cargo: Cargo occasionally fails to detect changed source code files

Normally when I run cargo build, test, etc then any changes I’ve made to the code are picked up as expected & it re-compiles those parts of the binary.

Occasionally it does not do so, and I need to run cargo clean, then recompile to have my changes recognised.

This seems very similar to #2426 and would probably be solved by #6529

Meta

rustc --version --verbose:

$ rustc --version --verbose
rustc 1.42.0 (b8cedc004 2020-03-09)
binary: rustc
commit-hash: b8cedc00407a4c56a3bda1ed605c6fc166655447
commit-date: 2020-03-09
host: x86_64-unknown-linux-gnu
release: 1.42.0
LLVM version: 9.0

Checking whether it happens in nightly isn’t currently possible as it’s an intermittent issue. I will have to remember to check the next time the issue appears.