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comments](https://triagebot.infra.rust-lang.org/gh-comments/rust-lang/cargo/pull/16796)*
### What does this PR try to resolve?
This allows users to either
- hide warnings (#14258)
- error on warnings (#8424)
`build.warnings` serves a similar purpose as `RUSTFLAGS=-Dwarnings` /
`RUSTFLAGS=-Awarnings` but without invalidation caches.
`build.warnings = "deny"` will
- only errors for lint warnings and not hard warnings
- only errors for local warnings and not non-local warnings visible with
`--verbose --verbose`
- stop the build without `--keep-going`
(this matches `RUSTFLAGS=-Dwarnings`)
These conditions were not originally met and also came as feedback from
rust-lang/rust which has been dogfooding this since the merge of
rust-lang/rust#148332.
`build.warnings = "allow"` will
- only hide lint warnings and not hard warnings
- Note: `RUSTFLAGS=-Awarnings` will suppress rustc hard warnings
- hide non-local warnings for `--verbose --verbose`
- hide the warning summary line (number of warnings per crate)
Closes#14802
### How to test and review this PR?
My main concern over this was how the naming scheme would extend to
https://github.com/rust-lang/rfcs/pull/3730 but that RFC has not gained
much interest
`build` seems as good of a home as any.
e5de173a30