src/librustdoc/core.rs

use rustc_attr as attr;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_data_structures::sync::{self, Lrc};
use rustc_driver::abort_on_err;
use rustc_errors::emitter::{Emitter, EmitterWriter};
use rustc_errors::json::JsonEmitter;
use rustc_feature::UnstableFeatures;
use rustc_hir::def::{Namespace::TypeNS, Res};
use rustc_hir::def_id::{CrateNum, DefId, DefIndex, LocalDefId, CRATE_DEF_INDEX, LOCAL_CRATE};
use rustc_hir::HirId;
use rustc_hir::{
    intravisit::{self, NestedVisitorMap, Visitor},
    Path,
};
use rustc_interface::interface;
use rustc_middle::hir::map::Map;
use rustc_middle::middle::cstore::CrateStore;
use rustc_middle::middle::privacy::AccessLevels;
use rustc_middle::ty::{Ty, TyCtxt};
use rustc_resolve as resolve;
use rustc_session::config::{self, CrateType, ErrorOutputType};
use rustc_session::lint;
use rustc_session::DiagnosticOutput;
use rustc_session::Session;
use rustc_span::source_map;
use rustc_span::symbol::sym;
use rustc_span::DUMMY_SP;

use std::cell::RefCell;
use std::mem;
use std::rc::Rc;

use crate::clean;
use crate::clean::{AttributesExt, MAX_DEF_ID};
use crate::config::{Options as RustdocOptions, RenderOptions};
use crate::config::{OutputFormat, RenderInfo};
use crate::passes::{self, Condition::*, ConditionalPass};

pub use rustc_session::config::{CodegenOptions, DebuggingOptions, Input, Options};
pub use rustc_session::search_paths::SearchPath;

pub type ExternalPaths = FxHashMap<DefId, (Vec<String>, clean::TypeKind)>;

pub struct DocContext<'tcx> {
    pub tcx: TyCtxt<'tcx>,
    pub resolver: Rc<RefCell<interface::BoxedResolver>>,
    /// Later on moved into `CACHE_KEY`
    pub renderinfo: RefCell<RenderInfo>,
    /// Later on moved through `clean::Crate` into `CACHE_KEY`
    pub external_traits: Rc<RefCell<FxHashMap<DefId, clean::Trait>>>,
    /// Used while populating `external_traits` to ensure we don't process the same trait twice at
    /// the same time.
    pub active_extern_traits: RefCell<FxHashSet<DefId>>,
    // The current set of type and lifetime substitutions,
    // for expanding type aliases at the HIR level:
    /// Table `DefId` of type parameter -> substituted type
    pub ty_substs: RefCell<FxHashMap<DefId, clean::Type>>,
    /// Table `DefId` of lifetime parameter -> substituted lifetime
    pub lt_substs: RefCell<FxHashMap<DefId, clean::Lifetime>>,
    /// Table `DefId` of const parameter -> substituted const
    pub ct_substs: RefCell<FxHashMap<DefId, clean::Constant>>,
    /// Table synthetic type parameter for `impl Trait` in argument position -> bounds
    pub impl_trait_bounds: RefCell<FxHashMap<ImplTraitParam, Vec<clean::GenericBound>>>,
    pub fake_def_ids: RefCell<FxHashMap<CrateNum, DefId>>,
    pub all_fake_def_ids: RefCell<FxHashSet<DefId>>,
    /// Auto-trait or blanket impls processed so far, as `(self_ty, trait_def_id)`.
    // FIXME(eddyb) make this a `ty::TraitRef<'tcx>` set.
    pub generated_synthetics: RefCell<FxHashSet<(Ty<'tcx>, DefId)>>,
    pub auto_traits: Vec<DefId>,
    /// The options given to rustdoc that could be relevant to a pass.
    pub render_options: RenderOptions,
    /// The traits in scope for a given module.
    ///
    /// See `collect_intra_doc_links::traits_implemented_by` for more details.
    /// `map<module, set<trait>>`
    pub module_trait_cache: RefCell<FxHashMap<DefId, FxHashSet<DefId>>>,
}

impl<'tcx> DocContext<'tcx> {
    pub fn sess(&self) -> &Session {
        &self.tcx.sess
    }

    pub fn enter_resolver<F, R>(&self, f: F) -> R
    where
        F: FnOnce(&mut resolve::Resolver<'_>) -> R,
    {
        self.resolver.borrow_mut().access(f)
    }

