prints clippy warnigs from cache during normal "cargo build"

[matthiaskrgr]

Problem
While building rustc, I have observed, that when running clippy (./x.py clippy) and than running a normal build afterwards (./x.py build), some of the clippy warnings will be printed from the message cache, although clippy is not executed during x.py build.

Steps

1. x.py clippy
2. x.py build

Looks like the clippy messages are retrieved from the cache when they are not supposed to.

Notes

Output of cargo version:
rustc repo @ 4ff8fb9cb210a9f06e0eafc364bd12de2b67f087
cargo version cargo 1.42.0-nightly (9d32b7b01 2020-01-26)

[ehuss]

I think it is because cargo clippy also enables clippy when building build dependencies. Those build dependencies are reused with cargo build. This normally doesn't come up because build dependencies are normally not local path packages.

I think with #7533 it'll get fixed because it would modify the metadata hash so that it won't share the built dependencies with cargo build.

[ehuss]

Closing in favor of #8143 and rust-lang/rust-clippy#3837.