rustc_lint_defs/

lib.rs

use std::borrow::Cow;
use std::fmt::Display;

use rustc_ast::attr::version::RustcVersion;
use rustc_data_structures::fx::FxIndexSet;
use rustc_data_structures::stable_hash::{StableCompare, StableHash, StableHashCtxt, StableHasher};
use rustc_error_messages::{DiagArgValue, IntoDiagArg};
use rustc_hir_id::HirId;
use rustc_macros::{Decodable, Encodable, StableHash};
pub use rustc_span::edition::Edition;
use rustc_span::{AttrId, Ident, Symbol, sym};
use serde::{Deserialize, Serialize};

pub use self::Level::*;

pub mod builtin;

#[macro_export]
macro_rules! pluralize {
    // Pluralize based on count (e.g., apples)
    ($x:expr) => {
        if $x == 1 { "" } else { "s" }
    };
    ("has", $x:expr) => {
        if $x == 1 { "has" } else { "have" }
    };
    ("is", $x:expr) => {
        if $x == 1 { "is" } else { "are" }
    };
    ("was", $x:expr) => {
        if $x == 1 { "was" } else { "were" }
    };
    ("this", $x:expr) => {
        if $x == 1 { "this" } else { "these" }
    };
}

/// Grammatical tool for displaying messages to end users in a nice form.
///
/// Take a list of items and a function to turn those items into a `String`, and output a display
/// friendly comma separated list of those items.
// FIXME(estebank): this needs to be changed to go through the translation machinery.
pub fn listify<T>(list: &[T], fmt: impl Fn(&T) -> String) -> Option<String> {
    Some(match list {
        [only] => fmt(&only),
        [others @ .., last] => format!(
            "{} and {}",
            others.iter().map(|i| fmt(i)).collect::<Vec<_>>().join(", "),
            fmt(&last),
        ),
        [] => return None,
    })
}

/// Indicates the confidence in the correctness of a suggestion.
///
/// All suggestions are marked with an `Applicability`. Tools use the applicability of a suggestion
/// to determine whether it should be automatically applied or if the user should be consulted
/// before applying the suggestion.
#[derive(Copy, Clone, Debug, Hash, Encodable, Decodable, Serialize, Deserialize)]
#[derive(PartialEq, Eq, PartialOrd, Ord)]
pub enum Applicability {
    /// The suggestion is definitely what the user intended, or maintains the exact meaning of the code.
    /// This suggestion should be automatically applied.
    ///
    /// In case of multiple `MachineApplicable` suggestions (whether as part of
    /// the same `multipart_suggestion` or not), all of them should be
    /// automatically applied.
    MachineApplicable,

    /// The suggestion may be what the user intended, but it is uncertain. The suggestion should
    /// result in valid Rust code if it is applied.
    MaybeIncorrect,

    /// The suggestion contains placeholders like `(...)` or `{ /* fields */ }`. The suggestion
    /// cannot be applied automatically because it will not result in valid Rust code. The user
    /// will need to fill in the placeholders.
    HasPlaceholders,

    /// The applicability of the suggestion is unknown.
    Unspecified,
}

/// Each lint expectation has a `LintExpectationId` assigned by the `LintLevelsBuilder`.
/// Expected diagnostics get the lint level `Expect` which stores the `LintExpectationId`
/// to match it with the actual expectation later on.
///
/// The `LintExpectationId` has to be stable between compilations, as diagnostic
/// instances might be loaded from cache. Lint messages can be emitted during an
/// `EarlyLintPass` operating on the AST and during a `LateLintPass` traversing the
/// HIR tree. The AST doesn't have enough information to create a stable id. The
/// `LintExpectationId` will instead store the [`AttrId`] defining the expectation.
/// These `LintExpectationId` will be updated to use the stable [`HirId`] once the
/// AST has been lowered. The transformation is done by the `LintLevelsBuilder`
///
/// Each lint inside the `expect` attribute is tracked individually, the `lint_index`
/// identifies the lint inside the attribute and ensures that the IDs are unique.
///
/// The index values have a type of `u16` to reduce the size of the `LintExpectationId`.
/// It's reasonable to assume that no user will define 2^16 attributes on one node or
/// have that amount of lints listed. `u16` values should therefore suffice.
#[derive(Clone, Copy, PartialEq, Eq, Debug, Hash, Encodable, Decodable)]
pub enum LintExpectationId {
    Unstable(UnstableLintExpectationId),
    Stable(StableLintExpectationId),
}

