Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

2 files changed, 3116 insertions, 0 deletions

diff --git a/compiler/rustc_middle/src/ty/print/mod.rs b/compiler/rustc_middle/src/ty/print/mod.rs
new file mode 100644
index 000000000..d57cf8f01
--- /dev/null
+++ b/compiler/rustc_middle/src/ty/print/mod.rs
@@ -0,0 +1,327 @@
+use crate::ty::subst::{GenericArg, Subst};
+use crate::ty::{self, DefIdTree, Ty, TyCtxt};
+
+use rustc_data_structures::fx::FxHashSet;
+use rustc_data_structures::sso::SsoHashSet;
+use rustc_hir::def_id::{CrateNum, DefId};
+use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
+
+// `pretty` is a separate module only for organization.
+mod pretty;
+pub use self::pretty::*;
+
+// FIXME(eddyb) false positive, the lifetime parameters are used with `P:  Printer<...>`.
+#[allow(unused_lifetimes)]
+pub trait Print<'tcx, P> {
+    type Output;
+    type Error;
+
+    fn print(&self, cx: P) -> Result<Self::Output, Self::Error>;
+}
+
+/// Interface for outputting user-facing "type-system entities"
+/// (paths, types, lifetimes, constants, etc.) as a side-effect
+/// (e.g. formatting, like `PrettyPrinter` implementors do) or by
+/// constructing some alternative representation (e.g. an AST),
+/// which the associated types allow passing through the methods.
+///
+/// For pretty-printing/formatting in particular, see `PrettyPrinter`.
+//
+// FIXME(eddyb) find a better name; this is more general than "printing".
+pub trait Printer<'tcx>: Sized {
+    type Error;
+
+    type Path;
+    type Region;
+    type Type;
+    type DynExistential;
+    type Const;
+
+    fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
+
+    fn print_def_path(
+        self,
+        def_id: DefId,
+        substs: &'tcx [GenericArg<'tcx>],
+    ) -> Result<Self::Path, Self::Error> {
+        self.default_print_def_path(def_id, substs)
+    }
+
+    fn print_impl_path(
+        self,
+        impl_def_id: DefId,
+        substs: &'tcx [GenericArg<'tcx>],
+        self_ty: Ty<'tcx>,
+        trait_ref: Option<ty::TraitRef<'tcx>>,
+    ) -> Result<Self::Path, Self::Error> {
+        self.default_print_impl_path(impl_def_id, substs, self_ty, trait_ref)
+    }
+
+    fn print_region(self, region: ty::Region<'tcx>) -> Result<Self::Region, Self::Error>;
+
+    fn print_type(self, ty: Ty<'tcx>) -> Result<Self::Type, Self::Error>;
+
+    fn print_dyn_existential(
+        self,
+        predicates: &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>,
+    ) -> Result<Self::DynExistential, Self::Error>;
+
+    fn print_const(self, ct: ty::Const<'tcx>) -> Result<Self::Const, Self::Error>;
+
+    fn path_crate(self, cnum: CrateNum) -> Result<Self::Path, Self::Error>;
+
+    fn path_qualified(
+        self,
+        self_ty: Ty<'tcx>,
+        trait_ref: Option<ty::TraitRef<'tcx>>,
+    ) -> Result<Self::Path, Self::Error>;
+
+    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>;
+
+    fn path_append(
+        self,
+        print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
+        disambiguated_data: &DisambiguatedDefPathData,
+    ) -> Result<Self::Path, Self::Error>;
+
+    fn path_generic_args(
+        self,
+        print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
+        args: &[GenericArg<'tcx>],
+    ) -> Result<Self::Path, Self::Error>;
+
+    // Defaults (should not be overridden):
+
+    #[instrument(skip(self), level = "debug")]
+    fn default_print_def_path(
+        self,
+        def_id: DefId,
+        substs: &'tcx [GenericArg<'tcx>],
+    ) -> Result<Self::Path, Self::Error> {
+        let key = self.tcx().def_key(def_id);
+        debug!(?key);
+
+        match key.disambiguated_data.data {
+            DefPathData::CrateRoot => {
+                assert!(key.parent.is_none());
+                self.path_crate(def_id.krate)
+            }
+
+            DefPathData::Impl => {
+                let generics = self.tcx().generics_of(def_id);
+                let self_ty = self.tcx().bound_type_of(def_id);
+                let impl_trait_ref = self.tcx().bound_impl_trait_ref(def_id);
+                let (self_ty, impl_trait_ref) = if substs.len() >= generics.count() {
+                    (
+                        self_ty.subst(self.tcx(), substs),
+                        impl_trait_ref.map(|i| i.subst(self.tcx(), substs)),
+                    )
+                } else {
+                    (self_ty.0, impl_trait_ref.map(|i| i.0))
+                };
+                self.print_impl_path(def_id, substs, self_ty, impl_trait_ref)
+            }
+
+            _ => {
+                let parent_def_id = DefId { index: key.parent.unwrap(), ..def_id };
+
+                let mut parent_substs = substs;
+                let mut trait_qualify_parent = false;
+                if !substs.is_empty() {
+                    let generics = self.tcx().generics_of(def_id);
+                    parent_substs = &substs[..generics.parent_count.min(substs.len())];
+
+                    match key.disambiguated_data.data {
+                        // Closures' own generics are only captures, don't print them.
+                        DefPathData::ClosureExpr => {}
+                        // This covers both `DefKind::AnonConst` and `DefKind::InlineConst`.
+                        // Anon consts doesn't have their own generics, and inline consts' own
+                        // generics are their inferred types, so don't print them.
+                        DefPathData::AnonConst => {}
+
+                        // If we have any generic arguments to print, we do that
+                        // on top of the same path, but without its own generics.
+                        _ => {
+                            if !generics.params.is_empty() && substs.len() >= generics.count() {
+                                let args = generics.own_substs_no_defaults(self.tcx(), substs);
+                                return self.path_generic_args(
+                                    |cx| cx.print_def_path(def_id, parent_substs),
+                                    args,
+                                );
+                            }
+                        }
+                    }
+
+                    // FIXME(eddyb) try to move this into the parent's printing
+                    // logic, instead of doing it when printing the child.
+                    trait_qualify_parent = generics.has_self
+                        && generics.parent == Some(parent_def_id)
+                        && parent_substs.len() == generics.parent_count
+                        && self.tcx().generics_of(parent_def_id).parent_count == 0;
+                }
+
+                self.path_append(
+                    |cx: Self| {
+                        if trait_qualify_parent {
+                            let trait_ref = ty::TraitRef::new(
+                                parent_def_id,
+                                cx.tcx().intern_substs(parent_substs),
+                            );
+                            cx.path_qualified(trait_ref.self_ty(), Some(trait_ref))
+                        } else {
+                            cx.print_def_path(parent_def_id, parent_substs)
+                        }
+                    },
+                    &key.disambiguated_data,
+                )
+            }
+        }
+    }
+
+    fn default_print_impl_path(
+        self,
+        impl_def_id: DefId,
+        _substs: &'tcx [GenericArg<'tcx>],
+        self_ty: Ty<'tcx>,
+        impl_trait_ref: Option<ty::TraitRef<'tcx>>,
+    ) -> Result<Self::Path, Self::Error> {
+        debug!(
+            "default_print_impl_path: impl_def_id={:?}, self_ty={}, impl_trait_ref={:?}",
+            impl_def_id, self_ty, impl_trait_ref
+        );
+
+        let key = self.tcx().def_key(impl_def_id);
+        let parent_def_id = DefId { index: key.parent.unwrap(), ..impl_def_id };
+
+        // Decide whether to print the parent path for the impl.
+        // Logically, since impls are global, it's never needed, but
+        // users may find it useful. Currently, we omit the parent if
+        // the impl is either in the same module as the self-type or
+        // as the trait.
+        let in_self_mod = match characteristic_def_id_of_type(self_ty) {
+            None => false,
+            Some(ty_def_id) => self.tcx().parent(ty_def_id) == parent_def_id,
+        };
+        let in_trait_mod = match impl_trait_ref {
+            None => false,
+            Some(trait_ref) => self.tcx().parent(trait_ref.def_id) == parent_def_id,
+        };
+
+        if !in_self_mod && !in_trait_mod {
+            // If the impl is not co-located with either self-type or
+            // trait-type, then fallback to a format that identifies
+            // the module more clearly.
+            self.path_append_impl(
+                |cx| cx.print_def_path(parent_def_id, &[]),
+                &key.disambiguated_data,
+                self_ty,
+                impl_trait_ref,
+            )
+        } else {
+            // Otherwise, try to give a good form that would be valid language
+            // syntax. Preferably using associated item notation.
+            self.path_qualified(self_ty, impl_trait_ref)
+        }
+    }
+}
+
+/// As a heuristic, when we see an impl, if we see that the
+/// 'self type' is a type defined in the same module as the impl,
+/// we can omit including the path to the impl itself. This
+/// function tries to find a "characteristic `DefId`" for a
+/// type. It's just a heuristic so it makes some questionable
+/// decisions and we may want to adjust it later.
+///
+/// Visited set is needed to avoid full iteration over
+/// deeply nested tuples that have no DefId.
+fn characteristic_def_id_of_type_cached<'a>(
+    ty: Ty<'a>,
+    visited: &mut SsoHashSet<Ty<'a>>,
+) -> Option<DefId> {
+    match *ty.kind() {
+        ty::Adt(adt_def, _) => Some(adt_def.did()),
+
+        ty::Dynamic(data, ..) => data.principal_def_id(),
+
+        ty::Array(subty, _) | ty::Slice(subty) => {
+            characteristic_def_id_of_type_cached(subty, visited)
+        }
+
+        ty::RawPtr(mt) => characteristic_def_id_of_type_cached(mt.ty, visited),
+
+        ty::Ref(_, ty, _) => characteristic_def_id_of_type_cached(ty, visited),
+
+        ty::Tuple(ref tys) => tys.iter().find_map(|ty| {
+            if visited.insert(ty) {
+                return characteristic_def_id_of_type_cached(ty, visited);
+            }
+            return None;
+        }),
+
+        ty::FnDef(def_id, _)
+        | ty::Closure(def_id, _)
+        | ty::Generator(def_id, _, _)
+        | ty::Foreign(def_id) => Some(def_id),
+
+        ty::Bool
+        | ty::Char
+        | ty::Int(_)
+        | ty::Uint(_)
+        | ty::Str
+        | ty::FnPtr(_)
+        | ty::Projection(_)
+        | ty::Placeholder(..)
+        | ty::Param(_)
+        | ty::Opaque(..)
+        | ty::Infer(_)
+        | ty::Bound(..)
+        | ty::Error(_)
+        | ty::GeneratorWitness(..)
+        | ty::Never
+        | ty::Float(_) => None,
+    }
+}
+pub fn characteristic_def_id_of_type(ty: Ty<'_>) -> Option<DefId> {
+    characteristic_def_id_of_type_cached(ty, &mut SsoHashSet::new())
+}
+
+impl<'tcx, P: Printer<'tcx>> Print<'tcx, P> for ty::Region<'tcx> {
+    type Output = P::Region;
+    type Error = P::Error;
+    fn print(&self, cx: P) -> Result<Self::Output, Self::Error> {
+        cx.print_region(*self)
+    }
+}
+
+impl<'tcx, P: Printer<'tcx>> Print<'tcx, P> for Ty<'tcx> {
+    type Output = P::Type;
+    type Error = P::Error;
+
+    fn print(&self, cx: P) -> Result<Self::Output, Self::Error> {
+        cx.print_type(*self)
+    }
+}
+
+impl<'tcx, P: Printer<'tcx>> Print<'tcx, P>
+    for &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>
+{
+    type Output = P::DynExistential;
+    type Error = P::Error;
+    fn print(&self, cx: P) -> Result<Self::Output, Self::Error> {
+        cx.print_dyn_existential(self)
+    }
+}
+
+impl<'tcx, P: Printer<'tcx>> Print<'tcx, P> for ty::Const<'tcx> {
+    type Output = P::Const;
+    type Error = P::Error;
+    fn print(&self, cx: P) -> Result<Self::Output, Self::Error> {
+        cx.print_const(*self)
+    }
+}
diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
new file mode 100644
index 000000000..7f2e81a71
--- /dev/null
+++ b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -0,0 +1,2789 @@
+use crate::mir::interpret::{AllocRange, GlobalAlloc, Pointer, Provenance, Scalar};
+use crate::ty::subst::{GenericArg, GenericArgKind, Subst};
+use crate::ty::{
+    self, ConstInt, DefIdTree, ParamConst, ScalarInt, Term, Ty, TyCtxt, TypeFoldable,
+    TypeSuperFoldable, TypeSuperVisitable, TypeVisitable,
+};
+use rustc_apfloat::ieee::{Double, Single};
+use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
+use rustc_data_structures::sso::SsoHashSet;
+use rustc_hir as hir;
+use rustc_hir::def::{self, CtorKind, DefKind, Namespace};
+use rustc_hir::def_id::{DefId, DefIdSet, CRATE_DEF_ID, LOCAL_CRATE};
+use rustc_hir::definitions::{DefPathData, DefPathDataName, DisambiguatedDefPathData};
+use rustc_session::config::TrimmedDefPaths;
+use rustc_session::cstore::{ExternCrate, ExternCrateSource};
+use rustc_span::symbol::{kw, Ident, Symbol};
+use rustc_target::abi::Size;
+use rustc_target::spec::abi::Abi;
+
+use std::cell::Cell;
+use std::char;
+use std::collections::BTreeMap;
+use std::convert::TryFrom;
+use std::fmt::{self, Write as _};
+use std::iter;
+use std::ops::{ControlFlow, Deref, DerefMut};
+
+// `pretty` is a separate module only for organization.
+use super::*;
+
+macro_rules! p {
+    (@$lit:literal) => {
+        write!(scoped_cx!(), $lit)?
+    };
+    (@write($($data:expr),+)) => {
+        write!(scoped_cx!(), $($data),+)?
+    };
+    (@print($x:expr)) => {
+        scoped_cx!() = $x.print(scoped_cx!())?
+    };
+    (@$method:ident($($arg:expr),*)) => {
+        scoped_cx!() = scoped_cx!().$method($($arg),*)?
