1 use rustc_data_structures::fx::FxHashSet;
3 use rustc_hir::lang_items::LangItem;
4 use rustc_middle::ty::{self, Region, RegionVid, TypeFoldable, TypeSuperFoldable};
5 use rustc_trait_selection::traits::auto_trait::{self, AutoTraitResult};
11 #[derive(Eq, PartialEq, Hash, Copy, Clone, Debug)]
12 enum RegionTarget<'tcx> {
17 #[derive(Default, Debug, Clone)]
18 struct RegionDeps<'tcx> {
19 larger: FxHashSet<RegionTarget<'tcx>>,
20 smaller: FxHashSet<RegionTarget<'tcx>>,
23 pub(crate) struct AutoTraitFinder<'a, 'tcx> {
24 pub(crate) cx: &'a mut core::DocContext<'tcx>,
27 impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> {
28 pub(crate) fn new(cx: &'a mut core::DocContext<'tcx>) -> Self {
29 AutoTraitFinder { cx }
32 fn generate_for_trait(
36 param_env: ty::ParamEnv<'tcx>,
38 f: &auto_trait::AutoTraitFinder<'tcx>,
39 // If this is set, show only negative trait implementations, not positive ones.
40 discard_positive_impl: bool,
42 let tcx = self.cx.tcx;
43 let trait_ref = ty::TraitRef { def_id: trait_def_id, substs: tcx.mk_substs_trait(ty, &[]) };
44 if !self.cx.generated_synthetics.insert((ty, trait_def_id)) {
45 debug!("get_auto_trait_impl_for({:?}): already generated, aborting", trait_ref);
49 let result = f.find_auto_trait_generics(ty, param_env, trait_def_id, |info| {
50 let region_data = info.region_data;
53 .generics_of(item_def_id)
56 .filter_map(|param| match param.kind {
57 ty::GenericParamDefKind::Lifetime => Some(param.name),
60 .map(|name| (name, Lifetime(name)))
62 let lifetime_predicates = Self::handle_lifetimes(®ion_data, &names_map);
63 let new_generics = self.param_env_to_generics(
71 "find_auto_trait_generics(item_def_id={:?}, trait_def_id={:?}): \
73 item_def_id, trait_def_id, new_generics
80 let new_generics = match result {
81 AutoTraitResult::PositiveImpl(new_generics) => {
82 polarity = ty::ImplPolarity::Positive;
83 if discard_positive_impl {
88 AutoTraitResult::NegativeImpl => {
89 polarity = ty::ImplPolarity::Negative;
91 // For negative impls, we use the generic params, but *not* the predicates,
92 // from the original type. Otherwise, the displayed impl appears to be a
93 // conditional negative impl, when it's really unconditional.
95 // For example, consider the struct Foo<T: Copy>(*mut T). Using
96 // the original predicates in our impl would cause us to generate
97 // `impl !Send for Foo<T: Copy>`, which makes it appear that Foo
98 // implements Send where T is not copy.
100 // Instead, we generate `impl !Send for Foo<T>`, which better
101 // expresses the fact that `Foo<T>` never implements `Send`,
102 // regardless of the choice of `T`.
103 let raw_generics = clean_ty_generics(
105 tcx.generics_of(item_def_id),
106 ty::GenericPredicates::default(),
108 let params = raw_generics.params;
110 Generics { params, where_predicates: Vec::new() }
112 AutoTraitResult::ExplicitImpl => return None,
117 attrs: Default::default(),
118 visibility: Inherited,
119 item_id: ItemId::Auto { trait_: trait_def_id, for_: item_def_id },
120 kind: box ImplItem(Impl {
121 unsafety: hir::Unsafety::Normal,
122 generics: new_generics,
123 trait_: Some(trait_ref.clean(self.cx)),
124 for_: ty.clean(self.cx),
127 kind: ImplKind::Auto,
133 pub(crate) fn get_auto_trait_impls(&mut self, item_def_id: DefId) -> Vec<Item> {
134 let tcx = self.cx.tcx;
135 let param_env = tcx.param_env(item_def_id);
136 let ty = tcx.type_of(item_def_id);
137 let f = auto_trait::AutoTraitFinder::new(tcx);
139 debug!("get_auto_trait_impls({:?})", ty);
140 let auto_traits: Vec<_> = self.cx.auto_traits.iter().copied().collect();
141 let mut auto_traits: Vec<Item> = auto_traits
143 .filter_map(|trait_def_id| {
144 self.generate_for_trait(ty, trait_def_id, param_env, item_def_id, &f, false)
147 // We are only interested in case the type *doesn't* implement the Sized trait.