/// Used for lints emitted during the `EarlyLintPass`. This id is not hash
/// stable and should not be cached.
#[derive(Clone, Copy, PartialEq, Eq, Debug, Hash, Encodable, Decodable)]
pub struct UnstableLintExpectationId {
    pub attr_id: AttrId,
    pub lint_index: u16,
}

impl From<UnstableLintExpectationId> for LintExpectationId {
    fn from(id: UnstableLintExpectationId) -> LintExpectationId {
        LintExpectationId::Unstable(id)
    }
}

/// The [`HirId`] that the lint expectation is attached to. This id is stable
/// and can be cached. The additional index ensures that nodes with several
/// expectations can correctly match diagnostics to the individual expectation.
#[derive(Clone, Copy, PartialEq, Eq, Debug, Hash, Encodable, Decodable)]
pub struct StableLintExpectationId {
    pub hir_id: HirId,
    pub attr_index: u16,
    pub lint_index: u16,
}

impl StableHash for StableLintExpectationId {
    #[inline]
    fn stable_hash<Hcx: StableHashCtxt>(&self, hcx: &mut Hcx, hasher: &mut StableHasher) {
        let StableLintExpectationId { hir_id, attr_index, lint_index } = self;

        hir_id.stable_hash(hcx, hasher);
        attr_index.stable_hash(hcx, hasher);
        lint_index.stable_hash(hcx, hasher);
    }
}

impl From<StableLintExpectationId> for LintExpectationId {
    fn from(id: StableLintExpectationId) -> LintExpectationId {
        LintExpectationId::Stable(id)
    }
}

/// Setting for how to handle a lint.
///
/// See: <https://doc.rust-lang.org/rustc/lints/levels.html>
#[derive(
    Clone, Copy, PartialEq, PartialOrd, Eq, Ord, Debug, Hash, Encodable, Decodable, StableHash
)]
pub enum Level {
    /// The `allow` level will not issue any message.
    Allow,
    /// The `expect` level will suppress the lint message but in turn produce a message
    /// if the lint wasn't issued in the expected scope. `Expect` should not be used as
    /// an initial level for a lint.
    ///
    /// Note that this still means that the lint is enabled in this position and should
    /// be emitted, this will in turn fulfill the expectation and suppress the lint.
    ///
    /// See RFC 2383.
    ///
    /// Requires a [`LintExpectationId`] to later link a lint emission to the actual
    /// expectation. It can be ignored in most cases.
    Expect,
    /// The `warn` level will produce a warning if the lint was violated, however the
    /// compiler will continue with its execution.
    Warn,
    /// This lint level is a special case of [`Warn`], that can't be overridden. This is used
    /// to ensure that a lint can't be suppressed. This lint level can currently only be set
    /// via the console and is therefore session specific.
    ///
    /// Requires a [`LintExpectationId`] to fulfill expectations marked via the
    /// `#[expect]` attribute, that will still be suppressed due to the level.
    ForceWarn,
    /// The `deny` level will produce an error and stop further execution after the lint
    /// pass is complete.
    Deny,
    /// `Forbid` is equivalent to the `deny` level but can't be overwritten like the previous
    /// levels.
    Forbid,
}

impl Level {
    /// Converts a level to a lower-case string.
    pub fn as_str(self) -> &'static str {
        match self {
            Level::Allow => "allow",
            Level::Expect => "expect",
            Level::Warn => "warn",
            Level::ForceWarn => "force-warn",
            Level::Deny => "deny",
            Level::Forbid => "forbid",
        }
    }

