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< h1 id = "denywarnings" > < a class = "header" href = "#denywarnings" > < code > #![deny(warnings)]< / code > < / a > < / h1 >
< h2 id = "description" > < a class = "header" href = "#description" > Description< / a > < / h2 >
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< p > A well-intentioned crate author wants to ensure their code builds without
warnings. So they annotate their crate root with the following:< / p >
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< h2 id = "example" > < a class = "header" href = "#example" > Example< / a > < / h2 >
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< pre > < pre class = "playground" > < code class = "language-rust edition2018" >
< span class = "boring" > #![allow(unused)]
< / span > #![deny(warnings)]
< span class = "boring" > fn main() {
< / span > // All is well.
< span class = "boring" > }
< / span > < / code > < / pre > < / pre >
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< h2 id = "advantages" > < a class = "header" href = "#advantages" > Advantages< / a > < / h2 >
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< p > It is short and will stop the build if anything is amiss.< / p >
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< h2 id = "drawbacks" > < a class = "header" href = "#drawbacks" > Drawbacks< / a > < / h2 >
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< p > By disallowing the compiler to build with warnings, a crate author opts out of
Rust's famed stability. Sometimes new features or old misfeatures need a change
in how things are done, thus lints are written that < code > warn< / code > for a certain grace
period before being turned to < code > deny< / code > .< / p >
< p > For example, it was discovered that a type could have two < code > impl< / code > s with the same
method. This was deemed a bad idea, but in order to make the transition smooth,
the < code > overlapping-inherent-impls< / code > lint was introduced to give a warning to those
stumbling on this fact, before it becomes a hard error in a future release.< / p >
< p > Also sometimes APIs get deprecated, so their use will emit a warning where
before there was none.< / p >
< p > All this conspires to potentially break the build whenever something changes.< / p >
< p > Furthermore, crates that supply additional lints (e.g. < a href = "https://github.com/Manishearth/rust-clippy" > rust-clippy< / a > ) can no
longer be used unless the annotation is removed. This is mitigated with
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< a href = "https://doc.rust-lang.org/rustc/lints/levels.html#capping-lints" > --cap-lints< / a > . The < code > --cap-lints=warn< / code > command line argument, turns all < code > deny< / code >
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lint errors into warnings.< / p >
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< h2 id = "alternatives" > < a class = "header" href = "#alternatives" > Alternatives< / a > < / h2 >
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< p > There are two ways of tackling this problem: First, we can decouple the build
setting from the code, and second, we can name the lints we want to deny
explicitly.< / p >
< p > The following command line will build with all warnings set to < code > deny< / code > :< / p >
< p > < code > RUSTFLAGS=" -D warnings" cargo build< / code > < / p >
< p > This can be done by any individual developer (or be set in a CI tool like
Travis, but remember that this may break the build when something changes)
without requiring a change to the code.< / p >
< p > Alternatively, we can specify the lints that we want to < code > deny< / code > in the code.
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Here is a list of warning lints that is (hopefully) safe to deny (as of Rustc 1.48.0):< / p >
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< pre > < code class = "language-rust ignore" > #[deny(bad-style,
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const-err,
dead-code,
improper-ctypes,
non-shorthand-field-patterns,
no-mangle-generic-items,
overflowing-literals,
path-statements ,
patterns-in-fns-without-body,
private-in-public,
unconditional-recursion,
unused,
unused-allocation,
unused-comparisons,
unused-parens,
while-true)]
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< / code > < / pre >
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< p > In addition, the following < code > allow< / code > ed lints may be a good idea to < code > deny< / code > :< / p >
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< pre > < code class = "language-rust ignore" > #[deny(missing-debug-implementations,
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missing-docs,
trivial-casts,
trivial-numeric-casts,
unused-extern-crates,
unused-import-braces,
unused-qualifications,
unused-results)]
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< / code > < / pre >
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< p > Some may also want to add < code > missing-copy-implementations< / code > to their list.< / p >
< p > Note that we explicitly did not add the < code > deprecated< / code > lint, as it is fairly
certain that there will be more deprecated APIs in the future.< / p >
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< h2 id = "see-also" > < a class = "header" href = "#see-also" > See also< / a > < / h2 >
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< ul >
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< li > < a href = "https://rust-lang.github.io/rust-clippy/master" > A collection of all clippy lints< / a > < / li >
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< li > < a href = "https://doc.rust-lang.org/reference/attributes.html#deprecation" > deprecate attribute< / a > documentation< / li >
< li > Type < code > rustc -W help< / code > for a list of lints on your system. Also type
< code > rustc --help< / code > for a general list of options< / li >
< li > < a href = "https://github.com/Manishearth/rust-clippy" > rust-clippy< / a > is a collection of lints for better Rust code< / li >
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