builtin.rs

//! Lints in the Rust compiler.
//!
//! This contains lints which can feasibly be implemented as their own
//! AST visitor. Also see `rustc::lint::builtin`, which contains the
//! definitions of lints that are emitted directly inside the main
//! compiler.
//!
//! To add a new lint to rustc, declare it here using `declare_lint!()`.
//! Then add code to emit the new lint in the appropriate circumstances.
//! You can do that in an existing `LintPass` if it makes sense, or in a
//! new `LintPass`, or using `Session::add_lint` elsewhere in the
//! compiler. Only do the latter if the check can't be written cleanly as a
//! `LintPass` (also, note that such lints will need to be defined in
//! `rustc::lint::builtin`, not here).
//!
//! If you define a new `EarlyLintPass`, you will also need to add it to the
//! `add_early_builtin!` or `add_early_builtin_with_new!` invocation in
//! `lib.rs`. Use the former for unit-like structs and the latter for structs
//! with a `pub fn new()`.
//!
//! If you define a new `LateLintPass`, you will also need to add it to the
//! `late_lint_methods!` invocation in `lib.rs`.

use std::fmt::Write;

use rustc::hir::def::{Res, DefKind};
use rustc::hir::def_id::{DefId, LOCAL_CRATE};
use rustc::ty::{self, Ty, TyCtxt, layout::VariantIdx};
use rustc::{lint, util};
use hir::Node;
use util::nodemap::HirIdSet;
use lint::{LateContext, LintContext, LintArray};
use lint::{LintPass, LateLintPass, EarlyLintPass, EarlyContext};

use rustc::util::nodemap::FxHashSet;

use syntax::tokenstream::{TokenTree, TokenStream};
use syntax::ast::{self, Expr};
use syntax::ptr::P;
use syntax::attr::{self, HasAttrs, AttributeTemplate};
use syntax::source_map::Spanned;
use syntax::edition::Edition;
use syntax::feature_gate::{self, AttributeGate, AttributeType};
use syntax::feature_gate::{Stability, deprecated_attributes};
use syntax_pos::{BytePos, Span};
use syntax::symbol::{Symbol, kw, sym};
use syntax::errors::{Applicability, DiagnosticBuilder};
use syntax::print::pprust::{self, expr_to_string};
use syntax::visit::FnKind;

use rustc::hir::{self, GenericParamKind, PatKind};

use crate::nonstandard_style::{MethodLateContext, method_context};

use log::debug;

// hardwired lints from librustc
pub use lint::builtin::*;

declare_lint! {
    WHILE_TRUE,
    Warn,
    "suggest using `loop { }` instead of `while true { }`"
}

declare_lint_pass!(WhileTrue => [WHILE_TRUE]);

/// Traverse through any amount of parenthesis and return the first non-parens expression.
fn pierce_parens(mut expr: &ast::Expr) -> &ast::Expr {
    while let ast::ExprKind::Paren(sub) = &expr.kind {
        expr = sub;
    }
    expr
}

impl EarlyLintPass for WhileTrue {
    fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
        if let ast::ExprKind::While(cond, ..) = &e.kind {
            if let ast::ExprKind::Lit(ref lit) = pierce_parens(cond).kind {
                if let ast::LitKind::Bool(true) = lit.kind {
                    if !lit.span.from_expansion() {
                        let msg = "denote infinite loops with `loop { ... }`";
                        let condition_span = cx.sess.source_map().def_span(e.span);
                        cx.struct_span_lint(WHILE_TRUE, condition_span, msg)
                            .span_suggestion_short(
                                condition_span,
                                "use `loop`",
                                "loop".to_owned(),
                                Applicability::MachineApplicable
                            )
                            .emit();
                    }
                }
            }
        }
    }
}

declare_lint! {
    BOX_POINTERS,
    Allow,
    "use of owned (Box type) heap memory"
}

declare_lint_pass!(BoxPointers => [BOX_POINTERS]);

impl BoxPointers {
    fn check_heap_type(&self, cx: &LateContext<'_, '_>, span: Span, ty: Ty<'_>) {
        for leaf_ty in ty.walk() {
            if leaf_ty.is_box() {
                let m = format!("type uses owned (Box type) pointers: {}", ty);
                cx.span_lint(BOX_POINTERS, span, &m);
            }
        }
    }
}

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BoxPointers {
    fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item) {
        match it.kind {
            hir::ItemKind::Fn(..) |
            hir::ItemKind::TyAlias(..) |
            hir::ItemKind::Enum(..) |
            hir::ItemKind::Struct(..) |
            hir::ItemKind::Union(..) => {
                let def_id = cx.tcx.hir().local_def_id(it.hir_id);
                self.check_heap_type(cx, it.span, cx.tcx.type_of(def_id))
            }
            _ => ()
        }

        // If it's a struct, we also have to check the fields' types
        match it.kind {
            hir::ItemKind::Struct(ref struct_def, _) |
            hir::ItemKind::Union(ref struct_def, _) => {
                for struct_field in struct_def.fields() {
                    let def_id = cx.tcx.hir().local_def_id(struct_field.hir_id);
                    self.check_heap_type(cx, struct_field.span,
                                         cx.tcx.type_of(def_id));
                }
            }
            _ => (),
        }
    }

    fn check_expr(&mut self, cx: &LateContext<'_, '_>, e: &hir::Expr) {
        let ty = cx.tables.node_type(e.hir_id);
        self.check_heap_type(cx, e.span, ty);
    }
}

declare_lint! {
    NON_SHORTHAND_FIELD_PATTERNS,
    Warn,
    "using `Struct { x: x }` instead of `Struct { x }` in a pattern"
}

declare_lint_pass!(NonShorthandFieldPatterns => [NON_SHORTHAND_FIELD_PATTERNS]);

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NonShorthandFieldPatterns {
    fn check_pat(&mut self, cx: &LateContext<'_, '_>, pat: &hir::Pat) {
        if let PatKind::Struct(ref qpath, ref field_pats, _) = pat.kind {
            let variant = cx.tables.pat_ty(pat).ty_adt_def()
                                   .expect("struct pattern type is not an ADT")
                                   .variant_of_res(cx.tables.qpath_res(qpath, pat.hir_id));
            for fieldpat in field_pats {
                if fieldpat.is_shorthand {
                    continue;
                }
                if fieldpat.span.from_expansion() {
                    // Don't lint if this is a macro expansion: macro authors
                    // shouldn't have to worry about this kind of style issue
                    // (Issue #49588)
                    continue;
                }
                if let PatKind::Binding(_, _, ident, None) = fieldpat.pat.kind {
                    if cx.tcx.find_field_index(ident, &variant) ==
                       Some(cx.tcx.field_index(fieldpat.hir_id, cx.tables)) {
                        let mut err = cx.struct_span_lint(NON_SHORTHAND_FIELD_PATTERNS,
                                     fieldpat.span,
                                     &format!("the `{}:` in this pattern is redundant", ident));
                        let subspan = cx.tcx.sess.source_map().span_through_char(fieldpat.span,
                                                                                 ':');
                        err.span_suggestion_short(
                            subspan,
                            "remove this",
                            ident.to_string(),
                            Applicability::MachineApplicable
                        );
                        err.emit();
                    }
                }
            }
        }
    }
}

declare_lint! {
    UNSAFE_CODE,
    Allow,
    "usage of `unsafe` code"
}

declare_lint_pass!(UnsafeCode => [UNSAFE_CODE]);

impl UnsafeCode {
    fn report_unsafe(&self, cx: &EarlyContext<'_>, span: Span, desc: &'static str) {
        // This comes from a macro that has `#[allow_internal_unsafe]`.
        if span.allows_unsafe() {
            return;
        }

        cx.span_lint(UNSAFE_CODE, span, desc);
    }
}

impl EarlyLintPass for UnsafeCode {
    fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
        if attr.check_name(sym::allow_internal_unsafe) {
            self.report_unsafe(cx, attr.span, "`allow_internal_unsafe` allows defining \
                                               macros using unsafe without triggering \
                                               the `unsafe_code` lint at their call site");
        }
    }

    fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
        if let ast::ExprKind::Block(ref blk, _) = e.kind {
            // Don't warn about generated blocks; that'll just pollute the output.
            if blk.rules == ast::BlockCheckMode::Unsafe(ast::UserProvided) {
                self.report_unsafe(cx, blk.span, "usage of an `unsafe` block");
            }
        }
    }

    fn check_item(&mut self, cx: &EarlyContext<'_>, it: &ast::Item) {
        match it.kind {
            ast::ItemKind::Trait(_, ast::Unsafety::Unsafe, ..) => {
                self.report_unsafe(cx, it.span, "declaration of an `unsafe` trait")
            }

            ast::ItemKind::Impl(ast::Unsafety::Unsafe, ..) => {
                self.report_unsafe(cx, it.span, "implementation of an `unsafe` trait")
            }