148 if !ty.is_sized(tcx.at(rustc_span::DUMMY_SP), param_env) {
149 // In case `#![no_core]` is used, `sized_trait` returns nothing.
150 if let Some(item) = tcx.lang_items().sized_trait().and_then(|sized_trait_did| {
151 self.generate_for_trait(ty, sized_trait_did, param_env, item_def_id, &f, true)
153 auto_traits.push(item);
159 fn get_lifetime(region: Region<'_>, names_map: &FxHashMap<Symbol, Lifetime>) -> Lifetime {
162 names_map.get(&name).unwrap_or_else(|| {
163 panic!("Missing lifetime with name {:?} for {:?}", name.as_str(), region)
166 .unwrap_or(&Lifetime::statik())
170 /// This method calculates two things: Lifetime constraints of the form `'a: 'b`,
171 /// and region constraints of the form `RegionVid: 'a`
173 /// This is essentially a simplified version of lexical_region_resolve. However,
174 /// handle_lifetimes determines what *needs be* true in order for an impl to hold.
175 /// lexical_region_resolve, along with much of the rest of the compiler, is concerned
176 /// with determining if a given set up constraints/predicates *are* met, given some
177 /// starting conditions (e.g., user-provided code). For this reason, it's easier
178 /// to perform the calculations we need on our own, rather than trying to make
179 /// existing inference/solver code do what we want.
180 fn handle_lifetimes<'cx>(
181 regions: &RegionConstraintData<'cx>,
182 names_map: &FxHashMap<Symbol, Lifetime>,
183 ) -> Vec<WherePredicate> {
184 // Our goal is to 'flatten' the list of constraints by eliminating
185 // all intermediate RegionVids. At the end, all constraints should
186 // be between Regions (aka region variables). This gives us the information
187 // we need to create the Generics.
188 let mut finished: FxHashMap<_, Vec<_>> = Default::default();
190 let mut vid_map: FxHashMap<RegionTarget<'_>, RegionDeps<'_>> = Default::default();
192 // Flattening is done in two parts. First, we insert all of the constraints
193 // into a map. Each RegionTarget (either a RegionVid or a Region) maps
194 // to its smaller and larger regions. Note that 'larger' regions correspond
195 // to sub-regions in Rust code (e.g., in 'a: 'b, 'a is the larger region).
196 for constraint in regions.constraints.keys() {
198 Constraint::VarSubVar(r1, r2) => {
200 let deps1 = vid_map.entry(RegionTarget::RegionVid(r1)).or_default();
201 deps1.larger.insert(RegionTarget::RegionVid(r2));
204 let deps2 = vid_map.entry(RegionTarget::RegionVid(r2)).or_default();
205 deps2.smaller.insert(RegionTarget::RegionVid(r1));
207 Constraint::RegSubVar(region, vid) => {
208 let deps = vid_map.entry(RegionTarget::RegionVid(vid)).or_default();
209 deps.smaller.insert(RegionTarget::Region(region));
211 Constraint::VarSubReg(vid, region) => {
212 let deps = vid_map.entry(RegionTarget::RegionVid(vid)).or_default();
213 deps.larger.insert(RegionTarget::Region(region));
215 Constraint::RegSubReg(r1, r2) => {
216 // The constraint is already in the form that we want, so we're done with it
217 // Desired order is 'larger, smaller', so flip then
218 if region_name(r1) != region_name(r2) {
220 .entry(region_name(r2).expect("no region_name found"))
228 // Here, we 'flatten' the map one element at a time.
229 // All of the element's sub and super regions are connected
230 // to each other. For example, if we have a graph that looks like this:
232 // (A, B) - C - (D, E)
233 // Where (A, B) are subregions, and (D,E) are super-regions
235 // then after deleting 'C', the graph will look like this:
236 // ... - A - (D, E ...)
