1 use rustc_data_structures::fx::FxHashSet;
3 use rustc_hir::lang_items::LangItem;
4 use rustc_middle::ty::{self, Region, RegionVid, TypeFoldable};
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 crate struct AutoTraitFinder<'a, 'tcx> {
24 crate cx: &'a mut core::DocContext<'tcx>,
27 impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> {
28 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
79 let negative_polarity;
80 let new_generics = match result {
81 AutoTraitResult::PositiveImpl(new_generics) => {
82 negative_polarity = false;
83 if discard_positive_impl {
88 AutoTraitResult::NegativeImpl => {
89 negative_polarity = true;
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 params = (tcx.generics_of(item_def_id), ty::GenericPredicates::default())
107 Generics { params, where_predicates: Vec::new() }
109 AutoTraitResult::ExplicitImpl => return None,
114 attrs: Default::default(),
115 visibility: Inherited,
116 def_id: ItemId::Auto { trait_: trait_def_id, for_: item_def_id },
117 kind: box ImplItem(Impl {
119 unsafety: hir::Unsafety::Normal,
120 generics: new_generics,
121 trait_: Some(trait_ref.clean(self.cx).get_trait_type().unwrap()),
122 for_: ty.clean(self.cx),
132 crate fn get_auto_trait_impls(&mut self, item_def_id: DefId) -> Vec<Item> {
133 let tcx = self.cx.tcx;
134 let param_env = tcx.param_env(item_def_id);
135 let ty = tcx.type_of(item_def_id);
136 let f = auto_trait::AutoTraitFinder::new(tcx);
138 debug!("get_auto_trait_impls({:?})", ty);
139 let auto_traits: Vec<_> = self.cx.auto_traits.iter().cloned().collect();
140 let mut auto_traits: Vec<Item> = auto_traits
142 .filter_map(|trait_def_id| {
143 self.generate_for_trait(ty, trait_def_id, param_env, item_def_id, &f, false)
146 // We are only interested in case the type *doesn't* implement the Sized trait.
147 if !ty.is_sized(tcx.at(rustc_span::DUMMY_SP), param_env) {
148 // In case `#![no_core]` is used, `sized_trait` returns nothing.
149 if let Some(item) = tcx.lang_items().sized_trait().and_then(|sized_trait_did| {
150 self.generate_for_trait(ty, sized_trait_did, param_env, item_def_id, &f, true)
152 auto_traits.push(item);
158 fn get_lifetime(region: Region<'_>, names_map: &FxHashMap<Symbol, Lifetime>) -> Lifetime {
161 names_map.get(&name).unwrap_or_else(|| {
162 panic!("Missing lifetime with name {:?} for {:?}", name.as_str(), region)
165 .unwrap_or(&Lifetime::statik())
169 // This method calculates two things: Lifetime constraints of the form 'a: 'b,
170 // and region constraints of the form ReVar: 'a
172 // This is essentially a simplified version of lexical_region_resolve. However,
173 // handle_lifetimes determines what *needs be* true in order for an impl to hold.
174 // lexical_region_resolve, along with much of the rest of the compiler, is concerned
175 // with determining if a given set up constraints/predicates *are* met, given some
176 // starting conditions (e.g., user-provided code). For this reason, it's easier
177 // to perform the calculations we need on our own, rather than trying to make
178 // existing inference/solver code do what we want.
179 fn handle_lifetimes<'cx>(
180 regions: &RegionConstraintData<'cx>,
181 names_map: &FxHashMap<Symbol, Lifetime>,
182 ) -> Vec<WherePredicate> {
183 // Our goal is to 'flatten' the list of constraints by eliminating
184 // all intermediate RegionVids. At the end, all constraints should
185 // be between Regions (aka region variables). This gives us the information
186 // we need to create the Generics.
187 let mut finished: FxHashMap<_, Vec<_>> = Default::default();
189 let mut vid_map: FxHashMap<RegionTarget<'_>, RegionDeps<'_>> = Default::default();
191 // Flattening is done in two parts. First, we insert all of the constraints
192 // into a map. Each RegionTarget (either a RegionVid or a Region) maps
193 // to its smaller and larger regions. Note that 'larger' regions correspond
194 // to sub-regions in Rust code (e.g., in 'a: 'b, 'a is the larger region).