            _ => return,
        }
    }

    fn check_fn(&mut self,
                cx: &EarlyContext<'_>,
                fk: FnKind<'_>,
                _: &ast::FnDecl,
                span: Span,
                _: ast::NodeId) {
        match fk {
            FnKind::ItemFn(_, ast::FnHeader { unsafety: ast::Unsafety::Unsafe, .. }, ..) => {
                self.report_unsafe(cx, span, "declaration of an `unsafe` function")
            }

            FnKind::Method(_, sig, ..) => {
                if sig.header.unsafety == ast::Unsafety::Unsafe {
                    self.report_unsafe(cx, span, "implementation of an `unsafe` method")
                }
            }

            _ => (),
        }
    }

    fn check_trait_item(&mut self, cx: &EarlyContext<'_>, item: &ast::TraitItem) {
        if let ast::TraitItemKind::Method(ref sig, None) = item.kind {
            if sig.header.unsafety == ast::Unsafety::Unsafe {
                self.report_unsafe(cx, item.span, "declaration of an `unsafe` method")
            }
        }
    }
}

declare_lint! {
    pub MISSING_DOCS,
    Allow,
    "detects missing documentation for public members",
    report_in_external_macro: true
}

pub struct MissingDoc {
    /// Stack of whether `#[doc(hidden)]` is set at each level which has lint attributes.
    doc_hidden_stack: Vec<bool>,

    /// Private traits or trait items that leaked through. Don't check their methods.
    private_traits: FxHashSet<hir::HirId>,
}

impl_lint_pass!(MissingDoc => [MISSING_DOCS]);

fn has_doc(attr: &ast::Attribute) -> bool {
    if !attr.check_name(sym::doc) {
        return false;
    }

    if attr.is_value_str() {
        return true;
    }

    if let Some(list) = attr.meta_item_list() {
        for meta in list {
            if meta.check_name(sym::include) || meta.check_name(sym::hidden) {
                return true;
            }
        }
    }

    false
}

impl MissingDoc {
    pub fn new() -> MissingDoc {
        MissingDoc {
            doc_hidden_stack: vec![false],
            private_traits: FxHashSet::default(),
        }
    }

    fn doc_hidden(&self) -> bool {
        *self.doc_hidden_stack.last().expect("empty doc_hidden_stack")
    }

    fn check_missing_docs_attrs(&self,
                                cx: &LateContext<'_, '_>,
                                id: Option<hir::HirId>,
                                attrs: &[ast::Attribute],
                                sp: Span,
                                desc: &'static str) {
        // If we're building a test harness, then warning about
        // documentation is probably not really relevant right now.
        if cx.sess().opts.test {
            return;
        }

        // `#[doc(hidden)]` disables missing_docs check.
        if self.doc_hidden() {
            return;
        }

        // Only check publicly-visible items, using the result from the privacy pass.
        // It's an option so the crate root can also use this function (it doesn't
        // have a `NodeId`).
        if let Some(id) = id {
            if !cx.access_levels.is_exported(id) {
                return;
            }
        }

        let has_doc = attrs.iter().any(|a| has_doc(a));
        if !has_doc {
            cx.span_lint(MISSING_DOCS,
                         cx.tcx.sess.source_map().def_span(sp),
                         &format!("missing documentation for {}", desc));
        }
    }
}

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MissingDoc {
    fn enter_lint_attrs(&mut self, _: &LateContext<'_, '_>, attrs: &[ast::Attribute]) {
        let doc_hidden = self.doc_hidden() ||
                         attrs.iter().any(|attr| {
            attr.check_name(sym::doc) &&
            match attr.meta_item_list() {
                None => false,
                Some(l) => attr::list_contains_name(&l, sym::hidden),
            }
        });
        self.doc_hidden_stack.push(doc_hidden);
    }

    fn exit_lint_attrs(&mut self, _: &LateContext<'_, '_>, _attrs: &[ast::Attribute]) {
        self.doc_hidden_stack.pop().expect("empty doc_hidden_stack");
    }

    fn check_crate(&mut self, cx: &LateContext<'_, '_>, krate: &hir::Crate) {
        self.check_missing_docs_attrs(cx, None, &krate.attrs, krate.span, "crate");

        for macro_def in &krate.exported_macros {
            let has_doc = macro_def.attrs.iter().any(|a| has_doc(a));
            if !has_doc {
                cx.span_lint(MISSING_DOCS,
                             cx.tcx.sess.source_map().def_span(macro_def.span),
                             "missing documentation for macro");
            }
        }
    }

    fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item) {
        let desc = match it.kind {
            hir::ItemKind::Fn(..) => "a function",
            hir::ItemKind::Mod(..) => "a module",
            hir::ItemKind::Enum(..) => "an enum",
            hir::ItemKind::Struct(..) => "a struct",
            hir::ItemKind::Union(..) => "a union",
            hir::ItemKind::Trait(.., ref trait_item_refs) => {
                // Issue #11592: traits are always considered exported, even when private.
                if let hir::VisibilityKind::Inherited = it.vis.node {
                    self.private_traits.insert(it.hir_id);
                    for trait_item_ref in trait_item_refs {
                        self.private_traits.insert(trait_item_ref.id.hir_id);
                    }
                    return;
                }
                "a trait"
            }
            hir::ItemKind::TyAlias(..) => "a type alias",
            hir::ItemKind::Impl(.., Some(ref trait_ref), _, ref impl_item_refs) => {
                // If the trait is private, add the impl items to `private_traits` so they don't get
                // reported for missing docs.
                let real_trait = trait_ref.path.res.def_id();
                if let Some(hir_id) = cx.tcx.hir().as_local_hir_id(real_trait) {
                    match cx.tcx.hir().find(hir_id) {
                        Some(Node::Item(item)) => {
                            if let hir::VisibilityKind::Inherited = item.vis.node {
                                for impl_item_ref in impl_item_refs {
                                    self.private_traits.insert(impl_item_ref.id.hir_id);
                                }
                            }
                        }
                        _ => {}
                    }
                }
                return;
            }
            hir::ItemKind::Const(..) => "a constant",
            hir::ItemKind::Static(..) => "a static",
            _ => return,
        };

        self.check_missing_docs_attrs(cx, Some(it.hir_id), &it.attrs, it.span, desc);
    }

    fn check_trait_item(&mut self, cx: &LateContext<'_, '_>, trait_item: &hir::TraitItem) {
        if self.private_traits.contains(&trait_item.hir_id) {
            return;
        }

        let desc = match trait_item.kind {
            hir::TraitItemKind::Const(..) => "an associated constant",
            hir::TraitItemKind::Method(..) => "a trait method",
            hir::TraitItemKind::Type(..) => "an associated type",
        };

        self.check_missing_docs_attrs(cx,
                                      Some(trait_item.hir_id),
                                      &trait_item.attrs,
                                      trait_item.span,
                                      desc);
    }

    fn check_impl_item(&mut self, cx: &LateContext<'_, '_>, impl_item: &hir::ImplItem) {
        // If the method is an impl for a trait, don't doc.
        if method_context(cx, impl_item.hir_id) == MethodLateContext::TraitImpl {
            return;
        }

        let desc = match impl_item.kind {
            hir::ImplItemKind::Const(..) => "an associated constant",
            hir::ImplItemKind::Method(..) => "a method",
            hir::ImplItemKind::TyAlias(_) => "an associated type",
            hir::ImplItemKind::OpaqueTy(_) => "an associated `impl Trait` type",
        };
        self.check_missing_docs_attrs(cx,
                                      Some(impl_item.hir_id),
                                      &impl_item.attrs,
                                      impl_item.span,
                                      desc);
    }

    fn check_struct_field(&mut self, cx: &LateContext<'_, '_>, sf: &hir::StructField) {
        if !sf.is_positional() {
            self.check_missing_docs_attrs(cx,
                                          Some(sf.hir_id),
                                          &sf.attrs,
                                          sf.span,
                                          "a struct field")
        }
    }

    fn check_variant(&mut self, cx: &LateContext<'_, '_>, v: &hir::Variant) {
        self.check_missing_docs_attrs(cx,
                                      Some(v.id),
                                      &v.attrs,
                                      v.span,
                                      "a variant");
    }
}

declare_lint! {
    pub MISSING_COPY_IMPLEMENTATIONS,
    Allow,
    "detects potentially-forgotten implementations of `Copy`"
}

declare_lint_pass!(MissingCopyImplementations => [MISSING_COPY_IMPLEMENTATIONS]);