+    };
+    ($($elem:tt $(($($args:tt)*))?),+) => {{
+        $(p!(@ $elem $(($($args)*))?);)+
+    }};
+}
+macro_rules! define_scoped_cx {
+    ($cx:ident) => {
+        #[allow(unused_macros)]
+        macro_rules! scoped_cx {
+            () => {
+                $cx
+            };
+        }
+    };
+}
+
+thread_local! {
+    static FORCE_IMPL_FILENAME_LINE: Cell<bool> = const { Cell::new(false) };
+    static SHOULD_PREFIX_WITH_CRATE: Cell<bool> = const { Cell::new(false) };
+    static NO_TRIMMED_PATH: Cell<bool> = const { Cell::new(false) };
+    static NO_QUERIES: Cell<bool> = const { Cell::new(false) };
+    static NO_VISIBLE_PATH: Cell<bool> = const { Cell::new(false) };
+}
+
+macro_rules! define_helper {
+    ($($(#[$a:meta])* fn $name:ident($helper:ident, $tl:ident);)+) => {
+        $(
+            #[must_use]
+            pub struct $helper(bool);
+
+            impl $helper {
+                pub fn new() -> $helper {
+                    $helper($tl.with(|c| c.replace(true)))
+                }
+            }
+
+            $(#[$a])*
+            pub macro $name($e:expr) {
+                {
+                    let _guard = $helper::new();
+                    $e
+                }
+            }
+
+            impl Drop for $helper {
+                fn drop(&mut self) {
+                    $tl.with(|c| c.set(self.0))
+                }
+            }
+        )+
+    }
+}
+
+define_helper!(
+    /// Avoids running any queries during any prints that occur
+    /// during the closure. This may alter the appearance of some
+    /// types (e.g. forcing verbose printing for opaque types).
+    /// This method is used during some queries (e.g. `explicit_item_bounds`
+    /// for opaque types), to ensure that any debug printing that
+    /// occurs during the query computation does not end up recursively
+    /// calling the same query.
+    fn with_no_queries(NoQueriesGuard, NO_QUERIES);
+    /// Force us to name impls with just the filename/line number. We
+    /// normally try to use types. But at some points, notably while printing
+    /// cycle errors, this can result in extra or suboptimal error output,
+    /// so this variable disables that check.
+    fn with_forced_impl_filename_line(ForcedImplGuard, FORCE_IMPL_FILENAME_LINE);
+    /// Adds the `crate::` prefix to paths where appropriate.
+    fn with_crate_prefix(CratePrefixGuard, SHOULD_PREFIX_WITH_CRATE);
+    /// Prevent path trimming if it is turned on. Path trimming affects `Display` impl
+    /// of various rustc types, for example `std::vec::Vec` would be trimmed to `Vec`,
+    /// if no other `Vec` is found.
+    fn with_no_trimmed_paths(NoTrimmedGuard, NO_TRIMMED_PATH);
+    /// Prevent selection of visible paths. `Display` impl of DefId will prefer
+    /// visible (public) reexports of types as paths.
+    fn with_no_visible_paths(NoVisibleGuard, NO_VISIBLE_PATH);
+);
+
+/// The "region highlights" are used to control region printing during
+/// specific error messages. When a "region highlight" is enabled, it
+/// gives an alternate way to print specific regions. For now, we
+/// always print those regions using a number, so something like "`'0`".
+///
+/// Regions not selected by the region highlight mode are presently
+/// unaffected.
+#[derive(Copy, Clone)]
+pub struct RegionHighlightMode<'tcx> {
+    tcx: TyCtxt<'tcx>,
+
+    /// If enabled, when we see the selected region, use "`'N`"
+    /// instead of the ordinary behavior.
+    highlight_regions: [Option<(ty::Region<'tcx>, usize)>; 3],
+
+    /// If enabled, when printing a "free region" that originated from
+    /// the given `ty::BoundRegionKind`, print it as "`'1`". Free regions that would ordinarily
+    /// have names print as normal.
+    ///
+    /// This is used when you have a signature like `fn foo(x: &u32,
+    /// y: &'a u32)` and we want to give a name to the region of the
+    /// reference `x`.
+    highlight_bound_region: Option<(ty::BoundRegionKind, usize)>,
+}
+
+impl<'tcx> RegionHighlightMode<'tcx> {
+    pub fn new(tcx: TyCtxt<'tcx>) -> Self {
+        Self {
+            tcx,
+            highlight_regions: Default::default(),
+            highlight_bound_region: Default::default(),
+        }
+    }
+
+    /// If `region` and `number` are both `Some`, invokes
+    /// `highlighting_region`.
+    pub fn maybe_highlighting_region(
+        &mut self,
+        region: Option<ty::Region<'tcx>>,
+        number: Option<usize>,
+    ) {
+        if let Some(k) = region {
+            if let Some(n) = number {
+                self.highlighting_region(k, n);
+            }
+        }
+    }
+
+    /// Highlights the region inference variable `vid` as `'N`.
+    pub fn highlighting_region(&mut self, region: ty::Region<'tcx>, number: usize) {
+        let num_slots = self.highlight_regions.len();
+        let first_avail_slot =
+            self.highlight_regions.iter_mut().find(|s| s.is_none()).unwrap_or_else(|| {
+                bug!("can only highlight {} placeholders at a time", num_slots,)
+            });
+        *first_avail_slot = Some((region, number));
+    }
+
+    /// Convenience wrapper for `highlighting_region`.
+    pub fn highlighting_region_vid(&mut self, vid: ty::RegionVid, number: usize) {
+        self.highlighting_region(self.tcx.mk_region(ty::ReVar(vid)), number)
+    }
+
+    /// Returns `Some(n)` with the number to use for the given region, if any.
+    fn region_highlighted(&self, region: ty::Region<'tcx>) -> Option<usize> {
+        self.highlight_regions.iter().find_map(|h| match h {
+            Some((r, n)) if *r == region => Some(*n),
+            _ => None,
+        })
+    }
+
+    /// Highlight the given bound region.
+    /// We can only highlight one bound region at a time. See
+    /// the field `highlight_bound_region` for more detailed notes.
+    pub fn highlighting_bound_region(&mut self, br: ty::BoundRegionKind, number: usize) {
+        assert!(self.highlight_bound_region.is_none());
+        self.highlight_bound_region = Some((br, number));
+    }
+}
+
+/// Trait for printers that pretty-print using `fmt::Write` to the printer.
+pub trait PrettyPrinter<'tcx>:
+    Printer<
+        'tcx,
+        Error = fmt::Error,
+        Path = Self,
+        Region = Self,
+        Type = Self,
+        DynExistential = Self,
+        Const = Self,
+    > + fmt::Write
+{
+    /// Like `print_def_path` but for value paths.
+    fn print_value_path(
+        self,
+        def_id: DefId,
+        substs: &'tcx [GenericArg<'tcx>],
+    ) -> Result<Self::Path, Self::Error> {
+        self.print_def_path(def_id, substs)
+    }
+
+    fn in_binder<T>(self, value: &ty::Binder<'tcx, T>) -> Result<Self, Self::Error>
+    where
+        T: Print<'tcx, Self, Output = Self, Error = Self::Error> + TypeFoldable<'tcx>,
+    {
+        value.as_ref().skip_binder().print(self)
+    }
+
+    fn wrap_binder<T, F: FnOnce(&T, Self) -> Result<Self, fmt::Error>>(
+        self,
+        value: &ty::Binder<'tcx, T>,
+        f: F,
+    ) -> Result<Self, Self::Error>
+    where
+        T: Print<'tcx, Self, Output = Self, Error = Self::Error> + TypeFoldable<'tcx>,
+    {
+        f(value.as_ref().skip_binder(), self)
+    }
+
+    /// Prints comma-separated elements.
+    fn comma_sep<T>(mut self, mut elems: impl Iterator<Item = T>) -> Result<Self, Self::Error>
+    where
+        T: Print<'tcx, Self, Output = Self, Error = Self::Error>,
+    {
+        if let Some(first) = elems.next() {
+            self = first.print(self)?;
+            for elem in elems {
+                self.write_str(", ")?;
+                self = elem.print(self)?;
+            }
+        }
+        Ok(self)
+    }
+
+    /// Prints `{f: t}` or `{f as t}` depending on the `cast` argument
+    fn typed_value(
+        mut self,
+        f: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        t: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        conversion: &str,
+    ) -> Result<Self::Const, Self::Error> {
+        self.write_str("{")?;
+        self = f(self)?;
+        self.write_str(conversion)?;
+        self = t(self)?;
+        self.write_str("}")?;
+        Ok(self)
+    }
+
+    /// Prints `<...>` around what `f` prints.
+    fn generic_delimiters(
+        self,
+        f: impl FnOnce(Self) -> Result<Self, Self::Error>,
+    ) -> Result<Self, Self::Error>;
+
+    /// Returns `true` if the region should be printed in
+    /// optional positions, e.g., `&'a T` or `dyn Tr + 'b`.
+    /// This is typically the case for all non-`'_` regions.
+    fn should_print_region(&self, region: ty::Region<'tcx>) -> bool;
+
+    // Defaults (should not be overridden):
+
+    /// If possible, this returns a global path resolving to `def_id` that is visible
+    /// from at least one local module, and returns `true`. If the crate defining `def_id` is
+    /// declared with an `extern crate`, the path is guaranteed to use the `extern crate`.
+    fn try_print_visible_def_path(self, def_id: DefId) -> Result<(Self, bool), Self::Error> {
+        if NO_VISIBLE_PATH.with(|flag| flag.get()) {
+            return Ok((self, false));
+        }
+
+        let mut callers = Vec::new();
+        self.try_print_visible_def_path_recur(def_id, &mut callers)
+    }
+
+    /// Try to see if this path can be trimmed to a unique symbol name.
+    fn try_print_trimmed_def_path(
+        mut self,
+        def_id: DefId,
+    ) -> Result<(Self::Path, bool), Self::Error> {
+        if !self.tcx().sess.opts.unstable_opts.trim_diagnostic_paths
+            || matches!(self.tcx().sess.opts.trimmed_def_paths, TrimmedDefPaths::Never)
+            || NO_TRIMMED_PATH.with(|flag| flag.get())
+            || SHOULD_PREFIX_WITH_CRATE.with(|flag| flag.get())
+        {
+            return Ok((self, false));
+        }
+
+        match self.tcx().trimmed_def_paths(()).get(&def_id) {
+            None => Ok((self, false)),
+            Some(symbol) => {
+                self.write_str(symbol.as_str())?;
+                Ok((self, true))
+            }
+        }
+    }
+
+    /// Does the work of `try_print_visible_def_path`, building the
+    /// full definition path recursively before attempting to
+    /// post-process it into the valid and visible version that
+    /// accounts for re-exports.
+    ///
+    /// This method should only be called by itself or
+    /// `try_print_visible_def_path`.
+    ///
+    /// `callers` is a chain of visible_parent's leading to `def_id`,
+    /// to support cycle detection during recursion.
+    ///
+    /// This method returns false if we can't print the visible path, so
+    /// `print_def_path` can fall back on the item's real definition path.
+    fn try_print_visible_def_path_recur(
+        mut self,
+        def_id: DefId,
+        callers: &mut Vec<DefId>,
+    ) -> Result<(Self, bool), Self::Error> {
+        define_scoped_cx!(self);
+
+        debug!("try_print_visible_def_path: def_id={:?}", def_id);
+
+        // If `def_id` is a direct or injected extern crate, return the
+        // path to the crate followed by the path to the item within the crate.
+        if let Some(cnum) = def_id.as_crate_root() {
+            if cnum == LOCAL_CRATE {
+                return Ok((self.path_crate(cnum)?, true));
+            }
+
+            // In local mode, when we encounter a crate other than
+            // LOCAL_CRATE, execution proceeds in one of two ways:
+            //
+            // 1. For a direct dependency, where user added an
+            //    `extern crate` manually, we put the `extern
+            //    crate` as the parent. So you wind up with
+            //    something relative to the current crate.
+            // 2. For an extern inferred from a path or an indirect crate,
+            //    where there is no explicit `extern crate`, we just prepend
+            //    the crate name.
+            match self.tcx().extern_crate(def_id) {
+                Some(&ExternCrate { src, dependency_of, span, .. }) => match (src, dependency_of) {
+                    (ExternCrateSource::Extern(def_id), LOCAL_CRATE) => {
+                        // NOTE(eddyb) the only reason `span` might be dummy,
+                        // that we're aware of, is that it's the `std`/`core`
+                        // `extern crate` injected by default.
+                        // FIXME(eddyb) find something better to key this on,
+                        // or avoid ending up with `ExternCrateSource::Extern`,
+                        // for the injected `std`/`core`.
+                        if span.is_dummy() {
+                            return Ok((self.path_crate(cnum)?, true));
+                        }
+
+                        // Disable `try_print_trimmed_def_path` behavior within
+                        // the `print_def_path` call, to avoid infinite recursion
+                        // in cases where the `extern crate foo` has non-trivial
+                        // parents, e.g. it's nested in `impl foo::Trait for Bar`
+                        // (see also issues #55779 and #87932).
+                        self = with_no_visible_paths!(self.print_def_path(def_id, &[])?);
+
+                        return Ok((self, true));
+                    }
+                    (ExternCrateSource::Path, LOCAL_CRATE) => {
+                        return Ok((self.path_crate(cnum)?, true));
+                    }
+                    _ => {}
+                },
+                None => {
+                    return Ok((self.path_crate(cnum)?, true));
+                }
+            }
+        }
+
+        if def_id.is_local() {
+            return Ok((self, false));
+        }
+
+        let visible_parent_map = self.tcx().visible_parent_map(());
+
+        let mut cur_def_key = self.tcx().def_key(def_id);
+        debug!("try_print_visible_def_path: cur_def_key={:?}", cur_def_key);
+
+        // For a constructor, we want the name of its parent rather than <unnamed>.
+        if let DefPathData::Ctor = cur_def_key.disambiguated_data.data {
+            let parent = DefId {
+                krate: def_id.krate,
+                index: cur_def_key
+                    .parent
+                    .expect("`DefPathData::Ctor` / `VariantData` missing a parent"),
+            };
+
+            cur_def_key = self.tcx().def_key(parent);
+        }
+
+        let Some(visible_parent) = visible_parent_map.get(&def_id).cloned() else {
+            return Ok((self, false));
+        };
+
+        let actual_parent = self.tcx().opt_parent(def_id);
+        debug!(
+            "try_print_visible_def_path: visible_parent={:?} actual_parent={:?}",
+            visible_parent, actual_parent,
+        );
+
+        let mut data = cur_def_key.disambiguated_data.data;
+        debug!(
+            "try_print_visible_def_path: data={:?} visible_parent={:?} actual_parent={:?}",
+            data, visible_parent, actual_parent,
+        );
+
+        match data {
+            // In order to output a path that could actually be imported (valid and visible),
+            // we need to handle re-exports correctly.
