context.rs

//! Implementation of lint checking.
//!
//! The lint checking is mostly consolidated into one pass which runs
//! after all other analyses. Throughout compilation, lint warnings
//! can be added via the `add_lint` method on the Session structure. This
//! requires a span and an ID of the node that the lint is being added to. The
//! lint isn't actually emitted at that time because it is unknown what the
//! actual lint level at that location is.
//!
//! To actually emit lint warnings/errors, a separate pass is used.
//! A context keeps track of the current state of all lint levels.
//! Upon entering a node of the ast which can modify the lint settings, the
//! previous lint state is pushed onto a stack and the ast is then recursed
//! upon. As the ast is traversed, this keeps track of the current lint level
//! for all lint attributes.

use self::TargetLint::*;

use crate::hir::map::{definitions::DisambiguatedDefPathData, DefPathData};
use crate::lint::levels::{LintLevelSets, LintLevelsBuilder};
use crate::lint::{EarlyLintPassObject, LateLintPassObject};
use crate::middle::privacy::AccessLevels;
use crate::middle::stability;
use crate::session::Session;
use crate::ty::layout::{LayoutError, LayoutOf, TyLayout};
use crate::ty::{self, print::Printer, subst::GenericArg, Ty, TyCtxt};
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::sync;
use rustc_error_codes::*;
use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder};
use rustc_hir as hir;
use rustc_hir::def_id::{CrateNum, DefId};
use rustc_session::lint::BuiltinLintDiagnostics;
use rustc_session::lint::{FutureIncompatibleInfo, Level, Lint, LintBuffer, LintId};
use rustc_span::{symbol::Symbol, MultiSpan, Span, DUMMY_SP};
use syntax::ast;
use syntax::util::lev_distance::find_best_match_for_name;

use std::slice;

/// Information about the registered lints.
///
/// This is basically the subset of `Context` that we can
/// build early in the compile pipeline.
pub struct LintStore {
    /// Registered lints.
    lints: Vec<&'static Lint>,

    /// Constructor functions for each variety of lint pass.
    ///
    /// These should only be called once, but since we want to avoid locks or
    /// interior mutability, we don't enforce this (and lints should, in theory,
    /// be compatible with being constructed more than once, though not
    /// necessarily in a sane manner. This is safe though.)
    pub pre_expansion_passes: Vec<Box<dyn Fn() -> EarlyLintPassObject + sync::Send + sync::Sync>>,
    pub early_passes: Vec<Box<dyn Fn() -> EarlyLintPassObject + sync::Send + sync::Sync>>,
    pub late_passes: Vec<Box<dyn Fn() -> LateLintPassObject + sync::Send + sync::Sync>>,
    /// This is unique in that we construct them per-module, so not once.
    pub late_module_passes: Vec<Box<dyn Fn() -> LateLintPassObject + sync::Send + sync::Sync>>,

    /// Lints indexed by name.
    by_name: FxHashMap<String, TargetLint>,

    /// Map of registered lint groups to what lints they expand to.
    lint_groups: FxHashMap<&'static str, LintGroup>,
}

/// The target of the `by_name` map, which accounts for renaming/deprecation.
enum TargetLint {
    /// A direct lint target
    Id(LintId),

    /// Temporary renaming, used for easing migration pain; see #16545
    Renamed(String, LintId),

    /// Lint with this name existed previously, but has been removed/deprecated.
    /// The string argument is the reason for removal.
    Removed(String),
}

pub enum FindLintError {
    NotFound,
    Removed,
}

struct LintAlias {
    name: &'static str,
    /// Whether deprecation warnings should be suppressed for this alias.
    silent: bool,
}

struct LintGroup {
    lint_ids: Vec<LintId>,
    from_plugin: bool,
    depr: Option<LintAlias>,
}

pub enum CheckLintNameResult<'a> {
    Ok(&'a [LintId]),
    /// Lint doesn't exist. Potentially contains a suggestion for a correct lint name.
    NoLint(Option<Symbol>),
    /// The lint is either renamed or removed. This is the warning
    /// message, and an optional new name (`None` if removed).
    Warning(String, Option<String>),
    /// The lint is from a tool. If the Option is None, then either
    /// the lint does not exist in the tool or the code was not
    /// compiled with the tool and therefore the lint was never
    /// added to the `LintStore`. Otherwise the `LintId` will be
    /// returned as if it where a rustc lint.
    Tool(Result<&'a [LintId], (Option<&'a [LintId]>, String)>),
}