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MissingCopyImplementations {
    fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &hir::Item) {
        if !cx.access_levels.is_reachable(item.hir_id) {
            return;
        }
        let (def, ty) = match item.kind {
            hir::ItemKind::Struct(_, ref ast_generics) => {
                if !ast_generics.params.is_empty() {
                    return;
                }
                let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
                (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
            }
            hir::ItemKind::Union(_, ref ast_generics) => {
                if !ast_generics.params.is_empty() {
                    return;
                }
                let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
                (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
            }
            hir::ItemKind::Enum(_, ref ast_generics) => {
                if !ast_generics.params.is_empty() {
                    return;
                }
                let def = cx.tcx.adt_def(cx.tcx.hir().local_def_id(item.hir_id));
                (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
            }
            _ => return,
        };
        if def.has_dtor(cx.tcx) {
            return;
        }
        let param_env = ty::ParamEnv::empty();
        if ty.is_copy_modulo_regions(cx.tcx, param_env, item.span) {
            return;
        }
        if param_env.can_type_implement_copy(cx.tcx, ty).is_ok() {
            cx.span_lint(MISSING_COPY_IMPLEMENTATIONS,
                         item.span,
                         "type could implement `Copy`; consider adding `impl \
                          Copy`")
        }
    }
}

declare_lint! {
    MISSING_DEBUG_IMPLEMENTATIONS,
    Allow,
    "detects missing implementations of fmt::Debug"
}

#[derive(Default)]
pub struct MissingDebugImplementations {
    impling_types: Option<HirIdSet>,
}

impl_lint_pass!(MissingDebugImplementations => [MISSING_DEBUG_IMPLEMENTATIONS]);

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MissingDebugImplementations {
    fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &hir::Item) {
        if !cx.access_levels.is_reachable(item.hir_id) {
            return;
        }

        match item.kind {
            hir::ItemKind::Struct(..) |
            hir::ItemKind::Union(..) |
            hir::ItemKind::Enum(..) => {}
            _ => return,
        }

        let debug = match cx.tcx.get_diagnostic_item(sym::debug_trait) {
            Some(debug) => debug,
            None => return,
        };

        if self.impling_types.is_none() {
            let mut impls = HirIdSet::default();
            cx.tcx.for_each_impl(debug, |d| {
                if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() {
                    if let Some(hir_id) = cx.tcx.hir().as_local_hir_id(ty_def.did) {
                        impls.insert(hir_id);
                    }
                }
            });

            self.impling_types = Some(impls);
            debug!("{:?}", self.impling_types);
        }

        if !self.impling_types.as_ref().unwrap().contains(&item.hir_id) {
            cx.span_lint(MISSING_DEBUG_IMPLEMENTATIONS,
                         item.span,
                         "type does not implement `fmt::Debug`; consider adding `#[derive(Debug)]` \
                          or a manual implementation")
        }
    }
}

declare_lint! {
    pub ANONYMOUS_PARAMETERS,
    Allow,
    "detects anonymous parameters"
}

declare_lint_pass!(
    /// Checks for use of anonymous parameters (RFC 1685).
    AnonymousParameters => [ANONYMOUS_PARAMETERS]
);

impl EarlyLintPass for AnonymousParameters {
    fn check_trait_item(&mut self, cx: &EarlyContext<'_>, it: &ast::TraitItem) {
        match it.kind {
            ast::TraitItemKind::Method(ref sig, _) => {
                for arg in sig.decl.inputs.iter() {
                    match arg.pat.kind {
                        ast::PatKind::Ident(_, ident, None) => {
                            if ident.name == kw::Invalid {
                                let ty_snip = cx
                                    .sess
                                    .source_map()
                                    .span_to_snippet(arg.ty.span);

                                let (ty_snip, appl) = if let Ok(snip) = ty_snip {
                                    (snip, Applicability::MachineApplicable)
                                } else {
                                    ("<type>".to_owned(), Applicability::HasPlaceholders)
                                };

                                cx.struct_span_lint(
                                    ANONYMOUS_PARAMETERS,
                                    arg.pat.span,
                                    "anonymous parameters are deprecated and will be \
                                     removed in the next edition."
                                ).span_suggestion(
                                    arg.pat.span,
                                    "Try naming the parameter or explicitly \
                                    ignoring it",
                                    format!("_: {}", ty_snip),
                                    appl
                                ).emit();
                            }
                        }
                        _ => (),
                    }
                }
            },
            _ => (),
        }
    }
}

/// Check for use of attributes which have been deprecated.
#[derive(Clone)]
pub struct DeprecatedAttr {
    // This is not free to compute, so we want to keep it around, rather than
    // compute it for every attribute.
    depr_attrs: Vec<&'static (Symbol, AttributeType, AttributeTemplate, AttributeGate)>,
}

impl_lint_pass!(DeprecatedAttr => []);

impl DeprecatedAttr {
    pub fn new() -> DeprecatedAttr {
        DeprecatedAttr {
            depr_attrs: deprecated_attributes(),
        }
    }
}

fn lint_deprecated_attr(
    cx: &EarlyContext<'_>,
    attr: &ast::Attribute,
    msg: &str,
    suggestion: Option<&str>,
) {
    cx.struct_span_lint(DEPRECATED, attr.span, &msg)
        .span_suggestion_short(
            attr.span,
            suggestion.unwrap_or("remove this attribute"),
            String::new(),
            Applicability::MachineApplicable
        )
        .emit();
}

impl EarlyLintPass for DeprecatedAttr {
    fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
        for &&(n, _, _, ref g) in &self.depr_attrs {
            if attr.ident().map(|ident| ident.name) == Some(n) {
                if let &AttributeGate::Gated(Stability::Deprecated(link, suggestion),
                                             ref name,
                                             ref reason,
                                             _) = g {
                    let msg = format!("use of deprecated attribute `{}`: {}. See {}",
                                      name, reason, link);
                    lint_deprecated_attr(cx, attr, &msg, suggestion);
                }
                return;
            }
        }
        if attr.check_name(sym::no_start) || attr.check_name(sym::crate_id) {
            let path_str = pprust::path_to_string(&attr.path);
            let msg = format!("use of deprecated attribute `{}`: no longer used.", path_str);
            lint_deprecated_attr(cx, attr, &msg, None);
        }
    }
}

declare_lint! {
    pub UNUSED_DOC_COMMENTS,
    Warn,
    "detects doc comments that aren't used by rustdoc"
}

declare_lint_pass!(UnusedDocComment => [UNUSED_DOC_COMMENTS]);

impl UnusedDocComment {
    fn warn_if_doc(
        &self,
        cx: &EarlyContext<'_>,
        node_span: Span,
        node_kind: &str,
        is_macro_expansion: bool,
        attrs: &[ast::Attribute]
    ) {
        let mut attrs = attrs.into_iter().peekable();

        // Accumulate a single span for sugared doc comments.
        let mut sugared_span: Option<Span> = None;

        while let Some(attr) = attrs.next() {
            if attr.is_sugared_doc {
                sugared_span = Some(
                    sugared_span.map_or_else(
                        || attr.span,
                        |span| span.with_hi(attr.span.hi()),
                    ),
                );
            }

            if attrs.peek().map(|next_attr| next_attr.is_sugared_doc).unwrap_or_default() {
                continue;
            }

            let span = sugared_span.take().unwrap_or_else(|| attr.span);

            if attr.check_name(sym::doc) {
                let mut err = cx.struct_span_lint(UNUSED_DOC_COMMENTS, span, "unused doc comment");

                err.span_label(
                    node_span,
                    format!("rustdoc does not generate documentation for {}", node_kind)
                );

                if is_macro_expansion {
                    err.help("to document an item produced by a macro, \
                              the macro must produce the documentation as part of its expansion");
                }

                err.emit();
            }
        }
    }
}

impl EarlyLintPass for UnusedDocComment {
    fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) {
        if let ast::ItemKind::Mac(..) = item.kind {
            self.warn_if_doc(cx, item.span, "macro expansions", true, &item.attrs);
        }
    }

    fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &ast::Stmt) {
        let (kind, is_macro_expansion) = match stmt.kind {
            ast::StmtKind::Local(..) => ("statements", false),
            ast::StmtKind::Item(..) => ("inner items", false),
            ast::StmtKind::Mac(..) => ("macro expansions", true),
            // expressions will be reported by `check_expr`.
            ast::StmtKind::Semi(..) |
            ast::StmtKind::Expr(..) => return,
        };

        self.warn_if_doc(cx, stmt.span, kind, is_macro_expansion, stmt.kind.attrs());
    }

    fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) {
        let arm_span = arm.pat.span.with_hi(arm.body.span.hi());
        self.warn_if_doc(cx, arm_span, "match arms", false, &arm.attrs);
    }

    fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
        self.warn_if_doc(cx, expr.span, "expressions", false, &expr.attrs);
    }
}

declare_lint! {
    PLUGIN_AS_LIBRARY,
    Warn,
    "compiler plugin used as ordinary library in non-plugin crate"
}

declare_lint_pass!(PluginAsLibrary => [PLUGIN_AS_LIBRARY]);

