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

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

1 files changed, 742 insertions, 0 deletions

diff --git a/src/librustdoc/clean/auto_trait.rs b/src/librustdoc/clean/auto_trait.rs
new file mode 100644
index 000000000..af33c1a6a
--- /dev/null
+++ b/src/librustdoc/clean/auto_trait.rs
@@ -0,0 +1,742 @@
+use rustc_data_structures::fx::FxHashSet;
+use rustc_hir as hir;
+use rustc_hir::lang_items::LangItem;
+use rustc_middle::ty::{self, Region, RegionVid, TypeFoldable, TypeSuperFoldable};
+use rustc_trait_selection::traits::auto_trait::{self, AutoTraitResult};
+
+use std::fmt::Debug;
+
+use super::*;
+
+#[derive(Eq, PartialEq, Hash, Copy, Clone, Debug)]
+enum RegionTarget<'tcx> {
+    Region(Region<'tcx>),
+    RegionVid(RegionVid),
+}
+
+#[derive(Default, Debug, Clone)]
+struct RegionDeps<'tcx> {
+    larger: FxHashSet<RegionTarget<'tcx>>,
+    smaller: FxHashSet<RegionTarget<'tcx>>,
+}
+
+pub(crate) struct AutoTraitFinder<'a, 'tcx> {
+    pub(crate) cx: &'a mut core::DocContext<'tcx>,
+}
+
+impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx>
+where
+    'tcx: 'a, // should be an implied bound; rustc bug #98852.
+{
+    pub(crate) fn new(cx: &'a mut core::DocContext<'tcx>) -> Self {
+        AutoTraitFinder { cx }
+    }
+
+    fn generate_for_trait(
+        &mut self,
+        ty: Ty<'tcx>,
+        trait_def_id: DefId,
+        param_env: ty::ParamEnv<'tcx>,
+        item_def_id: DefId,
+        f: &auto_trait::AutoTraitFinder<'tcx>,
+        // If this is set, show only negative trait implementations, not positive ones.
+        discard_positive_impl: bool,
+    ) -> Option<Item> {
+        let tcx = self.cx.tcx;
+        let trait_ref = ty::TraitRef { def_id: trait_def_id, substs: tcx.mk_substs_trait(ty, &[]) };
+        if !self.cx.generated_synthetics.insert((ty, trait_def_id)) {
+            debug!("get_auto_trait_impl_for({:?}): already generated, aborting", trait_ref);
+            return None;
+        }
+
+        let result = f.find_auto_trait_generics(ty, param_env, trait_def_id, |info| {
+            let region_data = info.region_data;
+
+            let names_map = tcx
+                .generics_of(item_def_id)
+                .params
+                .iter()
+                .filter_map(|param| match param.kind {
+                    ty::GenericParamDefKind::Lifetime => Some(param.name),
+                    _ => None,
+                })
+                .map(|name| (name, Lifetime(name)))
+                .collect();
+            let lifetime_predicates = Self::handle_lifetimes(&region_data, &names_map);
+            let new_generics = self.param_env_to_generics(
+                item_def_id,
+                info.full_user_env,
+                lifetime_predicates,
+                info.vid_to_region,
+            );
+
+            debug!(
+                "find_auto_trait_generics(item_def_id={:?}, trait_def_id={:?}): \
+                    finished with {:?}",
+                item_def_id, trait_def_id, new_generics
+            );
+
+            new_generics
+        });
+
+        let polarity;
+        let new_generics = match result {
+            AutoTraitResult::PositiveImpl(new_generics) => {
+                polarity = ty::ImplPolarity::Positive;
+                if discard_positive_impl {
+                    return None;
+                }
+                new_generics
+            }
+            AutoTraitResult::NegativeImpl => {
+                polarity = ty::ImplPolarity::Negative;
+
+                // For negative impls, we use the generic params, but *not* the predicates,
+                // from the original type. Otherwise, the displayed impl appears to be a
+                // conditional negative impl, when it's really unconditional.