impl LintStore {
    pub fn new() -> LintStore {
        LintStore {
            lints: vec![],
            pre_expansion_passes: vec![],
            early_passes: vec![],
            late_passes: vec![],
            late_module_passes: vec![],
            by_name: Default::default(),
            lint_groups: Default::default(),
        }
    }

    pub fn get_lints<'t>(&'t self) -> &'t [&'static Lint] {
        &self.lints
    }

    pub fn get_lint_groups<'t>(&'t self) -> Vec<(&'static str, Vec<LintId>, bool)> {
        self.lint_groups
            .iter()
            .filter(|(_, LintGroup { depr, .. })| {
                // Don't display deprecated lint groups.
                depr.is_none()
            })
            .map(|(k, LintGroup { lint_ids, from_plugin, .. })| {
                (*k, lint_ids.clone(), *from_plugin)
            })
            .collect()
    }

    pub fn register_early_pass(
        &mut self,
        pass: impl Fn() -> EarlyLintPassObject + 'static + sync::Send + sync::Sync,
    ) {
        self.early_passes.push(Box::new(pass));
    }

    pub fn register_pre_expansion_pass(
        &mut self,
        pass: impl Fn() -> EarlyLintPassObject + 'static + sync::Send + sync::Sync,
    ) {
        self.pre_expansion_passes.push(Box::new(pass));
    }

    pub fn register_late_pass(
        &mut self,
        pass: impl Fn() -> LateLintPassObject + 'static + sync::Send + sync::Sync,
    ) {
        self.late_passes.push(Box::new(pass));
    }

    pub fn register_late_mod_pass(
        &mut self,
        pass: impl Fn() -> LateLintPassObject + 'static + sync::Send + sync::Sync,
    ) {
        self.late_module_passes.push(Box::new(pass));
    }

    // Helper method for register_early/late_pass
    pub fn register_lints(&mut self, lints: &[&'static Lint]) {
        for lint in lints {
            self.lints.push(lint);

            let id = LintId::of(lint);
            if self.by_name.insert(lint.name_lower(), Id(id)).is_some() {
                bug!("duplicate specification of lint {}", lint.name_lower())
            }

            if let Some(FutureIncompatibleInfo { edition, .. }) = lint.future_incompatible {
                if let Some(edition) = edition {
                    self.lint_groups
                        .entry(edition.lint_name())
                        .or_insert(LintGroup {
                            lint_ids: vec![],
                            from_plugin: lint.is_plugin,
                            depr: None,
                        })
                        .lint_ids
                        .push(id);
                }

                self.lint_groups
                    .entry("future_incompatible")
                    .or_insert(LintGroup {
                        lint_ids: vec![],
                        from_plugin: lint.is_plugin,
                        depr: None,
                    })
                    .lint_ids
                    .push(id);
            }
        }
    }

    pub fn register_group_alias(&mut self, lint_name: &'static str, alias: &'static str) {
        self.lint_groups.insert(
            alias,
            LintGroup {
                lint_ids: vec![],
                from_plugin: false,
                depr: Some(LintAlias { name: lint_name, silent: true }),
            },
        );
    }

    pub fn register_group(
        &mut self,
        from_plugin: bool,
        name: &'static str,
        deprecated_name: Option<&'static str>,
        to: Vec<LintId>,
    ) {
        let new = self
            .lint_groups
            .insert(name, LintGroup { lint_ids: to, from_plugin, depr: None })
            .is_none();
        if let Some(deprecated) = deprecated_name {
            self.lint_groups.insert(
                deprecated,
                LintGroup {
                    lint_ids: vec![],
                    from_plugin,
                    depr: Some(LintAlias { name, silent: false }),
                },
            );
        }

        if !new {
            bug!("duplicate specification of lint group {}", name);
        }
    }

    pub fn register_renamed(&mut self, old_name: &str, new_name: &str) {
        let target = match self.by_name.get(new_name) {
            Some(&Id(lint_id)) => lint_id.clone(),
            _ => bug!("invalid lint renaming of {} to {}", old_name, new_name),
        };
        self.by_name.insert(old_name.to_string(), Renamed(new_name.to_string(), target));
    }