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for PluginAsLibrary {
    fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item) {
        if cx.tcx.plugin_registrar_fn(LOCAL_CRATE).is_some() {
            // We're compiling a plugin; it's fine to link other plugins.
            return;
        }

        match it.kind {
            hir::ItemKind::ExternCrate(..) => (),
            _ => return,
        };

        let def_id = cx.tcx.hir().local_def_id(it.hir_id);
        let prfn = match cx.tcx.extern_mod_stmt_cnum(def_id) {
            Some(cnum) => cx.tcx.plugin_registrar_fn(cnum),
            None => {
                // Probably means we aren't linking the crate for some reason.
                //
                // Not sure if / when this could happen.
                return;
            }
        };

        if prfn.is_some() {
            cx.span_lint(PLUGIN_AS_LIBRARY,
                         it.span,
                         "compiler plugin used as an ordinary library");
        }
    }
}

declare_lint! {
    NO_MANGLE_CONST_ITEMS,
    Deny,
    "const items will not have their symbols exported"
}

declare_lint! {
    NO_MANGLE_GENERIC_ITEMS,
    Warn,
    "generic items must be mangled"
}

declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS, NO_MANGLE_GENERIC_ITEMS]);

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for InvalidNoMangleItems {
    fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item) {
        match it.kind {
            hir::ItemKind::Fn(.., ref generics, _) => {
                if let Some(no_mangle_attr) = attr::find_by_name(&it.attrs, sym::no_mangle) {
                    for param in &generics.params {
                        match param.kind {
                            GenericParamKind::Lifetime { .. } => {}
                            GenericParamKind::Type { .. } |
                            GenericParamKind::Const { .. } => {
                                let mut err = cx.struct_span_lint(
                                    NO_MANGLE_GENERIC_ITEMS,
                                    it.span,
                                    "functions generic over types or consts must be mangled",
                                );
                                err.span_suggestion_short(
                                    no_mangle_attr.span,
                                    "remove this attribute",
                                    String::new(),
                                    // Use of `#[no_mangle]` suggests FFI intent; correct
                                    // fix may be to monomorphize source by hand
                                    Applicability::MaybeIncorrect
                                );
                                err.emit();
                                break;
                            }
                        }
                    }
                }
            }
            hir::ItemKind::Const(..) => {
                if attr::contains_name(&it.attrs, sym::no_mangle) {
                    // Const items do not refer to a particular location in memory, and therefore
                    // don't have anything to attach a symbol to
                    let msg = "const items should never be `#[no_mangle]`";
                    let mut err = cx.struct_span_lint(NO_MANGLE_CONST_ITEMS, it.span, msg);

                    // account for "pub const" (#45562)
                    let start = cx.tcx.sess.source_map().span_to_snippet(it.span)
                        .map(|snippet| snippet.find("const").unwrap_or(0))
                        .unwrap_or(0) as u32;
                    // `const` is 5 chars
                    let const_span = it.span.with_hi(BytePos(it.span.lo().0 + start + 5));
                    err.span_suggestion(
                        const_span,
                        "try a static value",
                        "pub static".to_owned(),
                        Applicability::MachineApplicable
                    );
                    err.emit();
                }
            }
            _ => {}
        }
    }
}

declare_lint! {
    MUTABLE_TRANSMUTES,
    Deny,
    "mutating transmuted &mut T from &T may cause undefined behavior"
}

declare_lint_pass!(MutableTransmutes => [MUTABLE_TRANSMUTES]);

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MutableTransmutes {
    fn check_expr(&mut self, cx: &LateContext<'_, '_>, expr: &hir::Expr) {
        use rustc_target::spec::abi::Abi::RustIntrinsic;

        let msg = "mutating transmuted &mut T from &T may cause undefined behavior, \
                   consider instead using an UnsafeCell";
        match get_transmute_from_to(cx, expr).map(|(ty1, ty2)| (&ty1.kind, &ty2.kind)) {
            Some((&ty::Ref(_, _, from_mt), &ty::Ref(_, _, to_mt))) => {
                if to_mt == hir::Mutability::MutMutable &&
                   from_mt == hir::Mutability::MutImmutable {
                    cx.span_lint(MUTABLE_TRANSMUTES, expr.span, msg);
                }
            }
            _ => (),
        }

        fn get_transmute_from_to<'a, 'tcx>
            (cx: &LateContext<'a, 'tcx>,
             expr: &hir::Expr)
             -> Option<(Ty<'tcx>, Ty<'tcx>)> {
            let def = if let hir::ExprKind::Path(ref qpath) = expr.kind {
                cx.tables.qpath_res(qpath, expr.hir_id)
            } else {
                return None;
            };
            if let Res::Def(DefKind::Fn, did) = def {
                if !def_id_is_transmute(cx, did) {
                    return None;
                }
                let sig = cx.tables.node_type(expr.hir_id).fn_sig(cx.tcx);
                let from = sig.inputs().skip_binder()[0];
                let to = *sig.output().skip_binder();
                return Some((from, to));
            }
            None
        }

        fn def_id_is_transmute(cx: &LateContext<'_, '_>, def_id: DefId) -> bool {
            cx.tcx.fn_sig(def_id).abi() == RustIntrinsic &&
            cx.tcx.item_name(def_id) == sym::transmute
        }
    }
}

declare_lint! {
    UNSTABLE_FEATURES,
    Allow,
    "enabling unstable features (deprecated. do not use)"
}

declare_lint_pass!(
    /// Forbids using the `#[feature(...)]` attribute
    UnstableFeatures => [UNSTABLE_FEATURES]
);

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnstableFeatures {
    fn check_attribute(&mut self, ctx: &LateContext<'_, '_>, attr: &ast::Attribute) {
        if attr.check_name(sym::feature) {
            if let Some(items) = attr.meta_item_list() {
                for item in items {
                    ctx.span_lint(UNSTABLE_FEATURES, item.span(), "unstable feature");
                }
            }
        }
    }
}

declare_lint! {
    UNIONS_WITH_DROP_FIELDS,
    Warn,
    "use of unions that contain fields with possibly non-trivial drop code"
}

declare_lint_pass!(
    /// Lint for unions that contain fields with possibly non-trivial destructors.
    UnionsWithDropFields => [UNIONS_WITH_DROP_FIELDS]
);

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnionsWithDropFields {
    fn check_item(&mut self, ctx: &LateContext<'_, '_>, item: &hir::Item) {
        if let hir::ItemKind::Union(ref vdata, _) = item.kind {
            for field in vdata.fields() {
                let field_ty = ctx.tcx.type_of(
                    ctx.tcx.hir().local_def_id(field.hir_id));
                if field_ty.needs_drop(ctx.tcx, ctx.param_env) {
                    ctx.span_lint(UNIONS_WITH_DROP_FIELDS,
                                  field.span,
                                  "union contains a field with possibly non-trivial drop code, \
                                   drop code of union fields is ignored when dropping the union");
                    return;
                }
            }
        }
    }
}

declare_lint! {
    pub UNREACHABLE_PUB,
    Allow,
    "`pub` items not reachable from crate root"
}

declare_lint_pass!(
    /// Lint for items marked `pub` that aren't reachable from other crates.
    UnreachablePub => [UNREACHABLE_PUB]
);

impl UnreachablePub {
    fn perform_lint(&self, cx: &LateContext<'_, '_>, what: &str, id: hir::HirId,
                    vis: &hir::Visibility, span: Span, exportable: bool) {
        let mut applicability = Applicability::MachineApplicable;
        match vis.node {
            hir::VisibilityKind::Public if !cx.access_levels.is_reachable(id) => {
                if span.from_expansion() {
                    applicability = Applicability::MaybeIncorrect;
                }
                let def_span = cx.tcx.sess.source_map().def_span(span);
                let mut err = cx.struct_span_lint(UNREACHABLE_PUB, def_span,
                                                  &format!("unreachable `pub` {}", what));
                let replacement = if cx.tcx.features().crate_visibility_modifier {
                    "crate"
                } else {
                    "pub(crate)"
                }.to_owned();

                err.span_suggestion(
                    vis.span,
                    "consider restricting its visibility",
                    replacement,
                    applicability,
                );
                if exportable {
                    err.help("or consider exporting it for use by other crates");
                }
                err.emit();
            },
            _ => {}
        }
    }
}