+                //
+                // For example, consider the struct Foo<T: Copy>(*mut T). Using
+                // the original predicates in our impl would cause us to generate
+                // `impl !Send for Foo<T: Copy>`, which makes it appear that Foo
+                // implements Send where T is not copy.
+                //
+                // Instead, we generate `impl !Send for Foo<T>`, which better
+                // expresses the fact that `Foo<T>` never implements `Send`,
+                // regardless of the choice of `T`.
+                let raw_generics = clean_ty_generics(
+                    self.cx,
+                    tcx.generics_of(item_def_id),
+                    ty::GenericPredicates::default(),
+                );
+                let params = raw_generics.params;
+
+                Generics { params, where_predicates: Vec::new() }
+            }
+            AutoTraitResult::ExplicitImpl => return None,
+        };
+
+        Some(Item {
+            name: None,
+            attrs: Default::default(),
+            visibility: Inherited,
+            item_id: ItemId::Auto { trait_: trait_def_id, for_: item_def_id },
+            kind: Box::new(ImplItem(Box::new(Impl {
+                unsafety: hir::Unsafety::Normal,
+                generics: new_generics,
+                trait_: Some(clean_trait_ref_with_bindings(self.cx, trait_ref, &[])),
+                for_: clean_middle_ty(ty, self.cx, None),
+                items: Vec::new(),
+                polarity,
+                kind: ImplKind::Auto,
+            }))),
+            cfg: None,
+        })
+    }
+
+    pub(crate) fn get_auto_trait_impls(&mut self, item_def_id: DefId) -> Vec<Item> {
+        let tcx = self.cx.tcx;
+        let param_env = tcx.param_env(item_def_id);
+        let ty = tcx.type_of(item_def_id);
+        let f = auto_trait::AutoTraitFinder::new(tcx);
+
+        debug!("get_auto_trait_impls({:?})", ty);
+        let auto_traits: Vec<_> = self.cx.auto_traits.iter().copied().collect();
+        let mut auto_traits: Vec<Item> = auto_traits
+            .into_iter()
+            .filter_map(|trait_def_id| {
+                self.generate_for_trait(ty, trait_def_id, param_env, item_def_id, &f, false)
+            })
+            .collect();
+        // We are only interested in case the type *doesn't* implement the Sized trait.
+        if !ty.is_sized(tcx.at(rustc_span::DUMMY_SP), param_env) {
+            // In case `#![no_core]` is used, `sized_trait` returns nothing.
+            if let Some(item) = tcx.lang_items().sized_trait().and_then(|sized_trait_did| {
+                self.generate_for_trait(ty, sized_trait_did, param_env, item_def_id, &f, true)
+            }) {
+                auto_traits.push(item);
+            }
+        }
+        auto_traits
+    }
+
+    fn get_lifetime(region: Region<'_>, names_map: &FxHashMap<Symbol, Lifetime>) -> Lifetime {
+        region_name(region)
+            .map(|name| {
+                names_map.get(&name).unwrap_or_else(|| {
+                    panic!("Missing lifetime with name {:?} for {:?}", name.as_str(), region)
+                })
+            })
+            .unwrap_or(&Lifetime::statik())
+            .clone()
+    }
+
+    /// This method calculates two things: Lifetime constraints of the form `'a: 'b`,
+    /// and region constraints of the form `RegionVid: 'a`
+    ///
+    /// This is essentially a simplified version of lexical_region_resolve. However,
+    /// handle_lifetimes determines what *needs be* true in order for an impl to hold.
+    /// lexical_region_resolve, along with much of the rest of the compiler, is concerned
+    /// with determining if a given set up constraints/predicates *are* met, given some
+    /// starting conditions (e.g., user-provided code). For this reason, it's easier
+    /// to perform the calculations we need on our own, rather than trying to make
+    /// existing inference/solver code do what we want.