    pub fn register_removed(&mut self, name: &str, reason: &str) {
        self.by_name.insert(name.into(), Removed(reason.into()));
    }

    pub fn find_lints(&self, mut lint_name: &str) -> Result<Vec<LintId>, FindLintError> {
        match self.by_name.get(lint_name) {
            Some(&Id(lint_id)) => Ok(vec![lint_id]),
            Some(&Renamed(_, lint_id)) => Ok(vec![lint_id]),
            Some(&Removed(_)) => Err(FindLintError::Removed),
            None => loop {
                return match self.lint_groups.get(lint_name) {
                    Some(LintGroup { lint_ids, depr, .. }) => {
                        if let Some(LintAlias { name, .. }) = depr {
                            lint_name = name;
                            continue;
                        }
                        Ok(lint_ids.clone())
                    }
                    None => Err(FindLintError::Removed),
                };
            },
        }
    }

    /// Checks the validity of lint names derived from the command line
    pub fn check_lint_name_cmdline(&self, sess: &Session, lint_name: &str, level: Level) {
        let db = match self.check_lint_name(lint_name, None) {
            CheckLintNameResult::Ok(_) => None,
            CheckLintNameResult::Warning(ref msg, _) => Some(sess.struct_warn(msg)),
            CheckLintNameResult::NoLint(suggestion) => {
                let mut err =
                    struct_span_err!(sess, DUMMY_SP, E0602, "unknown lint: `{}`", lint_name);

                if let Some(suggestion) = suggestion {
                    err.help(&format!("did you mean: `{}`", suggestion));
                }

                Some(err)
            }
            CheckLintNameResult::Tool(result) => match result {
                Err((Some(_), new_name)) => Some(sess.struct_warn(&format!(
                    "lint name `{}` is deprecated \
                     and does not have an effect anymore. \
                     Use: {}",
                    lint_name, new_name
                ))),
                _ => None,
            },
        };

        if let Some(mut db) = db {
            let msg = format!(
                "requested on the command line with `{} {}`",
                match level {
                    Level::Allow => "-A",
                    Level::Warn => "-W",
                    Level::Deny => "-D",
                    Level::Forbid => "-F",
                },
                lint_name
            );
            db.note(&msg);
            db.emit();
        }
    }

    /// Checks the name of a lint for its existence, and whether it was
    /// renamed or removed. Generates a DiagnosticBuilder containing a
    /// warning for renamed and removed lints. This is over both lint
    /// names from attributes and those passed on the command line. Since
    /// it emits non-fatal warnings and there are *two* lint passes that
    /// inspect attributes, this is only run from the late pass to avoid
    /// printing duplicate warnings.
    pub fn check_lint_name(
        &self,
        lint_name: &str,
        tool_name: Option<Symbol>,
    ) -> CheckLintNameResult<'_> {
        let complete_name = if let Some(tool_name) = tool_name {
            format!("{}::{}", tool_name, lint_name)
        } else {
            lint_name.to_string()
        };
        // If the lint was scoped with `tool::` check if the tool lint exists
        if let Some(_) = tool_name {
            match self.by_name.get(&complete_name) {
                None => match self.lint_groups.get(&*complete_name) {
                    None => return CheckLintNameResult::Tool(Err((None, String::new()))),
                    Some(LintGroup { lint_ids, .. }) => {
                        return CheckLintNameResult::Tool(Ok(&lint_ids));
                    }
                },
                Some(&Id(ref id)) => return CheckLintNameResult::Tool(Ok(slice::from_ref(id))),
                // If the lint was registered as removed or renamed by the lint tool, we don't need
                // to treat tool_lints and rustc lints different and can use the code below.
                _ => {}
            }
        }
        match self.by_name.get(&complete_name) {
            Some(&Renamed(ref new_name, _)) => CheckLintNameResult::Warning(
                format!("lint `{}` has been renamed to `{}`", complete_name, new_name),
                Some(new_name.to_owned()),
            ),
            Some(&Removed(ref reason)) => CheckLintNameResult::Warning(
                format!("lint `{}` has been removed: `{}`", complete_name, reason),
                None,
            ),
            None => match self.lint_groups.get(&*complete_name) {
                // If neither the lint, nor the lint group exists check if there is a `clippy::`
                // variant of this lint
                None => self.check_tool_name_for_backwards_compat(&complete_name, "clippy"),
                Some(LintGroup { lint_ids, depr, .. }) => {
                    // Check if the lint group name is deprecated
                    if let Some(LintAlias { name, silent }) = depr {
                        let LintGroup { lint_ids, .. } = self.lint_groups.get(name).unwrap();
                        return if *silent {
                            CheckLintNameResult::Ok(&lint_ids)
                        } else {
                            CheckLintNameResult::Tool(Err((Some(&lint_ids), name.to_string())))
                        };
                    }
                    CheckLintNameResult::Ok(&lint_ids)
                }
            },
            Some(&Id(ref id)) => CheckLintNameResult::Ok(slice::from_ref(id)),
        }
    }