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnreachablePub {
    fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &hir::Item) {
        self.perform_lint(cx, "item", item.hir_id, &item.vis, item.span, true);
    }

    fn check_foreign_item(&mut self, cx: &LateContext<'_, '_>, foreign_item: &hir::ForeignItem) {
        self.perform_lint(cx, "item", foreign_item.hir_id, &foreign_item.vis,
                          foreign_item.span, true);
    }

    fn check_struct_field(&mut self, cx: &LateContext<'_, '_>, field: &hir::StructField) {
        self.perform_lint(cx, "field", field.hir_id, &field.vis, field.span, false);
    }

    fn check_impl_item(&mut self, cx: &LateContext<'_, '_>, impl_item: &hir::ImplItem) {
        self.perform_lint(cx, "item", impl_item.hir_id, &impl_item.vis, impl_item.span, false);
    }
}

declare_lint! {
    TYPE_ALIAS_BOUNDS,
    Warn,
    "bounds in type aliases are not enforced"
}

declare_lint_pass!(
    /// Lint for trait and lifetime bounds in type aliases being mostly ignored.
    /// They are relevant when using associated types, but otherwise neither checked
    /// at definition site nor enforced at use site.
    TypeAliasBounds => [TYPE_ALIAS_BOUNDS]
);

impl TypeAliasBounds {
    fn is_type_variable_assoc(qpath: &hir::QPath) -> bool {
        match *qpath {
            hir::QPath::TypeRelative(ref ty, _) => {
                // If this is a type variable, we found a `T::Assoc`.
                match ty.kind {
                    hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
                        match path.res {
                            Res::Def(DefKind::TyParam, _) => true,
                            _ => false
                        }
                    }
                    _ => false
                }
            }
            hir::QPath::Resolved(..) => false,
        }
    }

    fn suggest_changing_assoc_types(ty: &hir::Ty, err: &mut DiagnosticBuilder<'_>) {
        // Access to associates types should use `<T as Bound>::Assoc`, which does not need a
        // bound.  Let's see if this type does that.

        // We use a HIR visitor to walk the type.
        use rustc::hir::intravisit::{self, Visitor};
        struct WalkAssocTypes<'a, 'db> {
            err: &'a mut DiagnosticBuilder<'db>
        }
        impl<'a, 'db, 'v> Visitor<'v> for WalkAssocTypes<'a, 'db> {
            fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'v>
            {
                intravisit::NestedVisitorMap::None
            }

            fn visit_qpath(&mut self, qpath: &'v hir::QPath, id: hir::HirId, span: Span) {
                if TypeAliasBounds::is_type_variable_assoc(qpath) {
                    self.err.span_help(span,
                        "use fully disambiguated paths (i.e., `<T as Trait>::Assoc`) to refer to \
                         associated types in type aliases");
                }
                intravisit::walk_qpath(self, qpath, id, span)
            }
        }

        // Let's go for a walk!
        let mut visitor = WalkAssocTypes { err };
        visitor.visit_ty(ty);
    }
}

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeAliasBounds {
    fn check_item(&mut self, cx: &LateContext<'_, '_>, item: &hir::Item) {
        let (ty, type_alias_generics) = match item.kind {
            hir::ItemKind::TyAlias(ref ty, ref generics) => (&*ty, generics),
            _ => return,
        };
        let mut suggested_changing_assoc_types = false;
        // There must not be a where clause
        if !type_alias_generics.where_clause.predicates.is_empty() {
            let spans : Vec<_> = type_alias_generics.where_clause.predicates.iter()
                .map(|pred| pred.span()).collect();
            let mut err = cx.struct_span_lint(TYPE_ALIAS_BOUNDS, spans,
                "where clauses are not enforced in type aliases");
            err.help("the clause will not be checked when the type alias is used, \
                      and should be removed");
            if !suggested_changing_assoc_types {
                TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
                suggested_changing_assoc_types = true;
            }
            err.emit();
        }
        // The parameters must not have bounds
        for param in type_alias_generics.params.iter() {
            let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
            if !spans.is_empty() {
                let mut err = cx.struct_span_lint(
                    TYPE_ALIAS_BOUNDS,
                    spans,
                    "bounds on generic parameters are not enforced in type aliases",
                );
                err.help("the bound will not be checked when the type alias is used, \
                          and should be removed");
                if !suggested_changing_assoc_types {
                    TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
                    suggested_changing_assoc_types = true;
                }
                err.emit();
            }
        }
    }
}

declare_lint_pass!(
    /// Lint constants that are erroneous.
    /// Without this lint, we might not get any diagnostic if the constant is
    /// unused within this crate, even though downstream crates can't use it
    /// without producing an error.
    UnusedBrokenConst => []
);

fn check_const(cx: &LateContext<'_, '_>, body_id: hir::BodyId) {
    let def_id = cx.tcx.hir().body_owner_def_id(body_id);
    let param_env = if cx.tcx.is_static(def_id) {
        // Use the same param_env as `codegen_static_initializer`, to reuse the cache.
        ty::ParamEnv::reveal_all()
    } else {
        cx.tcx.param_env(def_id)
    };
    let cid = ::rustc::mir::interpret::GlobalId {
        instance: ty::Instance::mono(cx.tcx, def_id),
        promoted: None
    };
    // trigger the query once for all constants since that will already report the errors
    // FIXME: Use ensure here
    let _ = cx.tcx.const_eval(param_env.and(cid));
}

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedBrokenConst {
    fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item) {
        match it.kind {
            hir::ItemKind::Const(_, body_id) => {
                check_const(cx, body_id);
            },
            hir::ItemKind::Static(_, _, body_id) => {
                check_const(cx, body_id);
            },
            _ => {},
        }
    }
}

declare_lint! {
    TRIVIAL_BOUNDS,
    Warn,
    "these bounds don't depend on an type parameters"
}

declare_lint_pass!(
    /// Lint for trait and lifetime bounds that don't depend on type parameters
    /// which either do nothing, or stop the item from being used.
    TrivialConstraints => [TRIVIAL_BOUNDS]
);

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TrivialConstraints {
    fn check_item(
        &mut self,
        cx: &LateContext<'a, 'tcx>,
        item: &'tcx hir::Item,
    ) {
        use rustc::ty::fold::TypeFoldable;
        use rustc::ty::Predicate::*;

        if cx.tcx.features().trivial_bounds {
            let def_id = cx.tcx.hir().local_def_id(item.hir_id);
            let predicates = cx.tcx.predicates_of(def_id);
            for &(predicate, span) in predicates.predicates {
                let predicate_kind_name = match predicate {
                    Trait(..) => "Trait",
                    TypeOutlives(..) |
                    RegionOutlives(..) => "Lifetime",

                    // Ignore projections, as they can only be global
                    // if the trait bound is global
                    Projection(..) |
                    // Ignore bounds that a user can't type
                    WellFormed(..) |
                    ObjectSafe(..) |
                    ClosureKind(..) |
                    Subtype(..) |
                    ConstEvaluatable(..) => continue,
                };
                if predicate.is_global() {
                    cx.span_lint(
                        TRIVIAL_BOUNDS,
                        span,
                        &format!("{} bound {} does not depend on any type \
                                or lifetime parameters", predicate_kind_name, predicate),
                    );
                }
            }
        }
    }
}

declare_lint_pass!(
    /// Does nothing as a lint pass, but registers some `Lint`s
    /// which are used by other parts of the compiler.
    SoftLints => [
        WHILE_TRUE,
        BOX_POINTERS,
        NON_SHORTHAND_FIELD_PATTERNS,
        UNSAFE_CODE,
        MISSING_DOCS,
        MISSING_COPY_IMPLEMENTATIONS,
        MISSING_DEBUG_IMPLEMENTATIONS,
        ANONYMOUS_PARAMETERS,
        UNUSED_DOC_COMMENTS,
        PLUGIN_AS_LIBRARY,
        NO_MANGLE_CONST_ITEMS,
        NO_MANGLE_GENERIC_ITEMS,
        MUTABLE_TRANSMUTES,
        UNSTABLE_FEATURES,
        UNIONS_WITH_DROP_FIELDS,
        UNREACHABLE_PUB,
        TYPE_ALIAS_BOUNDS,
        TRIVIAL_BOUNDS
    ]
);

declare_lint! {
    pub ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
    Warn,
    "`...` range patterns are deprecated"
}