195 for constraint in regions.constraints.keys() {
197 &Constraint::VarSubVar(r1, r2) => {
199 let deps1 = vid_map.entry(RegionTarget::RegionVid(r1)).or_default();
200 deps1.larger.insert(RegionTarget::RegionVid(r2));
203 let deps2 = vid_map.entry(RegionTarget::RegionVid(r2)).or_default();
204 deps2.smaller.insert(RegionTarget::RegionVid(r1));
206 &Constraint::RegSubVar(region, vid) => {
207 let deps = vid_map.entry(RegionTarget::RegionVid(vid)).or_default();
208 deps.smaller.insert(RegionTarget::Region(region));
210 &Constraint::VarSubReg(vid, region) => {
211 let deps = vid_map.entry(RegionTarget::RegionVid(vid)).or_default();
212 deps.larger.insert(RegionTarget::Region(region));
214 &Constraint::RegSubReg(r1, r2) => {
215 // The constraint is already in the form that we want, so we're done with it
216 // Desired order is 'larger, smaller', so flip then
217 if region_name(r1) != region_name(r2) {
219 .entry(region_name(r2).expect("no region_name found"))
227 // Here, we 'flatten' the map one element at a time.
228 // All of the element's sub and super regions are connected
229 // to each other. For example, if we have a graph that looks like this:
231 // (A, B) - C - (D, E)
232 // Where (A, B) are subregions, and (D,E) are super-regions
234 // then after deleting 'C', the graph will look like this:
235 // ... - A - (D, E ...)
236 // ... - B - (D, E, ...)
237 // (A, B, ...) - D - ...
238 // (A, B, ...) - E - ...
240 // where '...' signifies the existing sub and super regions of an entry
241 // When two adjacent ty::Regions are encountered, we've computed a final
242 // constraint, and add it to our list. Since we make sure to never re-add
243 // deleted items, this process will always finish.
244 while !vid_map.is_empty() {
245 let target = *vid_map.keys().next().expect("Keys somehow empty");
246 let deps = vid_map.remove(&target).expect("Entry somehow missing");
248 for smaller in deps.smaller.iter() {
249 for larger in deps.larger.iter() {
250 match (smaller, larger) {
251 (&RegionTarget::Region(r1), &RegionTarget::Region(r2)) => {
252 if region_name(r1) != region_name(r2) {
254 .entry(region_name(r2).expect("no region name found"))
256 .push(r1) // Larger, smaller
259 (&RegionTarget::RegionVid(_), &RegionTarget::Region(_)) => {
260 if let Entry::Occupied(v) = vid_map.entry(*smaller) {
261 let smaller_deps = v.into_mut();
262 smaller_deps.larger.insert(*larger);
263 smaller_deps.larger.remove(&target);
266 (&RegionTarget::Region(_), &RegionTarget::RegionVid(_)) => {
267 if let Entry::Occupied(v) = vid_map.entry(*larger) {
268 let deps = v.into_mut();
269 deps.smaller.insert(*smaller);
270 deps.smaller.remove(&target);
273 (&RegionTarget::RegionVid(_), &RegionTarget::RegionVid(_)) => {
274 if let Entry::Occupied(v) = vid_map.entry(*smaller) {
275 let smaller_deps = v.into_mut();
276 smaller_deps.larger.insert(*larger);
277 smaller_deps.larger.remove(&target);
280 if let Entry::Occupied(v) = vid_map.entry(*larger) {
281 let larger_deps = v.into_mut();
282 larger_deps.smaller.insert(*smaller);
283 larger_deps.smaller.remove(&target);
291 let lifetime_predicates = names_map
293 .flat_map(|(name, lifetime)| {
294 let empty = Vec::new();
295 let bounds: FxHashSet<GenericBound> = finished
299 .map(|region| GenericBound::Outlives(Self::get_lifetime(region, names_map)))
302 if bounds.is_empty() {
305 Some(WherePredicate::RegionPredicate {
306 lifetime: lifetime.clone(),
307 bounds: bounds.into_iter().collect(),
315 fn extract_for_generics(&self, pred: ty::Predicate<'tcx>) -> FxHashSet<GenericParamDef> {
316 let bound_predicate = pred.kind();
317 let tcx = self.cx.tcx;
318 let regions = match bound_predicate.skip_binder() {
319 ty::PredicateKind::Trait(poly_trait_pred, _) => {
320 tcx.collect_referenced_late_bound_regions(&bound_predicate.rebind(poly_trait_pred))
322 ty::PredicateKind::Projection(poly_proj_pred) => {
323 tcx.collect_referenced_late_bound_regions(&bound_predicate.rebind(poly_proj_pred))
325 _ => return FxHashSet::default(),