    fn check_tool_name_for_backwards_compat(
        &self,
        lint_name: &str,
        tool_name: &str,
    ) -> CheckLintNameResult<'_> {
        let complete_name = format!("{}::{}", tool_name, lint_name);
        match self.by_name.get(&complete_name) {
            None => match self.lint_groups.get(&*complete_name) {
                // Now we are sure, that this lint exists nowhere
                None => {
                    let symbols =
                        self.by_name.keys().map(|name| Symbol::intern(&name)).collect::<Vec<_>>();

                    let suggestion =
                        find_best_match_for_name(symbols.iter(), &lint_name.to_lowercase(), None);

                    CheckLintNameResult::NoLint(suggestion)
                }
                Some(LintGroup { lint_ids, depr, .. }) => {
                    // Reaching this would be weird, but let's cover this case anyway
                    if let Some(LintAlias { name, silent }) = depr {
                        let LintGroup { lint_ids, .. } = self.lint_groups.get(name).unwrap();
                        return if *silent {
                            CheckLintNameResult::Tool(Err((Some(&lint_ids), complete_name)))
                        } else {
                            CheckLintNameResult::Tool(Err((Some(&lint_ids), name.to_string())))
                        };
                    }
                    CheckLintNameResult::Tool(Err((Some(&lint_ids), complete_name)))
                }
            },
            Some(&Id(ref id)) => {
                CheckLintNameResult::Tool(Err((Some(slice::from_ref(id)), complete_name)))
            }
            _ => CheckLintNameResult::NoLint(None),
        }
    }
}

/// Context for lint checking after type checking.
pub struct LateContext<'a, 'tcx> {
    /// Type context we're checking in.
    pub tcx: TyCtxt<'tcx>,

    /// Side-tables for the body we are in.
    // FIXME: Make this lazy to avoid running the TypeckTables query?
    pub tables: &'a ty::TypeckTables<'tcx>,

    /// Parameter environment for the item we are in.
    pub param_env: ty::ParamEnv<'tcx>,

    /// Items accessible from the crate being checked.
    pub access_levels: &'a AccessLevels,

    /// The store of registered lints and the lint levels.
    pub lint_store: &'tcx LintStore,

    pub last_node_with_lint_attrs: hir::HirId,

    /// Generic type parameters in scope for the item we are in.
    pub generics: Option<&'tcx hir::Generics<'tcx>>,

    /// We are only looking at one module
    pub only_module: bool,
}

/// Context for lint checking of the AST, after expansion, before lowering to
/// HIR.
pub struct EarlyContext<'a> {
    /// Type context we're checking in.
    pub sess: &'a Session,

    /// The crate being checked.
    pub krate: &'a ast::Crate,

    pub builder: LintLevelsBuilder<'a>,

    /// The store of registered lints and the lint levels.
    pub lint_store: &'a LintStore,

