builtin.rs

// Copyright 2012-2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! 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 `LintPass`, you will also need to add it to the
//! `add_builtin!` or `add_builtin_with_new!` invocation in `lib.rs`.
//! Use the former for unit-like structs and the latter for structs with
//! a `pub fn new()`.

use rustc::hir::def::Def;
use rustc::hir::def_id::DefId;
use rustc::cfg;
use rustc::ty::subst::Substs;
use rustc::ty::{self, Ty};
use rustc::traits;
use rustc::hir::map as hir_map;
use util::nodemap::NodeSet;
use lint::{LateContext, LintContext, LintArray};
use lint::{LintPass, LateLintPass, EarlyLintPass, EarlyContext};

use std::collections::HashSet;

use syntax::ast;
use syntax::attr;
use syntax::feature_gate::{AttributeGate, AttributeType, Stability, deprecated_attributes};
use syntax_pos::{BytePos, Span, SyntaxContext};
use syntax::symbol::keywords;
use syntax::errors::{Applicability, DiagnosticBuilder};

use rustc::hir::{self, PatKind};
use rustc::hir::intravisit::FnKind;

use bad_style::{MethodLateContext, method_context};

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

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

#[derive(Copy, Clone)]
pub struct WhileTrue;

impl LintPass for WhileTrue {
    fn get_lints(&self) -> LintArray {
        lint_array!(WHILE_TRUE)
    }
}

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for WhileTrue {
    fn check_expr(&mut self, cx: &LateContext, e: &hir::Expr) {
        if let hir::ExprWhile(ref cond, ..) = e.node {
            if let hir::ExprLit(ref lit) = cond.node {
                if let ast::LitKind::Bool(true) = lit.node {
                    if lit.span.ctxt() == SyntaxContext::empty() {
                        let msg = "denote infinite loops with `loop { ... }`";
                        let condition_span = cx.tcx.sess.codemap().def_span(e.span);
                        let mut err = cx.struct_span_lint(WHILE_TRUE, condition_span, msg);
                        err.span_suggestion_short(condition_span, "use `loop`", "loop".to_owned());
                        err.emit();
                    }
                }
            }
        }
    }
}

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

#[derive(Copy, Clone)]
pub struct BoxPointers;

impl BoxPointers {
    fn check_heap_type<'a, 'tcx>(&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 LintPass for BoxPointers {
    fn get_lints(&self) -> LintArray {
        lint_array!(BOX_POINTERS)
    }
}

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BoxPointers {
    fn check_item(&mut self, cx: &LateContext, it: &hir::Item) {
        match it.node {
            hir::ItemFn(..) |
            hir::ItemTy(..) |
            hir::ItemEnum(..) |
            hir::ItemStruct(..) |
            hir::ItemUnion(..) => {
                let def_id = cx.tcx.hir.local_def_id(it.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.node {
            hir::ItemStruct(ref struct_def, _) |
            hir::ItemUnion(ref struct_def, _) => {
                for struct_field in struct_def.fields() {
                    let def_id = cx.tcx.hir.local_def_id(struct_field.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_id_to_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"
}

#[derive(Copy, Clone)]
pub struct NonShorthandFieldPatterns;

impl LintPass for NonShorthandFieldPatterns {
    fn get_lints(&self) -> LintArray {
        lint_array!(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.node {
            let variant = cx.tables.pat_ty(pat).ty_adt_def()
                                   .expect("struct pattern type is not an ADT")
                                   .variant_of_def(cx.tables.qpath_def(qpath, pat.hir_id));
            for fieldpat in field_pats {
                if fieldpat.node.is_shorthand {
                    continue;
                }
                if fieldpat.span.ctxt().outer().expn_info().is_some() {
                    // 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(_, _, name, None) = fieldpat.node.pat.node {
                    let binding_ident = ast::Ident::new(name.node, name.span);
                    if cx.tcx.find_field_index(binding_ident, &variant) ==
                       Some(cx.tcx.field_index(fieldpat.node.id, cx.tables)) {
                        let mut err = cx.struct_span_lint(NON_SHORTHAND_FIELD_PATTERNS,
                                     fieldpat.span,
                                     &format!("the `{}:` in this pattern is redundant",
                                              name.node));
                        let subspan = cx.tcx.sess.codemap().span_through_char(fieldpat.span, ':');
                        err.span_suggestion_short(subspan,
                                                  "remove this",
                                                  format!("{}", name.node));
                        err.emit();
                    }
                }
            }
        }
    }
}