+            //
+            // For example, take `std::os::unix::process::CommandExt`, this trait is actually
+            // defined at `std::sys::unix::ext::process::CommandExt` (at time of writing).
+            //
+            // `std::os::unix` reexports the contents of `std::sys::unix::ext`. `std::sys` is
+            // private so the "true" path to `CommandExt` isn't accessible.
+            //
+            // In this case, the `visible_parent_map` will look something like this:
+            //
+            // (child) -> (parent)
+            // `std::sys::unix::ext::process::CommandExt` -> `std::sys::unix::ext::process`
+            // `std::sys::unix::ext::process` -> `std::sys::unix::ext`
+            // `std::sys::unix::ext` -> `std::os`
+            //
+            // This is correct, as the visible parent of `std::sys::unix::ext` is in fact
+            // `std::os`.
+            //
+            // When printing the path to `CommandExt` and looking at the `cur_def_key` that
+            // corresponds to `std::sys::unix::ext`, we would normally print `ext` and then go
+            // to the parent - resulting in a mangled path like
+            // `std::os::ext::process::CommandExt`.
+            //
+            // Instead, we must detect that there was a re-export and instead print `unix`
+            // (which is the name `std::sys::unix::ext` was re-exported as in `std::os`). To
+            // do this, we compare the parent of `std::sys::unix::ext` (`std::sys::unix`) with
+            // the visible parent (`std::os`). If these do not match, then we iterate over
+            // the children of the visible parent (as was done when computing
+            // `visible_parent_map`), looking for the specific child we currently have and then
+            // have access to the re-exported name.
+            DefPathData::TypeNs(ref mut name) if Some(visible_parent) != actual_parent => {
+                // Item might be re-exported several times, but filter for the one
+                // that's public and whose identifier isn't `_`.
+                let reexport = self
+                    .tcx()
+                    .module_children(visible_parent)
+                    .iter()
+                    .filter(|child| child.res.opt_def_id() == Some(def_id))
+                    .find(|child| child.vis.is_public() && child.ident.name != kw::Underscore)
+                    .map(|child| child.ident.name);
+
+                if let Some(new_name) = reexport {
+                    *name = new_name;
+                } else {
+                    // There is no name that is public and isn't `_`, so bail.
+                    return Ok((self, false));
+                }
+            }
+            // Re-exported `extern crate` (#43189).
+            DefPathData::CrateRoot => {
+                data = DefPathData::TypeNs(self.tcx().crate_name(def_id.krate));
+            }
+            _ => {}
+        }
+        debug!("try_print_visible_def_path: data={:?}", data);
+
+        if callers.contains(&visible_parent) {
+            return Ok((self, false));
+        }
+        callers.push(visible_parent);
+        // HACK(eddyb) this bypasses `path_append`'s prefix printing to avoid
+        // knowing ahead of time whether the entire path will succeed or not.
+        // To support printers that do not implement `PrettyPrinter`, a `Vec` or
+        // linked list on the stack would need to be built, before any printing.
+        match self.try_print_visible_def_path_recur(visible_parent, callers)? {
+            (cx, false) => return Ok((cx, false)),
+            (cx, true) => self = cx,
+        }
+        callers.pop();
+
+        Ok((self.path_append(Ok, &DisambiguatedDefPathData { data, disambiguator: 0 })?, true))
+    }
+
+    fn pretty_path_qualified(
+        self,
+        self_ty: Ty<'tcx>,
+        trait_ref: Option<ty::TraitRef<'tcx>>,
+    ) -> Result<Self::Path, Self::Error> {
+        if trait_ref.is_none() {
+            // Inherent impls. Try to print `Foo::bar` for an inherent
+            // impl on `Foo`, but fallback to `<Foo>::bar` if self-type is
+            // anything other than a simple path.
+            match self_ty.kind() {
+                ty::Adt(..)
+                | ty::Foreign(_)
+                | ty::Bool
+                | ty::Char
+                | ty::Str
+                | ty::Int(_)
+                | ty::Uint(_)
+                | ty::Float(_) => {
+                    return self_ty.print(self);
+                }
+
+                _ => {}
+            }
+        }
+
+        self.generic_delimiters(|mut cx| {
+            define_scoped_cx!(cx);
+
+            p!(print(self_ty));
+            if let Some(trait_ref) = trait_ref {
+                p!(" as ", print(trait_ref.print_only_trait_path()));
+            }
+            Ok(cx)
+        })
+    }
+
+    fn pretty_path_append_impl(
+        mut self,
+        print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
+        self_ty: Ty<'tcx>,
+        trait_ref: Option<ty::TraitRef<'tcx>>,
+    ) -> Result<Self::Path, Self::Error> {
+        self = print_prefix(self)?;
+
+        self.generic_delimiters(|mut cx| {
+            define_scoped_cx!(cx);
+
+            p!("impl ");
+            if let Some(trait_ref) = trait_ref {
+                p!(print(trait_ref.print_only_trait_path()), " for ");
+            }
+            p!(print(self_ty));
+
+            Ok(cx)
+        })
+    }
+
+    fn pretty_print_type(mut self, ty: Ty<'tcx>) -> Result<Self::Type, Self::Error> {
+        define_scoped_cx!(self);
+
+        match *ty.kind() {
+            ty::Bool => p!("bool"),
+            ty::Char => p!("char"),
+            ty::Int(t) => p!(write("{}", t.name_str())),
+            ty::Uint(t) => p!(write("{}", t.name_str())),
+            ty::Float(t) => p!(write("{}", t.name_str())),
+            ty::RawPtr(ref tm) => {
+                p!(write(
+                    "*{} ",
+                    match tm.mutbl {
+                        hir::Mutability::Mut => "mut",
+                        hir::Mutability::Not => "const",
+                    }
+                ));
+                p!(print(tm.ty))
+            }
+            ty::Ref(r, ty, mutbl) => {
+                p!("&");
+                if self.should_print_region(r) {
+                    p!(print(r), " ");
+                }
+                p!(print(ty::TypeAndMut { ty, mutbl }))
+            }
+            ty::Never => p!("!"),
+            ty::Tuple(ref tys) => {
+                p!("(", comma_sep(tys.iter()));
+                if tys.len() == 1 {
+                    p!(",");
+                }
+                p!(")")
+            }
+            ty::FnDef(def_id, substs) => {
+                let sig = self.tcx().bound_fn_sig(def_id).subst(self.tcx(), substs);
+                p!(print(sig), " {{", print_value_path(def_id, substs), "}}");
+            }
+            ty::FnPtr(ref bare_fn) => p!(print(bare_fn)),
+            ty::Infer(infer_ty) => {
+                let verbose = self.tcx().sess.verbose();
+                if let ty::TyVar(ty_vid) = infer_ty {
+                    if let Some(name) = self.ty_infer_name(ty_vid) {
+                        p!(write("{}", name))
+                    } else {
+                        if verbose {
+                            p!(write("{:?}", infer_ty))
+                        } else {
+                            p!(write("{}", infer_ty))
+                        }
+                    }
+                } else {
+                    if verbose { p!(write("{:?}", infer_ty)) } else { p!(write("{}", infer_ty)) }
+                }
+            }
+            ty::Error(_) => p!("[type error]"),
+            ty::Param(ref param_ty) => p!(print(param_ty)),
+            ty::Bound(debruijn, bound_ty) => match bound_ty.kind {
+                ty::BoundTyKind::Anon => self.pretty_print_bound_var(debruijn, bound_ty.var)?,
+                ty::BoundTyKind::Param(p) => p!(write("{}", p)),
+            },
+            ty::Adt(def, substs) => {
+                p!(print_def_path(def.did(), substs));
+            }
+            ty::Dynamic(data, r) => {
+                let print_r = self.should_print_region(r);
+                if print_r {
+                    p!("(");
+                }
+                p!("dyn ", print(data));
+                if print_r {
+                    p!(" + ", print(r), ")");
+                }
+            }
+            ty::Foreign(def_id) => {
+                p!(print_def_path(def_id, &[]));
+            }
+            ty::Projection(ref data) => p!(print(data)),
+            ty::Placeholder(placeholder) => p!(write("Placeholder({:?})", placeholder)),
+            ty::Opaque(def_id, substs) => {
+                // FIXME(eddyb) print this with `print_def_path`.
+                // We use verbose printing in 'NO_QUERIES' mode, to
+                // avoid needing to call `predicates_of`. This should
+                // only affect certain debug messages (e.g. messages printed
+                // from `rustc_middle::ty` during the computation of `tcx.predicates_of`),
+                // and should have no effect on any compiler output.
+                if self.tcx().sess.verbose() || NO_QUERIES.with(|q| q.get()) {
+                    p!(write("Opaque({:?}, {:?})", def_id, substs));
+                    return Ok(self);
+                }
+
+                let parent = self.tcx().parent(def_id);
+                match self.tcx().def_kind(parent) {
+                    DefKind::TyAlias | DefKind::AssocTy => {
+                        if let ty::Opaque(d, _) = *self.tcx().type_of(parent).kind() {
+                            if d == def_id {
+                                // If the type alias directly starts with the `impl` of the
+                                // opaque type we're printing, then skip the `::{opaque#1}`.
+                                p!(print_def_path(parent, substs));
+                                return Ok(self);
+                            }
+                        }
+                        // Complex opaque type, e.g. `type Foo = (i32, impl Debug);`
+                        p!(print_def_path(def_id, substs));
+                        return Ok(self);
+                    }
+                    _ => return self.pretty_print_opaque_impl_type(def_id, substs),
+                }
+            }
+            ty::Str => p!("str"),
+            ty::Generator(did, substs, movability) => {
+                p!(write("["));
+                match movability {
+                    hir::Movability::Movable => {}
+                    hir::Movability::Static => p!("static "),
+                }
+
+                if !self.tcx().sess.verbose() {
+                    p!("generator");
+                    // FIXME(eddyb) should use `def_span`.
+                    if let Some(did) = did.as_local() {
+                        let span = self.tcx().def_span(did);
+                        p!(write(
+                            "@{}",
+                            // This may end up in stderr diagnostics but it may also be emitted
+                            // into MIR. Hence we use the remapped path if available
+                            self.tcx().sess.source_map().span_to_embeddable_string(span)
+                        ));
+                    } else {
+                        p!(write("@"), print_def_path(did, substs));
+                    }
+                } else {
+                    p!(print_def_path(did, substs));
+                    p!(" upvar_tys=(");
+                    if !substs.as_generator().is_valid() {
+                        p!("unavailable");
+                    } else {
+                        self = self.comma_sep(substs.as_generator().upvar_tys())?;
+                    }
+                    p!(")");
+
+                    if substs.as_generator().is_valid() {
+                        p!(" ", print(substs.as_generator().witness()));
+                    }
+                }
+
+                p!("]")
+            }
+            ty::GeneratorWitness(types) => {
+                p!(in_binder(&types));
+            }
+            ty::Closure(did, substs) => {
+                p!(write("["));
+                if !self.tcx().sess.verbose() {
+                    p!(write("closure"));
+                    // FIXME(eddyb) should use `def_span`.
+                    if let Some(did) = did.as_local() {
+                        if self.tcx().sess.opts.unstable_opts.span_free_formats {
+                            p!("@", print_def_path(did.to_def_id(), substs));
+                        } else {
+                            let span = self.tcx().def_span(did);
+                            p!(write(
+                                "@{}",
+                                // This may end up in stderr diagnostics but it may also be emitted
+                                // into MIR. Hence we use the remapped path if available
+                                self.tcx().sess.source_map().span_to_embeddable_string(span)
+                            ));
+                        }
+                    } else {
+                        p!(write("@"), print_def_path(did, substs));
+                    }
+                } else {
+                    p!(print_def_path(did, substs));
+                    if !substs.as_closure().is_valid() {
+                        p!(" closure_substs=(unavailable)");
+                        p!(write(" substs={:?}", substs));
+                    } else {
+                        p!(" closure_kind_ty=", print(substs.as_closure().kind_ty()));
+                        p!(
+                            " closure_sig_as_fn_ptr_ty=",
+                            print(substs.as_closure().sig_as_fn_ptr_ty())
+                        );
+                        p!(" upvar_tys=(");
+                        self = self.comma_sep(substs.as_closure().upvar_tys())?;
+                        p!(")");
+                    }
+                }
+                p!("]");
+            }
+            ty::Array(ty, sz) => {
+                p!("[", print(ty), "; ");
+                if self.tcx().sess.verbose() {
+                    p!(write("{:?}", sz));
+                } else if let ty::ConstKind::Unevaluated(..) = sz.kind() {
+                    // Do not try to evaluate unevaluated constants. If we are const evaluating an
+                    // array length anon const, rustc will (with debug assertions) print the
+                    // constant's path. Which will end up here again.
+                    p!("_");
+                } else if let Some(n) = sz.kind().try_to_bits(self.tcx().data_layout.pointer_size) {
+                    p!(write("{}", n));
+                } else if let ty::ConstKind::Param(param) = sz.kind() {
+                    p!(print(param));
+                } else {
+                    p!("_");
+                }
+                p!("]")
+            }
+            ty::Slice(ty) => p!("[", print(ty), "]"),
+        }
+
+        Ok(self)
+    }
+
+    fn pretty_print_opaque_impl_type(
+        mut self,
+        def_id: DefId,
+        substs: &'tcx ty::List<ty::GenericArg<'tcx>>,
+    ) -> Result<Self::Type, Self::Error> {
+        let tcx = self.tcx();
+
+        // Grab the "TraitA + TraitB" from `impl TraitA + TraitB`,
+        // by looking up the projections associated with the def_id.
+        let bounds = tcx.bound_explicit_item_bounds(def_id);
+
+        let mut traits = FxIndexMap::default();
+        let mut fn_traits = FxIndexMap::default();
+        let mut is_sized = false;
+
+        for predicate in bounds.transpose_iter().map(|e| e.map_bound(|(p, _)| *p)) {
+            let predicate = predicate.subst(tcx, substs);
+            let bound_predicate = predicate.kind();
+
+            match bound_predicate.skip_binder() {
+                ty::PredicateKind::Trait(pred) => {
+                    let trait_ref = bound_predicate.rebind(pred.trait_ref);
+
+                    // Don't print + Sized, but rather + ?Sized if absent.