    /// Call the closure with the given parameters set as
    /// the substitutions for a type alias' RHS.
    pub fn enter_alias<F, R>(
        &self,
        ty_substs: FxHashMap<DefId, clean::Type>,
        lt_substs: FxHashMap<DefId, clean::Lifetime>,
        ct_substs: FxHashMap<DefId, clean::Constant>,
        f: F,
    ) -> R
    where
        F: FnOnce() -> R,
    {
        let (old_tys, old_lts, old_cts) = (
            mem::replace(&mut *self.ty_substs.borrow_mut(), ty_substs),
            mem::replace(&mut *self.lt_substs.borrow_mut(), lt_substs),
            mem::replace(&mut *self.ct_substs.borrow_mut(), ct_substs),
        );
        let r = f();
        *self.ty_substs.borrow_mut() = old_tys;
        *self.lt_substs.borrow_mut() = old_lts;
        *self.ct_substs.borrow_mut() = old_cts;
        r
    }

    // This is an ugly hack, but it's the simplest way to handle synthetic impls without greatly
    // refactoring either librustdoc or librustc_middle. In particular, allowing new DefIds to be
    // registered after the AST is constructed would require storing the defid mapping in a
    // RefCell, decreasing the performance for normal compilation for very little gain.
    //
    // Instead, we construct 'fake' def ids, which start immediately after the last DefId.
    // In the Debug impl for clean::Item, we explicitly check for fake
    // def ids, as we'll end up with a panic if we use the DefId Debug impl for fake DefIds
    pub fn next_def_id(&self, crate_num: CrateNum) -> DefId {
        let start_def_id = {
            let num_def_ids = if crate_num == LOCAL_CRATE {
                self.tcx.hir().definitions().def_path_table().num_def_ids()
            } else {
                self.enter_resolver(|r| r.cstore().num_def_ids(crate_num))
            };

            DefId { krate: crate_num, index: DefIndex::from_usize(num_def_ids) }
        };

        let mut fake_ids = self.fake_def_ids.borrow_mut();

        let def_id = *fake_ids.entry(crate_num).or_insert(start_def_id);
        fake_ids.insert(
            crate_num,
            DefId { krate: crate_num, index: DefIndex::from(def_id.index.index() + 1) },
        );

        MAX_DEF_ID.with(|m| {
            m.borrow_mut().entry(def_id.krate).or_insert(start_def_id);
        });

        self.all_fake_def_ids.borrow_mut().insert(def_id);

        def_id
    }

    /// Like `hir().local_def_id_to_hir_id()`, but skips calling it on fake DefIds.
    /// (This avoids a slice-index-out-of-bounds panic.)
    pub fn as_local_hir_id(&self, def_id: DefId) -> Option<HirId> {
        if self.all_fake_def_ids.borrow().contains(&def_id) {
            None
        } else {
            def_id.as_local().map(|def_id| self.tcx.hir().local_def_id_to_hir_id(def_id))
        }
    }

    pub fn stability(&self, id: HirId) -> Option<attr::Stability> {
        self.tcx
            .hir()
            .opt_local_def_id(id)
            .and_then(|def_id| self.tcx.lookup_stability(def_id.to_def_id()))
            .cloned()
    }

    pub fn deprecation(&self, id: HirId) -> Option<attr::Deprecation> {
        self.tcx
            .hir()
            .opt_local_def_id(id)
            .and_then(|def_id| self.tcx.lookup_deprecation(def_id.to_def_id()))
    }
}