332 // We only care about named late bound regions, as we need to add them
333 // to the 'for<>' section
334 ty::BrNamed(_, name) => {
335 Some(GenericParamDef { name, kind: GenericParamDefKind::Lifetime })
343 fn make_final_bounds(
345 ty_to_bounds: FxHashMap<Type, FxHashSet<GenericBound>>,
346 ty_to_fn: FxHashMap<Type, (Option<PolyTrait>, Option<Type>)>,
347 lifetime_to_bounds: FxHashMap<Lifetime, FxHashSet<GenericBound>>,
348 ) -> Vec<WherePredicate> {
351 .flat_map(|(ty, mut bounds)| {
352 if let Some(data) = ty_to_fn.get(&ty) {
353 let (poly_trait, output) =
354 (data.0.as_ref().expect("as_ref failed").clone(), data.1.as_ref().cloned());
355 let new_ty = match poly_trait.trait_ {
356 Type::ResolvedPath { ref path, ref did, ref is_generic } => {
357 let mut new_path = path.clone();
359 new_path.segments.pop().expect("segments were empty");
361 let (old_input, old_output) = match last_segment.args {
362 GenericArgs::AngleBracketed { args, .. } => {
365 .filter_map(|arg| match arg {
366 GenericArg::Type(ty) => Some(ty.clone()),
372 GenericArgs::Parenthesized { inputs, output, .. } => {
377 if old_output.is_some() && old_output != output {
379 "Output mismatch for {:?} {:?} {:?}",
380 ty, old_output, data.1
385 GenericArgs::Parenthesized { inputs: old_input, output };
389 .push(PathSegment { name: last_segment.name, args: new_params });
394 is_generic: *is_generic,
397 _ => panic!("Unexpected data: {:?}, {:?}", ty, data),
399 bounds.insert(GenericBound::TraitBound(
400 PolyTrait { trait_: new_ty, generic_params: poly_trait.generic_params },
401 hir::TraitBoundModifier::None,
404 if bounds.is_empty() {
408 let mut bounds_vec = bounds.into_iter().collect();
409 self.sort_where_bounds(&mut bounds_vec);
411 Some(WherePredicate::BoundPredicate {
414 bound_params: Vec::new(),
418 lifetime_to_bounds.into_iter().filter(|&(_, ref bounds)| !bounds.is_empty()).map(
419 |(lifetime, bounds)| {
420 let mut bounds_vec = bounds.into_iter().collect();
421 self.sort_where_bounds(&mut bounds_vec);
422 WherePredicate::RegionPredicate { lifetime, bounds: bounds_vec }
429 // Converts the calculated ParamEnv and lifetime information to a clean::Generics, suitable for
430 // display on the docs page. Cleaning the Predicates produces sub-optimal `WherePredicate`s,
431 // so we fix them up:
433 // * Multiple bounds for the same type are coalesced into one: e.g., 'T: Copy', 'T: Debug'
434 // becomes 'T: Copy + Debug'
435 // * Fn bounds are handled specially - instead of leaving it as 'T: Fn(), <T as Fn::Output> =
436 // K', we use the dedicated syntax 'T: Fn() -> K'
437 // * We explicitly add a '?Sized' bound if we didn't find any 'Sized' predicates for a type
438 fn param_env_to_generics(
441 param_env: ty::ParamEnv<'tcx>,
442 mut existing_predicates: Vec<WherePredicate>,
443 vid_to_region: FxHashMap<ty::RegionVid, ty::Region<'tcx>>,
446 "param_env_to_generics(item_def_id={:?}, param_env={:?}, \
447 existing_predicates={:?})",
448 item_def_id, param_env, existing_predicates
451 let tcx = self.cx.tcx;
453 // The `Sized` trait must be handled specially, since we only display it when
454 // it is *not* required (i.e., '?Sized')
455 let sized_trait = tcx.require_lang_item(LangItem::Sized, None);
457 let mut replacer = RegionReplacer { vid_to_region: &vid_to_region, tcx };
459 let orig_bounds: FxHashSet<_> = tcx.param_env(item_def_id).caller_bounds().iter().collect();
460 let clean_where_predicates = param_env
464 !orig_bounds.contains(p)
465 || match p.kind().skip_binder() {
466 ty::PredicateKind::Trait(pred, _) => pred.def_id() == sized_trait,
470 .map(|p| p.fold_with(&mut replacer));
472 let mut generic_params =
473 (tcx.generics_of(item_def_id), tcx.explicit_predicates_of(item_def_id))
477 debug!("param_env_to_generics({:?}): generic_params={:?}", item_def_id, generic_params);
479 let mut has_sized = FxHashSet::default();
480 let mut ty_to_bounds: FxHashMap<_, FxHashSet<_>> = Default::default();
481 let mut lifetime_to_bounds: FxHashMap<_, FxHashSet<_>> = Default::default();