+    fn handle_lifetimes<'cx>(
+        regions: &RegionConstraintData<'cx>,
+        names_map: &FxHashMap<Symbol, Lifetime>,
+    ) -> Vec<WherePredicate> {
+        // Our goal is to 'flatten' the list of constraints by eliminating
+        // all intermediate RegionVids. At the end, all constraints should
+        // be between Regions (aka region variables). This gives us the information
+        // we need to create the Generics.
+        let mut finished: FxHashMap<_, Vec<_>> = Default::default();
+
+        let mut vid_map: FxHashMap<RegionTarget<'_>, RegionDeps<'_>> = Default::default();
+
+        // Flattening is done in two parts. First, we insert all of the constraints
+        // into a map. Each RegionTarget (either a RegionVid or a Region) maps
+        // to its smaller and larger regions. Note that 'larger' regions correspond
+        // to sub-regions in Rust code (e.g., in 'a: 'b, 'a is the larger region).
+        for constraint in regions.constraints.keys() {
+            match *constraint {
+                Constraint::VarSubVar(r1, r2) => {
+                    {
+                        let deps1 = vid_map.entry(RegionTarget::RegionVid(r1)).or_default();
+                        deps1.larger.insert(RegionTarget::RegionVid(r2));
+                    }
+
+                    let deps2 = vid_map.entry(RegionTarget::RegionVid(r2)).or_default();
+                    deps2.smaller.insert(RegionTarget::RegionVid(r1));
+                }
+                Constraint::RegSubVar(region, vid) => {
+                    let deps = vid_map.entry(RegionTarget::RegionVid(vid)).or_default();
+                    deps.smaller.insert(RegionTarget::Region(region));
+                }
+                Constraint::VarSubReg(vid, region) => {
+                    let deps = vid_map.entry(RegionTarget::RegionVid(vid)).or_default();
+                    deps.larger.insert(RegionTarget::Region(region));
+                }
+                Constraint::RegSubReg(r1, r2) => {
+                    // The constraint is already in the form that we want, so we're done with it
+                    // Desired order is 'larger, smaller', so flip then
+                    if region_name(r1) != region_name(r2) {
+                        finished
+                            .entry(region_name(r2).expect("no region_name found"))
+                            .or_default()
+                            .push(r1);
+                    }
+                }
+            }
+        }
+
+        // Here, we 'flatten' the map one element at a time.
+        // All of the element's sub and super regions are connected
+        // to each other. For example, if we have a graph that looks like this:
+        //
+        // (A, B) - C - (D, E)
+        // Where (A, B) are subregions, and (D,E) are super-regions
+        //
+        // then after deleting 'C', the graph will look like this:
+        //  ... - A - (D, E ...)
+        //  ... - B - (D, E, ...)
+        //  (A, B, ...) - D - ...
+        //  (A, B, ...) - E - ...
+        //
+        //  where '...' signifies the existing sub and super regions of an entry
+        //  When two adjacent ty::Regions are encountered, we've computed a final
+        //  constraint, and add it to our list. Since we make sure to never re-add
+        //  deleted items, this process will always finish.
