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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};
use rustc_trait_selection::traits::auto_trait::{self, AutoTraitResult};
use thin_vec::ThinVec;
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::Binder::dummy(ty::TraitRef::new(tcx, trait_def_id, [ty]));
if !self.cx.generated_synthetics.insert((ty, trait_def_id)) {
debug!("get_auto_trait_impl_for({trait_ref:?}): already generated, aborting");
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(®ion_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: ThinVec::new() }
}
AutoTraitResult::ExplicitImpl => return None,
};
Some(Item {
name: None,
attrs: Default::default(),
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, ThinVec::new())),
for_: clean_middle_ty(ty::Binder::dummy(ty), self.cx, None, None),
items: Vec::new(),
polarity,
kind: ImplKind::Auto,
}))),
cfg: None,
inline_stmt_id: 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).instantiate_identity();
let f = auto_trait::AutoTraitFinder::new(tcx);
debug!("get_auto_trait_impls({ty:?})");
let auto_traits: Vec<_> = self.cx.auto_traits.to_vec();
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, 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 {name:?} for {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>,
) -> ThinVec<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::Clause<'tcx>) -> FxHashSet<GenericParamDef> {
let bound_predicate = pred.kind();
let tcx = self.cx.tcx;
let regions = match bound_predicate.skip_binder() {
ty::ClauseKind::Trait(poly_trait_pred) => {
tcx.collect_referenced_late_bound_regions(&bound_predicate.rebind(poly_trait_pred))
}
ty::ClauseKind::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::lifetime(name)),
_ => 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(|(_, 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: ThinVec<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::ClauseKind::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({item_def_id:?}): generic_params={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();
// FIXME: This code shares much of the logic found in `clean_ty_generics` and
// `simplify::where_clause`. Consider deduplicating it to avoid diverging
// implementations.
// Further, the code below does not merge (partially re-sugared) bounds like
// `Tr<A = T>` & `Tr<B = U>` and it does not render higher-ranked parameters
// originating from equality predicates.
for p in clean_where_predicates {
let (orig_p, p) = (p, clean_predicate(p, 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.drain(..));
p.generic_params.extend(for_generics);
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(box QPathData {
ref assoc,
ref self_type,
trait_: Some(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 {lhs:?} for {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 [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 [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<TyCtxt<'tcx>> for RegionReplacer<'a, 'tcx> {
fn interner(&self) -> TyCtxt<'tcx> {
self.tcx
}
fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
match *r {
// These are the regions that can be seen in the AST.
ty::ReVar(vid) => self.vid_to_region.get(&vid).cloned().unwrap_or(r),
ty::ReEarlyBound(_) | ty::ReStatic | ty::ReLateBound(..) | ty::ReError(_) => r,
r => bug!("unexpected region: {r:?}"),
}
}
}