237 // ... - B - (D, E, ...)
238 // (A, B, ...) - D - ...
239 // (A, B, ...) - E - ...
241 // where '...' signifies the existing sub and super regions of an entry
242 // When two adjacent ty::Regions are encountered, we've computed a final
243 // constraint, and add it to our list. Since we make sure to never re-add
244 // deleted items, this process will always finish.
245 while !vid_map.is_empty() {
246 let target = *vid_map.keys().next().expect("Keys somehow empty");
247 let deps = vid_map.remove(&target).expect("Entry somehow missing");
249 for smaller in deps.smaller.iter() {
250 for larger in deps.larger.iter() {
251 match (smaller, larger) {
252 (&RegionTarget::Region(r1), &RegionTarget::Region(r2)) => {
253 if region_name(r1) != region_name(r2) {
255 .entry(region_name(r2).expect("no region name found"))
257 .push(r1) // Larger, smaller
260 (&RegionTarget::RegionVid(_), &RegionTarget::Region(_)) => {
261 if let Entry::Occupied(v) = vid_map.entry(*smaller) {
262 let smaller_deps = v.into_mut();
263 smaller_deps.larger.insert(*larger);
264 smaller_deps.larger.remove(&target);
267 (&RegionTarget::Region(_), &RegionTarget::RegionVid(_)) => {
268 if let Entry::Occupied(v) = vid_map.entry(*larger) {
269 let deps = v.into_mut();
270 deps.smaller.insert(*smaller);
271 deps.smaller.remove(&target);
274 (&RegionTarget::RegionVid(_), &RegionTarget::RegionVid(_)) => {
275 if let Entry::Occupied(v) = vid_map.entry(*smaller) {
276 let smaller_deps = v.into_mut();
277 smaller_deps.larger.insert(*larger);
278 smaller_deps.larger.remove(&target);
281 if let Entry::Occupied(v) = vid_map.entry(*larger) {
282 let larger_deps = v.into_mut();
283 larger_deps.smaller.insert(*smaller);
284 larger_deps.smaller.remove(&target);
292 let lifetime_predicates = names_map
294 .flat_map(|(name, lifetime)| {
295 let empty = Vec::new();
296 let bounds: FxHashSet<GenericBound> = finished
300 .map(|region| GenericBound::Outlives(Self::get_lifetime(*region, names_map)))
303 if bounds.is_empty() {
306 Some(WherePredicate::RegionPredicate {
307 lifetime: lifetime.clone(),
308 bounds: bounds.into_iter().collect(),
316 fn extract_for_generics(&self, pred: ty::Predicate<'tcx>) -> FxHashSet<GenericParamDef> {
317 let bound_predicate = pred.kind();
318 let tcx = self.cx.tcx;
319 let regions = match bound_predicate.skip_binder() {
320 ty::PredicateKind::Trait(poly_trait_pred) => {
321 tcx.collect_referenced_late_bound_regions(&bound_predicate.rebind(poly_trait_pred))
323 ty::PredicateKind::Projection(poly_proj_pred) => {
324 tcx.collect_referenced_late_bound_regions(&bound_predicate.rebind(poly_proj_pred))
326 _ => return FxHashSet::default(),
333 // We only care about named late bound regions, as we need to add them
334 // to the 'for<>' section
335 ty::BrNamed(_, name) => Some(GenericParamDef {
337 kind: GenericParamDefKind::Lifetime { outlives: vec![] },
345 fn make_final_bounds(
347 ty_to_bounds: FxHashMap<Type, FxHashSet<GenericBound>>,
348 ty_to_fn: FxHashMap<Type, (Option<PolyTrait>, Option<Type>)>,
349 lifetime_to_bounds: FxHashMap<Lifetime, FxHashSet<GenericBound>>,
350 ) -> Vec<WherePredicate> {
353 .flat_map(|(ty, mut bounds)| {
354 if let Some(data) = ty_to_fn.get(&ty) {
355 let (poly_trait, output) =
356 (data.0.as_ref().unwrap().clone(), data.1.as_ref().cloned().map(Box::new));
357 let mut new_path = poly_trait.trait_.clone();
358 let last_segment = new_path.segments.pop().expect("segments were empty");
360 let (old_input, old_output) = match last_segment.args {