+        while !vid_map.is_empty() {
+            let target = *vid_map.keys().next().expect("Keys somehow empty");
+            let deps = vid_map.remove(&target).expect("Entry somehow missing");
+
+            for smaller in deps.smaller.iter() {
+                for larger in deps.larger.iter() {
+                    match (smaller, larger) {
+                        (&RegionTarget::Region(r1), &RegionTarget::Region(r2)) => {
+                            if region_name(r1) != region_name(r2) {
+                                finished
+                                    .entry(region_name(r2).expect("no region name found"))
+                                    .or_default()
+                                    .push(r1) // Larger, smaller
+                            }
+                        }
+                        (&RegionTarget::RegionVid(_), &RegionTarget::Region(_)) => {
+                            if let Entry::Occupied(v) = vid_map.entry(*smaller) {
+                                let smaller_deps = v.into_mut();
+                                smaller_deps.larger.insert(*larger);
+                                smaller_deps.larger.remove(&target);
+                            }
+                        }
+                        (&RegionTarget::Region(_), &RegionTarget::RegionVid(_)) => {
+                            if let Entry::Occupied(v) = vid_map.entry(*larger) {
+                                let deps = v.into_mut();
+                                deps.smaller.insert(*smaller);
+                                deps.smaller.remove(&target);
+                            }
+                        }
+                        (&RegionTarget::RegionVid(_), &RegionTarget::RegionVid(_)) => {
+                            if let Entry::Occupied(v) = vid_map.entry(*smaller) {
+                                let smaller_deps = v.into_mut();
+                                smaller_deps.larger.insert(*larger);
+                                smaller_deps.larger.remove(&target);
+                            }
+
+                            if let Entry::Occupied(v) = vid_map.entry(*larger) {
+                                let larger_deps = v.into_mut();
+                                larger_deps.smaller.insert(*smaller);
+                                larger_deps.smaller.remove(&target);
+                            }
+                        }
+                    }
+                }
+            }
+        }
+
+        let lifetime_predicates = names_map
+            .iter()
+            .flat_map(|(name, lifetime)| {
+                let empty = Vec::new();
+                let bounds: FxHashSet<GenericBound> = finished
+                    .get(name)
+                    .unwrap_or(&empty)
+                    .iter()
+                    .map(|region| GenericBound::Outlives(Self::get_lifetime(*region, names_map)))
+                    .collect();
+
+                if bounds.is_empty() {
+                    return None;
+                }
+                Some(WherePredicate::RegionPredicate {
+                    lifetime: lifetime.clone(),
+                    bounds: bounds.into_iter().collect(),
+                })
+            })
+            .collect();
+
+        lifetime_predicates
+    }
+
+    fn extract_for_generics(&self, pred: ty::Predicate<'tcx>) -> FxHashSet<GenericParamDef> {
+        let bound_predicate = pred.kind();
+        let tcx = self.cx.tcx;
+        let regions = match bound_predicate.skip_binder() {
+            ty::PredicateKind::Trait(poly_trait_pred) => {
+                tcx.collect_referenced_late_bound_regions(&bound_predicate.rebind(poly_trait_pred))
+            }
+            ty::PredicateKind::Projection(poly_proj_pred) => {
+                tcx.collect_referenced_late_bound_regions(&bound_predicate.rebind(poly_proj_pred))
+            }
+            _ => return FxHashSet::default(),
+        };
+
+        regions
+            .into_iter()
+            .filter_map(|br| {
+                match br {
+                    // We only care about named late bound regions, as we need to add them
+                    // to the 'for<>' section
+                    ty::BrNamed(_, name) => Some(GenericParamDef {
+                        name,
+                        kind: GenericParamDefKind::Lifetime { outlives: vec![] },
+                    }),
+                    _ => None,
+                }
+            })
+            .collect()
+    }
+
+    fn make_final_bounds(
+        &self,
+        ty_to_bounds: FxHashMap<Type, FxHashSet<GenericBound>>,
+        ty_to_fn: FxHashMap<Type, (PolyTrait, Option<Type>)>,
+        lifetime_to_bounds: FxHashMap<Lifetime, FxHashSet<GenericBound>>,
+    ) -> Vec<WherePredicate> {
+        ty_to_bounds
+            .into_iter()
+            .flat_map(|(ty, mut bounds)| {