/// Creates a new diagnostic `Handler` that can be used to emit warnings and errors.
///
/// If the given `error_format` is `ErrorOutputType::Json` and no `SourceMap` is given, a new one
/// will be created for the handler.
pub fn new_handler(
    error_format: ErrorOutputType,
    source_map: Option<Lrc<source_map::SourceMap>>,
    debugging_opts: &DebuggingOptions,
) -> rustc_errors::Handler {
    let emitter: Box<dyn Emitter + sync::Send> = match error_format {
        ErrorOutputType::HumanReadable(kind) => {
            let (short, color_config) = kind.unzip();
            Box::new(
                EmitterWriter::stderr(
                    color_config,
                    source_map.map(|sm| sm as _),
                    short,
                    debugging_opts.teach,
                    debugging_opts.terminal_width,
                    false,
                )
                .ui_testing(debugging_opts.ui_testing),
            )
        }
        ErrorOutputType::Json { pretty, json_rendered } => {
            let source_map = source_map.unwrap_or_else(|| {
                Lrc::new(source_map::SourceMap::new(source_map::FilePathMapping::empty()))
            });
            Box::new(
                JsonEmitter::stderr(
                    None,
                    source_map,
                    pretty,
                    json_rendered,
                    debugging_opts.terminal_width,
                    false,
                )
                .ui_testing(debugging_opts.ui_testing),
            )
        }
    };

    rustc_errors::Handler::with_emitter_and_flags(
        emitter,
        debugging_opts.diagnostic_handler_flags(true),
    )
}

/// This function is used to setup the lint initialization. By default, in rustdoc, everything
/// is "allowed". Depending if we run in test mode or not, we want some of them to be at their
/// default level. For example, the "INVALID_CODEBLOCK_ATTRIBUTES" lint is activated in both
/// modes.
///
/// A little detail easy to forget is that there is a way to set the lint level for all lints
/// through the "WARNINGS" lint. To prevent this to happen, we set it back to its "normal" level
/// inside this function.
///
/// It returns a tuple containing:
///  * Vector of tuples of lints' name and their associated "max" level
///  * HashMap of lint id with their associated "max" level
pub(crate) fn init_lints<F>(
    mut allowed_lints: Vec<String>,
    lint_opts: Vec<(String, lint::Level)>,
    filter_call: F,
) -> (Vec<(String, lint::Level)>, FxHashMap<lint::LintId, lint::Level>)
where
    F: Fn(&lint::Lint) -> Option<(String, lint::Level)>,
{
    let warnings_lint_name = lint::builtin::WARNINGS.name;

    allowed_lints.push(warnings_lint_name.to_owned());
    allowed_lints.extend(lint_opts.iter().map(|(lint, _)| lint).cloned());

    let lints = || {
        lint::builtin::HardwiredLints::get_lints()
            .into_iter()
            .chain(rustc_lint::SoftLints::get_lints().into_iter())
    };

    let lint_opts = lints()
        .filter_map(|lint| {
            // Permit feature-gated lints to avoid feature errors when trying to
            // allow all lints.
            if lint.feature_gate.is_some() || allowed_lints.iter().any(|l| lint.name == l) {
                None
            } else {
                filter_call(lint)
            }
        })
        .chain(lint_opts.into_iter())
        .collect::<Vec<_>>();

    let lint_caps = lints()
        .filter_map(|lint| {
            // We don't want to allow *all* lints so let's ignore
            // those ones.
            if allowed_lints.iter().any(|l| lint.name == l) {
                None
            } else {
                Some((lint::LintId::of(lint), lint::Allow))
            }
        })
        .collect();
    (lint_opts, lint_caps)
}

pub fn run_core(
    options: RustdocOptions,
) -> (clean::Crate, RenderInfo, RenderOptions, Lrc<Session>) {
    // Parse, resolve, and typecheck the given crate.