361 GenericArgs::AngleBracketed { args, .. } => {
364 .filter_map(|arg| match arg {
365 GenericArg::Type(ty) => Some(ty.clone()),
371 GenericArgs::Parenthesized { inputs, output } => (inputs, output),
374 if old_output.is_some() && old_output != output {
375 panic!("Output mismatch for {:?} {:?} {:?}", ty, old_output, data.1);
378 let new_params = GenericArgs::Parenthesized { inputs: old_input, output };
382 .push(PathSegment { name: last_segment.name, args: new_params });
384 bounds.insert(GenericBound::TraitBound(
385 PolyTrait { trait_: new_path, generic_params: poly_trait.generic_params },
386 hir::TraitBoundModifier::None,
389 if bounds.is_empty() {
393 let mut bounds_vec = bounds.into_iter().collect();
394 self.sort_where_bounds(&mut bounds_vec);
396 Some(WherePredicate::BoundPredicate {
399 bound_params: Vec::new(),
403 lifetime_to_bounds.into_iter().filter(|&(_, ref bounds)| !bounds.is_empty()).map(
404 |(lifetime, bounds)| {
405 let mut bounds_vec = bounds.into_iter().collect();
406 self.sort_where_bounds(&mut bounds_vec);
407 WherePredicate::RegionPredicate { lifetime, bounds: bounds_vec }
414 /// Converts the calculated `ParamEnv` and lifetime information to a [`clean::Generics`](Generics), suitable for
415 /// display on the docs page. Cleaning the `Predicates` produces sub-optimal [`WherePredicate`]s,
416 /// so we fix them up:
418 /// * Multiple bounds for the same type are coalesced into one: e.g., `T: Copy`, `T: Debug`
419 /// becomes `T: Copy + Debug`
420 /// * `Fn` bounds are handled specially - instead of leaving it as `T: Fn(), <T as Fn::Output> =
421 /// K`, we use the dedicated syntax `T: Fn() -> K`
422 /// * We explicitly add a `?Sized` bound if we didn't find any `Sized` predicates for a type
423 fn param_env_to_generics(
426 param_env: ty::ParamEnv<'tcx>,
427 mut existing_predicates: Vec<WherePredicate>,
428 vid_to_region: FxHashMap<ty::RegionVid, ty::Region<'tcx>>,
431 "param_env_to_generics(item_def_id={:?}, param_env={:?}, \
432 existing_predicates={:?})",
433 item_def_id, param_env, existing_predicates
436 let tcx = self.cx.tcx;
438 // The `Sized` trait must be handled specially, since we only display it when
439 // it is *not* required (i.e., '?Sized')
440 let sized_trait = tcx.require_lang_item(LangItem::Sized, None);
442 let mut replacer = RegionReplacer { vid_to_region: &vid_to_region, tcx };
444 let orig_bounds: FxHashSet<_> = tcx.param_env(item_def_id).caller_bounds().iter().collect();
445 let clean_where_predicates = param_env
449 !orig_bounds.contains(p)
450 || match p.kind().skip_binder() {
451 ty::PredicateKind::Trait(pred) => pred.def_id() == sized_trait,
455 .map(|p| p.fold_with(&mut replacer));
457 let raw_generics = clean_ty_generics(
459 tcx.generics_of(item_def_id),
460 tcx.explicit_predicates_of(item_def_id),
462 let mut generic_params = raw_generics.params;
464 debug!("param_env_to_generics({:?}): generic_params={:?}", item_def_id, generic_params);
466 let mut has_sized = FxHashSet::default();
467 let mut ty_to_bounds: FxHashMap<_, FxHashSet<_>> = Default::default();
468 let mut lifetime_to_bounds: FxHashMap<_, FxHashSet<_>> = Default::default();
469 let mut ty_to_traits: FxHashMap<Type, FxHashSet<Path>> = Default::default();
471 let mut ty_to_fn: FxHashMap<Type, (Option<PolyTrait>, Option<Type>)> = Default::default();
473 for p in clean_where_predicates {
474 let (orig_p, p) = (p, p.clean(self.cx));
480 WherePredicate::BoundPredicate { ty, mut bounds, .. } => {
481 // Writing a projection trait bound of the form
482 // <T as Trait>::Name : ?Sized