+                if let Some((ref poly_trait, ref output)) = ty_to_fn.get(&ty) {
+                    let mut new_path = poly_trait.trait_.clone();
+                    let last_segment = new_path.segments.pop().expect("segments were empty");
+
+                    let (old_input, old_output) = match last_segment.args {
+                        GenericArgs::AngleBracketed { args, .. } => {
+                            let types = args
+                                .iter()
+                                .filter_map(|arg| match arg {
+                                    GenericArg::Type(ty) => Some(ty.clone()),
+                                    _ => None,
+                                })
+                                .collect();
+                            (types, None)
+                        }
+                        GenericArgs::Parenthesized { inputs, output } => (inputs, output),
+                    };
+
+                    let output = output.as_ref().cloned().map(Box::new);
+                    if old_output.is_some() && old_output != output {
+                        panic!("Output mismatch for {:?} {:?} {:?}", ty, old_output, output);
+                    }
+
+                    let new_params = GenericArgs::Parenthesized { inputs: old_input, output };
+
+                    new_path
+                        .segments
+                        .push(PathSegment { name: last_segment.name, args: new_params });
+
+                    bounds.insert(GenericBound::TraitBound(
+                        PolyTrait {
+                            trait_: new_path,
+                            generic_params: poly_trait.generic_params.clone(),
+                        },
+                        hir::TraitBoundModifier::None,
+                    ));
+                }
+                if bounds.is_empty() {
+                    return None;
+                }
+
+                let mut bounds_vec = bounds.into_iter().collect();
+                self.sort_where_bounds(&mut bounds_vec);
+
+                Some(WherePredicate::BoundPredicate {
+                    ty,
+                    bounds: bounds_vec,
+                    bound_params: Vec::new(),
+                })
+            })
+            .chain(
+                lifetime_to_bounds.into_iter().filter(|&(_, ref bounds)| !bounds.is_empty()).map(
+                    |(lifetime, bounds)| {
+                        let mut bounds_vec = bounds.into_iter().collect();
+                        self.sort_where_bounds(&mut bounds_vec);
+                        WherePredicate::RegionPredicate { lifetime, bounds: bounds_vec }
+                    },
+                ),
+            )
+            .collect()
+    }
+
+    /// Converts the calculated `ParamEnv` and lifetime information to a [`clean::Generics`](Generics), suitable for
+    /// display on the docs page. Cleaning the `Predicates` produces sub-optimal [`WherePredicate`]s,
+    /// so we fix them up:
+    ///
+    /// * Multiple bounds for the same type are coalesced into one: e.g., `T: Copy`, `T: Debug`
+    /// becomes `T: Copy + Debug`
+    /// * `Fn` bounds are handled specially - instead of leaving it as `T: Fn(), <T as Fn::Output> =
+    /// K`, we use the dedicated syntax `T: Fn() -> K`
+    /// * We explicitly add a `?Sized` bound if we didn't find any `Sized` predicates for a type
+    fn param_env_to_generics(
+        &mut self,
+        item_def_id: DefId,
+        param_env: ty::ParamEnv<'tcx>,
+        mut existing_predicates: Vec<WherePredicate>,
+        vid_to_region: FxHashMap<ty::RegionVid, ty::Region<'tcx>>,
+    ) -> Generics {
+        debug!(
+            "param_env_to_generics(item_def_id={:?}, param_env={:?}, \
+             existing_predicates={:?})",
+            item_def_id, param_env, existing_predicates
+        );
+
+        let tcx = self.cx.tcx;
+
+        // The `Sized` trait must be handled specially, since we only display it when
+        // it is *not* required (i.e., '?Sized')
+        let sized_trait = tcx.require_lang_item(LangItem::Sized, None);
+
+        let mut replacer = RegionReplacer { vid_to_region: &vid_to_region, tcx };
+
+        let orig_bounds: FxHashSet<_> = tcx.param_env(item_def_id).caller_bounds().iter().collect();
+        let clean_where_predicates = param_env
+            .caller_bounds()
+            .iter()
+            .filter(|p| {
+                !orig_bounds.contains(p)
+                    || match p.kind().skip_binder() {
+                        ty::PredicateKind::Trait(pred) => pred.def_id() == sized_trait,
+                        _ => false,
+                    }
+            })
+            .map(|p| p.fold_with(&mut replacer));
+
+        let raw_generics = clean_ty_generics(
+            self.cx,
+            tcx.generics_of(item_def_id),
