Counting is difficult: compiler errors are sometimes double-counted

While looking at compile errors reported by Rust Analyzer in VS Code in the file explorer, I've noticed that RA will often report double the numbers of compile errors compared to say, cargo check. I've just tried to reproduce this with a minimal project and I can't, so I'm guessing it might have something to do with compiling the library code for multiple Cargo targets or something.

This is from a work project, but I've also often noticed this while working on rustls (this is after renaming the Vec it is pushing to):

The easy path to a minimal reproduction doesn't work:

This is not a particularly recent regression, I think this has been happening for months for me (mostly noticed while working on rustls) -- but usually I want to drive the error count to zero anyway, so it's not a big issue. Still would be nice to report the number accurately!

rust-analyzer version: rust-analyzer version: 17afa2e77 2022-01-24 stable

rustc version:

djc-2021 proxy domains $ rustc -vV
rustc 1.58.0 (02072b482 2022-01-11)
binary: rustc
commit-hash: 02072b482a8b5357f7fb5e5637444ae30e423c40
commit-date: 2022-01-11
host: aarch64-apple-darwin
release: 1.58.0
LLVM version: 13.0.0

Start by investigating the Rust Analyzer error count shown in the VS Code file explorer and compare it with cargo check on a project that builds library code for multiple Cargo targets. The issue is done when a reproducible case is found and the displayed count matches the distinct compile errors; no source files or tests are identified in the report.