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<ol class="chapter"><li class="chapter-item expanded "><a href="../intro.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../translations.html"><strong aria-hidden="true">1.1.</strong> Translations</a></li></ol></li><li class="chapter-item expanded "><a href="../idioms/index.html"><strong aria-hidden="true">2.</strong> Idioms</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../idioms/coercion-arguments.html"><strong aria-hidden="true">2.1.</strong> Use borrowed types for arguments</a></li><li class="chapter-item expanded "><a href="../idioms/concat-format.html"><strong aria-hidden="true">2.2.</strong> Concatenating Strings with format!</a></li><li class="chapter-item expanded "><a href="../idioms/ctor.html"><strong aria-hidden="true">2.3.</strong> Constructor</a></li><li class="chapter-item expanded "><a href="../idioms/default.html"><strong aria-hidden="true">2.4.</strong> 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mutability</a></li><li class="chapter-item expanded "><a href="../idioms/return-consumed-arg-on-error.html"><strong aria-hidden="true">2.15.</strong> Return consumed arg on error</a></li></ol></li><li class="chapter-item expanded "><a href="../patterns/index.html"><strong aria-hidden="true">3.</strong> Design Patterns</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../patterns/behavioural/intro.html"><strong aria-hidden="true">3.1.</strong> Behavioural</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../patterns/behavioural/command.html"><strong aria-hidden="true">3.1.1.</strong> Command</a></li><li class="chapter-item expanded "><a href="../patterns/behavioural/interpreter.html"><strong aria-hidden="true">3.1.2.</strong> Interpreter</a></li><li class="chapter-item expanded "><a href="../patterns/behavioural/newtype.html"><strong aria-hidden="true">3.1.3.</strong> Newtype</a></li><li class="chapter-item expanded "><a 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class="section"><li class="chapter-item expanded "><a href="../patterns/structural/compose-structs.html"><strong aria-hidden="true">3.3.1.</strong> Compose Structs</a></li><li class="chapter-item expanded "><a href="../patterns/structural/small-crates.html"><strong aria-hidden="true">3.3.2.</strong> Prefer Small Crates</a></li><li class="chapter-item expanded "><a href="../patterns/structural/unsafe-mods.html"><strong aria-hidden="true">3.3.3.</strong> Contain unsafety in small modules</a></li></ol></li><li class="chapter-item expanded "><a href="../patterns/ffi/intro.html"><strong aria-hidden="true">3.4.</strong> Foreign function interface (FFI)</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../patterns/ffi/export.html"><strong aria-hidden="true">3.4.1.</strong> Object-Based APIs</a></li><li class="chapter-item expanded "><a href="../patterns/ffi/wrappers.html"><strong aria-hidden="true">3.4.2.</strong> Type Consolidation into Wrappers</a></li></ol></li></ol></li><li class="chapter-item expanded "><a href="../anti_patterns/index.html"><strong aria-hidden="true">4.</strong> Anti-patterns</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../anti_patterns/borrow_clone.html"><strong aria-hidden="true">4.1.</strong> Clone to satisfy the borrow checker</a></li><li class="chapter-item expanded "><a href="../anti_patterns/deny-warnings.html" class="active"><strong aria-hidden="true">4.2.</strong> #[deny(warnings)]</a></li><li class="chapter-item expanded "><a href="../anti_patterns/deref.html"><strong aria-hidden="true">4.3.</strong> Deref Polymorphism</a></li></ol></li><li class="chapter-item expanded "><a href="../functional/index.html"><strong aria-hidden="true">5.</strong> Functional Programming</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../functional/paradigms.html"><strong aria-hidden="true">5.1.</strong> Programming paradigms</a></li><li 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<h1 id="denywarnings"><a class="header" href="#denywarnings"><code>#![deny(warnings)]</code></a></h1>
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<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
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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)]
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</span>#![deny(warnings)]
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<span class="boring">fn main() {
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</span>// All is well.
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<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
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Rust's famed stability. Sometimes new features or old misfeatures need a change
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in how things are done, thus lints are written that <code>warn</code> for a certain grace
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period before being turned to <code>deny</code>.</p>
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<p>For example, it was discovered that a type could have two <code>impl</code>s with the same
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method. This was deemed a bad idea, but in order to make the transition smooth,
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the <code>overlapping-inherent-impls</code> lint was introduced to give a warning to those
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stumbling on this fact, before it becomes a hard error in a future release.</p>
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<p>Also sometimes APIs get deprecated, so their use will emit a warning where
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before there was none.</p>
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<p>All this conspires to potentially break the build whenever something changes.</p>
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<p>Furthermore, crates that supply additional lints (e.g. <a href="https://github.com/Manishearth/rust-clippy">rust-clippy</a>) can no
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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
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setting from the code, and second, we can name the lints we want to deny
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explicitly.</p>
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<p>The following command line will build with all warnings set to <code>deny</code>:</p>
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<p><code>RUSTFLAGS="-D warnings" cargo build</code></p>
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<p>This can be done by any individual developer (or be set in a CI tool like
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Travis, but remember that this may break the build when something changes)
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without requiring a change to the code.</p>
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<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,
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dead_code,
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improper_ctypes,
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non_shorthand_field_patterns,
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no_mangle_generic_items,
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overflowing_literals,
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path_statements,
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patterns_in_fns_without_body,
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private_in_public,
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unconditional_recursion,
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unused,
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unused_allocation,
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unused_comparisons,
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unused_parens,
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while_true)]</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,
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trivial_casts,
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trivial_numeric_casts,
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unused_extern_crates,
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unused_import_braces,
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unused_qualifications,
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unused_results)]</code></pre>
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<p>Some may also want to add <code>missing-copy-implementations</code> to their list.</p>
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<p>Note that we explicitly did not add the <code>deprecated</code> lint, as it is fairly
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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>
|
|
<li><a href="https://doc.rust-lang.org/reference/attributes.html#deprecation">deprecate attribute</a> documentation</li>
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<li>Type <code>rustc -W help</code> for a list of lints on your system. Also type
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<code>rustc --help</code> for a general list of options</li>
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<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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</ul>
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