    /// Converts a lower-case string to a level. This will never construct the expect
    /// level as that would require a [`LintExpectationId`].
    pub fn from_str(x: &str) -> Option<Self> {
        match x {
            "allow" => Some(Level::Allow),
            "warn" => Some(Level::Warn),
            "deny" => Some(Level::Deny),
            "forbid" => Some(Level::Forbid),
            "expect" | _ => None,
        }
    }

    /// Converts an `Option<Symbol>` to a level.
    pub fn from_opt_symbol(s: Option<Symbol>) -> Option<Self> {
        s.and_then(Self::from_symbol)
    }

    /// Converts a `Symbol` to a level.
    pub fn from_symbol(s: Symbol) -> Option<Self> {
        match s {
            sym::allow => Some(Level::Allow),
            sym::expect => Some(Level::Expect),
            sym::warn => Some(Level::Warn),
            sym::deny => Some(Level::Deny),
            sym::forbid => Some(Level::Forbid),
            _ => None,
        }
    }

    pub fn to_cmd_flag(self) -> &'static str {
        match self {
            Level::Warn => "-W",
            Level::Deny => "-D",
            Level::Forbid => "-F",
            Level::Allow => "-A",
            Level::ForceWarn => "--force-warn",
            Level::Expect => {
                unreachable!("the expect level does not have a commandline flag")
            }
        }
    }

    pub fn is_error(self) -> bool {
        match self {
            Level::Allow | Level::Expect | Level::Warn | Level::ForceWarn => false,
            Level::Deny | Level::Forbid => true,
        }
    }
}

impl IntoDiagArg for Level {
    fn into_diag_arg(self, _: &mut Option<std::path::PathBuf>) -> DiagArgValue {
        DiagArgValue::Str(Cow::Borrowed(self.to_cmd_flag()))
    }
}

/// Specification of a single lint.
#[derive(Copy, Clone, Debug)]
pub struct Lint {
    /// A string identifier for the lint.
    ///
    /// This identifies the lint in attributes and in command-line arguments.
    /// In those contexts it is always lowercase, but this field is compared
    /// in a way which is case-insensitive for ASCII characters. This allows
    /// `declare_lint!()` invocations to follow the convention of upper-case
    /// statics without repeating the name.
    ///
    /// The name is written with underscores, e.g., "unused_imports".
    /// On the command line, underscores become dashes.
    ///
    /// See <https://rustc-dev-guide.rust-lang.org/diagnostics.html#lint-naming>
    /// for naming guidelines.
    pub name: &'static str,

    /// Default level for the lint.
    ///
    /// See <https://rustc-dev-guide.rust-lang.org/diagnostics.html#diagnostic-levels>
    /// for guidelines on choosing a default level.
    pub default_level: Level,

    /// Description of the lint or the issue it detects.
    ///
    /// e.g., "imports that are never used"
    pub desc: &'static str,

    /// Starting at the given edition, default to the given lint level. If this is `None`, then use
    /// `default_level`.
    pub edition_lint_opts: Option<(Edition, Level)>,

    /// `true` if this lint is reported even inside expansions of external macros.
    pub report_in_external_macro: bool,

    pub future_incompatible: Option<FutureIncompatibleInfo>,

    /// `true` if this lint is being loaded by another tool (e.g. Clippy).
    pub is_externally_loaded: bool,

    /// `Some` if this lint is feature gated, otherwise `None`.
    pub feature_gate: Option<Symbol>,

    pub crate_level_only: bool,

    /// `true` if this lint should not be filtered out under any circustamces
    /// (e.g. the unknown_attributes lint)
    pub eval_always: bool,

    /// `true` if this lint is unaffected by `-D warnings`
    pub ignore_deny_warnings: bool,