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

#[derive(Copy, Clone)]
pub struct UnsafeCode;

impl LintPass for UnsafeCode {
    fn get_lints(&self) -> LintArray {
        lint_array!(UNSAFE_CODE)
    }
}

impl UnsafeCode {
    fn report_unsafe(&self, cx: &LateContext, 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<'a, 'tcx> LateLintPass<'a, 'tcx> for UnsafeCode {
    fn check_expr(&mut self, cx: &LateContext, e: &hir::Expr) {
        if let hir::ExprBlock(ref blk) = e.node {
            // Don't warn about generated blocks, that'll just pollute the output.
            if blk.rules == hir::UnsafeBlock(hir::UserProvided) {
                self.report_unsafe(cx, blk.span, "usage of an `unsafe` block");
            }
        }
    }

    fn check_item(&mut self, cx: &LateContext, it: &hir::Item) {
        match it.node {
            hir::ItemTrait(_, hir::Unsafety::Unsafe, ..) => {
                self.report_unsafe(cx, it.span, "declaration of an `unsafe` trait")
            }

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

            _ => return,
        }
    }

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

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

            _ => (),
        }
    }

    fn check_trait_item(&mut self, cx: &LateContext, item: &hir::TraitItem) {
        if let hir::TraitItemKind::Method(ref sig, hir::TraitMethod::Required(_)) = item.node {
            if sig.unsafety == hir::Unsafety::Unsafe {
                self.report_unsafe(cx, item.span, "declaration of an `unsafe` method")
            }
        }
    }
}

declare_lint! {
    MISSING_DOCS,
    Allow,
    "detects missing documentation for public members"
}

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: HashSet<ast::NodeId>,
}

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

    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<ast::NodeId>,
                                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;
            }
        }

        fn has_doc(attr: &ast::Attribute) -> bool {
            if !attr.check_name("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("include") {
                        return true;
                    }
                }
            }

            false
        }

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

impl LintPass for MissingDoc {
    fn get_lints(&self) -> LintArray {
        lint_array!(MISSING_DOCS)
    }
}

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("doc") &&
            match attr.meta_item_list() {
                None => false,
                Some(l) => attr::list_contains_name(&l, "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");
    }

    fn check_item(&mut self, cx: &LateContext, it: &hir::Item) {
        let desc = match it.node {
            hir::ItemFn(..) => "a function",
            hir::ItemMod(..) => "a module",
            hir::ItemEnum(..) => "an enum",
            hir::ItemStruct(..) => "a struct",
            hir::ItemUnion(..) => "a union",
            hir::ItemTrait(.., ref trait_item_refs) => {
                // Issue #11592, traits are always considered exported, even when private.
                if it.vis == hir::Visibility::Inherited {
                    self.private_traits.insert(it.id);
                    for trait_item_ref in trait_item_refs {
                        self.private_traits.insert(trait_item_ref.id.node_id);
                    }
                    return;
                }
                "a trait"
            }
            hir::ItemTy(..) => "a type alias",
            hir::ItemImpl(.., 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.def.def_id();
                if let Some(node_id) = cx.tcx.hir.as_local_node_id(real_trait) {
                    match cx.tcx.hir.find(node_id) {
                        Some(hir_map::NodeItem(item)) => {
                            if item.vis == hir::Visibility::Inherited {
                                for impl_item_ref in impl_item_refs {
                                    self.private_traits.insert(impl_item_ref.id.node_id);
                                }
                            }
                        }
                        _ => {}
                    }
                }
                return;
            }
            hir::ItemConst(..) => "a constant",
            hir::ItemStatic(..) => "a static",
            _ => return,
        };

        self.check_missing_docs_attrs(cx, Some(it.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.id) {
            return;
        }

        let desc = match trait_item.node {
            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.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.id) == MethodLateContext::TraitImpl {
            return;
        }

        let desc = match impl_item.node {
            hir::ImplItemKind::Const(..) => "an associated constant",
            hir::ImplItemKind::Method(..) => "a method",
            hir::ImplItemKind::Type(_) => "an associated type",
        };
        self.check_missing_docs_attrs(cx,
                                      Some(impl_item.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.id),
                                          &sf.attrs,
                                          sf.span,
                                          "a struct field")
        }
    }