    let RustdocOptions {
        input,
        crate_name,
        proc_macro_crate,
        error_format,
        libs,
        externs,
        mut cfgs,
        codegen_options,
        debugging_opts,
        target,
        edition,
        maybe_sysroot,
        lint_opts,
        describe_lints,
        lint_cap,
        default_passes,
        manual_passes,
        display_warnings,
        render_options,
        output_format,
        ..
    } = options;

    let extern_names: Vec<String> = externs
        .iter()
        .filter(|(_, entry)| entry.add_prelude)
        .map(|(name, _)| name)
        .cloned()
        .collect();

    // Add the doc cfg into the doc build.
    cfgs.push("doc".to_string());

    let cpath = Some(input.clone());
    let input = Input::File(input);

    let intra_link_resolution_failure_name = lint::builtin::BROKEN_INTRA_DOC_LINKS.name;
    let missing_docs = rustc_lint::builtin::MISSING_DOCS.name;
    let missing_doc_example = rustc_lint::builtin::MISSING_DOC_CODE_EXAMPLES.name;
    let private_doc_tests = rustc_lint::builtin::PRIVATE_DOC_TESTS.name;
    let no_crate_level_docs = rustc_lint::builtin::MISSING_CRATE_LEVEL_DOCS.name;
    let invalid_codeblock_attributes_name = rustc_lint::builtin::INVALID_CODEBLOCK_ATTRIBUTES.name;
    let invalid_html_tags = rustc_lint::builtin::INVALID_HTML_TAGS.name;
    let renamed_and_removed_lints = rustc_lint::builtin::RENAMED_AND_REMOVED_LINTS.name;
    let unknown_lints = rustc_lint::builtin::UNKNOWN_LINTS.name;

    // In addition to those specific lints, we also need to allow those given through
    // command line, otherwise they'll get ignored and we don't want that.
    let lints_to_show = vec![
        intra_link_resolution_failure_name.to_owned(),
        missing_docs.to_owned(),
        missing_doc_example.to_owned(),
        private_doc_tests.to_owned(),
        no_crate_level_docs.to_owned(),
        invalid_codeblock_attributes_name.to_owned(),
        invalid_html_tags.to_owned(),
        renamed_and_removed_lints.to_owned(),
        unknown_lints.to_owned(),
    ];

    let (lint_opts, lint_caps) = init_lints(lints_to_show, lint_opts, |lint| {
        if lint.name == intra_link_resolution_failure_name
            || lint.name == invalid_codeblock_attributes_name
        {
            None
        } else {
            Some((lint.name_lower(), lint::Allow))
        }
    });

    let crate_types =
        if proc_macro_crate { vec![CrateType::ProcMacro] } else { vec![CrateType::Rlib] };
    // plays with error output here!
    let sessopts = config::Options {
        maybe_sysroot,
        search_paths: libs,
        crate_types,
        lint_opts: if !display_warnings { lint_opts } else { vec![] },
        lint_cap,
        cg: codegen_options,
        externs,
        target_triple: target,
        unstable_features: UnstableFeatures::from_environment(),
        actually_rustdoc: true,
        debugging_opts,
        error_format,
        edition,
        describe_lints,
        ..Options::default()
    };

    let config = interface::Config {
        opts: sessopts,
        crate_cfg: interface::parse_cfgspecs(cfgs),
        input,
        input_path: cpath,
        output_file: None,
        output_dir: None,
        file_loader: None,
        diagnostic_output: DiagnosticOutput::Default,
        stderr: None,
        crate_name,
        lint_caps,
        register_lints: None,
        override_queries: Some(|_sess, providers, _external_providers| {
            // Most lints will require typechecking, so just don't run them.
            providers.lint_mod = |_, _| {};
            // Prevent `rustc_typeck::check_crate` from calling `typeck` on all bodies.
            providers.typeck_item_bodies = |_, _| {};
            // hack so that `used_trait_imports` won't try to call typeck
            providers.used_trait_imports = |_, _| {
                lazy_static! {
                    static ref EMPTY_SET: FxHashSet<LocalDefId> = FxHashSet::default();
                }
                &EMPTY_SET
            };
            // In case typeck does end up being called, don't ICE in case there were name resolution errors
            providers.typeck = move |tcx, def_id| {
                // Closures' tables come from their outermost function,
                // as they are part of the same "inference environment".
                // This avoids emitting errors for the parent twice (see similar code in `typeck_with_fallback`)
                let outer_def_id = tcx.closure_base_def_id(def_id.to_def_id()).expect_local();
                if outer_def_id != def_id {
                    return tcx.typeck(outer_def_id);
                }