    /// Used to avoid lints which would affect MSRV
    pub rust_version: Option<RustcVersion>,
}

/// Extra information for a future incompatibility lint.
#[derive(Copy, Clone, Debug)]
pub struct FutureIncompatibleInfo {
    /// The reason for the lint used by diagnostics to provide
    /// the right help message
    pub reason: FutureIncompatibilityReason,
    /// Whether to explain the reason to the user.
    ///
    /// Set to false for lints that already include a more detailed
    /// explanation.
    pub explain_reason: bool,
    /// If set to `true`, this will make future incompatibility warnings show up in cargo's
    /// reports.
    ///
    /// When a future incompatibility warning is first inroduced, set this to `false`
    /// (or, rather, don't override the default). This allows crate developers an opportunity
    /// to fix the warning before blasting all dependents with a warning they can't fix
    /// (dependents have to wait for a new release of the affected crate to be published).
    ///
    /// After a lint has been in this state for a while, consider setting this to true, so it
    /// warns for everyone. It is a good signal that it is ready if you can determine that all
    /// or most affected crates on crates.io have been updated.
    pub report_in_deps: bool,
}

#[derive(Copy, Clone, Debug)]
pub struct EditionFcw {
    pub edition: Edition,
    pub page_slug: &'static str,
}

#[derive(Copy, Clone, Debug)]
pub struct ReleaseFcw {
    pub issue_number: usize,
}

/// The reason for future incompatibility
///
/// Future-incompatible lints come in roughly two categories:
///
/// 1. There was a mistake in the compiler (such as a soundness issue), and
///    we're trying to fix it, but it may be a breaking change.
/// 2. A change across an Edition boundary, typically used for the
///    introduction of new language features that can't otherwise be
///    introduced in a backwards-compatible way.
///
/// See <https://rustc-dev-guide.rust-lang.org/bug-fix-procedure.html> and
/// <https://rustc-dev-guide.rust-lang.org/diagnostics.html#future-incompatible-lints>
/// for more information.
#[derive(Copy, Clone, Debug)]
pub enum FutureIncompatibilityReason {
    /// This will be an error in a future release for all editions
    ///
    /// Choose this variant when you are first introducing a "future
    /// incompatible" warning that is intended to eventually be fixed in the
    /// future.
    ///
    /// After a lint has been in this state for a while and you feel like it is ready to graduate
    /// to warning everyone, consider setting [`FutureIncompatibleInfo::report_in_deps`] to true.
    /// (see its documentation for more guidance)
    ///
    /// After some period of time, lints with this variant can be turned into
    /// hard errors (and the lint removed). Preferably when there is some
    /// confidence that the number of impacted projects is very small (few
    /// should have a broken dependency in their dependency tree).
    FutureReleaseError(ReleaseFcw),
    /// Code that changes meaning in some way in a
    /// future release.
    ///
    /// Choose this variant when the semantics of existing code is changing,
    /// (as opposed to [`FutureIncompatibilityReason::FutureReleaseError`],
    /// which is for when code is going to be rejected in the future).
    FutureReleaseSemanticsChange(ReleaseFcw),
    /// Previously accepted code that will become an
    /// error in the provided edition
    ///
    /// Choose this variant for code that you want to start rejecting across
    /// an edition boundary. This will automatically include the lint in the
    /// `rust-20xx-compatibility` lint group, which is used by `cargo fix
    /// --edition` to do migrations. The lint *should* be auto-fixable with
    /// [`Applicability::MachineApplicable`].
    ///
    /// The lint can either be `Allow` or `Warn` by default. If it is `Allow`,
    /// users usually won't see this warning unless they are doing an edition
    /// migration manually or there is a problem during the migration (cargo's
    /// automatic migrations will force the level to `Warn`). If it is `Warn`
    /// by default, users on all editions will see this warning (only do this
    /// if you think it is important for everyone to be aware of the change,
    /// and to encourage people to update their code on all editions).
    ///
    /// See also [`FutureIncompatibilityReason::EditionSemanticsChange`] if
    /// you have code that is changing semantics across the edition (as
    /// opposed to being rejected).
    EditionError(EditionFcw),
    /// Code that changes meaning in some way in
    /// the provided edition
    ///
    /// This is the same as [`FutureIncompatibilityReason::EditionError`],
    /// except for situations where the semantics change across an edition. It
    /// slightly changes the text of the diagnostic, but is otherwise the
    /// same.
    EditionSemanticsChange(EditionFcw),
    /// This will be an error in the provided edition *and* in a future
    /// release.
    ///
    /// This variant a combination of [`FutureReleaseError`] and [`EditionError`].
    /// This is useful in rare cases when we want to have "preview" of a breaking
    /// change in an edition, but do a breaking change later on all editions anyway.
    ///
    /// [`EditionError`]: FutureIncompatibilityReason::EditionError
    /// [`FutureReleaseError`]: FutureIncompatibilityReason::FutureReleaseError
    EditionAndFutureReleaseError(EditionFcw),
    /// This will change meaning in the provided edition *and* in a future
    /// release.
    ///
    /// This variant a combination of [`FutureReleaseSemanticsChange`]
    /// and [`EditionSemanticsChange`]. This is useful in rare cases when we
    /// want to have "preview" of a breaking change in an edition, but do a
    /// breaking change later on all editions anyway.
    ///
    /// [`EditionSemanticsChange`]: FutureIncompatibilityReason::EditionSemanticsChange
    /// [`FutureReleaseSemanticsChange`]: FutureIncompatibilityReason::FutureReleaseSemanticsChange
    EditionAndFutureReleaseSemanticsChange(EditionFcw),
    /// A custom reason.
    ///
    /// Choose this variant if the built-in text of the diagnostic of the
    /// other variants doesn't match your situation. This is behaviorally
    /// equivalent to
    /// [`FutureIncompatibilityReason::FutureReleaseError`].
    Custom(&'static str, ReleaseFcw),