+            tcx.explicit_predicates_of(item_def_id),
+        );
+        let mut generic_params = raw_generics.params;
+
+        debug!("param_env_to_generics({:?}): generic_params={:?}", item_def_id, generic_params);
+
+        let mut has_sized = FxHashSet::default();
+        let mut ty_to_bounds: FxHashMap<_, FxHashSet<_>> = Default::default();
+        let mut lifetime_to_bounds: FxHashMap<_, FxHashSet<_>> = Default::default();
+        let mut ty_to_traits: FxHashMap<Type, FxHashSet<Path>> = Default::default();
+
+        let mut ty_to_fn: FxHashMap<Type, (PolyTrait, Option<Type>)> = Default::default();
+
+        for p in clean_where_predicates {
+            let (orig_p, p) = (p, p.clean(self.cx));
+            if p.is_none() {
+                continue;
+            }
+            let p = p.unwrap();
+            match p {
+                WherePredicate::BoundPredicate { ty, mut bounds, .. } => {
+                    // Writing a projection trait bound of the form
+                    // <T as Trait>::Name : ?Sized
+                    // is illegal, because ?Sized bounds can only
+                    // be written in the (here, nonexistent) definition
+                    // of the type.
+                    // Therefore, we make sure that we never add a ?Sized
+                    // bound for projections
+                    if let Type::QPath { .. } = ty {
+                        has_sized.insert(ty.clone());
+                    }
+
+                    if bounds.is_empty() {
+                        continue;
+                    }
+
+                    let mut for_generics = self.extract_for_generics(orig_p);
+
+                    assert!(bounds.len() == 1);
+                    let mut b = bounds.pop().expect("bounds were empty");
+
+                    if b.is_sized_bound(self.cx) {
+                        has_sized.insert(ty.clone());
+                    } else if !b
+                        .get_trait_path()
+                        .and_then(|trait_| {
+                            ty_to_traits
+                                .get(&ty)
+                                .map(|bounds| bounds.contains(&strip_path_generics(trait_)))
+                        })
+                        .unwrap_or(false)
+                    {
+                        // If we've already added a projection bound for the same type, don't add
+                        // this, as it would be a duplicate
+
+                        // Handle any 'Fn/FnOnce/FnMut' bounds specially,
+                        // as we want to combine them with any 'Output' qpaths
+                        // later
+
+                        let is_fn = match b {
+                            GenericBound::TraitBound(ref mut p, _) => {
+                                // Insert regions into the for_generics hash map first, to ensure
+                                // that we don't end up with duplicate bounds (e.g., for<'b, 'b>)
+                                for_generics.extend(p.generic_params.clone());
+                                p.generic_params = for_generics.into_iter().collect();
+                                self.is_fn_trait(&p.trait_)
+                            }
+                            _ => false,
+                        };
+
+                        let poly_trait = b.get_poly_trait().expect("Cannot get poly trait");
+
+                        if is_fn {
+                            ty_to_fn
+                                .entry(ty.clone())
+                                .and_modify(|e| *e = (poly_trait.clone(), e.1.clone()))
+                                .or_insert(((poly_trait.clone()), None));
+
+                            ty_to_bounds.entry(ty.clone()).or_default();
+                        } else {
+                            ty_to_bounds.entry(ty.clone()).or_default().insert(b.clone());
+                        }
+                    }
+                }
+                WherePredicate::RegionPredicate { lifetime, bounds } => {
+                    lifetime_to_bounds.entry(lifetime).or_default().extend(bounds);
+                }
+                WherePredicate::EqPredicate { lhs, rhs } => {
+                    match lhs {
+                        Type::QPath { ref assoc, ref self_type, ref trait_, .. } => {
+                            let ty = &*self_type;
+                            let mut new_trait = trait_.clone();
+
+                            if self.is_fn_trait(trait_) && assoc.name == sym::Output {
+                                ty_to_fn
+                                    .entry(*ty.clone())
+                                    .and_modify(|e| {
+                                        *e = (e.0.clone(), Some(rhs.ty().unwrap().clone()))
+                                    })