#[derive(Default)]
pub struct EllipsisInclusiveRangePatterns {
    /// If `Some(_)`, suppress all subsequent pattern
    /// warnings for better diagnostics.
    node_id: Option<ast::NodeId>,
}

impl_lint_pass!(EllipsisInclusiveRangePatterns => [ELLIPSIS_INCLUSIVE_RANGE_PATTERNS]);

impl EarlyLintPass for EllipsisInclusiveRangePatterns {
    fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &ast::Pat) {
        if self.node_id.is_some() {
            // Don't recursively warn about patterns inside range endpoints.
            return
        }

        use self::ast::{PatKind, RangeEnd, RangeSyntax::DotDotDot};

        /// If `pat` is a `...` pattern, return the start and end of the range, as well as the span
        /// corresponding to the ellipsis.
        fn matches_ellipsis_pat(pat: &ast::Pat) -> Option<(&P<Expr>, &P<Expr>, Span)> {
            match &pat.kind {
                PatKind::Range(a, b, Spanned { span, node: RangeEnd::Included(DotDotDot), .. }) => {
                    Some((a, b, *span))
                }
                _ => None,
            }
        }

        let (parenthesise, endpoints) = match &pat.kind {
            PatKind::Ref(subpat, _) => (true, matches_ellipsis_pat(&subpat)),
            _ => (false, matches_ellipsis_pat(pat)),
        };

        if let Some((start, end, join)) = endpoints {
            let msg = "`...` range patterns are deprecated";
            let suggestion = "use `..=` for an inclusive range";
            if parenthesise {
                self.node_id = Some(pat.id);
                let mut err = cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, pat.span, msg);
                err.span_suggestion(
                    pat.span,
                    suggestion,
                    format!("&({}..={})", expr_to_string(&start), expr_to_string(&end)),
                    Applicability::MachineApplicable,
                );
                err.emit();
            } else {
                let mut err = cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, join, msg);
                err.span_suggestion_short(
                    join,
                    suggestion,
                    "..=".to_owned(),
                    Applicability::MachineApplicable,
                );
                err.emit();
            };
        }
    }

    fn check_pat_post(&mut self, _cx: &EarlyContext<'_>, pat: &ast::Pat) {
        if let Some(node_id) = self.node_id {
            if pat.id == node_id {
                self.node_id = None
            }
        }
    }
}

declare_lint! {
    UNNAMEABLE_TEST_ITEMS,
    Warn,
    "detects an item that cannot be named being marked as `#[test_case]`",
    report_in_external_macro: true
}

pub struct UnnameableTestItems {
    boundary: hir::HirId, // HirId of the item under which things are not nameable
    items_nameable: bool,
}

impl_lint_pass!(UnnameableTestItems => [UNNAMEABLE_TEST_ITEMS]);

impl UnnameableTestItems {
    pub fn new() -> Self {
        Self {
            boundary: hir::DUMMY_HIR_ID,
            items_nameable: true
        }
    }
}

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnnameableTestItems {
    fn check_item(&mut self, cx: &LateContext<'_, '_>, it: &hir::Item) {
        if self.items_nameable {
            if let hir::ItemKind::Mod(..) = it.kind {}
            else {
                self.items_nameable = false;
                self.boundary = it.hir_id;
            }
            return;
        }

        if let Some(attr) = attr::find_by_name(&it.attrs, sym::rustc_test_marker) {
            cx.struct_span_lint(
                UNNAMEABLE_TEST_ITEMS,
                attr.span,
                "cannot test inner items",
            ).emit();
        }
    }

    fn check_item_post(&mut self, _cx: &LateContext<'_, '_>, it: &hir::Item) {
        if !self.items_nameable && self.boundary == it.hir_id {
            self.items_nameable = true;
        }
    }
}

declare_lint! {
    pub KEYWORD_IDENTS,
    Allow,
    "detects edition keywords being used as an identifier"
}

declare_lint_pass!(
    /// Check for uses of edition keywords used as an identifier.
    KeywordIdents => [KEYWORD_IDENTS]
);

struct UnderMacro(bool);

impl KeywordIdents {
    fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: TokenStream) {
        for tt in tokens.into_trees() {
            match tt {
                // Only report non-raw idents.
                TokenTree::Token(token) => if let Some((ident, false)) = token.ident() {
                    self.check_ident_token(cx, UnderMacro(true), ident);
                }
                TokenTree::Delimited(_, _, tts) => {
                    self.check_tokens(cx, tts)
                },
            }
        }
    }

    fn check_ident_token(&mut self,
                         cx: &EarlyContext<'_>,
                         UnderMacro(under_macro): UnderMacro,
                         ident: ast::Ident)
    {
        let next_edition = match cx.sess.edition() {
            Edition::Edition2015 => {
                match ident.name {
                    kw::Async | kw::Await | kw::Try => Edition::Edition2018,

                    // rust-lang/rust#56327: Conservatively do not
                    // attempt to report occurrences of `dyn` within
                    // macro definitions or invocations, because `dyn`
                    // can legitimately occur as a contextual keyword
                    // in 2015 code denoting its 2018 meaning, and we
                    // do not want rustfix to inject bugs into working
                    // code by rewriting such occurrences.
                    //
                    // But if we see `dyn` outside of a macro, we know
                    // its precise role in the parsed AST and thus are
                    // assured this is truly an attempt to use it as
                    // an identifier.
                    kw::Dyn if !under_macro => Edition::Edition2018,

                    _ => return,
                }
            }

            // There are no new keywords yet for the 2018 edition and beyond.
            _ => return,
        };

        // Don't lint `r#foo`.
        if cx.sess.parse_sess.raw_identifier_spans.borrow().contains(&ident.span) {
            return;
        }

        let mut lint = cx.struct_span_lint(
            KEYWORD_IDENTS,
            ident.span,
            &format!("`{}` is a keyword in the {} edition",
                     ident.as_str(),
                     next_edition),
        );
        lint.span_suggestion(
            ident.span,
            "you can use a raw identifier to stay compatible",
            format!("r#{}", ident.as_str()),
            Applicability::MachineApplicable,
        );
        lint.emit()
    }
}

impl EarlyLintPass for KeywordIdents {
    fn check_mac_def(&mut self, cx: &EarlyContext<'_>, mac_def: &ast::MacroDef, _id: ast::NodeId) {
        self.check_tokens(cx, mac_def.stream());
    }
    fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::Mac) {
        self.check_tokens(cx, mac.tts.clone().into());
    }
    fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: ast::Ident) {
        self.check_ident_token(cx, UnderMacro(false), ident);
    }
}

declare_lint_pass!(ExplicitOutlivesRequirements => [EXPLICIT_OUTLIVES_REQUIREMENTS]);

impl ExplicitOutlivesRequirements {
    fn lifetimes_outliving_lifetime<'tcx>(
        inferred_outlives: &'tcx [ty::Predicate<'tcx>],
        index: u32,
    ) -> Vec<ty::Region<'tcx>> {
        inferred_outlives.iter().filter_map(|pred| {
            match pred {
                ty::Predicate::RegionOutlives(outlives) => {
                    let outlives = outlives.skip_binder();
                    match outlives.0 {
                        ty::ReEarlyBound(ebr) if ebr.index == index => {
                            Some(outlives.1)
                        }
                        _ => None,
                    }
                }
                _ => None
            }
        }).collect()
    }

    fn lifetimes_outliving_type<'tcx>(
        inferred_outlives: &'tcx [ty::Predicate<'tcx>],
        index: u32,
    ) -> Vec<ty::Region<'tcx>> {
        inferred_outlives.iter().filter_map(|pred| {
            match pred {
                ty::Predicate::TypeOutlives(outlives) => {
                    let outlives = outlives.skip_binder();
                    if outlives.0.is_param(index) {
                        Some(outlives.1)
                    } else {
                        None
                    }
                }
                _ => None
            }
        }).collect()
    }