483 // is illegal, because ?Sized bounds can only
484 // be written in the (here, nonexistent) definition
486 // Therefore, we make sure that we never add a ?Sized
487 // bound for projections
488 if let Type::QPath { .. } = ty {
489 has_sized.insert(ty.clone());
492 if bounds.is_empty() {
496 let mut for_generics = self.extract_for_generics(orig_p);
498 assert!(bounds.len() == 1);
499 let mut b = bounds.pop().expect("bounds were empty");
501 if b.is_sized_bound(self.cx) {
502 has_sized.insert(ty.clone());
508 .map(|bounds| bounds.contains(&strip_path_generics(trait_)))
512 // If we've already added a projection bound for the same type, don't add
513 // this, as it would be a duplicate
515 // Handle any 'Fn/FnOnce/FnMut' bounds specially,
516 // as we want to combine them with any 'Output' qpaths
519 let is_fn = match b {
520 GenericBound::TraitBound(ref mut p, _) => {
521 // Insert regions into the for_generics hash map first, to ensure
522 // that we don't end up with duplicate bounds (e.g., for<'b, 'b>)
523 for_generics.extend(p.generic_params.clone());
524 p.generic_params = for_generics.into_iter().collect();
525 self.is_fn_trait(&p.trait_)
530 let poly_trait = b.get_poly_trait().expect("Cannot get poly trait");
535 .and_modify(|e| *e = (Some(poly_trait.clone()), e.1.clone()))
536 .or_insert(((Some(poly_trait.clone())), None));
538 ty_to_bounds.entry(ty.clone()).or_default();
540 ty_to_bounds.entry(ty.clone()).or_default().insert(b.clone());
544 WherePredicate::RegionPredicate { lifetime, bounds } => {
545 lifetime_to_bounds.entry(lifetime).or_default().extend(bounds);
547 WherePredicate::EqPredicate { lhs, rhs } => {
549 Type::QPath { ref assoc, ref self_type, ref trait_, .. } => {
550 let ty = &*self_type;
551 let mut new_trait = trait_.clone();
553 if self.is_fn_trait(trait_) && assoc.name == sym::Output {
557 *e = (e.0.clone(), Some(rhs.ty().unwrap().clone()))
559 .or_insert((None, Some(rhs.ty().unwrap().clone())));
563 let args = &mut new_trait
566 .expect("segments were empty")
570 // Convert something like '<T as Iterator::Item> = u8'
571 // to 'T: Iterator<Item=u8>'
572 GenericArgs::AngleBracketed { ref mut bindings, .. } => {
573 bindings.push(TypeBinding {
574 assoc: *assoc.clone(),
575 kind: TypeBindingKind::Equality { term: rhs },
578 GenericArgs::Parenthesized { .. } => {
579 existing_predicates.push(WherePredicate::EqPredicate {
583 continue; // If something other than a Fn ends up
584 // with parentheses, leave it alone
588 let bounds = ty_to_bounds.entry(*ty.clone()).or_default();
590 bounds.insert(GenericBound::TraitBound(
591 PolyTrait { trait_: new_trait, generic_params: Vec::new() },
592 hir::TraitBoundModifier::None,
595 // Remove any existing 'plain' bound (e.g., 'T: Iterator`) so
596 // that we don't see a
597 // duplicate bound like `T: Iterator + Iterator<Item=u8>`
599 bounds.remove(&GenericBound::TraitBound(
600 PolyTrait { trait_: trait_.clone(), generic_params: Vec::new() },
601 hir::TraitBoundModifier::None,
603 // Avoid creating any new duplicate bounds later in the outer
605 ty_to_traits.entry(*ty.clone()).or_default().insert(trait_.clone());
607 _ => panic!("Unexpected LHS {:?} for {:?}", lhs, item_def_id),
613 let final_bounds = self.make_final_bounds(ty_to_bounds, ty_to_fn, lifetime_to_bounds);
615 existing_predicates.extend(final_bounds);
617 for param in generic_params.iter_mut() {
619 GenericParamDefKind::Type { ref mut default, ref mut bounds, .. } => {
620 // We never want something like `impl<T=Foo>`.
