rustc metadata header.

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A-linkageArea: linking into static, shared libraries and binariesC-enhancementCategory: An issue proposing an enhancement or a PR with one.T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.

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