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) => Some(GenericParamDef {
336 kind: GenericParamDefKind::Lifetime { outlives: vec![] },
344 fn make_final_bounds(
346 ty_to_bounds: FxHashMap<Type, FxHashSet<GenericBound>>,
347 ty_to_fn: FxHashMap<Type, (Option<PolyTrait>, Option<Type>)>,
348 lifetime_to_bounds: FxHashMap<Lifetime, FxHashSet<GenericBound>>,
349 ) -> Vec<WherePredicate> {
352 .flat_map(|(ty, mut bounds)| {
353 if let Some(data) = ty_to_fn.get(&ty) {
354 let (poly_trait, output) =
355 (data.0.as_ref().unwrap().clone(), data.1.as_ref().cloned().map(Box::new));
356 let new_ty = match poly_trait.trait_ {
357 Type::ResolvedPath { ref path, ref did } => {
358 let mut new_path = path.clone();
360 new_path.segments.pop().expect("segments were empty");
362 let (old_input, old_output) = match last_segment.args {
363 GenericArgs::AngleBracketed { args, .. } => {
366 .filter_map(|arg| match arg {
367 GenericArg::Type(ty) => Some(ty.clone()),
373 GenericArgs::Parenthesized { inputs, output, .. } => {
378 if old_output.is_some() && old_output != output {
380 "Output mismatch for {:?} {:?} {:?}",
381 ty, old_output, data.1
386 GenericArgs::Parenthesized { inputs: old_input, output };
390 .push(PathSegment { name: last_segment.name, args: new_params });
392 Type::ResolvedPath { path: new_path, did: *did }
394 _ => panic!("Unexpected data: {:?}, {:?}", ty, data),
396 bounds.insert(GenericBound::TraitBound(
397 PolyTrait { trait_: new_ty, generic_params: poly_trait.generic_params },
398 hir::TraitBoundModifier::None,
401 if bounds.is_empty() {
405 let mut bounds_vec = bounds.into_iter().collect();
406 self.sort_where_bounds(&mut bounds_vec);
408 Some(WherePredicate::BoundPredicate {
411 bound_params: Vec::new(),
415 lifetime_to_bounds.into_iter().filter(|&(_, ref bounds)| !bounds.is_empty()).map(
416 |(lifetime, bounds)| {
417 let mut bounds_vec = bounds.into_iter().collect();
418 self.sort_where_bounds(&mut bounds_vec);
419 WherePredicate::RegionPredicate { lifetime, bounds: bounds_vec }
426 // Converts the calculated ParamEnv and lifetime information to a clean::Generics, suitable for
427 // display on the docs page. Cleaning the Predicates produces sub-optimal `WherePredicate`s,
428 // so we fix them up:
430 // * Multiple bounds for the same type are coalesced into one: e.g., 'T: Copy', 'T: Debug'
431 // becomes 'T: Copy + Debug'
432 // * Fn bounds are handled specially - instead of leaving it as 'T: Fn(), <T as Fn::Output> =
433 // K', we use the dedicated syntax 'T: Fn() -> K'
434 // * We explicitly add a '?Sized' bound if we didn't find any 'Sized' predicates for a type
435 fn param_env_to_generics(
438 param_env: ty::ParamEnv<'tcx>,
439 mut existing_predicates: Vec<WherePredicate>,
440 vid_to_region: FxHashMap<ty::RegionVid, ty::Region<'tcx>>,
443 "param_env_to_generics(item_def_id={:?}, param_env={:?}, \
444 existing_predicates={:?})",
445 item_def_id, param_env, existing_predicates
448 let tcx = self.cx.tcx;
450 // The `Sized` trait must be handled specially, since we only display it when
451 // it is *not* required (i.e., '?Sized')
452 let sized_trait = tcx.require_lang_item(LangItem::Sized, None);
454 let mut replacer = RegionReplacer { vid_to_region: &vid_to_region, tcx };
456 let orig_bounds: FxHashSet<_> = tcx.param_env(item_def_id).caller_bounds().iter().collect();
457 let clean_where_predicates = param_env
461 !orig_bounds.contains(p)
462 || match p.kind().skip_binder() {
463 ty::PredicateKind::Trait(pred) => pred.def_id() == sized_trait,
467 .map(|p| p.fold_with(&mut replacer));
469 let mut generic_params =
470 (tcx.generics_of(item_def_id), tcx.explicit_predicates_of(item_def_id))
474 debug!("param_env_to_generics({:?}): generic_params={:?}", item_def_id, generic_params);
476 let mut has_sized = FxHashSet::default();
477 let mut ty_to_bounds: FxHashMap<_, FxHashSet<_>> = Default::default();
478 let mut lifetime_to_bounds: FxHashMap<_, FxHashSet<_>> = Default::default();
479 let mut ty_to_traits: FxHashMap<Type, FxHashSet<Type>> = Default::default();