482 let mut ty_to_traits: FxHashMap<Type, FxHashSet<Type>> = Default::default();
484 let mut ty_to_fn: FxHashMap<Type, (Option<PolyTrait>, Option<Type>)> = Default::default();
486 for p in clean_where_predicates {
487 let (orig_p, p) = (p, p.clean(self.cx));
493 WherePredicate::BoundPredicate { ty, mut bounds, .. } => {
494 // Writing a projection trait bound of the form
495 // <T as Trait>::Name : ?Sized
496 // is illegal, because ?Sized bounds can only
497 // be written in the (here, nonexistent) definition
499 // Therefore, we make sure that we never add a ?Sized
500 // bound for projections
501 if let Type::QPath { .. } = ty {
502 has_sized.insert(ty.clone());
505 if bounds.is_empty() {
509 let mut for_generics = self.extract_for_generics(orig_p);
511 assert!(bounds.len() == 1);
512 let mut b = bounds.pop().expect("bounds were empty");
514 if b.is_sized_bound(self.cx) {
515 has_sized.insert(ty.clone());
521 .map(|bounds| bounds.contains(&strip_type(t.clone())))
525 // If we've already added a projection bound for the same type, don't add
526 // this, as it would be a duplicate
528 // Handle any 'Fn/FnOnce/FnMut' bounds specially,
529 // as we want to combine them with any 'Output' qpaths
532 let is_fn = match &mut b {
533 &mut GenericBound::TraitBound(ref mut p, _) => {
534 // Insert regions into the for_generics hash map first, to ensure
535 // that we don't end up with duplicate bounds (e.g., for<'b, 'b>)
536 for_generics.extend(p.generic_params.clone());
537 p.generic_params = for_generics.into_iter().collect();
538 self.is_fn_ty(&p.trait_)
543 let poly_trait = b.get_poly_trait().expect("Cannot get poly trait");
548 .and_modify(|e| *e = (Some(poly_trait.clone()), e.1.clone()))
549 .or_insert(((Some(poly_trait.clone())), None));
551 ty_to_bounds.entry(ty.clone()).or_default();
553 ty_to_bounds.entry(ty.clone()).or_default().insert(b.clone());
557 WherePredicate::RegionPredicate { lifetime, bounds } => {
558 lifetime_to_bounds.entry(lifetime).or_default().extend(bounds);
560 WherePredicate::EqPredicate { lhs, rhs } => {
562 Type::QPath { name: left_name, ref self_type, ref trait_, .. } => {
563 let ty = &*self_type;
566 path: ref trait_path,
570 let mut new_trait_path = trait_path.clone();
572 if self.is_fn_ty(trait_) && left_name == sym::Output {
575 .and_modify(|e| *e = (e.0.clone(), Some(rhs.clone())))
576 .or_insert((None, Some(rhs)));
580 let args = &mut new_trait_path
583 .expect("segments were empty")
587 // Convert something like '<T as Iterator::Item> = u8'
588 // to 'T: Iterator<Item=u8>'
589 GenericArgs::AngleBracketed {
592 bindings.push(TypeBinding {
594 kind: TypeBindingKind::Equality { ty: rhs },
597 GenericArgs::Parenthesized { .. } => {
598 existing_predicates.push(WherePredicate::EqPredicate {
602 continue; // If something other than a Fn ends up
603 // with parenthesis, leave it alone
607 let bounds = ty_to_bounds.entry(*ty.clone()).or_default();
609 bounds.insert(GenericBound::TraitBound(
611 trait_: Type::ResolvedPath {
612 path: new_trait_path,
614 is_generic: *is_generic,
616 generic_params: Vec::new(),
618 hir::TraitBoundModifier::None,
621 // Remove any existing 'plain' bound (e.g., 'T: Iterator`) so
622 // that we don't see a
623 // duplicate bound like `T: Iterator + Iterator<Item=u8>`
625 bounds.remove(&GenericBound::TraitBound(
627 trait_: *trait_.clone(),
628 generic_params: Vec::new(),
630 hir::TraitBoundModifier::None,
632 // Avoid creating any new duplicate bounds later in the outer
637 .insert(*trait_.clone());
639 _ => panic!("Unexpected trait {:?} for {:?}", trait_, item_def_id),
642 _ => panic!("Unexpected LHS {:?} for {:?}", lhs, item_def_id),
648 let final_bounds = self.make_final_bounds(ty_to_bounds, ty_to_fn, lifetime_to_bounds);
650 existing_predicates.extend(final_bounds);
652 for param in generic_params.iter_mut() {
654 GenericParamDefKind::Type { ref mut default, ref mut bounds, .. } => {
655 // We never want something like `impl<T=Foo>`.