    fn collect_outlived_lifetimes<'tcx>(
        &self,
        param: &'tcx hir::GenericParam,
        tcx: TyCtxt<'tcx>,
        inferred_outlives: &'tcx [ty::Predicate<'tcx>],
        ty_generics: &'tcx ty::Generics,
    ) -> Vec<ty::Region<'tcx>> {
        let index = ty_generics.param_def_id_to_index[
            &tcx.hir().local_def_id(param.hir_id)];

        match param.kind {
            hir::GenericParamKind::Lifetime { .. } => {
                Self::lifetimes_outliving_lifetime(inferred_outlives, index)
            }
            hir::GenericParamKind::Type { .. } => {
                Self::lifetimes_outliving_type(inferred_outlives, index)
            }
            hir::GenericParamKind::Const { .. } => Vec::new(),
        }
    }


    fn collect_outlives_bound_spans<'tcx>(
        &self,
        tcx: TyCtxt<'tcx>,
        bounds: &hir::GenericBounds,
        inferred_outlives: &[ty::Region<'tcx>],
        infer_static: bool,
    ) -> Vec<(usize, Span)> {
        use rustc::middle::resolve_lifetime::Region;

        bounds
            .iter()
            .enumerate()
            .filter_map(|(i, bound)| {
                if let hir::GenericBound::Outlives(lifetime) = bound {
                    let is_inferred = match tcx.named_region(lifetime.hir_id) {
                        Some(Region::Static) if infer_static => {
                            inferred_outlives.iter()
                                .any(|r| if let ty::ReStatic = r { true } else { false })
                        }
                        Some(Region::EarlyBound(index, ..)) => inferred_outlives
                            .iter()
                            .any(|r| {
                                if let ty::ReEarlyBound(ebr) = r {
                                    ebr.index == index
                                } else {
                                    false
                                }
                            }),
                        _ => false,
                    };
                    if is_inferred {
                        Some((i, bound.span()))
                    } else {
                        None
                    }
                } else {
                    None
                }
            })
            .collect()
    }

    fn consolidate_outlives_bound_spans(
        &self,
        lo: Span,
        bounds: &hir::GenericBounds,
        bound_spans: Vec<(usize, Span)>
    ) -> Vec<Span> {
        if bounds.is_empty() {
            return Vec::new();
        }
        if bound_spans.len() == bounds.len() {
            let (_, last_bound_span) = bound_spans[bound_spans.len()-1];
            // If all bounds are inferable, we want to delete the colon, so
            // start from just after the parameter (span passed as argument)
            vec![lo.to(last_bound_span)]
        } else {
            let mut merged = Vec::new();
            let mut last_merged_i = None;

            let mut from_start = true;
            for (i, bound_span) in bound_spans {
                match last_merged_i {
                    // If the first bound is inferable, our span should also eat the leading `+`.
                    None if i == 0 => {
                        merged.push(bound_span.to(bounds[1].span().shrink_to_lo()));
                        last_merged_i = Some(0);
                    },
                    // If consecutive bounds are inferable, merge their spans
                    Some(h) if i == h+1 => {
                        if let Some(tail) = merged.last_mut() {
                            // Also eat the trailing `+` if the first
                            // more-than-one bound is inferable
                            let to_span = if from_start && i < bounds.len() {
                                bounds[i+1].span().shrink_to_lo()
                            } else {
                                bound_span
                            };
                            *tail = tail.to(to_span);
                            last_merged_i = Some(i);
                        } else {
                            bug!("another bound-span visited earlier");
                        }
                    },
                    _ => {
                        // When we find a non-inferable bound, subsequent inferable bounds
                        // won't be consecutive from the start (and we'll eat the leading
                        // `+` rather than the trailing one)
                        from_start = false;
                        merged.push(bounds[i-1].span().shrink_to_hi().to(bound_span));
                        last_merged_i = Some(i);
                    }
                }
            }
            merged
        }
    }
}

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ExplicitOutlivesRequirements {
    fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item) {
        use rustc::middle::resolve_lifetime::Region;

        let infer_static = cx.tcx.features().infer_static_outlives_requirements;
        let def_id = cx.tcx.hir().local_def_id(item.hir_id);
        if let hir::ItemKind::Struct(_, ref hir_generics)
            | hir::ItemKind::Enum(_, ref hir_generics)
            | hir::ItemKind::Union(_, ref hir_generics) = item.kind
        {
            let inferred_outlives = cx.tcx.inferred_outlives_of(def_id);
            if inferred_outlives.is_empty() {
                return;
            }

            let ty_generics = cx.tcx.generics_of(def_id);

            let mut bound_count = 0;
            let mut lint_spans = Vec::new();

            for param in &hir_generics.params {
                let has_lifetime_bounds = param.bounds.iter().any(|bound| {
                    if let hir::GenericBound::Outlives(_) = bound {
                        true
                    } else {
                        false
                    }
                });
                if !has_lifetime_bounds {
                    continue;
                }

                let relevant_lifetimes = self.collect_outlived_lifetimes(
                    param,
                    cx.tcx,
                    inferred_outlives,
                    ty_generics,
                );
                if relevant_lifetimes.is_empty() {
                    continue;
                }

                let bound_spans = self.collect_outlives_bound_spans(
                    cx.tcx, &param.bounds, &relevant_lifetimes, infer_static,
                );
                bound_count += bound_spans.len();
                lint_spans.extend(
                    self.consolidate_outlives_bound_spans(
                        param.span.shrink_to_hi(), &param.bounds, bound_spans
                    )
                );
            }

            let mut where_lint_spans = Vec::new();
            let mut dropped_predicate_count = 0;
            let num_predicates = hir_generics.where_clause.predicates.len();
            for (i, where_predicate) in hir_generics.where_clause.predicates.iter().enumerate() {
                let (relevant_lifetimes, bounds, span) = match where_predicate {
                    hir::WherePredicate::RegionPredicate(predicate) => {
                        if let Some(Region::EarlyBound(index, ..))
                            = cx.tcx.named_region(predicate.lifetime.hir_id)
                        {
                            (
                                Self::lifetimes_outliving_lifetime(inferred_outlives, index),
                                &predicate.bounds,
                                predicate.span,
                            )
                        } else {
                            continue;
                        }
                    }
                    hir::WherePredicate::BoundPredicate(predicate) => {
                        // FIXME we can also infer bounds on associated types,
                        // and should check for them here.
                        match predicate.bounded_ty.kind {
                            hir::TyKind::Path(hir::QPath::Resolved(
                                None,
                                ref path,
                            )) => {
                                if let Res::Def(DefKind::TyParam, def_id) = path.res {
                                    let index = ty_generics.param_def_id_to_index[&def_id];
                                    (
                                        Self::lifetimes_outliving_type(inferred_outlives, index),
                                        &predicate.bounds,
                                        predicate.span,
                                    )
                                } else {
                                    continue;
                                }
                            },
                            _ => { continue; }
                        }
                    }
                    _ => continue,
                };
                if relevant_lifetimes.is_empty() {
                    continue;
                }

                let bound_spans = self.collect_outlives_bound_spans(
                    cx.tcx, bounds, &relevant_lifetimes, infer_static,
                );
                bound_count += bound_spans.len();

                let drop_predicate = bound_spans.len() == bounds.len();
                if drop_predicate {
                    dropped_predicate_count += 1;
                }

                // If all the bounds on a predicate were inferable and there are
                // further predicates, we want to eat the trailing comma.
                if drop_predicate && i + 1 < num_predicates {
                    let next_predicate_span = hir_generics.where_clause.predicates[i + 1].span();
                    where_lint_spans.push(
                        span.to(next_predicate_span.shrink_to_lo())
                    );
                } else {
                    where_lint_spans.extend(
                        self.consolidate_outlives_bound_spans(
                            span.shrink_to_lo(),
                            bounds,
                            bound_spans
                        )
                    );
                }
            }