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

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

#[derive(Copy, Clone)]
pub struct MissingCopyImplementations;

impl LintPass for MissingCopyImplementations {
    fn get_lints(&self) -> LintArray {
        lint_array!(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.id) {
            return;
        }
        let (def, ty) = match item.node {
            hir::ItemStruct(_, ref ast_generics) => {
                if !ast_generics.params.is_empty() {
                    return;
                }
                let def = cx.tcx.adt_def(cx.tcx.hir.local_def_id(item.id));
                (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
            }
            hir::ItemUnion(_, ref ast_generics) => {
                if !ast_generics.params.is_empty() {
                    return;
                }
                let def = cx.tcx.adt_def(cx.tcx.hir.local_def_id(item.id));
                (def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
            }
            hir::ItemEnum(_, ref ast_generics) => {
                if !ast_generics.params.is_empty() {
                    return;
                }
                let def = cx.tcx.adt_def(cx.tcx.hir.local_def_id(item.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.moves_by_default(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"
}

pub struct MissingDebugImplementations {
    impling_types: Option<NodeSet>,
}

impl MissingDebugImplementations {
    pub fn new() -> MissingDebugImplementations {
        MissingDebugImplementations { impling_types: None }
    }
}

impl LintPass for MissingDebugImplementations {
    fn get_lints(&self) -> LintArray {
        lint_array!(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.id) {
            return;
        }

        match item.node {
            hir::ItemStruct(..) |
            hir::ItemUnion(..) |
            hir::ItemEnum(..) => {}
            _ => return,
        }

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

        if self.impling_types.is_none() {
            let mut impls = NodeSet();
            cx.tcx.for_each_impl(debug, |d| {
                if let Some(ty_def) = cx.tcx.type_of(d).ty_to_def_id() {
                    if let Some(node_id) = cx.tcx.hir.as_local_node_id(ty_def) {
                        impls.insert(node_id);
                    }
                }
            });

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

        if !self.impling_types.as_ref().unwrap().contains(&item.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"
}

/// Checks for use of anonymous parameters (RFC 1685)
#[derive(Clone)]
pub struct AnonymousParameters;

impl LintPass for AnonymousParameters {
    fn get_lints(&self) -> LintArray {
        lint_array!(ANONYMOUS_PARAMETERS)
    }
}

impl EarlyLintPass for AnonymousParameters {
    fn check_trait_item(&mut self, cx: &EarlyContext, it: &ast::TraitItem) {
        match it.node {
            ast::TraitItemKind::Method(ref sig, _) => {
                for arg in sig.decl.inputs.iter() {
                    match arg.pat.node {
                        ast::PatKind::Ident(_, ident, None) => {
                            if ident.name == keywords::Invalid.name() {
                                cx.span_lint(ANONYMOUS_PARAMETERS,
                                             arg.pat.span,
                                             "use of deprecated anonymous parameter");
                            }
                        }
                        _ => (),
                    }
                }
            },
            _ => (),
        }
    }
}

/// Checks 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 (&'static str, AttributeType, AttributeGate)>,
}

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

impl LintPass for DeprecatedAttr {
    fn get_lints(&self) -> LintArray {
        lint_array!()
    }
}

impl EarlyLintPass for DeprecatedAttr {
    fn check_attribute(&mut self, cx: &EarlyContext, attr: &ast::Attribute) {
        for &&(n, _, ref g) in &self.depr_attrs {
            if attr.name() == n {
                if let &AttributeGate::Gated(Stability::Deprecated(link),
                                             ref name,
                                             ref reason,
                                             _) = g {
                    let msg = format!("use of deprecated attribute `{}`: {}. See {}",
                                      name, reason, link);
                    let mut err = cx.struct_span_lint(DEPRECATED, attr.span, &msg);
                    err.span_suggestion_short(attr.span, "remove this attribute", "".to_owned());
                    err.emit();
                }
                return;
            }
        }
    }
}

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

#[derive(Copy, Clone)]
pub struct UnusedDocComment;

impl LintPass for UnusedDocComment {
    fn get_lints(&self) -> LintArray {
        lint_array![UNUSED_DOC_COMMENT]
    }
}

impl UnusedDocComment {
    fn warn_if_doc<'a, 'tcx,
                   I: Iterator<Item=&'a ast::Attribute>,
                   C: LintContext<'tcx>>(&self, mut attrs: I, cx: &C) {
        if let Some(attr) = attrs.find(|a| a.is_value_str() && a.check_name("doc")) {
            cx.struct_span_lint(UNUSED_DOC_COMMENT, attr.span, "doc comment not used by rustdoc")
              .emit();
        }
    }
}

impl EarlyLintPass for UnusedDocComment {
    fn check_local(&mut self, cx: &EarlyContext, decl: &ast::Local) {
        self.warn_if_doc(decl.attrs.iter(), cx);
    }

    fn check_arm(&mut self, cx: &EarlyContext, arm: &ast::Arm) {
        self.warn_if_doc(arm.attrs.iter(), cx);
    }

    fn check_expr(&mut self, cx: &EarlyContext, expr: &ast::Expr) {
        self.warn_if_doc(expr.attrs.iter(), cx);
    }
}

declare_lint! {
    pub UNCONDITIONAL_RECURSION,
    Warn,
    "functions that cannot return without calling themselves"
}