    pub buffered: LintBuffer,
}

pub trait LintPassObject: Sized {}

impl LintPassObject for EarlyLintPassObject {}

impl LintPassObject for LateLintPassObject {}

pub fn add_elided_lifetime_in_path_suggestion(
    sess: &Session,
    db: &mut DiagnosticBuilder<'_>,
    n: usize,
    path_span: Span,
    incl_angl_brckt: bool,
    insertion_span: Span,
    anon_lts: String,
) {
    let (replace_span, suggestion) = if incl_angl_brckt {
        (insertion_span, anon_lts)
    } else {
        // When possible, prefer a suggestion that replaces the whole
        // `Path<T>` expression with `Path<'_, T>`, rather than inserting `'_, `
        // at a point (which makes for an ugly/confusing label)
        if let Ok(snippet) = sess.source_map().span_to_snippet(path_span) {
            // But our spans can get out of whack due to macros; if the place we think
            // we want to insert `'_` isn't even within the path expression's span, we
            // should bail out of making any suggestion rather than panicking on a
            // subtract-with-overflow or string-slice-out-out-bounds (!)
            // FIXME: can we do better?
            if insertion_span.lo().0 < path_span.lo().0 {
                return;
            }
            let insertion_index = (insertion_span.lo().0 - path_span.lo().0) as usize;
            if insertion_index > snippet.len() {
                return;
            }
            let (before, after) = snippet.split_at(insertion_index);
            (path_span, format!("{}{}{}", before, anon_lts, after))
        } else {
            (insertion_span, anon_lts)
        }
    };
    db.span_suggestion(
        replace_span,
        &format!("indicate the anonymous lifetime{}", pluralize!(n)),
        suggestion,
        Applicability::MachineApplicable,
    );
}

pub trait LintContext: Sized {
    type PassObject: LintPassObject;

    fn sess(&self) -> &Session;
    fn lints(&self) -> &LintStore;

    fn lookup_and_emit<S: Into<MultiSpan>>(&self, lint: &'static Lint, span: Option<S>, msg: &str) {
        self.lookup(lint, span, msg).emit();
    }

    fn lookup_and_emit_with_diagnostics<S: Into<MultiSpan>>(
        &self,
        lint: &'static Lint,
        span: Option<S>,
        msg: &str,
        diagnostic: BuiltinLintDiagnostics,
    ) {
        let mut db = self.lookup(lint, span, msg);

        let sess = self.sess();
        match diagnostic {
            BuiltinLintDiagnostics::Normal => (),
            BuiltinLintDiagnostics::BareTraitObject(span, is_global) => {
                let (sugg, app) = match sess.source_map().span_to_snippet(span) {
                    Ok(s) if is_global => {
                        (format!("dyn ({})", s), Applicability::MachineApplicable)
                    }
                    Ok(s) => (format!("dyn {}", s), Applicability::MachineApplicable),
                    Err(_) => ("dyn <type>".to_string(), Applicability::HasPlaceholders),
                };
                db.span_suggestion(span, "use `dyn`", sugg, app);
            }
            BuiltinLintDiagnostics::AbsPathWithModule(span) => {
                let (sugg, app) = match sess.source_map().span_to_snippet(span) {
                    Ok(ref s) => {
                        // FIXME(Manishearth) ideally the emitting code
                        // can tell us whether or not this is global
                        let opt_colon = if s.trim_start().starts_with("::") { "" } else { "::" };

                        (format!("crate{}{}", opt_colon, s), Applicability::MachineApplicable)
                    }
                    Err(_) => ("crate::<path>".to_string(), Applicability::HasPlaceholders),
                };
                db.span_suggestion(span, "use `crate`", sugg, app);
            }
            BuiltinLintDiagnostics::ProcMacroDeriveResolutionFallback(span) => {
                db.span_label(
                    span,
                    "names from parent modules are not accessible without an explicit import",
                );
            }
            BuiltinLintDiagnostics::MacroExpandedMacroExportsAccessedByAbsolutePaths(span_def) => {
                db.span_note(span_def, "the macro is defined here");
            }
            BuiltinLintDiagnostics::ElidedLifetimesInPaths(
                n,
                path_span,
                incl_angl_brckt,
                insertion_span,
                anon_lts,
            ) => {
                add_elided_lifetime_in_path_suggestion(
                    sess,
                    &mut db,
                    n,
                    path_span,
                    incl_angl_brckt,
                    insertion_span,
                    anon_lts,
                );
            }
            BuiltinLintDiagnostics::UnknownCrateTypes(span, note, sugg) => {
                db.span_suggestion(span, &note, sugg, Applicability::MaybeIncorrect);
            }
            BuiltinLintDiagnostics::UnusedImports(message, replaces) => {
                if !replaces.is_empty() {
                    db.tool_only_multipart_suggestion(
                        &message,
                        replaces,
                        Applicability::MachineApplicable,
                    );
                }
            }
            BuiltinLintDiagnostics::RedundantImport(spans, ident) => {
                for (span, is_imported) in spans {
                    let introduced = if is_imported { "imported" } else { "defined" };
                    db.span_label(
                        span,
                        format!("the item `{}` is already {} here", ident, introduced),
                    );
                }
            }
            BuiltinLintDiagnostics::DeprecatedMacro(suggestion, span) => {
                stability::deprecation_suggestion(&mut db, suggestion, span)
            }
        }

        db.emit();
    }

    fn lookup<S: Into<MultiSpan>>(
        &self,
        lint: &'static Lint,
        span: Option<S>,
        msg: &str,
    ) -> DiagnosticBuilder<'_>;