                let hir = tcx.hir();
                let body = hir.body(hir.body_owned_by(hir.local_def_id_to_hir_id(def_id)));
                debug!("visiting body for {:?}", def_id);
                tcx.sess.time("emit_ignored_resolution_errors", || {
                    EmitIgnoredResolutionErrors::new(tcx).visit_body(body);
                });
                (rustc_interface::DEFAULT_QUERY_PROVIDERS.typeck)(tcx, def_id)
            };
        }),
        make_codegen_backend: None,
        registry: rustc_driver::diagnostics_registry(),
    };

    interface::create_compiler_and_run(config, |compiler| {
        compiler.enter(|queries| {
            let sess = compiler.session();

            // We need to hold on to the complete resolver, so we cause everything to be
            // cloned for the analysis passes to use. Suboptimal, but necessary in the
            // current architecture.
            let resolver = {
                let parts = abort_on_err(queries.expansion(), sess).peek();
                let resolver = parts.1.borrow();

                // Before we actually clone it, let's force all the extern'd crates to
                // actually be loaded, just in case they're only referred to inside
                // intra-doc-links
                resolver.borrow_mut().access(|resolver| {
                    sess.time("load_extern_crates", || {
                        for extern_name in &extern_names {
                            debug!("loading extern crate {}", extern_name);
                            resolver
                                .resolve_str_path_error(
                                    DUMMY_SP,
                                    extern_name,
                                    TypeNS,
                                    LocalDefId { local_def_index: CRATE_DEF_INDEX }.to_def_id(),
                                )
                                .unwrap_or_else(|()| {
                                    panic!("Unable to resolve external crate {}", extern_name)
                                });
                        }
                    });
                });

                // Now we're good to clone the resolver because everything should be loaded
                resolver.clone()
            };

            if sess.has_errors() {
                sess.fatal("Compilation failed, aborting rustdoc");
            }

            let mut global_ctxt = abort_on_err(queries.global_ctxt(), sess).take();

            let (krate, render_info, opts) = sess.time("run_global_ctxt", || {
                global_ctxt.enter(|tcx| {
                    run_global_ctxt(
                        tcx,
                        resolver,
                        default_passes,
                        manual_passes,
                        render_options,
                        output_format,
                    )
                })
            });
            (krate, render_info, opts, Lrc::clone(sess))
        })
    })
}

fn run_global_ctxt(
    tcx: TyCtxt<'_>,
    resolver: Rc<RefCell<interface::BoxedResolver>>,
    mut default_passes: passes::DefaultPassOption,
    mut manual_passes: Vec<String>,
    render_options: RenderOptions,
    output_format: Option<OutputFormat>,
) -> (clean::Crate, RenderInfo, RenderOptions) {
    // Certain queries assume that some checks were run elsewhere
    // (see https://github.com/rust-lang/rust/pull/73566#issuecomment-656954425),
    // so type-check everything other than function bodies in this crate before running lints.

    // NOTE: this does not call `tcx.analysis()` so that we won't
    // typeck function bodies or run the default rustc lints.
    // (see `override_queries` in the `config`)

    // HACK(jynelson) this calls an _extremely_ limited subset of `typeck`
    // and might break if queries change their assumptions in the future.