#[derive(Copy, Clone)]
pub struct UnconditionalRecursion;


impl LintPass for UnconditionalRecursion {
    fn get_lints(&self) -> LintArray {
        lint_array![UNCONDITIONAL_RECURSION]
    }
}

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnconditionalRecursion {
    fn check_fn(&mut self,
                cx: &LateContext,
                fn_kind: FnKind,
                _: &hir::FnDecl,
                body: &hir::Body,
                sp: Span,
                id: ast::NodeId) {
        let method = match fn_kind {
            FnKind::ItemFn(..) => None,
            FnKind::Method(..) => {
                Some(cx.tcx.associated_item(cx.tcx.hir.local_def_id(id)))
            }
            // closures can't recur, so they don't matter.
            FnKind::Closure(_) => return,
        };

        // Walk through this function (say `f`) looking to see if
        // every possible path references itself, i.e. the function is
        // called recursively unconditionally. This is done by trying
        // to find a path from the entry node to the exit node that
        // *doesn't* call `f` by traversing from the entry while
        // pretending that calls of `f` are sinks (i.e. ignoring any
        // exit edges from them).
        //
        // NB. this has an edge case with non-returning statements,
        // like `loop {}` or `panic!()`: control flow never reaches
        // the exit node through these, so one can have a function
        // that never actually calls itselfs but is still picked up by
        // this lint:
        //
        //     fn f(cond: bool) {
        //         if !cond { panic!() } // could come from `assert!(cond)`
        //         f(false)
        //     }
        //
        // In general, functions of that form may be able to call
        // itself a finite number of times and then diverge. The lint
        // considers this to be an error for two reasons, (a) it is
        // easier to implement, and (b) it seems rare to actually want
        // to have behaviour like the above, rather than
        // e.g. accidentally recurring after an assert.

        let cfg = cfg::CFG::new(cx.tcx, &body);

        let mut work_queue = vec![cfg.entry];
        let mut reached_exit_without_self_call = false;
        let mut self_call_spans = vec![];
        let mut visited = HashSet::new();

        while let Some(idx) = work_queue.pop() {
            if idx == cfg.exit {
                // found a path!
                reached_exit_without_self_call = true;
                break;
            }

            let cfg_id = idx.node_id();
            if visited.contains(&cfg_id) {
                // already done
                continue;
            }
            visited.insert(cfg_id);

            // is this a recursive call?
            let local_id = cfg.graph.node_data(idx).id();
            if local_id != hir::DUMMY_ITEM_LOCAL_ID {
                let node_id = cx.tcx.hir.hir_to_node_id(hir::HirId {
                    owner: body.value.hir_id.owner,
                    local_id
                });
                let self_recursive = match method {
                    Some(ref method) => expr_refers_to_this_method(cx, method, node_id),
                    None => expr_refers_to_this_fn(cx, id, node_id),
                };
                if self_recursive {
                    self_call_spans.push(cx.tcx.hir.span(node_id));
                    // this is a self call, so we shouldn't explore past
                    // this node in the CFG.
                    continue;
                }
            }

            // add the successors of this node to explore the graph further.
            for (_, edge) in cfg.graph.outgoing_edges(idx) {
                let target_idx = edge.target();
                let target_cfg_id = target_idx.node_id();
                if !visited.contains(&target_cfg_id) {
                    work_queue.push(target_idx)
                }
            }
        }

        // Check the number of self calls because a function that
        // doesn't return (e.g. calls a `-> !` function or `loop { /*
        // no break */ }`) shouldn't be linted unless it actually
        // recurs.
        if !reached_exit_without_self_call && !self_call_spans.is_empty() {
            let sp = cx.tcx.sess.codemap().def_span(sp);
            let mut db = cx.struct_span_lint(UNCONDITIONAL_RECURSION,
                                             sp,
                                             "function cannot return without recurring");
            db.span_label(sp, "cannot return without recurring");
            // offer some help to the programmer.
            for call in &self_call_spans {
                db.span_label(*call, "recursive call site");
            }
            db.help("a `loop` may express intention better if this is on purpose");
            db.emit();
        }