    /// Emit a lint at the appropriate level, for a particular span.
    fn span_lint<S: Into<MultiSpan>>(&self, lint: &'static Lint, span: S, msg: &str) {
        self.lookup_and_emit(lint, Some(span), msg);
    }

    fn struct_span_lint<S: Into<MultiSpan>>(
        &self,
        lint: &'static Lint,
        span: S,
        msg: &str,
    ) -> DiagnosticBuilder<'_> {
        self.lookup(lint, Some(span), msg)
    }

    /// Emit a lint and note at the appropriate level, for a particular span.
    fn span_lint_note(
        &self,
        lint: &'static Lint,
        span: Span,
        msg: &str,
        note_span: Span,
        note: &str,
    ) {
        let mut err = self.lookup(lint, Some(span), msg);
        if note_span == span {
            err.note(note);
        } else {
            err.span_note(note_span, note);
        }
        err.emit();
    }

    /// Emit a lint and help at the appropriate level, for a particular span.
    fn span_lint_help(&self, lint: &'static Lint, span: Span, msg: &str, help: &str) {
        let mut err = self.lookup(lint, Some(span), msg);
        self.span_lint(lint, span, msg);
        err.span_help(span, help);
        err.emit();
    }

    /// Emit a lint at the appropriate level, with no associated span.
    fn lint(&self, lint: &'static Lint, msg: &str) {
        self.lookup_and_emit(lint, None as Option<Span>, msg);
    }
}

impl<'a> EarlyContext<'a> {
    pub fn new(
        sess: &'a Session,
        lint_store: &'a LintStore,
        krate: &'a ast::Crate,
        buffered: LintBuffer,
        warn_about_weird_lints: bool,
    ) -> EarlyContext<'a> {
        EarlyContext {
            sess,
            krate,
            lint_store,
            builder: LintLevelSets::builder(sess, warn_about_weird_lints, lint_store),
            buffered,
        }
    }
}

impl LintContext for LateContext<'_, '_> {
    type PassObject = LateLintPassObject;

    /// Gets the overall compiler `Session` object.
    fn sess(&self) -> &Session {
        &self.tcx.sess
    }

    fn lints(&self) -> &LintStore {
        &*self.lint_store
    }

    fn lookup<S: Into<MultiSpan>>(
        &self,
        lint: &'static Lint,
        span: Option<S>,
        msg: &str,
    ) -> DiagnosticBuilder<'_> {
        let hir_id = self.last_node_with_lint_attrs;

        match span {
            Some(s) => self.tcx.struct_span_lint_hir(lint, hir_id, s, msg),
            None => self.tcx.struct_lint_node(lint, hir_id, msg),
        }
    }
}

impl LintContext for EarlyContext<'_> {
    type PassObject = EarlyLintPassObject;

    /// Gets the overall compiler `Session` object.
    fn sess(&self) -> &Session {
        &self.sess
    }

    fn lints(&self) -> &LintStore {
        &*self.lint_store
    }

    fn lookup<S: Into<MultiSpan>>(
        &self,
        lint: &'static Lint,
        span: Option<S>,
        msg: &str,
    ) -> DiagnosticBuilder<'_> {
        self.builder.struct_lint(lint, span.map(|s| s.into()), msg)
    }
}

impl<'a, 'tcx> LateContext<'a, 'tcx> {
    pub fn current_lint_root(&self) -> hir::HirId {
        self.last_node_with_lint_attrs
    }

    /// Check if a `DefId`'s path matches the given absolute type path usage.
    ///
    /// Anonymous scopes such as `extern` imports are matched with `kw::Invalid`;
    /// inherent `impl` blocks are matched with the name of the type.
    ///
    /// # Examples
    ///
    /// ```rust,ignore (no context or def id available)
    /// if cx.match_def_path(def_id, &[sym::core, sym::option, sym::Option]) {
    ///     // The given `def_id` is that of an `Option` type
    /// }
    /// ```
    pub fn match_def_path(&self, def_id: DefId, path: &[Symbol]) -> bool {
        let names = self.get_def_path(def_id);

        names.len() == path.len() && names.into_iter().zip(path.iter()).all(|(a, &b)| a == b)
    }