    // NOTE: This is copy/pasted from typeck/lib.rs and should be kept in sync with those changes.
    tcx.sess.time("item_types_checking", || {
        for &module in tcx.hir().krate().modules.keys() {
            tcx.ensure().check_mod_item_types(tcx.hir().local_def_id(module));
        }
    });
    tcx.sess.abort_if_errors();
    tcx.sess.time("missing_docs", || {
        rustc_lint::check_crate(tcx, rustc_lint::builtin::MissingDoc::new);
    });
    tcx.sess.time("check_mod_attrs", || {
        for &module in tcx.hir().krate().modules.keys() {
            let local_def_id = tcx.hir().local_def_id(module);
            tcx.ensure().check_mod_attrs(local_def_id);
        }
    });

    let access_levels = tcx.privacy_access_levels(LOCAL_CRATE);
    // Convert from a HirId set to a DefId set since we don't always have easy access
    // to the map from defid -> hirid
    let access_levels = AccessLevels {
        map: access_levels
            .map
            .iter()
            .map(|(&k, &v)| (tcx.hir().local_def_id(k).to_def_id(), v))
            .collect(),
    };

    let mut renderinfo = RenderInfo::default();
    renderinfo.access_levels = access_levels;
    renderinfo.output_format = output_format;

    let mut ctxt = DocContext {
        tcx,
        resolver,
        external_traits: Default::default(),
        active_extern_traits: Default::default(),
        renderinfo: RefCell::new(renderinfo),
        ty_substs: Default::default(),
        lt_substs: Default::default(),
        ct_substs: Default::default(),
        impl_trait_bounds: Default::default(),
        fake_def_ids: Default::default(),
        all_fake_def_ids: Default::default(),
        generated_synthetics: Default::default(),
        auto_traits: tcx
            .all_traits(LOCAL_CRATE)
            .iter()
            .cloned()
            .filter(|trait_def_id| tcx.trait_is_auto(*trait_def_id))
            .collect(),
        render_options,
        module_trait_cache: RefCell::new(FxHashMap::default()),
    };
    debug!("crate: {:?}", tcx.hir().krate());

    let mut krate = tcx.sess.time("clean_crate", || clean::krate(&mut ctxt));

    if let Some(ref m) = krate.module {
        if let None | Some("") = m.doc_value() {
            let help = "The following guide may be of use:\n\
                https://doc.rust-lang.org/nightly/rustdoc/how-to-write-documentation.html";
            tcx.struct_lint_node(
                rustc_lint::builtin::MISSING_CRATE_LEVEL_DOCS,
                ctxt.as_local_hir_id(m.def_id).unwrap(),
                |lint| {
                    let mut diag =
                        lint.build("no documentation found for this crate's top-level module");
                    diag.help(help);
                    diag.emit();
                },
            );
        }
    }

    fn report_deprecated_attr(name: &str, diag: &rustc_errors::Handler) {
        let mut msg = diag
            .struct_warn(&format!("the `#![doc({})]` attribute is considered deprecated", name));
        msg.warn(
            "see issue #44136 <https://github.com/rust-lang/rust/issues/44136> \
             for more information",
        );

        if name == "no_default_passes" {
            msg.help("you may want to use `#![doc(document_private_items)]`");
        }

        msg.emit();
    }

    // Process all of the crate attributes, extracting plugin metadata along
    // with the passes which we are supposed to run.
    for attr in krate.module.as_ref().unwrap().attrs.lists(sym::doc) {
        let diag = ctxt.sess().diagnostic();

        let name = attr.name_or_empty();
        if attr.is_word() {
            if name == sym::no_default_passes {
                report_deprecated_attr("no_default_passes", diag);
                if default_passes == passes::DefaultPassOption::Default {
                    default_passes = passes::DefaultPassOption::None;
                }
            }
        } else if let Some(value) = attr.value_str() {
            let sink = match name {
                sym::passes => {
                    report_deprecated_attr("passes = \"...\"", diag);
                    &mut manual_passes
                }
                sym::plugins => {
                    report_deprecated_attr("plugins = \"...\"", diag);
                    eprintln!(
                        "WARNING: `#![doc(plugins = \"...\")]` \
                         no longer functions; see CVE-2018-1000622"
                    );
                    continue;
                }
                _ => continue,
            };
            for name in value.as_str().split_whitespace() {
                sink.push(name.to_string());
            }
        }