+                                    .or_insert((
+                                        PolyTrait {
+                                            trait_: trait_.clone(),
+                                            generic_params: Vec::new(),
+                                        },
+                                        Some(rhs.ty().unwrap().clone()),
+                                    ));
+                                continue;
+                            }
+
+                            let args = &mut new_trait
+                                .segments
+                                .last_mut()
+                                .expect("segments were empty")
+                                .args;
+
+                            match args {
+                                // Convert something like '<T as Iterator::Item> = u8'
+                                // to 'T: Iterator<Item=u8>'
+                                GenericArgs::AngleBracketed { ref mut bindings, .. } => {
+                                    bindings.push(TypeBinding {
+                                        assoc: *assoc.clone(),
+                                        kind: TypeBindingKind::Equality { term: rhs },
+                                    });
+                                }
+                                GenericArgs::Parenthesized { .. } => {
+                                    existing_predicates.push(WherePredicate::EqPredicate {
+                                        lhs: lhs.clone(),
+                                        rhs,
+                                    });
+                                    continue; // If something other than a Fn ends up
+                                    // with parentheses, leave it alone
+                                }
+                            }
+
+                            let bounds = ty_to_bounds.entry(*ty.clone()).or_default();
+
+                            bounds.insert(GenericBound::TraitBound(
+                                PolyTrait { trait_: new_trait, generic_params: Vec::new() },
+                                hir::TraitBoundModifier::None,
+                            ));
+
+                            // Remove any existing 'plain' bound (e.g., 'T: Iterator`) so
+                            // that we don't see a
+                            // duplicate bound like `T: Iterator + Iterator<Item=u8>`
+                            // on the docs page.
+                            bounds.remove(&GenericBound::TraitBound(
+                                PolyTrait { trait_: trait_.clone(), generic_params: Vec::new() },
+                                hir::TraitBoundModifier::None,
+                            ));
+                            // Avoid creating any new duplicate bounds later in the outer
+                            // loop
+                            ty_to_traits.entry(*ty.clone()).or_default().insert(trait_.clone());
+                        }
+                        _ => panic!("Unexpected LHS {:?} for {:?}", lhs, item_def_id),
+                    }
+                }
+            };
+        }
+
+        let final_bounds = self.make_final_bounds(ty_to_bounds, ty_to_fn, lifetime_to_bounds);
+
+        existing_predicates.extend(final_bounds);
+
+        for param in generic_params.iter_mut() {
+            match param.kind {
+                GenericParamDefKind::Type { ref mut default, ref mut bounds, .. } => {
+                    // We never want something like `impl<T=Foo>`.
+                    default.take();
+                    let generic_ty = Type::Generic(param.name);
+                    if !has_sized.contains(&generic_ty) {
+                        bounds.insert(0, GenericBound::maybe_sized(self.cx));
+                    }
+                }
+                GenericParamDefKind::Lifetime { .. } => {}
+                GenericParamDefKind::Const { ref mut default, .. } => {
+                    // We never want something like `impl<const N: usize = 10>`
+                    default.take();
+                }
+            }
+        }
+
+        self.sort_where_predicates(&mut existing_predicates);
+
+        Generics { params: generic_params, where_predicates: existing_predicates }
+    }
+
+    /// Ensure that the predicates are in a consistent order. The precise
+    /// ordering doesn't actually matter, but it's important that
+    /// a given set of predicates always appears in the same order -
+    /// both for visual consistency between 'rustdoc' runs, and to
+    /// make writing tests much easier
+    #[inline]
+    fn sort_where_predicates(&self, predicates: &mut Vec<WherePredicate>) {
+        // We should never have identical bounds - and if we do,
+        // they're visually identical as well. Therefore, using
+        // an unstable sort is fine.