622 let generic_ty = Type::Generic(param.name);
623 if !has_sized.contains(&generic_ty) {
624 bounds.insert(0, GenericBound::maybe_sized(self.cx));
627 GenericParamDefKind::Lifetime { .. } => {}
628 GenericParamDefKind::Const { ref mut default, .. } => {
629 // We never want something like `impl<const N: usize = 10>`
635 self.sort_where_predicates(&mut existing_predicates);
637 Generics { params: generic_params, where_predicates: existing_predicates }
640 /// Ensure that the predicates are in a consistent order. The precise
641 /// ordering doesn't actually matter, but it's important that
642 /// a given set of predicates always appears in the same order -
643 /// both for visual consistency between 'rustdoc' runs, and to
644 /// make writing tests much easier
646 fn sort_where_predicates(&self, predicates: &mut Vec<WherePredicate>) {
647 // We should never have identical bounds - and if we do,
648 // they're visually identical as well. Therefore, using
649 // an unstable sort is fine.
650 self.unstable_debug_sort(predicates);
653 /// Ensure that the bounds are in a consistent order. The precise
654 /// ordering doesn't actually matter, but it's important that
655 /// a given set of bounds always appears in the same order -
656 /// both for visual consistency between 'rustdoc' runs, and to
657 /// make writing tests much easier
659 fn sort_where_bounds(&self, bounds: &mut Vec<GenericBound>) {
660 // We should never have identical bounds - and if we do,
661 // they're visually identical as well. Therefore, using
662 // an unstable sort is fine.
663 self.unstable_debug_sort(bounds);
666 /// This might look horrendously hacky, but it's actually not that bad.
668 /// For performance reasons, we use several different FxHashMaps
669 /// in the process of computing the final set of where predicates.
670 /// However, the iteration order of a HashMap is completely unspecified.
671 /// In fact, the iteration of an FxHashMap can even vary between platforms,
672 /// since FxHasher has different behavior for 32-bit and 64-bit platforms.
674 /// Obviously, it's extremely undesirable for documentation rendering
675 /// to be dependent on the platform it's run on. Apart from being confusing
676 /// to end users, it makes writing tests much more difficult, as predicates
677 /// can appear in any order in the final result.
679 /// To solve this problem, we sort WherePredicates and GenericBounds
680 /// by their Debug string. The thing to keep in mind is that we don't really
681 /// care what the final order is - we're synthesizing an impl or bound
682 /// ourselves, so any order can be considered equally valid. By sorting the
683 /// predicates and bounds, however, we ensure that for a given codebase, all
684 /// auto-trait impls always render in exactly the same way.
686 /// Using the Debug implementation for sorting prevents us from needing to
687 /// write quite a bit of almost entirely useless code (e.g., how should two
688 /// Types be sorted relative to each other). It also allows us to solve the
689 /// problem for both WherePredicates and GenericBounds at the same time. This
690 /// approach is probably somewhat slower, but the small number of items
691 /// involved (impls rarely have more than a few bounds) means that it
692 /// shouldn't matter in practice.
693 fn unstable_debug_sort<T: Debug>(&self, vec: &mut Vec<T>) {
694 vec.sort_by_cached_key(|x| format!("{:?}", x))
697 fn is_fn_trait(&self, path: &Path) -> bool {
698 let tcx = self.cx.tcx;
699 let did = path.def_id();
700 did == tcx.require_lang_item(LangItem::Fn, None)
701 || did == tcx.require_lang_item(LangItem::FnMut, None)
702 || did == tcx.require_lang_item(LangItem::FnOnce, None)
706 fn region_name(region: Region<'_>) -> Option<Symbol> {
708 ty::ReEarlyBound(r) => Some(r.name),
713 /// Replaces all [`ty::RegionVid`]s in a type with [`ty::Region`]s, using the provided map.
714 struct RegionReplacer<'a, 'tcx> {
715 vid_to_region: &'a FxHashMap<ty::RegionVid, ty::Region<'tcx>>,
719 impl<'a, 'tcx> TypeFolder<'tcx> for RegionReplacer<'a, 'tcx> {
720 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
724 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
726 ty::ReVar(vid) => self.vid_to_region.get(&vid).cloned(),
729 .unwrap_or_else(|| r.super_fold_with(self))