        if attr.is_word() && name == sym::document_private_items {
            ctxt.render_options.document_private = true;
        }
    }

    let passes = passes::defaults(default_passes).iter().copied().chain(
        manual_passes.into_iter().flat_map(|name| {
            if let Some(pass) = passes::find_pass(&name) {
                Some(ConditionalPass::always(pass))
            } else {
                error!("unknown pass {}, skipping", name);
                None
            }
        }),
    );

    info!("Executing passes");

    for p in passes {
        let run = match p.condition {
            Always => true,
            WhenDocumentPrivate => ctxt.render_options.document_private,
            WhenNotDocumentPrivate => !ctxt.render_options.document_private,
            WhenNotDocumentHidden => !ctxt.render_options.document_hidden,
        };
        if run {
            debug!("running pass {}", p.pass.name);
            krate = ctxt.tcx.sess.time(p.pass.name, || (p.pass.run)(krate, &ctxt));
        }
    }

    ctxt.sess().abort_if_errors();

    (krate, ctxt.renderinfo.into_inner(), ctxt.render_options)
}

/// Due to https://github.com/rust-lang/rust/pull/73566,
/// the name resolution pass may find errors that are never emitted.
/// If typeck is called after this happens, then we'll get an ICE:
/// 'Res::Error found but not reported'. To avoid this, emit the errors now.
struct EmitIgnoredResolutionErrors<'tcx> {
    tcx: TyCtxt<'tcx>,
}

impl<'tcx> EmitIgnoredResolutionErrors<'tcx> {
    fn new(tcx: TyCtxt<'tcx>) -> Self {
        Self { tcx }
    }
}

impl<'tcx> Visitor<'tcx> for EmitIgnoredResolutionErrors<'tcx> {
    type Map = Map<'tcx>;

    fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
        // We need to recurse into nested closures,
        // since those will fallback to the parent for type checking.
        NestedVisitorMap::OnlyBodies(self.tcx.hir())
    }

    fn visit_path(&mut self, path: &'tcx Path<'_>, _id: HirId) {
        debug!("visiting path {:?}", path);
        if path.res == Res::Err {
            // We have less context here than in rustc_resolve,
            // so we can only emit the name and span.
            // However we can give a hint that rustc_resolve will have more info.
            let label = format!(
                "could not resolve path `{}`",
                path.segments
                    .iter()
                    .map(|segment| segment.ident.as_str().to_string())
                    .collect::<Vec<_>>()
                    .join("::")
            );
            let mut err = rustc_errors::struct_span_err!(
                self.tcx.sess,
                path.span,
                E0433,
                "failed to resolve: {}",
                label
            );
            err.span_label(path.span, label);
            err.note("this error was originally ignored because you are running `rustdoc`");
            err.note("try running again with `rustc` or `cargo check` and you may get a more detailed error");
            err.emit();
        }
        // We could have an outer resolution that succeeded,
        // but with generic parameters that failed.
        // Recurse into the segments so we catch those too.
        intravisit::walk_path(self, path);
    }
}

/// `DefId` or parameter index (`ty::ParamTy.index`) of a synthetic type parameter
/// for `impl Trait` in argument position.
#[derive(Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
pub enum ImplTraitParam {
    DefId(DefId),
    ParamIndex(u32),
}

impl From<DefId> for ImplTraitParam {
    fn from(did: DefId) -> Self {
        ImplTraitParam::DefId(did)
    }
}

impl From<u32> for ImplTraitParam {
    fn from(idx: u32) -> Self {
        ImplTraitParam::ParamIndex(idx)
    }
}