+                    if Some(trait_ref.def_id()) == tcx.lang_items().sized_trait() {
+                        is_sized = true;
+                        continue;
+                    }
+
+                    self.insert_trait_and_projection(trait_ref, None, &mut traits, &mut fn_traits);
+                }
+                ty::PredicateKind::Projection(pred) => {
+                    let proj_ref = bound_predicate.rebind(pred);
+                    let trait_ref = proj_ref.required_poly_trait_ref(tcx);
+
+                    // Projection type entry -- the def-id for naming, and the ty.
+                    let proj_ty = (proj_ref.projection_def_id(), proj_ref.term());
+
+                    self.insert_trait_and_projection(
+                        trait_ref,
+                        Some(proj_ty),
+                        &mut traits,
+                        &mut fn_traits,
+                    );
+                }
+                _ => {}
+            }
+        }
+
+        write!(self, "impl ")?;
+
+        let mut first = true;
+        // Insert parenthesis around (Fn(A, B) -> C) if the opaque ty has more than one other trait
+        let paren_needed = fn_traits.len() > 1 || traits.len() > 0 || !is_sized;
+
+        for (fn_once_trait_ref, entry) in fn_traits {
+            write!(self, "{}", if first { "" } else { " + " })?;
+            write!(self, "{}", if paren_needed { "(" } else { "" })?;
+
+            self = self.wrap_binder(&fn_once_trait_ref, |trait_ref, mut cx| {
+                define_scoped_cx!(cx);
+                // Get the (single) generic ty (the args) of this FnOnce trait ref.
+                let generics = tcx.generics_of(trait_ref.def_id);
+                let args = generics.own_substs_no_defaults(tcx, trait_ref.substs);
+
+                match (entry.return_ty, args[0].expect_ty()) {
+                    // We can only print `impl Fn() -> ()` if we have a tuple of args and we recorded
+                    // a return type.
+                    (Some(return_ty), arg_tys) if matches!(arg_tys.kind(), ty::Tuple(_)) => {
+                        let name = if entry.fn_trait_ref.is_some() {
+                            "Fn"
+                        } else if entry.fn_mut_trait_ref.is_some() {
+                            "FnMut"
+                        } else {
+                            "FnOnce"
+                        };
+
+                        p!(write("{}(", name));
+
+                        for (idx, ty) in arg_tys.tuple_fields().iter().enumerate() {
+                            if idx > 0 {
+                                p!(", ");
+                            }
+                            p!(print(ty));
+                        }
+
+                        p!(")");
+                        if let Term::Ty(ty) = return_ty.skip_binder() {
+                            if !ty.is_unit() {
+                                p!(" -> ", print(return_ty));
+                            }
+                        }
+                        p!(write("{}", if paren_needed { ")" } else { "" }));
+
+                        first = false;
+                    }
+                    // If we got here, we can't print as a `impl Fn(A, B) -> C`. Just record the
+                    // trait_refs we collected in the OpaqueFnEntry as normal trait refs.
+                    _ => {
+                        if entry.has_fn_once {
+                            traits.entry(fn_once_trait_ref).or_default().extend(
+                                // Group the return ty with its def id, if we had one.
+                                entry
+                                    .return_ty
+                                    .map(|ty| (tcx.lang_items().fn_once_output().unwrap(), ty)),
+                            );
+                        }
+                        if let Some(trait_ref) = entry.fn_mut_trait_ref {
+                            traits.entry(trait_ref).or_default();
+                        }
+                        if let Some(trait_ref) = entry.fn_trait_ref {
+                            traits.entry(trait_ref).or_default();
+                        }
+                    }
+                }
+
+                Ok(cx)
+            })?;
+        }
+
+        // Print the rest of the trait types (that aren't Fn* family of traits)
+        for (trait_ref, assoc_items) in traits {
+            write!(self, "{}", if first { "" } else { " + " })?;
+
+            self = self.wrap_binder(&trait_ref, |trait_ref, mut cx| {
+                define_scoped_cx!(cx);
+                p!(print(trait_ref.print_only_trait_name()));
+
+                let generics = tcx.generics_of(trait_ref.def_id);
+                let args = generics.own_substs_no_defaults(tcx, trait_ref.substs);
+
+                if !args.is_empty() || !assoc_items.is_empty() {
+                    let mut first = true;
+
+                    for ty in args {
+                        if first {
+                            p!("<");
+                            first = false;
+                        } else {
+                            p!(", ");
+                        }
+                        p!(print(ty));
+                    }
+
+                    for (assoc_item_def_id, term) in assoc_items {
+                        // Skip printing `<[generator@] as Generator<_>>::Return` from async blocks,
+                        // unless we can find out what generator return type it comes from.
+                        let term = if let Some(ty) = term.skip_binder().ty()
+                            && let ty::Projection(ty::ProjectionTy { item_def_id, substs }) = ty.kind()
+                            && Some(*item_def_id) == tcx.lang_items().generator_return()
+                        {
+                            if let ty::Generator(_, substs, _) = substs.type_at(0).kind() {
+                                let return_ty = substs.as_generator().return_ty();
+                                if !return_ty.is_ty_infer() {
+                                    return_ty.into()
+                                } else {
+                                    continue;
+                                }
+                            } else {
+                                continue;
+                            }
+                        } else {
+                            term.skip_binder()
+                        };
+
+                        if first {
+                            p!("<");
+                            first = false;
+                        } else {
+                            p!(", ");
+                        }
+
+                        p!(write("{} = ", tcx.associated_item(assoc_item_def_id).name));
+
+                        match term {
+                            Term::Ty(ty) => {
+                                p!(print(ty))
+                            }
+                            Term::Const(c) => {
+                                p!(print(c));
+                            }
+                        };
+                    }
+
+                    if !first {
+                        p!(">");
+                    }
+                }
+
+                first = false;
+                Ok(cx)
+            })?;
+        }
+
+        if !is_sized {
+            write!(self, "{}?Sized", if first { "" } else { " + " })?;
+        } else if first {
+            write!(self, "Sized")?;
+        }
+
+        Ok(self)
+    }
+
+    /// Insert the trait ref and optionally a projection type associated with it into either the
+    /// traits map or fn_traits map, depending on if the trait is in the Fn* family of traits.
+    fn insert_trait_and_projection(
+        &mut self,
+        trait_ref: ty::PolyTraitRef<'tcx>,
+        proj_ty: Option<(DefId, ty::Binder<'tcx, Term<'tcx>>)>,
+        traits: &mut FxIndexMap<
+            ty::PolyTraitRef<'tcx>,
+            FxIndexMap<DefId, ty::Binder<'tcx, Term<'tcx>>>,
+        >,
+        fn_traits: &mut FxIndexMap<ty::PolyTraitRef<'tcx>, OpaqueFnEntry<'tcx>>,
+    ) {
+        let trait_def_id = trait_ref.def_id();
+
+        // If our trait_ref is FnOnce or any of its children, project it onto the parent FnOnce
+        // super-trait ref and record it there.
+        if let Some(fn_once_trait) = self.tcx().lang_items().fn_once_trait() {
+            // If we have a FnOnce, then insert it into
+            if trait_def_id == fn_once_trait {
+                let entry = fn_traits.entry(trait_ref).or_default();
+                // Optionally insert the return_ty as well.
+                if let Some((_, ty)) = proj_ty {
+                    entry.return_ty = Some(ty);
+                }
+                entry.has_fn_once = true;
+                return;
+            } else if Some(trait_def_id) == self.tcx().lang_items().fn_mut_trait() {
+                let super_trait_ref = crate::traits::util::supertraits(self.tcx(), trait_ref)
+                    .find(|super_trait_ref| super_trait_ref.def_id() == fn_once_trait)
+                    .unwrap();
+
+                fn_traits.entry(super_trait_ref).or_default().fn_mut_trait_ref = Some(trait_ref);
+                return;
+            } else if Some(trait_def_id) == self.tcx().lang_items().fn_trait() {
+                let super_trait_ref = crate::traits::util::supertraits(self.tcx(), trait_ref)
+                    .find(|super_trait_ref| super_trait_ref.def_id() == fn_once_trait)
+                    .unwrap();
+
+                fn_traits.entry(super_trait_ref).or_default().fn_trait_ref = Some(trait_ref);
+                return;
+            }
+        }
+
+        // Otherwise, just group our traits and projection types.
+        traits.entry(trait_ref).or_default().extend(proj_ty);
+    }
+
+    fn pretty_print_bound_var(
+        &mut self,
+        debruijn: ty::DebruijnIndex,
+        var: ty::BoundVar,
+    ) -> Result<(), Self::Error> {
+        if debruijn == ty::INNERMOST {
+            write!(self, "^{}", var.index())
+        } else {
+            write!(self, "^{}_{}", debruijn.index(), var.index())
+        }
+    }
+
+    fn ty_infer_name(&self, _: ty::TyVid) -> Option<Symbol> {
+        None
+    }
+
+    fn const_infer_name(&self, _: ty::ConstVid<'tcx>) -> Option<Symbol> {
+        None
+    }
+
+    fn pretty_print_dyn_existential(
+        mut self,
+        predicates: &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>,
+    ) -> Result<Self::DynExistential, Self::Error> {
+        // Generate the main trait ref, including associated types.
+        let mut first = true;
+
+        if let Some(principal) = predicates.principal() {
+            self = self.wrap_binder(&principal, |principal, mut cx| {
+                define_scoped_cx!(cx);
+                p!(print_def_path(principal.def_id, &[]));
+
+                let mut resugared = false;
+
+                // Special-case `Fn(...) -> ...` and re-sugar it.
+                let fn_trait_kind = cx.tcx().fn_trait_kind_from_lang_item(principal.def_id);
+                if !cx.tcx().sess.verbose() && fn_trait_kind.is_some() {
+                    if let ty::Tuple(tys) = principal.substs.type_at(0).kind() {
+                        let mut projections = predicates.projection_bounds();
+                        if let (Some(proj), None) = (projections.next(), projections.next()) {
+                            p!(pretty_fn_sig(
+                                tys,
+                                false,
+                                proj.skip_binder().term.ty().expect("Return type was a const")
+                            ));
+                            resugared = true;
+                        }
+                    }
+                }
+
+                // HACK(eddyb) this duplicates `FmtPrinter`'s `path_generic_args`,
+                // in order to place the projections inside the `<...>`.
+                if !resugared {
+                    // Use a type that can't appear in defaults of type parameters.
+                    let dummy_cx = cx.tcx().mk_ty_infer(ty::FreshTy(0));
+                    let principal = principal.with_self_ty(cx.tcx(), dummy_cx);
+
+                    let args = cx
+                        .tcx()
+                        .generics_of(principal.def_id)
+                        .own_substs_no_defaults(cx.tcx(), principal.substs);
+
+                    // Don't print `'_` if there's no unerased regions.
+                    let print_regions = args.iter().any(|arg| match arg.unpack() {
+                        GenericArgKind::Lifetime(r) => !r.is_erased(),
+                        _ => false,
+                    });
+                    let mut args = args.iter().cloned().filter(|arg| match arg.unpack() {
+                        GenericArgKind::Lifetime(_) => print_regions,
+                        _ => true,
+                    });
+                    let mut projections = predicates.projection_bounds();
+
+                    let arg0 = args.next();
+                    let projection0 = projections.next();
+                    if arg0.is_some() || projection0.is_some() {
+                        let args = arg0.into_iter().chain(args);
+                        let projections = projection0.into_iter().chain(projections);
+
+                        p!(generic_delimiters(|mut cx| {
+                            cx = cx.comma_sep(args)?;
+                            if arg0.is_some() && projection0.is_some() {
+                                write!(cx, ", ")?;
+                            }
+                            cx.comma_sep(projections)
+                        }));
+                    }
+                }
+                Ok(cx)
+            })?;
+
+            first = false;
+        }
+
+        define_scoped_cx!(self);
+
+        // Builtin bounds.
+        // FIXME(eddyb) avoid printing twice (needed to ensure
+        // that the auto traits are sorted *and* printed via cx).
+        let mut auto_traits: Vec<_> = predicates.auto_traits().collect();
+
+        // The auto traits come ordered by `DefPathHash`. While
+        // `DefPathHash` is *stable* in the sense that it depends on
+        // neither the host nor the phase of the moon, it depends
+        // "pseudorandomly" on the compiler version and the target.
+        //
+        // To avoid causing instabilities in compiletest
+        // output, sort the auto-traits alphabetically.
+        auto_traits.sort_by_cached_key(|did| self.tcx().def_path_str(*did));
+
+        for def_id in auto_traits {
+            if !first {
+                p!(" + ");
+            }
+            first = false;
+
+            p!(print_def_path(def_id, &[]));
+        }
+
+        Ok(self)
+    }
+
+    fn pretty_fn_sig(
+        mut self,
+        inputs: &[Ty<'tcx>],
+        c_variadic: bool,
+        output: Ty<'tcx>,
+    ) -> Result<Self, Self::Error> {
+        define_scoped_cx!(self);
+
+        p!("(", comma_sep(inputs.iter().copied()));
+        if c_variadic {
+            if !inputs.is_empty() {
+                p!(", ");
+            }
+            p!("...");
+        }
+        p!(")");
+        if !output.is_unit() {
+            p!(" -> ", print(output));
+        }
+
+        Ok(self)
+    }
+
+    fn pretty_print_const(
+        mut self,
+        ct: ty::Const<'tcx>,
+        print_ty: bool,
+    ) -> Result<Self::Const, Self::Error> {
+        define_scoped_cx!(self);
+
+        if self.tcx().sess.verbose() {
+            p!(write("Const({:?}: {:?})", ct.kind(), ct.ty()));
+            return Ok(self);
+        }
+
+        macro_rules! print_underscore {
+            () => {{
+                if print_ty {
+                    self = self.typed_value(
+                        |mut this| {
+                            write!(this, "_")?;
+                            Ok(this)
+                        },
+                        |this| this.print_type(ct.ty()),
+                        ": ",
+                    )?;
+                } else {
+                    write!(self, "_")?;
+                }
+            }};
+        }
+
+        match ct.kind() {
+            ty::ConstKind::Unevaluated(ty::Unevaluated {
+                def,
+                substs,
+                promoted: Some(promoted),
+            }) => {
+                p!(print_value_path(def.did, substs));
+                p!(write("::{:?}", promoted));
+            }
+            ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs, promoted: None }) => {
+                match self.tcx().def_kind(def.did) {
+                    DefKind::Static(..) | DefKind::Const | DefKind::AssocConst => {
+                        p!(print_value_path(def.did, substs))
+                    }
+                    _ => {
+                        if def.is_local() {
+                            let span = self.tcx().def_span(def.did);
+                            if let Ok(snip) = self.tcx().sess.source_map().span_to_snippet(span) {
+                                p!(write("{}", snip))
+                            } else {
+                                print_underscore!()
+                            }
+                        } else {
+                            print_underscore!()
+                        }
+                    }
+                }
+            }
+            ty::ConstKind::Infer(infer_ct) => {
+                match infer_ct {
+                    ty::InferConst::Var(ct_vid)
+                        if let Some(name) = self.const_infer_name(ct_vid) =>
+                            p!(write("{}", name)),
+                    _ => print_underscore!(),
+                }
+            }
+            ty::ConstKind::Param(ParamConst { name, .. }) => p!(write("{}", name)),
+            ty::ConstKind::Value(value) => {
+                return self.pretty_print_const_valtree(value, ct.ty(), print_ty);
+            }
+
+            ty::ConstKind::Bound(debruijn, bound_var) => {
+                self.pretty_print_bound_var(debruijn, bound_var)?