+        self.unstable_debug_sort(predicates);
+    }
+
+    /// Ensure that the bounds are in a consistent order. The precise
+    /// ordering doesn't actually matter, but it's important that
+    /// a given set of bounds always appears in the same order -
+    /// both for visual consistency between 'rustdoc' runs, and to
+    /// make writing tests much easier
+    #[inline]
+    fn sort_where_bounds(&self, bounds: &mut Vec<GenericBound>) {
+        // We should never have identical bounds - and if we do,
+        // they're visually identical as well. Therefore, using
+        // an unstable sort is fine.
+        self.unstable_debug_sort(bounds);
+    }
+
+    /// This might look horrendously hacky, but it's actually not that bad.
+    ///
+    /// For performance reasons, we use several different FxHashMaps
+    /// in the process of computing the final set of where predicates.
+    /// However, the iteration order of a HashMap is completely unspecified.
+    /// In fact, the iteration of an FxHashMap can even vary between platforms,
+    /// since FxHasher has different behavior for 32-bit and 64-bit platforms.
+    ///
+    /// Obviously, it's extremely undesirable for documentation rendering
+    /// to be dependent on the platform it's run on. Apart from being confusing
+    /// to end users, it makes writing tests much more difficult, as predicates
+    /// can appear in any order in the final result.
+    ///
+    /// To solve this problem, we sort WherePredicates and GenericBounds
+    /// by their Debug string. The thing to keep in mind is that we don't really
+    /// care what the final order is - we're synthesizing an impl or bound
+    /// ourselves, so any order can be considered equally valid. By sorting the
+    /// predicates and bounds, however, we ensure that for a given codebase, all
+    /// auto-trait impls always render in exactly the same way.
+    ///
+    /// Using the Debug implementation for sorting prevents us from needing to
+    /// write quite a bit of almost entirely useless code (e.g., how should two
+    /// Types be sorted relative to each other). It also allows us to solve the
+    /// problem for both WherePredicates and GenericBounds at the same time. This
+    /// approach is probably somewhat slower, but the small number of items
+    /// involved (impls rarely have more than a few bounds) means that it
+    /// shouldn't matter in practice.
+    fn unstable_debug_sort<T: Debug>(&self, vec: &mut Vec<T>) {
+        vec.sort_by_cached_key(|x| format!("{:?}", x))
+    }
+
+    fn is_fn_trait(&self, path: &Path) -> bool {
+        let tcx = self.cx.tcx;
+        let did = path.def_id();
+        did == tcx.require_lang_item(LangItem::Fn, None)
+            || did == tcx.require_lang_item(LangItem::FnMut, None)
+            || did == tcx.require_lang_item(LangItem::FnOnce, None)
+    }
+}
+
+fn region_name(region: Region<'_>) -> Option<Symbol> {
+    match *region {
+        ty::ReEarlyBound(r) => Some(r.name),
+        _ => None,
+    }
+}
+
+/// Replaces all [`ty::RegionVid`]s in a type with [`ty::Region`]s, using the provided map.
+struct RegionReplacer<'a, 'tcx> {
+    vid_to_region: &'a FxHashMap<ty::RegionVid, ty::Region<'tcx>>,
+    tcx: TyCtxt<'tcx>,
+}
+
+impl<'a, 'tcx> TypeFolder<'tcx> for RegionReplacer<'a, 'tcx> {
+    fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
+        self.tcx
+    }
+
+    fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
+        (match *r {
+            ty::ReVar(vid) => self.vid_to_region.get(&vid).cloned(),
+            _ => None,
+        })
+        .unwrap_or_else(|| r.super_fold_with(self))
+    }
+}