    /// Using the declare_lint macro a reason always needs to be specified.
    /// So, this case can't actually be reached but a variant needs to exist for it.
    /// Any code panics on seeing this variant. Do not use.
    Unreachable,
}

impl FutureIncompatibleInfo {
    pub const fn default_fields_for_macro() -> Self {
        FutureIncompatibleInfo {
            reason: FutureIncompatibilityReason::Unreachable,
            explain_reason: true,
            report_in_deps: false,
        }
    }
}

impl FutureIncompatibilityReason {
    pub fn edition(self) -> Option<Edition> {
        match self {
            Self::EditionError(e)
            | Self::EditionSemanticsChange(e)
            | Self::EditionAndFutureReleaseError(e)
            | Self::EditionAndFutureReleaseSemanticsChange(e) => Some(e.edition),

            FutureIncompatibilityReason::FutureReleaseError(_)
            | FutureIncompatibilityReason::FutureReleaseSemanticsChange(_)
            | FutureIncompatibilityReason::Custom(_, _) => None,
            Self::Unreachable => unreachable!(),
        }
    }

    pub fn reference(&self) -> String {
        match self {
            Self::FutureReleaseSemanticsChange(release_fcw)
            | Self::FutureReleaseError(release_fcw)
            | Self::Custom(_, release_fcw) => release_fcw.to_string(),
            Self::EditionError(edition_fcw)
            | Self::EditionSemanticsChange(edition_fcw)
            | Self::EditionAndFutureReleaseError(edition_fcw)
            | Self::EditionAndFutureReleaseSemanticsChange(edition_fcw) => edition_fcw.to_string(),
            Self::Unreachable => unreachable!(),
        }
    }
}

impl Display for ReleaseFcw {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let issue_number = self.issue_number;
        write!(f, "issue #{issue_number} <https://github.com/rust-lang/rust/issues/{issue_number}>")
    }
}