+            }
+            ty::ConstKind::Placeholder(placeholder) => p!(write("Placeholder({:?})", placeholder)),
+            ty::ConstKind::Error(_) => p!("[const error]"),
+        };
+        Ok(self)
+    }
+
+    fn pretty_print_const_scalar(
+        self,
+        scalar: Scalar,
+        ty: Ty<'tcx>,
+        print_ty: bool,
+    ) -> Result<Self::Const, Self::Error> {
+        match scalar {
+            Scalar::Ptr(ptr, _size) => self.pretty_print_const_scalar_ptr(ptr, ty, print_ty),
+            Scalar::Int(int) => self.pretty_print_const_scalar_int(int, ty, print_ty),
+        }
+    }
+
+    fn pretty_print_const_scalar_ptr(
+        mut self,
+        ptr: Pointer,
+        ty: Ty<'tcx>,
+        print_ty: bool,
+    ) -> Result<Self::Const, Self::Error> {
+        define_scoped_cx!(self);
+
+        let (alloc_id, offset) = ptr.into_parts();
+        match ty.kind() {
+            // Byte strings (&[u8; N])
+            ty::Ref(_, inner, _) => {
+                if let ty::Array(elem, len) = inner.kind() {
+                    if let ty::Uint(ty::UintTy::U8) = elem.kind() {
+                        if let ty::ConstKind::Value(ty::ValTree::Leaf(int)) = len.kind() {
+                            match self.tcx().try_get_global_alloc(alloc_id) {
+                                Some(GlobalAlloc::Memory(alloc)) => {
+                                    let len = int.assert_bits(self.tcx().data_layout.pointer_size);
+                                    let range =
+                                        AllocRange { start: offset, size: Size::from_bytes(len) };
+                                    if let Ok(byte_str) =
+                                        alloc.inner().get_bytes(&self.tcx(), range)
+                                    {
+                                        p!(pretty_print_byte_str(byte_str))
+                                    } else {
+                                        p!("<too short allocation>")
+                                    }
+                                }
+                                // FIXME: for statics, vtables, and functions, we could in principle print more detail.
+                                Some(GlobalAlloc::Static(def_id)) => {
+                                    p!(write("<static({:?})>", def_id))
+                                }
+                                Some(GlobalAlloc::Function(_)) => p!("<function>"),
+                                Some(GlobalAlloc::VTable(..)) => p!("<vtable>"),
+                                None => p!("<dangling pointer>"),
+                            }
+                            return Ok(self);
+                        }
+                    }
+                }
+            }
+            ty::FnPtr(_) => {
+                // FIXME: We should probably have a helper method to share code with the "Byte strings"
+                // printing above (which also has to handle pointers to all sorts of things).
+                if let Some(GlobalAlloc::Function(instance)) =
+                    self.tcx().try_get_global_alloc(alloc_id)
+                {
+                    self = self.typed_value(
+                        |this| this.print_value_path(instance.def_id(), instance.substs),
+                        |this| this.print_type(ty),
+                        " as ",
+                    )?;
+                    return Ok(self);
+                }
+            }
+            _ => {}
+        }
+        // Any pointer values not covered by a branch above
+        self = self.pretty_print_const_pointer(ptr, ty, print_ty)?;
+        Ok(self)
+    }
+
+    fn pretty_print_const_scalar_int(
+        mut self,
+        int: ScalarInt,
+        ty: Ty<'tcx>,
+        print_ty: bool,
+    ) -> Result<Self::Const, Self::Error> {
+        define_scoped_cx!(self);
+
+        match ty.kind() {
+            // Bool
+            ty::Bool if int == ScalarInt::FALSE => p!("false"),
+            ty::Bool if int == ScalarInt::TRUE => p!("true"),
+            // Float
+            ty::Float(ty::FloatTy::F32) => {
+                p!(write("{}f32", Single::try_from(int).unwrap()))
+            }
+            ty::Float(ty::FloatTy::F64) => {
+                p!(write("{}f64", Double::try_from(int).unwrap()))
+            }
+            // Int
+            ty::Uint(_) | ty::Int(_) => {
+                let int =
+                    ConstInt::new(int, matches!(ty.kind(), ty::Int(_)), ty.is_ptr_sized_integral());
+                if print_ty { p!(write("{:#?}", int)) } else { p!(write("{:?}", int)) }
+            }
+            // Char
+            ty::Char if char::try_from(int).is_ok() => {
+                p!(write("{:?}", char::try_from(int).unwrap()))
+            }
+            // Pointer types
+            ty::Ref(..) | ty::RawPtr(_) | ty::FnPtr(_) => {
+                let data = int.assert_bits(self.tcx().data_layout.pointer_size);
+                self = self.typed_value(
+                    |mut this| {
+                        write!(this, "0x{:x}", data)?;
+                        Ok(this)
+                    },
+                    |this| this.print_type(ty),
+                    " as ",
+                )?;
+            }
+            // Nontrivial types with scalar bit representation
+            _ => {
+                let print = |mut this: Self| {
+                    if int.size() == Size::ZERO {
+                        write!(this, "transmute(())")?;
+                    } else {
+                        write!(this, "transmute(0x{:x})", int)?;
+                    }
+                    Ok(this)
+                };
+                self = if print_ty {
+                    self.typed_value(print, |this| this.print_type(ty), ": ")?
+                } else {
+                    print(self)?
+                };
+            }
+        }
+        Ok(self)
+    }
+
+    /// This is overridden for MIR printing because we only want to hide alloc ids from users, not
+    /// from MIR where it is actually useful.
+    fn pretty_print_const_pointer<Prov: Provenance>(
+        mut self,
+        _: Pointer<Prov>,
+        ty: Ty<'tcx>,
+        print_ty: bool,
+    ) -> Result<Self::Const, Self::Error> {
+        if print_ty {
+            self.typed_value(
+                |mut this| {
+                    this.write_str("&_")?;
+                    Ok(this)
+                },
+                |this| this.print_type(ty),
+                ": ",
+            )
+        } else {
+            self.write_str("&_")?;
+            Ok(self)
+        }
+    }
+
+    fn pretty_print_byte_str(mut self, byte_str: &'tcx [u8]) -> Result<Self::Const, Self::Error> {
+        define_scoped_cx!(self);
+        p!("b\"");
+        for &c in byte_str {
+            for e in std::ascii::escape_default(c) {
+                self.write_char(e as char)?;
+            }
+        }
+        p!("\"");
+        Ok(self)
+    }
+
+    fn pretty_print_const_valtree(
+        mut self,
+        valtree: ty::ValTree<'tcx>,
+        ty: Ty<'tcx>,
+        print_ty: bool,
+    ) -> Result<Self::Const, Self::Error> {
+        define_scoped_cx!(self);
+
+        if self.tcx().sess.verbose() {
+            p!(write("ValTree({:?}: ", valtree), print(ty), ")");
+            return Ok(self);
+        }
+
+        let u8_type = self.tcx().types.u8;
+        match (valtree, ty.kind()) {
+            (ty::ValTree::Branch(_), ty::Ref(_, inner_ty, _)) => match inner_ty.kind() {
+                ty::Slice(t) if *t == u8_type => {
+                    let bytes = valtree.try_to_raw_bytes(self.tcx(), ty).unwrap_or_else(|| {
+                        bug!(
+                            "expected to convert valtree {:?} to raw bytes for type {:?}",
+                            valtree,
+                            t
+                        )
+                    });
+                    return self.pretty_print_byte_str(bytes);
+                }
+                ty::Str => {
+                    let bytes = valtree.try_to_raw_bytes(self.tcx(), ty).unwrap_or_else(|| {
+                        bug!("expected to convert valtree to raw bytes for type {:?}", ty)
+                    });
+                    p!(write("{:?}", String::from_utf8_lossy(bytes)));
+                    return Ok(self);
+                }
+                _ => {
+                    p!("&");
+                    p!(pretty_print_const_valtree(valtree, *inner_ty, print_ty));
+                    return Ok(self);
+                }
+            },
+            (ty::ValTree::Branch(_), ty::Array(t, _)) if *t == u8_type => {
+                let bytes = valtree.try_to_raw_bytes(self.tcx(), ty).unwrap_or_else(|| {
+                    bug!("expected to convert valtree to raw bytes for type {:?}", t)
+                });
+                p!("*");
+                p!(pretty_print_byte_str(bytes));
+                return Ok(self);
+            }
+            // Aggregates, printed as array/tuple/struct/variant construction syntax.
+            (ty::ValTree::Branch(_), ty::Array(..) | ty::Tuple(..) | ty::Adt(..)) => {
+                let contents =
+                    self.tcx().destructure_const(ty::Const::from_value(self.tcx(), valtree, ty));
+                let fields = contents.fields.iter().copied();
+                match *ty.kind() {
+                    ty::Array(..) => {
+                        p!("[", comma_sep(fields), "]");
+                    }
+                    ty::Tuple(..) => {
+                        p!("(", comma_sep(fields));
+                        if contents.fields.len() == 1 {
+                            p!(",");
+                        }
+                        p!(")");
+                    }
+                    ty::Adt(def, _) if def.variants().is_empty() => {
+                        self = self.typed_value(
+                            |mut this| {
+                                write!(this, "unreachable()")?;
+                                Ok(this)
+                            },
+                            |this| this.print_type(ty),
+                            ": ",
+                        )?;
+                    }
+                    ty::Adt(def, substs) => {
+                        let variant_idx =
+                            contents.variant.expect("destructed const of adt without variant idx");
+                        let variant_def = &def.variant(variant_idx);
+                        p!(print_value_path(variant_def.def_id, substs));
+                        match variant_def.ctor_kind {
+                            CtorKind::Const => {}
+                            CtorKind::Fn => {
+                                p!("(", comma_sep(fields), ")");
+                            }
+                            CtorKind::Fictive => {
+                                p!(" {{ ");
+                                let mut first = true;
+                                for (field_def, field) in iter::zip(&variant_def.fields, fields) {
+                                    if !first {
+                                        p!(", ");
+                                    }
+                                    p!(write("{}: ", field_def.name), print(field));
+                                    first = false;
+                                }
+                                p!(" }}");
+                            }
+                        }
+                    }
+                    _ => unreachable!(),
+                }
+                return Ok(self);
+            }
+            (ty::ValTree::Leaf(leaf), _) => {
+                return self.pretty_print_const_scalar_int(leaf, ty, print_ty);
+            }
+            // FIXME(oli-obk): also pretty print arrays and other aggregate constants by reading
+            // their fields instead of just dumping the memory.
+            _ => {}
+        }
+
+        // fallback
+        if valtree == ty::ValTree::zst() {
+            p!(write("<ZST>"));
+        } else {
+            p!(write("{:?}", valtree));
+        }
+        if print_ty {
+            p!(": ", print(ty));
+        }
+        Ok(self)
+    }
+}
+
+// HACK(eddyb) boxed to avoid moving around a large struct by-value.
+pub struct FmtPrinter<'a, 'tcx>(Box<FmtPrinterData<'a, 'tcx>>);
+
+pub struct FmtPrinterData<'a, 'tcx> {
+    tcx: TyCtxt<'tcx>,
+    fmt: String,
+
+    empty_path: bool,
+    in_value: bool,
+    pub print_alloc_ids: bool,
+
+    used_region_names: FxHashSet<Symbol>,
+    region_index: usize,
+    binder_depth: usize,
+    printed_type_count: usize,
+
+    pub region_highlight_mode: RegionHighlightMode<'tcx>,
+
+    pub ty_infer_name_resolver: Option<Box<dyn Fn(ty::TyVid) -> Option<Symbol> + 'a>>,
+    pub const_infer_name_resolver: Option<Box<dyn Fn(ty::ConstVid<'tcx>) -> Option<Symbol> + 'a>>,
+}
+
+impl<'a, 'tcx> Deref for FmtPrinter<'a, 'tcx> {
+    type Target = FmtPrinterData<'a, 'tcx>;
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl DerefMut for FmtPrinter<'_, '_> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
+impl<'a, 'tcx> FmtPrinter<'a, 'tcx> {
+    pub fn new(tcx: TyCtxt<'tcx>, ns: Namespace) -> Self {
+        FmtPrinter(Box::new(FmtPrinterData {
+            tcx,
+            // Estimated reasonable capacity to allocate upfront based on a few
+            // benchmarks.
+            fmt: String::with_capacity(64),
+            empty_path: false,
+            in_value: ns == Namespace::ValueNS,
+            print_alloc_ids: false,
+            used_region_names: Default::default(),
+            region_index: 0,
+            binder_depth: 0,
+            printed_type_count: 0,
+            region_highlight_mode: RegionHighlightMode::new(tcx),
+            ty_infer_name_resolver: None,
+            const_infer_name_resolver: None,
+        }))
+    }
+
+    pub fn into_buffer(self) -> String {
+        self.0.fmt
+    }
+}
+
+// HACK(eddyb) get rid of `def_path_str` and/or pass `Namespace` explicitly always
+// (but also some things just print a `DefId` generally so maybe we need this?)
