Macro rustc_ap_rustc_session::declare_lint

macro_rules! declare_lint {
    ($(#[$attr:meta])* $vis: vis $NAME: ident, $Level: ident, $desc: expr) => { ... };
    ($(#[$attr:meta])* $vis: vis $NAME: ident, $Level: ident, $desc: expr,
     $(@future_incompatible = $fi:expr;)?
     $(@feature_gate = $gate:expr;)?
     $($v:ident),*) => { ... };
    ($(#[$attr:meta])* $vis: vis $NAME: ident, $Level: ident, $desc: expr,
     $lint_edition: expr => $edition_level: ident
    ) => { ... };
}

Declares a static item of type &'static Lint.

See https://rustc-dev-guide.rust-lang.org/diagnostics.html for documentation and guidelines on writing lints.

The macro call should start with a doc comment explaining the lint which will be embedded in the rustc user documentation book. It should be written in markdown and have a format that looks like this:

/// The `my_lint_name` lint detects [short explanation here].
///
/// ### Example
///
/// ```rust
/// [insert a concise example that triggers the lint]
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This should be a detailed explanation of *why* the lint exists,
/// and also include suggestions on how the user should fix the problem.
/// Try to keep the text simple enough that a beginner can understand,
/// and include links to other documentation for terminology that a
/// beginner may not be familiar with. If this is "allow" by default,
/// it should explain why (are there false positives or other issues?). If
/// this is a future-incompatible lint, it should say so, with text that
/// looks roughly like this:
///
/// This is a [future-incompatible] lint to transition this to a hard
/// error in the future. See [issue #xxxxx] for more details.
///
/// [issue #xxxxx]: https://github.com/rust-lang/rust/issues/xxxxx

The {{produces}} tag will be automatically replaced with the output from the example by the build system. You can build and view the rustc book with x.py doc --stage=1 src/doc/rustc --open. If the lint example is too complex to run as a simple example (for example, it needs an extern crate), mark it with ignore and manually paste the expected output below the example.