impl Display for EditionFcw {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(
            f,
            "<https://doc.rust-lang.org/edition-guide/{}/{}.html>",
            match self.edition {
                Edition::Edition2015 => "rust-2015",
                Edition::Edition2018 => "rust-2018",
                Edition::Edition2021 => "rust-2021",
                Edition::Edition2024 => "rust-2024",
                Edition::EditionFuture => "future",
            },
            self.page_slug,
        )
    }
}

impl Lint {
    pub const fn default_fields_for_macro() -> Self {
        Lint {
            name: "",
            default_level: Level::Forbid,
            desc: "",
            edition_lint_opts: None,
            is_externally_loaded: false,
            report_in_external_macro: false,
            future_incompatible: None,
            feature_gate: None,
            crate_level_only: false,
            eval_always: false,
            ignore_deny_warnings: false,
            rust_version: None,
        }
    }

    // FIXME(const-hack): This is used so that `declare_lint` can declare an MSRV statically.
    // `RustcVersion::parse_str_strict` should ideally be used instead.
    pub const fn parse_rust_version(version: &str) -> RustcVersion {
        const fn parse_part(input: &mut &[u8]) -> u16 {
            let mut val = 0;
            let mut idx = 0;
            while idx < input.len() {
                let v = input[idx];
                match v {
                    b'0'..=b'9' => {
                        val = val * 10 + (v - b'0') as u16;
                    }
                    b'.' => {
                        idx += 1;
                        break;
                    }
                    _ => panic!("invalid character in version"),
                }
                idx += 1;
            }
            *input = input.split_at(idx).1;
            val
        }

        let mut bytes = version.as_bytes();
        let major = parse_part(&mut bytes);
        let minor = parse_part(&mut bytes);
        let patch = parse_part(&mut bytes);
        assert!(bytes.is_empty());
        RustcVersion { major, minor, patch }
    }

    /// Gets the lint's name, with ASCII letters converted to lowercase.
    pub fn name_lower(&self) -> String {
        self.name.to_ascii_lowercase()
    }

    pub fn default_level(&self, edition: Edition) -> Level {
        self.edition_lint_opts
            .filter(|(e, _)| *e <= edition)
            .map(|(_, l)| l)
            .unwrap_or(self.default_level)
    }
}

/// Identifies a lint known to the compiler.
#[derive(Clone, Copy, Debug)]
pub struct LintId {
    // Identity is based on pointer equality of this field.
    pub lint: &'static Lint,
}

impl PartialEq for LintId {
    fn eq(&self, other: &LintId) -> bool {
        std::ptr::eq(self.lint, other.lint)
    }
}

impl Eq for LintId {}

impl std::hash::Hash for LintId {
    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
        let ptr = self.lint as *const Lint;
        ptr.hash(state);
    }
}

impl LintId {
    /// Gets the `LintId` for a `Lint`.
    pub fn of(lint: &'static Lint) -> LintId {
        LintId { lint }
    }

    pub fn lint_name_raw(&self) -> &'static str {
        self.lint.name
    }

    /// Gets the name of the lint.
    pub fn to_string(&self) -> String {
        self.lint.name_lower()
    }
}

impl StableHash for LintId {
    #[inline]
    fn stable_hash<Hcx: StableHashCtxt>(&self, hcx: &mut Hcx, hasher: &mut StableHasher) {
        self.lint_name_raw().stable_hash(hcx, hasher);
    }
}

impl StableCompare for LintId {
    const CAN_USE_UNSTABLE_SORT: bool = true;

    fn stable_cmp(&self, other: &Self) -> std::cmp::Ordering {
        self.lint_name_raw().cmp(&other.lint_name_raw())
    }
}