+fn guess_def_namespace(tcx: TyCtxt<'_>, def_id: DefId) -> Namespace {
+    match tcx.def_key(def_id).disambiguated_data.data {
+        DefPathData::TypeNs(..) | DefPathData::CrateRoot | DefPathData::ImplTrait => {
+            Namespace::TypeNS
+        }
+
+        DefPathData::ValueNs(..)
+        | DefPathData::AnonConst
+        | DefPathData::ClosureExpr
+        | DefPathData::Ctor => Namespace::ValueNS,
+
+        DefPathData::MacroNs(..) => Namespace::MacroNS,
+
+        _ => Namespace::TypeNS,
+    }
+}
+
+impl<'t> TyCtxt<'t> {
+    /// Returns a string identifying this `DefId`. This string is
+    /// suitable for user output.
+    pub fn def_path_str(self, def_id: DefId) -> String {
+        self.def_path_str_with_substs(def_id, &[])
+    }
+
+    pub fn def_path_str_with_substs(self, def_id: DefId, substs: &'t [GenericArg<'t>]) -> String {
+        let ns = guess_def_namespace(self, def_id);
+        debug!("def_path_str: def_id={:?}, ns={:?}", def_id, ns);
+        FmtPrinter::new(self, ns).print_def_path(def_id, substs).unwrap().into_buffer()
+    }
+}
+
+impl fmt::Write for FmtPrinter<'_, '_> {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        self.fmt.push_str(s);
+        Ok(())
+    }
+}
+
+impl<'tcx> Printer<'tcx> for FmtPrinter<'_, 'tcx> {
+    type Error = fmt::Error;
+
+    type Path = Self;
+    type Region = Self;
+    type Type = Self;
+    type DynExistential = Self;
+    type Const = Self;
+
+    fn tcx<'a>(&'a self) -> TyCtxt<'tcx> {
+        self.tcx
+    }
+
+    fn print_def_path(
+        mut self,
+        def_id: DefId,
+        substs: &'tcx [GenericArg<'tcx>],
+    ) -> Result<Self::Path, Self::Error> {
+        define_scoped_cx!(self);
+
+        if substs.is_empty() {
+            match self.try_print_trimmed_def_path(def_id)? {
+                (cx, true) => return Ok(cx),
+                (cx, false) => self = cx,
+            }
+
+            match self.try_print_visible_def_path(def_id)? {
+                (cx, true) => return Ok(cx),
+                (cx, false) => self = cx,
+            }
+        }
+
+        let key = self.tcx.def_key(def_id);
+        if let DefPathData::Impl = key.disambiguated_data.data {
+            // Always use types for non-local impls, where types are always
+            // available, and filename/line-number is mostly uninteresting.
+            let use_types = !def_id.is_local() || {
+                // Otherwise, use filename/line-number if forced.
+                let force_no_types = FORCE_IMPL_FILENAME_LINE.with(|f| f.get());
+                !force_no_types
+            };
+
+            if !use_types {
+                // If no type info is available, fall back to
+                // pretty printing some span information. This should
+                // only occur very early in the compiler pipeline.
+                let parent_def_id = DefId { index: key.parent.unwrap(), ..def_id };
+                let span = self.tcx.def_span(def_id);
+
+                self = self.print_def_path(parent_def_id, &[])?;
+
+                // HACK(eddyb) copy of `path_append` to avoid
+                // constructing a `DisambiguatedDefPathData`.
+                if !self.empty_path {
+                    write!(self, "::")?;
+                }
+                write!(
+                    self,
+                    "<impl at {}>",
+                    // This may end up in stderr diagnostics but it may also be emitted
+                    // into MIR. Hence we use the remapped path if available
+                    self.tcx.sess.source_map().span_to_embeddable_string(span)
+                )?;
+                self.empty_path = false;
+
+                return Ok(self);
+            }
+        }
+
+        self.default_print_def_path(def_id, substs)
+    }
+
+    fn print_region(self, region: ty::Region<'tcx>) -> Result<Self::Region, Self::Error> {
+        self.pretty_print_region(region)
+    }
+
+    fn print_type(mut self, ty: Ty<'tcx>) -> Result<Self::Type, Self::Error> {
+        let type_length_limit = self.tcx.type_length_limit();
+        if type_length_limit.value_within_limit(self.printed_type_count) {
+            self.printed_type_count += 1;
+            self.pretty_print_type(ty)
+        } else {
+            write!(self, "...")?;
+            Ok(self)
+        }
+    }
+
+    fn print_dyn_existential(
+        self,
+        predicates: &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>,
+    ) -> Result<Self::DynExistential, Self::Error> {
+        self.pretty_print_dyn_existential(predicates)
+    }
+
+    fn print_const(self, ct: ty::Const<'tcx>) -> Result<Self::Const, Self::Error> {
+        self.pretty_print_const(ct, false)
+    }
+
+    fn path_crate(mut self, cnum: CrateNum) -> Result<Self::Path, Self::Error> {
+        self.empty_path = true;
+        if cnum == LOCAL_CRATE {
+            if self.tcx.sess.rust_2018() {
+                // We add the `crate::` keyword on Rust 2018, only when desired.
+                if SHOULD_PREFIX_WITH_CRATE.with(|flag| flag.get()) {
+                    write!(self, "{}", kw::Crate)?;
+                    self.empty_path = false;
+                }
+            }
+        } else {
+            write!(self, "{}", self.tcx.crate_name(cnum))?;
+            self.empty_path = false;
+        }
+        Ok(self)
+    }
+
+    fn path_qualified(
+        mut self,
+        self_ty: Ty<'tcx>,
+        trait_ref: Option<ty::TraitRef<'tcx>>,
+    ) -> Result<Self::Path, Self::Error> {
+        self = self.pretty_path_qualified(self_ty, trait_ref)?;
+        self.empty_path = false;
+        Ok(self)
+    }
+
+    fn path_append_impl(
+        mut 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> {
+        self = self.pretty_path_append_impl(
+            |mut cx| {
+                cx = print_prefix(cx)?;
+                if !cx.empty_path {
+                    write!(cx, "::")?;
+                }
+
+                Ok(cx)
+            },
+            self_ty,
+            trait_ref,
+        )?;
+        self.empty_path = false;
+        Ok(self)
+    }
+
+    fn path_append(
+        mut self,
+        print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
+        disambiguated_data: &DisambiguatedDefPathData,
+    ) -> Result<Self::Path, Self::Error> {
+        self = print_prefix(self)?;
+
+        // Skip `::{{extern}}` blocks and `::{{constructor}}` on tuple/unit structs.
+        if let DefPathData::ForeignMod | DefPathData::Ctor = disambiguated_data.data {
+            return Ok(self);
+        }
+
+        let name = disambiguated_data.data.name();
+        if !self.empty_path {
+            write!(self, "::")?;
+        }
+
+        if let DefPathDataName::Named(name) = name {
+            if Ident::with_dummy_span(name).is_raw_guess() {
+                write!(self, "r#")?;
+            }
+        }
+
+        let verbose = self.tcx.sess.verbose();
+        disambiguated_data.fmt_maybe_verbose(&mut self, verbose)?;
+
+        self.empty_path = false;
+
+        Ok(self)
+    }
+
+    fn path_generic_args(
+        mut self,
+        print_prefix: impl FnOnce(Self) -> Result<Self::Path, Self::Error>,
+        args: &[GenericArg<'tcx>],
+    ) -> Result<Self::Path, Self::Error> {
+        self = print_prefix(self)?;
+
+        // Don't print `'_` if there's no unerased regions.
+        let print_regions = self.tcx.sess.verbose()
+            || args.iter().any(|arg| match arg.unpack() {
+                GenericArgKind::Lifetime(r) => !r.is_erased(),
+                _ => false,
+            });
+        let args = args.iter().cloned().filter(|arg| match arg.unpack() {
+            GenericArgKind::Lifetime(_) => print_regions,
+            _ => true,
+        });
+
+        if args.clone().next().is_some() {
+            if self.in_value {
+                write!(self, "::")?;
+            }
+            self.generic_delimiters(|cx| cx.comma_sep(args))
+        } else {
+            Ok(self)
+        }
+    }
+}
+
+impl<'tcx> PrettyPrinter<'tcx> for FmtPrinter<'_, 'tcx> {
+    fn ty_infer_name(&self, id: ty::TyVid) -> Option<Symbol> {
+        self.0.ty_infer_name_resolver.as_ref().and_then(|func| func(id))
+    }
+
+    fn const_infer_name(&self, id: ty::ConstVid<'tcx>) -> Option<Symbol> {
+        self.0.const_infer_name_resolver.as_ref().and_then(|func| func(id))
+    }
+
+    fn print_value_path(
+        mut self,
+        def_id: DefId,
+        substs: &'tcx [GenericArg<'tcx>],
+    ) -> Result<Self::Path, Self::Error> {
+        let was_in_value = std::mem::replace(&mut self.in_value, true);
+        self = self.print_def_path(def_id, substs)?;
+        self.in_value = was_in_value;
+
+        Ok(self)
+    }
+
+    fn in_binder<T>(self, value: &ty::Binder<'tcx, T>) -> Result<Self, Self::Error>
+    where
+        T: Print<'tcx, Self, Output = Self, Error = Self::Error> + TypeFoldable<'tcx>,
+    {
+        self.pretty_in_binder(value)
+    }
+
+    fn wrap_binder<T, C: FnOnce(&T, Self) -> Result<Self, Self::Error>>(
+        self,
+        value: &ty::Binder<'tcx, T>,
+        f: C,
+    ) -> Result<Self, Self::Error>
+    where
+        T: Print<'tcx, Self, Output = Self, Error = Self::Error> + TypeFoldable<'tcx>,
+    {
+        self.pretty_wrap_binder(value, f)
+    }
+
+    fn typed_value(
+        mut self,
+        f: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        t: impl FnOnce(Self) -> Result<Self, Self::Error>,
+        conversion: &str,
+    ) -> Result<Self::Const, Self::Error> {
+        self.write_str("{")?;
+        self = f(self)?;
+        self.write_str(conversion)?;
+        let was_in_value = std::mem::replace(&mut self.in_value, false);
+        self = t(self)?;
+        self.in_value = was_in_value;
+        self.write_str("}")?;
+        Ok(self)
+    }
+
+    fn generic_delimiters(
+        mut self,
+        f: impl FnOnce(Self) -> Result<Self, Self::Error>,
+    ) -> Result<Self, Self::Error> {
+        write!(self, "<")?;
+
+        let was_in_value = std::mem::replace(&mut self.in_value, false);
+        let mut inner = f(self)?;
+        inner.in_value = was_in_value;
+
+        write!(inner, ">")?;
+        Ok(inner)
+    }
+
+    fn should_print_region(&self, region: ty::Region<'tcx>) -> bool {
+        let highlight = self.region_highlight_mode;
+        if highlight.region_highlighted(region).is_some() {
+            return true;
+        }
+
+        if self.tcx.sess.verbose() {
+            return true;
+        }
+
+        let identify_regions = self.tcx.sess.opts.unstable_opts.identify_regions;
+
+        match *region {
+            ty::ReEarlyBound(ref data) => {
+                data.name != kw::Empty && data.name != kw::UnderscoreLifetime
+            }
+
+            ty::ReLateBound(_, ty::BoundRegion { kind: br, .. })
+            | ty::ReFree(ty::FreeRegion { bound_region: br, .. })
+            | ty::RePlaceholder(ty::Placeholder { name: br, .. }) => {
+                if let ty::BrNamed(_, name) = br {
+                    if name != kw::Empty && name != kw::UnderscoreLifetime {
+                        return true;
+                    }
+                }
+
+                if let Some((region, _)) = highlight.highlight_bound_region {
+                    if br == region {
+                        return true;
+                    }
+                }
+
+                false
+            }
+
+            ty::ReVar(_) if identify_regions => true,
+
+            ty::ReVar(_) | ty::ReErased => false,
+
+            ty::ReStatic | ty::ReEmpty(_) => true,
+        }
+    }
+
+    fn pretty_print_const_pointer<Prov: Provenance>(
+        self,
+        p: Pointer<Prov>,
+        ty: Ty<'tcx>,
+        print_ty: bool,
+    ) -> Result<Self::Const, Self::Error> {
+        let print = |mut this: Self| {
+            define_scoped_cx!(this);
+            if this.print_alloc_ids {
+                p!(write("{:?}", p));
+            } else {
+                p!("&_");
+            }
+            Ok(this)
+        };
+        if print_ty {
+            self.typed_value(print, |this| this.print_type(ty), ": ")
+        } else {
+            print(self)
+        }
+    }
+}
+
+// HACK(eddyb) limited to `FmtPrinter` because of `region_highlight_mode`.
+impl<'tcx> FmtPrinter<'_, 'tcx> {
+    pub fn pretty_print_region(mut self, region: ty::Region<'tcx>) -> Result<Self, fmt::Error> {
+        define_scoped_cx!(self);
+
+        // Watch out for region highlights.
+        let highlight = self.region_highlight_mode;
+        if let Some(n) = highlight.region_highlighted(region) {
+            p!(write("'{}", n));
+            return Ok(self);
+        }
+
+        if self.tcx.sess.verbose() {
+            p!(write("{:?}", region));
+            return Ok(self);
+        }
+
+        let identify_regions = self.tcx.sess.opts.unstable_opts.identify_regions;
+
+        // These printouts are concise.  They do not contain all the information
+        // the user might want to diagnose an error, but there is basically no way
+        // to fit that into a short string.  Hence the recommendation to use
+        // `explain_region()` or `note_and_explain_region()`.