        // all done
        return;

        // Functions for identifying if the given Expr NodeId `id`
        // represents a call to the function `fn_id`/method `method`.

        fn expr_refers_to_this_fn(cx: &LateContext, fn_id: ast::NodeId, id: ast::NodeId) -> bool {
            match cx.tcx.hir.get(id) {
                hir_map::NodeExpr(&hir::Expr { node: hir::ExprCall(ref callee, _), .. }) => {
                    let def = if let hir::ExprPath(ref qpath) = callee.node {
                        cx.tables.qpath_def(qpath, callee.hir_id)
                    } else {
                        return false;
                    };
                    match def {
                        Def::Local(..) | Def::Upvar(..) => false,
                        _ => def.def_id() == cx.tcx.hir.local_def_id(fn_id)
                    }
                }
                _ => false,
            }
        }

        // Check if the expression `id` performs a call to `method`.
        fn expr_refers_to_this_method(cx: &LateContext,
                                      method: &ty::AssociatedItem,
                                      id: ast::NodeId)
                                      -> bool {
            use rustc::ty::adjustment::*;

            // Ignore non-expressions.
            let expr = if let hir_map::NodeExpr(e) = cx.tcx.hir.get(id) {
                e
            } else {
                return false;
            };

            // Check for overloaded autoderef method calls.
            let mut source = cx.tables.expr_ty(expr);
            for adjustment in cx.tables.expr_adjustments(expr) {
                if let Adjust::Deref(Some(deref)) = adjustment.kind {
                    let (def_id, substs) = deref.method_call(cx.tcx, source);
                    if method_call_refers_to_method(cx, method, def_id, substs, id) {
                        return true;
                    }
                }
                source = adjustment.target;
            }

            // Check for method calls and overloaded operators.
            if cx.tables.is_method_call(expr) {
                let hir_id = cx.tcx.hir.definitions().node_to_hir_id(id);
                let def_id = cx.tables.type_dependent_defs()[hir_id].def_id();
                let substs = cx.tables.node_substs(hir_id);
                if method_call_refers_to_method(cx, method, def_id, substs, id) {
                    return true;
                }
            }

            // Check for calls to methods via explicit paths (e.g. `T::method()`).
            match expr.node {
                hir::ExprCall(ref callee, _) => {
                    let def = if let hir::ExprPath(ref qpath) = callee.node {
                        cx.tables.qpath_def(qpath, callee.hir_id)
                    } else {
                        return false;
                    };
                    match def {
                        Def::Method(def_id) => {
                            let substs = cx.tables.node_substs(callee.hir_id);
                            method_call_refers_to_method(cx, method, def_id, substs, id)
                        }
                        _ => false,
                    }
                }
                _ => false,
            }
        }

        // Check if the method call to the method with the ID `callee_id`
        // and instantiated with `callee_substs` refers to method `method`.
        fn method_call_refers_to_method<'a, 'tcx>(cx: &LateContext<'a, 'tcx>,
                                                  method: &ty::AssociatedItem,
                                                  callee_id: DefId,
                                                  callee_substs: &Substs<'tcx>,
                                                  expr_id: ast::NodeId)
                                                  -> bool {
            let tcx = cx.tcx;
            let callee_item = tcx.associated_item(callee_id);

            match callee_item.container {
                // This is an inherent method, so the `def_id` refers
                // directly to the method definition.
                ty::ImplContainer(_) => callee_id == method.def_id,

                // A trait method, from any number of possible sources.
                // Attempt to select a concrete impl before checking.
                ty::TraitContainer(trait_def_id) => {
                    let trait_ref = ty::TraitRef::from_method(tcx, trait_def_id, callee_substs);
                    let trait_ref = ty::Binder::bind(trait_ref);
                    let span = tcx.hir.span(expr_id);
                    let obligation =
                        traits::Obligation::new(traits::ObligationCause::misc(span, expr_id),
                                                cx.param_env,
                                                trait_ref.to_poly_trait_predicate());

                    tcx.infer_ctxt().enter(|infcx| {
                        let mut selcx = traits::SelectionContext::new(&infcx);
                        match selcx.select(&obligation) {
                            // The method comes from a `T: Trait` bound.
                            // If `T` is `Self`, then this call is inside
                            // a default method definition.
                            Ok(Some(traits::VtableParam(_))) => {
                                let on_self = trait_ref.self_ty().is_self();
                                // We can only be recurring in a default
                                // method if we're being called literally
                                // on the `Self` type.
                                on_self && callee_id == method.def_id
                            }