#[derive(Debug, Clone)]
pub enum DeprecatedSinceKind {
    InEffect,
    InFuture,
    InVersion(String),
}

pub type RegisteredTools = FxIndexSet<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:
///
/// ```rust,ignore (doc-example)
/// /// 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. If the lint example is too complex to run
/// as a simple example (for example, it needs an extern crate), mark the code
/// block with `ignore` and manually replace the `{{produces}}` line with the
/// expected output in a `text` code block.
///
/// If this is a rustdoc-only lint, then only include a brief introduction
/// with a link with the text `[rustdoc book]` so that the validator knows
/// that this is for rustdoc only (see BROKEN_INTRA_DOC_LINKS as an example).
///
/// Commands to view and test the documentation:
///
/// * `./x.py doc --stage=1 src/doc/rustc --open`: Builds the rustc book and opens it.
/// * `./x.py test src/tools/lint-docs`: Validates that the lint docs have the
///   correct style, and that the code example actually emits the expected
///   lint.
///
/// If you have already built the compiler, and you want to make changes to
/// just the doc comments, then use the `--keep-stage=0` flag with the above
/// commands to avoid rebuilding the compiler.
#[macro_export]
macro_rules! declare_lint {
    ($(#[$attr:meta])* $vis: vis $NAME: ident, $Level: ident, $desc: expr) => (
        $crate::declare_lint!(
            $(#[$attr])* $vis $NAME, $Level, $desc,
        );
    );
    ($(#[$attr:meta])* $vis: vis $NAME: ident, $Level: ident, $desc: expr,
     $(@eval_always = $eval_always:literal)?
     $(@feature_gate = $gate:ident;)?
     $(@future_incompatible = FutureIncompatibleInfo {
        reason: $reason:expr,
        $($field:ident : $val:expr),* $(,)*
     }; )?
     $(@edition $lint_edition:ident => $edition_level:ident;)?
     $(@msrv = $msrv:literal;)?
     $($v:ident),*) => (
        $(#[$attr])*
        $vis static $NAME: &$crate::Lint = &$crate::Lint {
            name: stringify!($NAME),
            default_level: $crate::$Level,
            desc: $desc,
            is_externally_loaded: false,
            $($v: true,)*
            $(feature_gate: Some(rustc_span::sym::$gate),)?
            $(future_incompatible: Some($crate::FutureIncompatibleInfo {
                reason: $reason,
                $($field: $val,)*
                ..$crate::FutureIncompatibleInfo::default_fields_for_macro()
            }),)?
            $(edition_lint_opts: Some(($crate::Edition::$lint_edition, $crate::$edition_level)),)?
            $(eval_always: $eval_always,)?
            $(rust_version: Some($crate::Lint::parse_rust_version($msrv)),)?
            ..$crate::Lint::default_fields_for_macro()
        };
    );
}

#[macro_export]
macro_rules! declare_tool_lint {
    (
        $(#[$attr:meta])* $vis:vis $tool:ident ::$NAME:ident, $Level: ident, $desc: expr
        $(, @eval_always = $eval_always:literal)?
        $(, @feature_gate = $gate:ident;)?
    ) => (
        $crate::declare_tool_lint!{$(#[$attr])* $vis $tool::$NAME, $Level, $desc, false $(, @eval_always = $eval_always)? $(, @feature_gate = $gate;)?}
    );
    (
        $(#[$attr:meta])* $vis:vis $tool:ident ::$NAME:ident, $Level:ident, $desc:expr,
        report_in_external_macro: $rep:expr
        $(, @eval_always = $eval_always: literal)?
        $(, @feature_gate = $gate:ident;)?
    ) => (
         $crate::declare_tool_lint!{$(#[$attr])* $vis $tool::$NAME, $Level, $desc, $rep  $(, @eval_always = $eval_always)? $(, @feature_gate = $gate;)?}
    );
    (
        $(#[$attr:meta])* $vis:vis $tool:ident ::$NAME:ident, $Level:ident, $desc:expr,
        $external:expr
        $(, @eval_always = $eval_always: literal)?
        $(, @feature_gate = $gate:ident;)?
    ) => (
        $(#[$attr])*
        $vis static $NAME: &$crate::Lint = &$crate::Lint {
            name: &concat!(stringify!($tool), "::", stringify!($NAME)),
            default_level: $crate::$Level,
            desc: $desc,
            edition_lint_opts: None,
            report_in_external_macro: $external,
            future_incompatible: None,
            is_externally_loaded: true,
            $(feature_gate: Some(rustc_span::sym::$gate),)?
            crate_level_only: false,
            $(eval_always: $eval_always,)?
            ..$crate::Lint::default_fields_for_macro()
        };
    );
}

