multiple_crate_versions triggered even when dependencies are macro-only

Disclaimer: not sure if this is a bug but the reasoning behind multiple_crate_versions suggests so. May be hard to fix.
Lint name: multiple_crate_versions

I tried this code:
Irrelevant here, but the dependencies are relevant: multiple versions of cfg-if

I expected to see this happen: multiple versions of cfg-if should be fine because macros don't bloat binary sizes

Instead, this happened: error: multiple versions for dependency cfg-if: 0.1.10, 1.0.0

Meta

IDK, I'm filing based on this comment: https://github.com/rust-lang/log/issues/437#issuecomment-760491522

@anthraxx could you provide this information?

• cargo clippy -V: e.g. clippy 0.0.212 (f455e46 2020-06-20)
• rustc -Vv:

  rustc 1.46.0-nightly (f455e46ea 2020-06-20)
  binary: rustc
  commit-hash: f455e46eae1a227d735091091144601b467e1565
  commit-date: 2020-06-20
  host: x86_64-unknown-linux-gnu
  release: 1.46.0-nightly
  LLVM version: 10.0
  

Start by reproducing the multiple_crate_versions diagnostic with the macro-only cfg-if dependency versions described in the issue, using the referenced cargo clippy and rustc -Vv context. Trace how the lint classifies dependencies and confirm that macro-only dependencies no longer trigger the error while ordinary duplicate versions still do.