                            // The `impl` is known, so we check that with a
                            // special case:
                            Ok(Some(traits::VtableImpl(vtable_impl))) => {
                                let container = ty::ImplContainer(vtable_impl.impl_def_id);
                                // It matches if it comes from the same impl,
                                // and has the same method name.
                                container == method.container && callee_item.name == method.name
                            }

                            // There's no way to know if this call is
                            // recursive, so we assume it's not.
                            _ => false,
                        }
                    })
                }
            }
        }
    }
}

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

#[derive(Copy, Clone)]
pub struct PluginAsLibrary;

impl LintPass for PluginAsLibrary {
    fn get_lints(&self) -> LintArray {
        lint_array![PLUGIN_AS_LIBRARY]
    }
}

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

        match it.node {
            hir::ItemExternCrate(..) => (),
            _ => return,
        };

        let def_id = cx.tcx.hir.local_def_id(it.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! {
    PRIVATE_NO_MANGLE_FNS,
    Warn,
    "functions marked #[no_mangle] should be exported"
}

declare_lint! {
    PRIVATE_NO_MANGLE_STATICS,
    Warn,
    "statics marked #[no_mangle] should be exported"
}

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"
}

#[derive(Copy, Clone)]
pub struct InvalidNoMangleItems;

impl LintPass for InvalidNoMangleItems {
    fn get_lints(&self) -> LintArray {
        lint_array!(PRIVATE_NO_MANGLE_FNS,
                    PRIVATE_NO_MANGLE_STATICS,
                    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.node {
            hir::ItemFn(.., ref generics, _) => {
                if let Some(no_mangle_attr) = attr::find_by_name(&it.attrs, "no_mangle") {
                    if attr::contains_name(&it.attrs, "linkage") {
                        return;
                    }
                    if !cx.access_levels.is_reachable(it.id) {
                        let msg = "function is marked #[no_mangle], but not exported";
                        let mut err = cx.struct_span_lint(PRIVATE_NO_MANGLE_FNS, it.span, msg);
                        let insertion_span = it.span.shrink_to_lo();
                        if it.vis == hir::Visibility::Inherited {
                            err.span_suggestion(insertion_span,
                                                "try making it public",
                                                "pub ".to_owned());
                        }
                        err.emit();
                    }
                    if generics.is_type_parameterized() {
                        let mut err = cx.struct_span_lint(NO_MANGLE_GENERIC_ITEMS,
                                                          it.span,
                                                          "functions generic over \
                                                           types must be mangled");
                        err.span_suggestion_short(no_mangle_attr.span,
                                                  "remove this attribute",
                                                  "".to_owned());
                        err.emit();
                    }
                }
            }
            hir::ItemStatic(..) => {
                if attr::contains_name(&it.attrs, "no_mangle") &&
                   !cx.access_levels.is_reachable(it.id) {
                       let msg = "static is marked #[no_mangle], but not exported";
                       let mut err = cx.struct_span_lint(PRIVATE_NO_MANGLE_STATICS, it.span, msg);
                       let insertion_span = it.span.shrink_to_lo();
                       if it.vis == hir::Visibility::Inherited {
                           err.span_suggestion(insertion_span,
                                               "try making it public",
                                               "pub ".to_owned());
                       }
                       err.emit();
                }
            }
            hir::ItemConst(..) => {
                if attr::contains_name(&it.attrs, "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.codemap().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());
                    err.emit();
                }
            }
            _ => {}
        }
    }
}

#[derive(Clone, Copy)]
pub struct MutableTransmutes;

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

impl LintPass for MutableTransmutes {
    fn get_lints(&self) -> LintArray {
        lint_array!(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) {
            Some((&ty::TyRef(_, _, from_mt), &ty::TyRef(_, _, 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<(&'tcx ty::TypeVariants<'tcx>, &'tcx ty::TypeVariants<'tcx>)> {
            let def = if let hir::ExprPath(ref qpath) = expr.node {
                cx.tables.qpath_def(qpath, expr.hir_id)
            } else {
                return None;
            };
            if let Def::Fn(did) = def {
                if !def_id_is_transmute(cx, did) {
                    return None;
                }
                let sig = cx.tables.node_id_to_type(expr.hir_id).fn_sig(cx.tcx);
                let from = sig.inputs().skip_binder()[0];
                let to = *sig.output().skip_binder();
                return Some((&from.sty, &to.sty));
            }
            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) == "transmute"
        }
    }
}