pub type LintVec = Vec<&'static Lint>;

pub trait LintPass {
    fn name(&self) -> &'static str;
    fn get_lints(&self) -> LintVec;
}

/// Implements `LintPass for $ty` with the given list of `Lint` statics.
#[macro_export]
macro_rules! impl_lint_pass {
    ($ty:ty => [$($lint:expr),* $(,)?]) => {
        impl $crate::LintPass for $ty {
            fn name(&self) -> &'static str { stringify!($ty) }
            fn get_lints(&self) -> $crate::LintVec { vec![$($lint),*] }
        }
        impl $ty {
            #[allow(unused)]
            pub fn lint_vec() -> $crate::LintVec { vec![$($lint),*] }
        }
    };
}

/// Declares a type named `$name` which implements `LintPass`.
/// To the right of `=>` a comma separated list of `Lint` statics is given.
#[macro_export]
macro_rules! declare_lint_pass {
    ($(#[$m:meta])* $name:ident => [$($lint:expr),* $(,)?]) => {
        $(#[$m])* #[derive(Copy, Clone)] pub struct $name;
        $crate::impl_lint_pass!($name => [$($lint),*]);
    };
}

#[macro_export]
macro_rules! fcw {
    (FutureReleaseError # $issue_number: literal) => {
       $crate:: FutureIncompatibilityReason::FutureReleaseError($crate::ReleaseFcw { issue_number: $issue_number })
    };
    (FutureReleaseSemanticsChange # $issue_number: literal) => {
        $crate::FutureIncompatibilityReason::FutureReleaseSemanticsChange($crate::ReleaseFcw {
            issue_number: $issue_number,
        })
    };
    ($description: literal # $issue_number: literal) => {
        $crate::FutureIncompatibilityReason::Custom($description, $crate::ReleaseFcw {
            issue_number: $issue_number,
        })
    };
    (EditionError $edition_name: tt $page_slug: literal) => {
        $crate::FutureIncompatibilityReason::EditionError($crate::EditionFcw {
            edition: fcw!(@edition $edition_name),
            page_slug: $page_slug,
        })
    };
    (EditionSemanticsChange $edition_name: tt $page_slug: literal) => {
        $crate::FutureIncompatibilityReason::EditionSemanticsChange($crate::EditionFcw {
            edition: fcw!(@edition $edition_name),
            page_slug: $page_slug,
        })
    };
    (EditionAndFutureReleaseSemanticsChange $edition_name: tt $page_slug: literal) => {
        $crate::FutureIncompatibilityReason::EditionAndFutureReleaseSemanticsChange($crate::EditionFcw {
            edition: fcw!(@edition $edition_name),
            page_slug: $page_slug,
        })
    };
    (EditionAndFutureReleaseError $edition_name: tt $page_slug: literal) => {
        $crate::FutureIncompatibilityReason::EditionAndFutureReleaseError($crate::EditionFcw {
            edition: fcw!(@edition $edition_name),
            page_slug: $page_slug,
        })
    };
    (@edition 2024) => {
        rustc_span::edition::Edition::Edition2024
    };
    (@edition 2021) => {
        rustc_span::edition::Edition::Edition2021
    };
    (@edition 2018) => {
        rustc_span::edition::Edition::Edition2018
    };
}