            // If all predicates are inferable, drop the entire clause
            // (including the `where`)
            if num_predicates > 0 && dropped_predicate_count == num_predicates {
                let where_span = hir_generics.where_clause.span()
                    .expect("span of (nonempty) where clause should exist");
                // Extend the where clause back to the closing `>` of the
                // generics, except for tuple struct, which have the `where`
                // after the fields of the struct.
                let full_where_span = if let hir::ItemKind::Struct(hir::VariantData::Tuple(..), _)
                        = item.kind
                {
                    where_span
                } else {
                    hir_generics.span.shrink_to_hi().to(where_span)
                };
                lint_spans.push(
                    full_where_span
                );
            } else {
                lint_spans.extend(where_lint_spans);
            }

            if !lint_spans.is_empty() {
                let mut err = cx.struct_span_lint(
                    EXPLICIT_OUTLIVES_REQUIREMENTS,
                    lint_spans.clone(),
                    "outlives requirements can be inferred"
                );
                err.multipart_suggestion(
                    if bound_count == 1 {
                        "remove this bound"
                    } else {
                        "remove these bounds"
                    },
                    lint_spans.into_iter().map(|span| (span, "".to_owned())).collect::<Vec<_>>(),
                    Applicability::MachineApplicable
                );
                err.emit();
            }
        }
    }
}

declare_lint! {
    pub INCOMPLETE_FEATURES,
    Warn,
    "incomplete features that may function improperly in some or all cases"
}

declare_lint_pass!(
    /// Check for used feature gates in `INCOMPLETE_FEATURES` in `feature_gate.rs`.
    IncompleteFeatures => [INCOMPLETE_FEATURES]
);

impl EarlyLintPass for IncompleteFeatures {
    fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
        let features = cx.sess.features_untracked();
        features.declared_lang_features
            .iter().map(|(name, span, _)| (name, span))
            .chain(features.declared_lib_features.iter().map(|(name, span)| (name, span)))
            .filter(|(name, _)| feature_gate::INCOMPLETE_FEATURES.iter().any(|f| name == &f))
            .for_each(|(name, &span)| {
                cx.struct_span_lint(
                    INCOMPLETE_FEATURES,
                    span,
                    &format!(
                        "the feature `{}` is incomplete and may cause the compiler to crash",
                        name,
                    )
                )
                .emit();
            });
    }
}

declare_lint! {
    pub INVALID_VALUE,
    Warn,
    "an invalid value is being created (such as a NULL reference)"
}

declare_lint_pass!(InvalidValue => [INVALID_VALUE]);

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for InvalidValue {
    fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &hir::Expr) {

        #[derive(Debug, Copy, Clone, PartialEq)]
        enum InitKind { Zeroed, Uninit };

        /// Information about why a type cannot be initialized this way.
        /// Contains an error message and optionally a span to point at.
        type InitError = (String, Option<Span>);

        /// Test if this constant is all-0.
        fn is_zero(expr: &hir::Expr) -> bool {
            use hir::ExprKind::*;
            use syntax::ast::LitKind::*;
            match &expr.kind {
                Lit(lit) =>
                    if let Int(i, _) = lit.node {
                        i == 0
                    } else {
                        false
                    },
                Tup(tup) =>
                    tup.iter().all(is_zero),
                _ =>
                    false
            }
        }

        /// Determine if this expression is a "dangerous initialization".
        fn is_dangerous_init(cx: &LateContext<'_, '_>, expr: &hir::Expr) -> Option<InitKind> {
            const ZEROED_PATH: &[Symbol] = &[sym::core, sym::mem, sym::zeroed];
            const UININIT_PATH: &[Symbol] = &[sym::core, sym::mem, sym::uninitialized];
            // `transmute` is inside an anonymous module (the `extern` block?);
            // `Invalid` represents the empty string and matches that.
            const TRANSMUTE_PATH: &[Symbol] =
                &[sym::core, sym::intrinsics, kw::Invalid, sym::transmute];

            if let hir::ExprKind::Call(ref path_expr, ref args) = expr.kind {
                if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
                    let def_id = cx.tables.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;

                    if cx.match_def_path(def_id, ZEROED_PATH) {
                        return Some(InitKind::Zeroed);
                    }
                    if cx.match_def_path(def_id, UININIT_PATH) {
                        return Some(InitKind::Uninit);
                    }
                    if cx.match_def_path(def_id, TRANSMUTE_PATH) {
                        if is_zero(&args[0]) {
                            return Some(InitKind::Zeroed);
                        }
                    }
                    // FIXME: Also detect `MaybeUninit::zeroed().assume_init()` and
                    // `MaybeUninit::uninit().assume_init()`.
                }
            }

            None
        }

        /// Return `Some` only if we are sure this type does *not*
        /// allow zero initialization.
        fn ty_find_init_error<'tcx>(
            tcx: TyCtxt<'tcx>,
            ty: Ty<'tcx>,
            init: InitKind,
        ) -> Option<InitError> {
            use rustc::ty::TyKind::*;
            match ty.kind {
                // Primitive types that don't like 0 as a value.
                Ref(..) => Some((format!("References must be non-null"), None)),
                Adt(..) if ty.is_box() => Some((format!("`Box` must be non-null"), None)),
                FnPtr(..) => Some((format!("Function pointers must be non-null"), None)),
                Never => Some((format!("The never type (`!`) has no valid value"), None)),
                // Primitive types with other constraints.
                Bool if init == InitKind::Uninit =>
                    Some((format!("Booleans must be `true` or `false`"), None)),
                Char if init == InitKind::Uninit =>
                    Some((format!("Characters must be a valid unicode codepoint"), None)),
                // Recurse and checks for some compound types.
                Adt(adt_def, substs) if !adt_def.is_union() => {
                    // First check f this ADT has a layout attribute (like `NonNull` and friends).
                    use std::ops::Bound;
                    match tcx.layout_scalar_valid_range(adt_def.did) {
                        // We exploit here that `layout_scalar_valid_range` will never
                        // return `Bound::Excluded`.  (And we have tests checking that we
                        // handle the attribute correctly.)
                        (Bound::Included(lo), _) if lo > 0 =>
                            return Some((format!("{} must be non-null", ty), None)),
                        (Bound::Included(_), _) | (_, Bound::Included(_))
                        if init == InitKind::Uninit =>
                            return Some((
                                format!("{} must be initialized inside its custom valid range", ty),
                                None,
                            )),
                        _ => {}
                    }
                    // Now, recurse.
                    match adt_def.variants.len() {
                        0 => Some((format!("0-variant enums have no valid value"), None)),
                        1 => {
                            // Struct, or enum with exactly one variant.
                            // Proceed recursively, check all fields.
                            let variant = &adt_def.variants[VariantIdx::from_u32(0)];
                            variant.fields.iter().find_map(|field| {
                                ty_find_init_error(
                                    tcx,
                                    field.ty(tcx, substs),
                                    init,
                                ).map(|(mut msg, span)| if span.is_none() {
                                    // Point to this field, should be helpful for figuring
                                    // out where the source of the error is.
                                    let span = tcx.def_span(field.did);
                                    write!(&mut msg, " (in this {} field)", adt_def.descr())
                                        .unwrap();
                                    (msg, Some(span))
                                } else {
                                    // Just forward.
                                    (msg, span)
                                })
                            })
                        }
                        // Multi-variant enums are tricky: if all but one variant are
                        // uninhabited, we might actually do layout like for a single-variant
                        // enum, and then even leaving them uninitialized could be okay.
                        _ => None, // Conservative fallback for multi-variant enum.
                    }
                }
                Tuple(..) => {
                    // Proceed recursively, check all fields.
                    ty.tuple_fields().find_map(|field| ty_find_init_error(tcx, field, init))
                }
                // Conservative fallback.
                _ => None,
            }
        }

        if let Some(init) = is_dangerous_init(cx, expr) {
            // This conjures an instance of a type out of nothing,
            // using zeroed or uninitialized memory.
            // We are extremely conservative with what we warn about.
            let conjured_ty = cx.tables.expr_ty(expr);
            if let Some((msg, span)) = ty_find_init_error(cx.tcx, conjured_ty, init) {
                let mut err = cx.struct_span_lint(
                    INVALID_VALUE,
                    expr.span,
                    &format!(
                        "the type `{}` does not permit {}",
                        conjured_ty,
                        match init {
                            InitKind::Zeroed => "zero-initialization",
                            InitKind::Uninit => "being left uninitialized",
                        },
                    ),
                );
                err.span_label(expr.span,
                    "this code causes undefined behavior when executed");
                err.span_label(expr.span, "help: use `MaybeUninit<T>` instead");
                if let Some(span) = span {
                    err.span_note(span, &msg);
                } else {
                    err.note(&msg);
                }
                err.emit();
            }
        }
    }
}