    /// Gets the absolute path of `def_id` as a vector of `Symbol`.
    ///
    /// # Examples
    ///
    /// ```rust,ignore (no context or def id available)
    /// let def_path = cx.get_def_path(def_id);
    /// if let &[sym::core, sym::option, sym::Option] = &def_path[..] {
    ///     // The given `def_id` is that of an `Option` type
    /// }
    /// ```
    pub fn get_def_path(&self, def_id: DefId) -> Vec<Symbol> {
        pub struct AbsolutePathPrinter<'tcx> {
            pub tcx: TyCtxt<'tcx>,
        }

        impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
            type Error = !;

            type Path = Vec<Symbol>;
            type Region = ();
            type Type = ();
            type DynExistential = ();
            type Const = ();

            fn tcx(&self) -> TyCtxt<'tcx> {
                self.tcx
            }

            fn print_region(self, _region: ty::Region<'_>) -> Result<Self::Region, Self::Error> {
                Ok(())
            }

            fn print_type(self, _ty: Ty<'tcx>) -> Result<Self::Type, Self::Error> {
                Ok(())
            }

            fn print_dyn_existential(
                self,
                _predicates: &'tcx ty::List<ty::ExistentialPredicate<'tcx>>,
            ) -> Result<Self::DynExistential, Self::Error> {
                Ok(())
            }

            fn print_const(self, _ct: &'tcx ty::Const<'tcx>) -> Result<Self::Const, Self::Error> {
                Ok(())
            }

            fn path_crate(self, cnum: CrateNum) -> Result<Self::Path, Self::Error> {
                Ok(vec![self.tcx.original_crate_name(cnum)])
            }

            fn path_qualified(
                self,
                self_ty: Ty<'tcx>,
                trait_ref: Option<ty::TraitRef<'tcx>>,
            ) -> Result<Self::Path, Self::Error> {
                if trait_ref.is_none() {
                    if let ty::Adt(def, substs) = self_ty.kind {
                        return self.print_def_path(def.did, substs);
                    }
                }

                // This shouldn't ever be needed, but just in case:
                Ok(vec![match trait_ref {
                    Some(trait_ref) => Symbol::intern(&format!("{:?}", trait_ref)),
                    None => Symbol::intern(&format!("<{}>", self_ty)),
                }])
            }

            fn path_append_impl(
                self,
                print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
                _disambiguated_data: &DisambiguatedDefPathData,
                self_ty: Ty<'tcx>,
                trait_ref: Option<ty::TraitRef<'tcx>>,
            ) -> Result<Self::Path, Self::Error> {
                let mut path = print_prefix(self)?;

                // This shouldn't ever be needed, but just in case:
                path.push(match trait_ref {
                    Some(trait_ref) => Symbol::intern(&format!(
                        "<impl {} for {}>",
                        trait_ref.print_only_trait_path(),
                        self_ty
                    )),
                    None => Symbol::intern(&format!("<impl {}>", self_ty)),
                });

                Ok(path)
            }

            fn path_append(
                self,
                print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
                disambiguated_data: &DisambiguatedDefPathData,
            ) -> Result<Self::Path, Self::Error> {
                let mut path = print_prefix(self)?;

                // Skip `::{{constructor}}` on tuple/unit structs.
                match disambiguated_data.data {
                    DefPathData::Ctor => return Ok(path),
                    _ => {}
                }

                path.push(disambiguated_data.data.as_symbol());
                Ok(path)
            }

            fn path_generic_args(
                self,
                print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
                _args: &[GenericArg<'tcx>],
            ) -> Result<Self::Path, Self::Error> {
                print_prefix(self)
            }
        }

        AbsolutePathPrinter { tcx: self.tcx }.print_def_path(def_id, &[]).unwrap()
    }
}

impl<'a, 'tcx> LayoutOf for LateContext<'a, 'tcx> {
    type Ty = Ty<'tcx>;
    type TyLayout = Result<TyLayout<'tcx>, LayoutError<'tcx>>;

    fn layout_of(&self, ty: Ty<'tcx>) -> Self::TyLayout {
        self.tcx.layout_of(self.param_env.and(ty))
    }
}