/// Forbids using the `#[feature(...)]` attribute
#[derive(Copy, Clone)]
pub struct UnstableFeatures;

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

impl LintPass for UnstableFeatures {
    fn get_lints(&self) -> LintArray {
        lint_array!(UNSTABLE_FEATURES)
    }
}

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

/// Lint for unions that contain fields with possibly non-trivial destructors.
pub struct UnionsWithDropFields;

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

impl LintPass for UnionsWithDropFields {
    fn get_lints(&self) -> LintArray {
        lint_array!(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::ItemUnion(ref vdata, _) = item.node {
            for field in vdata.fields() {
                let field_ty = ctx.tcx.type_of(ctx.tcx.hir.local_def_id(field.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;
                }
            }
        }
    }
}

/// Lint for items marked `pub` that aren't reachable from other crates
pub struct UnreachablePub;

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

impl LintPass for UnreachablePub {
    fn get_lints(&self) -> LintArray {
        lint_array!(UNREACHABLE_PUB)
    }
}

impl UnreachablePub {
    fn perform_lint(&self, cx: &LateContext, what: &str, id: ast::NodeId,
                    vis: &hir::Visibility, span: Span, exportable: bool,
                    mut applicability: Applicability) {
        if !cx.access_levels.is_reachable(id) && *vis == hir::Visibility::Public {
            if span.ctxt().outer().expn_info().is_some() {
                applicability = Applicability::MaybeIncorrect;
            }
            let def_span = cx.tcx.sess.codemap().def_span(span);
            let mut err = cx.struct_span_lint(UNREACHABLE_PUB, def_span,
                                              &format!("unreachable `pub` {}", what));
            // We are presuming that visibility is token at start of
            // declaration (can be macro variable rather than literal `pub`)
            let pub_span = cx.tcx.sess.codemap().span_until_char(def_span, ' ');
            let replacement = if cx.tcx.features().crate_visibility_modifier {
                "crate"
            } else {
                "pub(crate)"
            }.to_owned();
            err.span_suggestion_with_applicability(pub_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) {
        let applicability = match item.node {
            // suggestion span-manipulation is inadequate for `pub use
            // module::{item}` (Issue #50455)
            hir::ItemUse(..) => Applicability::MaybeIncorrect,
            _ => Applicability::MachineApplicable,
        };
        self.perform_lint(cx, "item", item.id, &item.vis, item.span, true, applicability);
    }

    fn check_foreign_item(&mut self, cx: &LateContext, foreign_item: &hir::ForeignItem) {
        self.perform_lint(cx, "item", foreign_item.id, &foreign_item.vis,
                          foreign_item.span, true, Applicability::MachineApplicable);
    }

    fn check_struct_field(&mut self, cx: &LateContext, field: &hir::StructField) {
        self.perform_lint(cx, "field", field.id, &field.vis, field.span, false,
                          Applicability::MachineApplicable);
    }

    fn check_impl_item(&mut self, cx: &LateContext, impl_item: &hir::ImplItem) {
        self.perform_lint(cx, "item", impl_item.id, &impl_item.vis, impl_item.span, false,
                          Applicability::MachineApplicable);
    }
}

/// 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.

pub struct TypeAliasBounds;

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

impl LintPass for TypeAliasBounds {
    fn get_lints(&self) -> LintArray {
        lint_array!(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.node {
                    hir::TyPath(hir::QPath::Resolved(None, ref path)) => {
                        match path.def {
                            Def::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};
        use syntax::ast::NodeId;
        struct WalkAssocTypes<'a, 'db> where 'db: 'a {
            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: NodeId, 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.node {
            hir::ItemTy(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<_> = match param {
                &hir::GenericParam::Lifetime(ref l) => l.bounds.iter().map(|b| b.span).collect(),
                &hir::GenericParam::Type(ref ty) => ty.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();
            }
        }
    }
}