+        match *region {
+            ty::ReEarlyBound(ref data) => {
+                if data.name != kw::Empty {
+                    p!(write("{}", data.name));
+                    return Ok(self);
+                }
+            }
+            ty::ReLateBound(_, ty::BoundRegion { kind: br, .. })
+            | ty::ReFree(ty::FreeRegion { bound_region: br, .. })
+            | ty::RePlaceholder(ty::Placeholder { name: br, .. }) => {
+                if let ty::BrNamed(_, name) = br {
+                    if name != kw::Empty && name != kw::UnderscoreLifetime {
+                        p!(write("{}", name));
+                        return Ok(self);
+                    }
+                }
+
+                if let Some((region, counter)) = highlight.highlight_bound_region {
+                    if br == region {
+                        p!(write("'{}", counter));
+                        return Ok(self);
+                    }
+                }
+            }
+            ty::ReVar(region_vid) if identify_regions => {
+                p!(write("{:?}", region_vid));
+                return Ok(self);
+            }
+            ty::ReVar(_) => {}
+            ty::ReErased => {}
+            ty::ReStatic => {
+                p!("'static");
+                return Ok(self);
+            }
+            ty::ReEmpty(ty::UniverseIndex::ROOT) => {
+                p!("'<empty>");
+                return Ok(self);
+            }
+            ty::ReEmpty(ui) => {
+                p!(write("'<empty:{:?}>", ui));
+                return Ok(self);
+            }
+        }
+
+        p!("'_");
+
+        Ok(self)
+    }
+}
+
+/// Folds through bound vars and placeholders, naming them
+struct RegionFolder<'a, 'tcx> {
+    tcx: TyCtxt<'tcx>,
+    current_index: ty::DebruijnIndex,
+    region_map: BTreeMap<ty::BoundRegion, ty::Region<'tcx>>,
+    name: &'a mut (dyn FnMut(ty::BoundRegion) -> ty::Region<'tcx> + 'a),
+}
+
+impl<'a, 'tcx> ty::TypeFolder<'tcx> for RegionFolder<'a, 'tcx> {
+    fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
+        self.tcx
+    }
+
+    fn fold_binder<T: TypeFoldable<'tcx>>(
+        &mut self,
+        t: ty::Binder<'tcx, T>,
+    ) -> ty::Binder<'tcx, T> {
+        self.current_index.shift_in(1);
+        let t = t.super_fold_with(self);
+        self.current_index.shift_out(1);
+        t
+    }
+
+    fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
+        match *t.kind() {
+            _ if t.has_vars_bound_at_or_above(self.current_index) || t.has_placeholders() => {
+                return t.super_fold_with(self);
+            }
+            _ => {}
+        }
+        t
+    }
+
+    fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
+        let name = &mut self.name;
+        let region = match *r {
+            ty::ReLateBound(_, br) => *self.region_map.entry(br).or_insert_with(|| name(br)),
+            ty::RePlaceholder(ty::PlaceholderRegion { name: kind, .. }) => {
+                // If this is an anonymous placeholder, don't rename. Otherwise, in some
+                // async fns, we get a `for<'r> Send` bound
+                match kind {
+                    ty::BrAnon(_) | ty::BrEnv => r,
+                    _ => {
+                        // Index doesn't matter, since this is just for naming and these never get bound
+                        let br = ty::BoundRegion { var: ty::BoundVar::from_u32(0), kind };
+                        *self.region_map.entry(br).or_insert_with(|| name(br))
+                    }
+                }
+            }
+            _ => return r,
+        };
+        if let ty::ReLateBound(debruijn1, br) = *region {
+            assert_eq!(debruijn1, ty::INNERMOST);
+            self.tcx.mk_region(ty::ReLateBound(self.current_index, br))
+        } else {
+            region
+        }
+    }
+}
+
+// HACK(eddyb) limited to `FmtPrinter` because of `binder_depth`,
+// `region_index` and `used_region_names`.
+impl<'tcx> FmtPrinter<'_, 'tcx> {
+    pub fn name_all_regions<T>(
+        mut self,
+        value: &ty::Binder<'tcx, T>,
+    ) -> Result<(Self, T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>), fmt::Error>
+    where
+        T: Print<'tcx, Self, Output = Self, Error = fmt::Error> + TypeFoldable<'tcx>,
+    {
+        fn name_by_region_index(index: usize) -> Symbol {
+            match index {
+                0 => Symbol::intern("'r"),
+                1 => Symbol::intern("'s"),
+                i => Symbol::intern(&format!("'t{}", i - 2)),
+            }
+        }
+
+        // Replace any anonymous late-bound regions with named
+        // variants, using new unique identifiers, so that we can
+        // clearly differentiate between named and unnamed regions in
+        // the output. We'll probably want to tweak this over time to
+        // decide just how much information to give.
+        if self.binder_depth == 0 {
+            self.prepare_late_bound_region_info(value);
+        }
+
+        let mut empty = true;
+        let mut start_or_continue = |cx: &mut Self, start: &str, cont: &str| {
+            let w = if empty {
+                empty = false;
+                start
+            } else {
+                cont
+            };
+            let _ = write!(cx, "{}", w);
+        };
+        let do_continue = |cx: &mut Self, cont: Symbol| {
+            let _ = write!(cx, "{}", cont);
+        };
+
+        define_scoped_cx!(self);
+
+        let mut region_index = self.region_index;
+        let mut next_name = |this: &Self| loop {
+            let name = name_by_region_index(region_index);
+            region_index += 1;
+            if !this.used_region_names.contains(&name) {
+                break name;
+            }
+        };
+
+        // If we want to print verbosely, then print *all* binders, even if they
+        // aren't named. Eventually, we might just want this as the default, but
+        // this is not *quite* right and changes the ordering of some output
+        // anyways.
+        let (new_value, map) = if self.tcx().sess.verbose() {
+            let regions: Vec<_> = value
+                .bound_vars()
+                .into_iter()
+                .map(|var| {
+                    let ty::BoundVariableKind::Region(var) = var else {
+                    // This doesn't really matter because it doesn't get used,
+                    // it's just an empty value
+                    return ty::BrAnon(0);
+                };
+                    match var {
+                        ty::BrAnon(_) | ty::BrEnv => {
+                            start_or_continue(&mut self, "for<", ", ");
+                            let name = next_name(&self);
+                            do_continue(&mut self, name);
+                            ty::BrNamed(CRATE_DEF_ID.to_def_id(), name)
+                        }
+                        ty::BrNamed(def_id, kw::UnderscoreLifetime) => {
+                            start_or_continue(&mut self, "for<", ", ");
+                            let name = next_name(&self);
+                            do_continue(&mut self, name);
+                            ty::BrNamed(def_id, name)
+                        }
+                        ty::BrNamed(def_id, name) => {
+                            start_or_continue(&mut self, "for<", ", ");
+                            do_continue(&mut self, name);
+                            ty::BrNamed(def_id, name)
+                        }
+                    }
+                })
+                .collect();
+            start_or_continue(&mut self, "", "> ");
+
+            self.tcx.replace_late_bound_regions(value.clone(), |br| {
+                let kind = regions[br.var.as_usize()];
+                self.tcx.mk_region(ty::ReLateBound(
+                    ty::INNERMOST,
+                    ty::BoundRegion { var: br.var, kind },
+                ))
+            })
+        } else {
+            let tcx = self.tcx;
+            let mut name = |br: ty::BoundRegion| {
+                start_or_continue(&mut self, "for<", ", ");
+                let kind = match br.kind {
+                    ty::BrAnon(_) | ty::BrEnv => {
+                        let name = next_name(&self);
+                        do_continue(&mut self, name);
+                        ty::BrNamed(CRATE_DEF_ID.to_def_id(), name)
+                    }
+                    ty::BrNamed(def_id, kw::UnderscoreLifetime) => {
+                        let name = next_name(&self);
+                        do_continue(&mut self, name);
+                        ty::BrNamed(def_id, name)
+                    }
+                    ty::BrNamed(_, name) => {
+                        do_continue(&mut self, name);
+                        br.kind
+                    }
+                };
+                tcx.mk_region(ty::ReLateBound(ty::INNERMOST, ty::BoundRegion { var: br.var, kind }))
+            };
+            let mut folder = RegionFolder {
+                tcx,
+                current_index: ty::INNERMOST,
+                name: &mut name,
+                region_map: BTreeMap::new(),
+            };
+            let new_value = value.clone().skip_binder().fold_with(&mut folder);
+            let region_map = folder.region_map;
+            start_or_continue(&mut self, "", "> ");
+            (new_value, region_map)
+        };
+
+        self.binder_depth += 1;
+        self.region_index = region_index;
+        Ok((self, new_value, map))
+    }
+
+    pub fn pretty_in_binder<T>(self, value: &ty::Binder<'tcx, T>) -> Result<Self, fmt::Error>
+    where
+        T: Print<'tcx, Self, Output = Self, Error = fmt::Error> + TypeFoldable<'tcx>,
+    {
+        let old_region_index = self.region_index;
+        let (new, new_value, _) = self.name_all_regions(value)?;
+        let mut inner = new_value.print(new)?;
+        inner.region_index = old_region_index;
+        inner.binder_depth -= 1;
+        Ok(inner)
+    }
+
+    pub fn pretty_wrap_binder<T, C: FnOnce(&T, Self) -> Result<Self, fmt::Error>>(
+        self,
+        value: &ty::Binder<'tcx, T>,
+        f: C,
+    ) -> Result<Self, fmt::Error>
+    where
+        T: Print<'tcx, Self, Output = Self, Error = fmt::Error> + TypeFoldable<'tcx>,
+    {
+        let old_region_index = self.region_index;
+        let (new, new_value, _) = self.name_all_regions(value)?;
+        let mut inner = f(&new_value, new)?;
+        inner.region_index = old_region_index;
+        inner.binder_depth -= 1;
+        Ok(inner)
+    }
+
+    fn prepare_late_bound_region_info<T>(&mut self, value: &ty::Binder<'tcx, T>)
+    where
+        T: TypeVisitable<'tcx>,
+    {
+        struct LateBoundRegionNameCollector<'a, 'tcx> {
+            used_region_names: &'a mut FxHashSet<Symbol>,
+            type_collector: SsoHashSet<Ty<'tcx>>,
+        }
+
+        impl<'tcx> ty::visit::TypeVisitor<'tcx> for LateBoundRegionNameCollector<'_, 'tcx> {
+            type BreakTy = ();
+
+            fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
+                trace!("address: {:p}", r.0.0);
+                if let ty::ReLateBound(_, ty::BoundRegion { kind: ty::BrNamed(_, name), .. }) = *r {
+                    self.used_region_names.insert(name);
+                } else if let ty::RePlaceholder(ty::PlaceholderRegion {
+                    name: ty::BrNamed(_, name),
+                    ..
+                }) = *r
+                {
+                    self.used_region_names.insert(name);
+                }
+                r.super_visit_with(self)
+            }
+
+            // We collect types in order to prevent really large types from compiling for
+            // a really long time. See issue #83150 for why this is necessary.
+            fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
+                let not_previously_inserted = self.type_collector.insert(ty);
+                if not_previously_inserted {
+                    ty.super_visit_with(self)
+                } else {
+                    ControlFlow::CONTINUE
+                }
+            }
+        }
+
+        self.used_region_names.clear();
+        let mut collector = LateBoundRegionNameCollector {
+            used_region_names: &mut self.used_region_names,
+            type_collector: SsoHashSet::new(),
+        };
+        value.visit_with(&mut collector);
+        self.region_index = 0;
+    }
+}
+
+impl<'tcx, T, P: PrettyPrinter<'tcx>> Print<'tcx, P> for ty::Binder<'tcx, T>
+where
+    T: Print<'tcx, P, Output = P, Error = P::Error> + TypeFoldable<'tcx>,
+{
+    type Output = P;
+    type Error = P::Error;
+
+    fn print(&self, cx: P) -> Result<Self::Output, Self::Error> {
+        cx.in_binder(self)
+    }
+}
+
+impl<'tcx, T, U, P: PrettyPrinter<'tcx>> Print<'tcx, P> for ty::OutlivesPredicate<T, U>
+where
+    T: Print<'tcx, P, Output = P, Error = P::Error>,
+    U: Print<'tcx, P, Output = P, Error = P::Error>,
+{
+    type Output = P;
+    type Error = P::Error;
+    fn print(&self, mut cx: P) -> Result<Self::Output, Self::Error> {
+        define_scoped_cx!(cx);
+        p!(print(self.0), ": ", print(self.1));
+        Ok(cx)
+    }
+}
+
+macro_rules! forward_display_to_print {
+    ($($ty:ty),+) => {
+        // Some of the $ty arguments may not actually use 'tcx
+        $(#[allow(unused_lifetimes)] impl<'tcx> fmt::Display for $ty {
+            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                ty::tls::with(|tcx| {
+                    let cx = tcx.lift(*self)
+                        .expect("could not lift for printing")
+                        .print(FmtPrinter::new(tcx, Namespace::TypeNS))?;
+                    f.write_str(&cx.into_buffer())?;
+                    Ok(())
+                })
+            }
+        })+
+    };
+}
+
+macro_rules! define_print_and_forward_display {
+    (($self:ident, $cx:ident): $($ty:ty $print:block)+) => {
+        $(impl<'tcx, P: PrettyPrinter<'tcx>> Print<'tcx, P> for $ty {
+            type Output = P;
+            type Error = fmt::Error;
+            fn print(&$self, $cx: P) -> Result<Self::Output, Self::Error> {
+                #[allow(unused_mut)]
+                let mut $cx = $cx;
+                define_scoped_cx!($cx);
+                let _: () = $print;
+                #[allow(unreachable_code)]
+                Ok($cx)
+            }
+        })+
+
+        forward_display_to_print!($($ty),+);
+    };
+}
+
+/// Wrapper type for `ty::TraitRef` which opts-in to pretty printing only
+/// the trait path. That is, it will print `Trait<U>` instead of
+/// `<T as Trait<U>>`.
+#[derive(Copy, Clone, TypeFoldable, TypeVisitable, Lift)]
+pub struct TraitRefPrintOnlyTraitPath<'tcx>(ty::TraitRef<'tcx>);
+
+impl<'tcx> fmt::Debug for TraitRefPrintOnlyTraitPath<'tcx> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(self, f)
+    }
+}
+
+/// Wrapper type for `ty::TraitRef` which opts-in to pretty printing only
+/// the trait name. That is, it will print `Trait` instead of
+/// `<T as Trait<U>>`.