657 let generic_ty = Type::Generic(param.name);
658 if !has_sized.contains(&generic_ty) {
659 bounds.insert(0, GenericBound::maybe_sized(self.cx));
662 GenericParamDefKind::Lifetime => {}
663 GenericParamDefKind::Const { ref mut default, .. } => {
664 // We never want something like `impl<const N: usize = 10>`
670 self.sort_where_predicates(&mut existing_predicates);
672 Generics { params: generic_params, where_predicates: existing_predicates }
675 // Ensure that the predicates are in a consistent order. The precise
676 // ordering doesn't actually matter, but it's important that
677 // a given set of predicates always appears in the same order -
678 // both for visual consistency between 'rustdoc' runs, and to
679 // make writing tests much easier
681 fn sort_where_predicates(&self, mut predicates: &mut Vec<WherePredicate>) {
682 // We should never have identical bounds - and if we do,
683 // they're visually identical as well. Therefore, using
684 // an unstable sort is fine.
685 self.unstable_debug_sort(&mut predicates);
688 // Ensure that the bounds are in a consistent order. The precise
689 // ordering doesn't actually matter, but it's important that
690 // a given set of bounds always appears in the same order -
691 // both for visual consistency between 'rustdoc' runs, and to
692 // make writing tests much easier
694 fn sort_where_bounds(&self, mut bounds: &mut Vec<GenericBound>) {
695 // We should never have identical bounds - and if we do,
696 // they're visually identical as well. Therefore, using
697 // an unstable sort is fine.
698 self.unstable_debug_sort(&mut bounds);
701 // This might look horrendously hacky, but it's actually not that bad.
703 // For performance reasons, we use several different FxHashMaps
704 // in the process of computing the final set of where predicates.
705 // However, the iteration order of a HashMap is completely unspecified.
706 // In fact, the iteration of an FxHashMap can even vary between platforms,
707 // since FxHasher has different behavior for 32-bit and 64-bit platforms.
709 // Obviously, it's extremely undesirable for documentation rendering
710 // to be dependent on the platform it's run on. Apart from being confusing
711 // to end users, it makes writing tests much more difficult, as predicates
712 // can appear in any order in the final result.
714 // To solve this problem, we sort WherePredicates and GenericBounds
715 // by their Debug string. The thing to keep in mind is that we don't really
716 // care what the final order is - we're synthesizing an impl or bound
717 // ourselves, so any order can be considered equally valid. By sorting the
718 // predicates and bounds, however, we ensure that for a given codebase, all
719 // auto-trait impls always render in exactly the same way.
721 // Using the Debug implementation for sorting prevents us from needing to
722 // write quite a bit of almost entirely useless code (e.g., how should two
723 // Types be sorted relative to each other). It also allows us to solve the
724 // problem for both WherePredicates and GenericBounds at the same time. This
725 // approach is probably somewhat slower, but the small number of items
726 // involved (impls rarely have more than a few bounds) means that it
727 // shouldn't matter in practice.
728 fn unstable_debug_sort<T: Debug>(&self, vec: &mut Vec<T>) {
729 vec.sort_by_cached_key(|x| format!("{:?}", x))
732 fn is_fn_ty(&self, ty: &Type) -> bool {
733 let tcx = self.cx.tcx;
735 &Type::ResolvedPath { did, .. } => {
736 did == tcx.require_lang_item(LangItem::Fn, None)
737 || did == tcx.require_lang_item(LangItem::FnMut, None)
738 || did == tcx.require_lang_item(LangItem::FnOnce, None)
745 fn region_name(region: Region<'_>) -> Option<Symbol> {
747 &ty::ReEarlyBound(r) => Some(r.name),
752 // Replaces all ReVars in a type with ty::Region's, using the provided map
753 struct RegionReplacer<'a, 'tcx> {
754 vid_to_region: &'a FxHashMap<ty::RegionVid, ty::Region<'tcx>>,
758 impl<'a, 'tcx> TypeFolder<'tcx> for RegionReplacer<'a, 'tcx> {
759 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
763 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
765 &ty::ReVar(vid) => self.vid_to_region.get(&vid).cloned(),
768 .unwrap_or_else(|| r.super_fold_with(self))