/// 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.
pub struct UnusedBrokenConst;

impl LintPass for UnusedBrokenConst {
    fn get_lints(&self) -> LintArray {
        lint_array!()
    }
}

fn check_const(cx: &LateContext, body_id: hir::BodyId, what: &str) {
    let def_id = cx.tcx.hir.body_owner_def_id(body_id);
    let param_env = cx.tcx.param_env(def_id);
    let cid = ::rustc::mir::interpret::GlobalId {
        instance: ty::Instance::mono(cx.tcx, def_id),
        promoted: None
    };
    if let Err(err) = cx.tcx.const_eval(param_env.and(cid)) {
        let span = cx.tcx.def_span(def_id);
        let mut diag = cx.struct_span_lint(
            CONST_ERR,
            span,
            &format!("this {} cannot be used", what),
        );
        use rustc::middle::const_val::ConstEvalErrDescription;
        match err.description() {
            ConstEvalErrDescription::Simple(message) => {
                diag.span_label(span, message);
            }
            ConstEvalErrDescription::Backtrace(miri, frames) => {
                diag.span_label(span, format!("{}", miri));
                for frame in frames {
                    diag.span_label(frame.span, format!("inside call to `{}`", frame.location));
                }
            }
        }
        diag.emit()
    }
}

struct UnusedBrokenConstVisitor<'a, 'tcx: 'a>(&'a LateContext<'a, 'tcx>);

impl<'a, 'tcx, 'v> hir::intravisit::Visitor<'v> for UnusedBrokenConstVisitor<'a, 'tcx> {
    fn visit_nested_body(&mut self, id: hir::BodyId) {
        check_const(self.0, id, "array length");
    }
    fn nested_visit_map<'this>(&'this mut self) -> hir::intravisit::NestedVisitorMap<'this, 'v> {
        hir::intravisit::NestedVisitorMap::None
    }
}

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedBrokenConst {
    fn check_item(&mut self, cx: &LateContext, it: &hir::Item) {
        match it.node {
            hir::ItemConst(_, body_id) => {
                check_const(cx, body_id, "constant");
            },
            hir::ItemTy(ref ty, _) => hir::intravisit::walk_ty(
                &mut UnusedBrokenConstVisitor(cx),
                ty
            ),
            _ => {},
        }
    }
}

declare_lint! {
    pub UNNECESSARY_EXTERN_CRATE,
    Allow,
    "suggest removing `extern crate` for the 2018 edition"
}

pub struct ExternCrate(/* depth */ u32);

impl ExternCrate {
    pub fn new() -> Self {
        ExternCrate(0)
    }
}

impl LintPass for ExternCrate {
    fn get_lints(&self) -> LintArray {
        lint_array!(UNNECESSARY_EXTERN_CRATE)
    }
}

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ExternCrate {
    fn check_item(&mut self, cx: &LateContext, it: &hir::Item) {
        if !cx.tcx.features().extern_absolute_paths {
            return
        }
        if let hir::ItemExternCrate(ref orig) =  it.node {
            if it.attrs.iter().any(|a| a.check_name("macro_use")) {
                return
            }
            let mut err = cx.struct_span_lint(UNNECESSARY_EXTERN_CRATE,
                it.span, "`extern crate` is unnecessary in the new edition");
            if it.vis == hir::Visibility::Public || self.0 > 1 || orig.is_some() {
                let pub_ = if it.vis == hir::Visibility::Public {
                    "pub "
                } else {
                    ""
                };

                let help = format!("use `{}use`", pub_);

                if let Some(orig) = orig {
                    err.span_suggestion(it.span, &help,
                        format!("{}use {} as {};", pub_, orig, it.name));
                } else {
                    err.span_suggestion(it.span, &help,
                        format!("{}use {};", pub_, it.name));
                }
            } else {
                err.span_suggestion(it.span, "remove it", "".into());
            }

            err.emit();
        }
    }

    fn check_mod(&mut self, _: &LateContext, _: &hir::Mod,
                 _: Span, _: ast::NodeId) {
        self.0 += 1;
    }

    fn check_mod_post(&mut self, _: &LateContext, _: &hir::Mod,
                      _: Span, _: ast::NodeId) {
        self.0 += 1;
    }
}

/// Lint for trait and lifetime bounds that don't depend on type parameters
/// which either do nothing, or stop the item from being used.
pub struct TrivialConstraints;

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

impl LintPass for TrivialConstraints {
    fn get_lints(&self) -> LintArray {
        lint_array!(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.id);
            let predicates = cx.tcx.predicates_of(def_id);
            for predicate 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,
                        item.span,
                        &format!("{} bound {} does not depend on any type \
                                or lifetime parameters", predicate_kind_name, predicate),
                    );
                }
            }
        }
    }
}