+#[derive(Copy, Clone, TypeFoldable, TypeVisitable, Lift)]
+pub struct TraitRefPrintOnlyTraitName<'tcx>(ty::TraitRef<'tcx>);
+
+impl<'tcx> fmt::Debug for TraitRefPrintOnlyTraitName<'tcx> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(self, f)
+    }
+}
+
+impl<'tcx> ty::TraitRef<'tcx> {
+    pub fn print_only_trait_path(self) -> TraitRefPrintOnlyTraitPath<'tcx> {
+        TraitRefPrintOnlyTraitPath(self)
+    }
+
+    pub fn print_only_trait_name(self) -> TraitRefPrintOnlyTraitName<'tcx> {
+        TraitRefPrintOnlyTraitName(self)
+    }
+}
+
+impl<'tcx> ty::Binder<'tcx, ty::TraitRef<'tcx>> {
+    pub fn print_only_trait_path(self) -> ty::Binder<'tcx, TraitRefPrintOnlyTraitPath<'tcx>> {
+        self.map_bound(|tr| tr.print_only_trait_path())
+    }
+}
+
+#[derive(Copy, Clone, TypeFoldable, TypeVisitable, Lift)]
+pub struct TraitPredPrintModifiersAndPath<'tcx>(ty::TraitPredicate<'tcx>);
+
+impl<'tcx> fmt::Debug for TraitPredPrintModifiersAndPath<'tcx> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(self, f)
+    }
+}
+
+impl<'tcx> ty::TraitPredicate<'tcx> {
+    pub fn print_modifiers_and_trait_path(self) -> TraitPredPrintModifiersAndPath<'tcx> {
+        TraitPredPrintModifiersAndPath(self)
+    }
+}
+
+impl<'tcx> ty::PolyTraitPredicate<'tcx> {
+    pub fn print_modifiers_and_trait_path(
+        self,
+    ) -> ty::Binder<'tcx, TraitPredPrintModifiersAndPath<'tcx>> {
+        self.map_bound(TraitPredPrintModifiersAndPath)
+    }
+}
+
+forward_display_to_print! {
+    ty::Region<'tcx>,
+    Ty<'tcx>,
+    &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>,
+    ty::Const<'tcx>,
+
+    // HACK(eddyb) these are exhaustive instead of generic,
+    // because `for<'tcx>` isn't possible yet.
+    ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>,
+    ty::Binder<'tcx, ty::TraitRef<'tcx>>,
+    ty::Binder<'tcx, ty::ExistentialTraitRef<'tcx>>,
+    ty::Binder<'tcx, TraitRefPrintOnlyTraitPath<'tcx>>,
+    ty::Binder<'tcx, TraitRefPrintOnlyTraitName<'tcx>>,
+    ty::Binder<'tcx, ty::FnSig<'tcx>>,
+    ty::Binder<'tcx, ty::TraitPredicate<'tcx>>,
+    ty::Binder<'tcx, TraitPredPrintModifiersAndPath<'tcx>>,
+    ty::Binder<'tcx, ty::SubtypePredicate<'tcx>>,
+    ty::Binder<'tcx, ty::ProjectionPredicate<'tcx>>,
+    ty::Binder<'tcx, ty::OutlivesPredicate<Ty<'tcx>, ty::Region<'tcx>>>,
+    ty::Binder<'tcx, ty::OutlivesPredicate<ty::Region<'tcx>, ty::Region<'tcx>>>,
+
+    ty::OutlivesPredicate<Ty<'tcx>, ty::Region<'tcx>>,
+    ty::OutlivesPredicate<ty::Region<'tcx>, ty::Region<'tcx>>
+}
+
+define_print_and_forward_display! {
+    (self, cx):
+
+    &'tcx ty::List<Ty<'tcx>> {
+        p!("{{", comma_sep(self.iter()), "}}")
+    }
+
+    ty::TypeAndMut<'tcx> {
+        p!(write("{}", self.mutbl.prefix_str()), print(self.ty))
+    }
+
+    ty::ExistentialTraitRef<'tcx> {
+        // Use a type that can't appear in defaults of type parameters.
+        let dummy_self = cx.tcx().mk_ty_infer(ty::FreshTy(0));
+        let trait_ref = self.with_self_ty(cx.tcx(), dummy_self);
+        p!(print(trait_ref.print_only_trait_path()))
+    }
+
+    ty::ExistentialProjection<'tcx> {
+        let name = cx.tcx().associated_item(self.item_def_id).name;
+        p!(write("{} = ", name), print(self.term))
+    }
+
+    ty::ExistentialPredicate<'tcx> {
+        match *self {
+            ty::ExistentialPredicate::Trait(x) => p!(print(x)),
+            ty::ExistentialPredicate::Projection(x) => p!(print(x)),
+            ty::ExistentialPredicate::AutoTrait(def_id) => {
+                p!(print_def_path(def_id, &[]));
+            }
+        }
+    }
+
+    ty::FnSig<'tcx> {
+        p!(write("{}", self.unsafety.prefix_str()));
+
+        if self.abi != Abi::Rust {
+            p!(write("extern {} ", self.abi));
+        }
+
+        p!("fn", pretty_fn_sig(self.inputs(), self.c_variadic, self.output()));
+    }
+
+    ty::TraitRef<'tcx> {
+        p!(write("<{} as {}>", self.self_ty(), self.print_only_trait_path()))
+    }
+
+    TraitRefPrintOnlyTraitPath<'tcx> {
+        p!(print_def_path(self.0.def_id, self.0.substs));
+    }
+
+    TraitRefPrintOnlyTraitName<'tcx> {
+        p!(print_def_path(self.0.def_id, &[]));
+    }
+
+    TraitPredPrintModifiersAndPath<'tcx> {
+        if let ty::BoundConstness::ConstIfConst = self.0.constness {
+            p!("~const ")
+        }
+
+        if let ty::ImplPolarity::Negative = self.0.polarity {
+            p!("!")
+        }
+
+        p!(print(self.0.trait_ref.print_only_trait_path()));
+    }
+
+    ty::ParamTy {
+        p!(write("{}", self.name))
+    }
+
+    ty::ParamConst {
+        p!(write("{}", self.name))
+    }
+
+    ty::SubtypePredicate<'tcx> {
+        p!(print(self.a), " <: ", print(self.b))
+    }
+
+    ty::CoercePredicate<'tcx> {
+        p!(print(self.a), " -> ", print(self.b))
+    }
+
+    ty::TraitPredicate<'tcx> {
+        p!(print(self.trait_ref.self_ty()), ": ");
+        if let ty::BoundConstness::ConstIfConst = self.constness && cx.tcx().features().const_trait_impl {
+            p!("~const ");
+        }
+        p!(print(self.trait_ref.print_only_trait_path()))
+    }
+
+    ty::ProjectionPredicate<'tcx> {
+        p!(print(self.projection_ty), " == ", print(self.term))
+    }
+
+    ty::Term<'tcx> {
+      match self {
+        ty::Term::Ty(ty) => p!(print(ty)),
+        ty::Term::Const(c) => p!(print(c)),
+      }
+    }
+
+    ty::ProjectionTy<'tcx> {
+        p!(print_def_path(self.item_def_id, self.substs));
+    }
+
+    ty::ClosureKind {
+        match *self {
+            ty::ClosureKind::Fn => p!("Fn"),
+            ty::ClosureKind::FnMut => p!("FnMut"),
+            ty::ClosureKind::FnOnce => p!("FnOnce"),
+        }
+    }
+
+    ty::Predicate<'tcx> {
+        let binder = self.kind();
+        p!(print(binder))
+    }
+
+    ty::PredicateKind<'tcx> {
+        match *self {
+            ty::PredicateKind::Trait(ref data) => {
+                p!(print(data))
+            }
+            ty::PredicateKind::Subtype(predicate) => p!(print(predicate)),
+            ty::PredicateKind::Coerce(predicate) => p!(print(predicate)),
+            ty::PredicateKind::RegionOutlives(predicate) => p!(print(predicate)),
+            ty::PredicateKind::TypeOutlives(predicate) => p!(print(predicate)),
+            ty::PredicateKind::Projection(predicate) => p!(print(predicate)),
+            ty::PredicateKind::WellFormed(arg) => p!(print(arg), " well-formed"),
+            ty::PredicateKind::ObjectSafe(trait_def_id) => {
+                p!("the trait `", print_def_path(trait_def_id, &[]), "` is object-safe")
+            }
+            ty::PredicateKind::ClosureKind(closure_def_id, _closure_substs, kind) => {
+                p!("the closure `",
+                print_value_path(closure_def_id, &[]),
+                write("` implements the trait `{}`", kind))
+            }
+            ty::PredicateKind::ConstEvaluatable(uv) => {
+                p!("the constant `", print_value_path(uv.def.did, uv.substs), "` can be evaluated")
+            }
+            ty::PredicateKind::ConstEquate(c1, c2) => {
+                p!("the constant `", print(c1), "` equals `", print(c2), "`")
+            }
+            ty::PredicateKind::TypeWellFormedFromEnv(ty) => {
+                p!("the type `", print(ty), "` is found in the environment")
+            }
+        }
+    }
+
+    GenericArg<'tcx> {
+        match self.unpack() {
+            GenericArgKind::Lifetime(lt) => p!(print(lt)),
+            GenericArgKind::Type(ty) => p!(print(ty)),
+            GenericArgKind::Const(ct) => p!(print(ct)),
+        }
+    }
+}
+
+fn for_each_def(tcx: TyCtxt<'_>, mut collect_fn: impl for<'b> FnMut(&'b Ident, Namespace, DefId)) {
+    // Iterate all local crate items no matter where they are defined.
+    let hir = tcx.hir();
+    for id in hir.items() {
+        if matches!(tcx.def_kind(id.def_id), DefKind::Use) {
+            continue;
+        }
+
+        let item = hir.item(id);
+        if item.ident.name == kw::Empty {
+            continue;
+        }
+
+        let def_id = item.def_id.to_def_id();
+        let ns = tcx.def_kind(def_id).ns().unwrap_or(Namespace::TypeNS);
+        collect_fn(&item.ident, ns, def_id);
+    }
+
+    // Now take care of extern crate items.
+    let queue = &mut Vec::new();
+    let mut seen_defs: DefIdSet = Default::default();
+
+    for &cnum in tcx.crates(()).iter() {
+        let def_id = cnum.as_def_id();
+
+        // Ignore crates that are not direct dependencies.
+        match tcx.extern_crate(def_id) {
+            None => continue,
+            Some(extern_crate) => {
+                if !extern_crate.is_direct() {
+                    continue;
+                }
+            }
+        }
+
+        queue.push(def_id);
+    }
+
+    // Iterate external crate defs but be mindful about visibility
+    while let Some(def) = queue.pop() {
+        for child in tcx.module_children(def).iter() {
+            if !child.vis.is_public() {
+                continue;
+            }
+
+            match child.res {
+                def::Res::Def(DefKind::AssocTy, _) => {}
+                def::Res::Def(DefKind::TyAlias, _) => {}
+                def::Res::Def(defkind, def_id) => {
+                    if let Some(ns) = defkind.ns() {
+                        collect_fn(&child.ident, ns, def_id);
+                    }
+
+                    if matches!(defkind, DefKind::Mod | DefKind::Enum | DefKind::Trait)
+                        && seen_defs.insert(def_id)
+                    {
+                        queue.push(def_id);
+                    }
+                }
+                _ => {}
+            }
+        }
+    }
+}
+
+/// The purpose of this function is to collect public symbols names that are unique across all
+/// crates in the build. Later, when printing about types we can use those names instead of the
+/// full exported path to them.
+///
+/// So essentially, if a symbol name can only be imported from one place for a type, and as
+/// long as it was not glob-imported anywhere in the current crate, we can trim its printed
+/// path and print only the name.
+///
+/// This has wide implications on error messages with types, for example, shortening
+/// `std::vec::Vec` to just `Vec`, as long as there is no other `Vec` importable anywhere.
+///
+/// The implementation uses similar import discovery logic to that of 'use' suggestions.
+fn trimmed_def_paths(tcx: TyCtxt<'_>, (): ()) -> FxHashMap<DefId, Symbol> {
+    let mut map: FxHashMap<DefId, Symbol> = FxHashMap::default();
+
+    if let TrimmedDefPaths::GoodPath = tcx.sess.opts.trimmed_def_paths {
+        // For good paths causing this bug, the `rustc_middle::ty::print::with_no_trimmed_paths`
+        // wrapper can be used to suppress this query, in exchange for full paths being formatted.
+        tcx.sess.delay_good_path_bug("trimmed_def_paths constructed");
+    }
+
+    let unique_symbols_rev: &mut FxHashMap<(Namespace, Symbol), Option<DefId>> =
+        &mut FxHashMap::default();
+
+    for symbol_set in tcx.resolutions(()).glob_map.values() {
+        for symbol in symbol_set {
+            unique_symbols_rev.insert((Namespace::TypeNS, *symbol), None);
+            unique_symbols_rev.insert((Namespace::ValueNS, *symbol), None);
+            unique_symbols_rev.insert((Namespace::MacroNS, *symbol), None);
+        }
+    }
+
+    for_each_def(tcx, |ident, ns, def_id| {
+        use std::collections::hash_map::Entry::{Occupied, Vacant};
+
+        match unique_symbols_rev.entry((ns, ident.name)) {
+            Occupied(mut v) => match v.get() {
+                None => {}
+                Some(existing) => {
+                    if *existing != def_id {
+                        v.insert(None);
+                    }
+                }
+            },
+            Vacant(v) => {
+                v.insert(Some(def_id));
+            }
+        }
+    });
+
+    for ((_, symbol), opt_def_id) in unique_symbols_rev.drain() {
+        use std::collections::hash_map::Entry::{Occupied, Vacant};
+
+        if let Some(def_id) = opt_def_id {
+            match map.entry(def_id) {
+                Occupied(mut v) => {
+                    // A single DefId can be known under multiple names (e.g.,
+                    // with a `pub use ... as ...;`). We need to ensure that the
+                    // name placed in this map is chosen deterministically, so
+                    // if we find multiple names (`symbol`) resolving to the
+                    // same `def_id`, we prefer the lexicographically smallest
+                    // name.
+                    //
+                    // Any stable ordering would be fine here though.
+                    if *v.get() != symbol {
+                        if v.get().as_str() > symbol.as_str() {
+                            v.insert(symbol);
+                        }
+                    }
+                }
+                Vacant(v) => {
+                    v.insert(symbol);
+                }
+            }
+        }
+    }
+
+    map
+}
+
+pub fn provide(providers: &mut ty::query::Providers) {
+    *providers = ty::query::Providers { trimmed_def_paths, ..*providers };
+}
+
+#[derive(Default)]
+pub struct OpaqueFnEntry<'tcx> {
+    // The trait ref is already stored as a key, so just track if we have it as a real predicate
+    has_fn_once: bool,
+    fn_mut_trait_ref: Option<ty::PolyTraitRef<'tcx>>,
+    fn_trait_ref: Option<ty::PolyTraitRef<'tcx>>,
+    return_ty: Option<ty::Binder<'tcx, Term<'tcx>>>,
+}