481 let mut ty_to_fn: FxHashMap<Type, (Option<PolyTrait>, Option<Type>)> = Default::default();
483 for p in clean_where_predicates {
484 let (orig_p, p) = (p, p.clean(self.cx));
490 WherePredicate::BoundPredicate { ty, mut bounds, .. } => {
491 // Writing a projection trait bound of the form
492 // <T as Trait>::Name : ?Sized
493 // is illegal, because ?Sized bounds can only
494 // be written in the (here, nonexistent) definition
496 // Therefore, we make sure that we never add a ?Sized
497 // bound for projections
498 if let Type::QPath { .. } = ty {
499 has_sized.insert(ty.clone());
502 if bounds.is_empty() {
506 let mut for_generics = self.extract_for_generics(orig_p);
508 assert!(bounds.len() == 1);
509 let mut b = bounds.pop().expect("bounds were empty");
511 if b.is_sized_bound(self.cx) {
512 has_sized.insert(ty.clone());
518 .map(|bounds| bounds.contains(&strip_type(t.clone())))
522 // If we've already added a projection bound for the same type, don't add
523 // this, as it would be a duplicate
525 // Handle any 'Fn/FnOnce/FnMut' bounds specially,
526 // as we want to combine them with any 'Output' qpaths
529 let is_fn = match &mut b {
530 &mut GenericBound::TraitBound(ref mut p, _) => {
531 // Insert regions into the for_generics hash map first, to ensure
532 // that we don't end up with duplicate bounds (e.g., for<'b, 'b>)
533 for_generics.extend(p.generic_params.clone());
534 p.generic_params = for_generics.into_iter().collect();
535 self.is_fn_ty(&p.trait_)
540 let poly_trait = b.get_poly_trait().expect("Cannot get poly trait");
545 .and_modify(|e| *e = (Some(poly_trait.clone()), e.1.clone()))
546 .or_insert(((Some(poly_trait.clone())), None));
548 ty_to_bounds.entry(ty.clone()).or_default();
550 ty_to_bounds.entry(ty.clone()).or_default().insert(b.clone());
554 WherePredicate::RegionPredicate { lifetime, bounds } => {
555 lifetime_to_bounds.entry(lifetime).or_default().extend(bounds);
557 WherePredicate::EqPredicate { lhs, rhs } => {
559 Type::QPath { name: left_name, ref self_type, ref trait_, .. } => {
560 let ty = &*self_type;
562 Type::ResolvedPath { path: ref trait_path, ref did } => {
563 let mut new_trait_path = trait_path.clone();
565 if self.is_fn_ty(trait_) && left_name == sym::Output {
568 .and_modify(|e| *e = (e.0.clone(), Some(rhs.clone())))
569 .or_insert((None, Some(rhs)));
573 let args = &mut new_trait_path
576 .expect("segments were empty")
580 // Convert something like '<T as Iterator::Item> = u8'
581 // to 'T: Iterator<Item=u8>'
582 GenericArgs::AngleBracketed {
585 bindings.push(TypeBinding {
587 kind: TypeBindingKind::Equality { ty: rhs },
590 GenericArgs::Parenthesized { .. } => {
591 existing_predicates.push(WherePredicate::EqPredicate {
595 continue; // If something other than a Fn ends up
596 // with parenthesis, leave it alone
600 let bounds = ty_to_bounds.entry(*ty.clone()).or_default();
602 bounds.insert(GenericBound::TraitBound(
604 trait_: Type::ResolvedPath {
605 path: new_trait_path,
608 generic_params: Vec::new(),
610 hir::TraitBoundModifier::None,
613 // Remove any existing 'plain' bound (e.g., 'T: Iterator`) so
614 // that we don't see a
615 // duplicate bound like `T: Iterator + Iterator<Item=u8>`
617 bounds.remove(&GenericBound::TraitBound(
619 trait_: *trait_.clone(),
620 generic_params: Vec::new(),
622 hir::TraitBoundModifier::None,
624 // Avoid creating any new duplicate bounds later in the outer
629 .insert(*trait_.clone());
631 _ => panic!("Unexpected trait {:?} for {:?}", trait_, item_def_id),
634 _ => panic!("Unexpected LHS {:?} for {:?}", lhs, item_def_id),
640 let final_bounds = self.make_final_bounds(ty_to_bounds, ty_to_fn, lifetime_to_bounds);
642 existing_predicates.extend(final_bounds);
644 for param in generic_params.iter_mut() {
646 GenericParamDefKind::Type { ref mut default, ref mut bounds, .. } => {
647 // We never want something like `impl<T=Foo>`.
649 let generic_ty = Type::Generic(param.name);
650 if !has_sized.contains(&generic_ty) {
651 bounds.insert(0, GenericBound::maybe_sized(self.cx));
654 GenericParamDefKind::Lifetime { .. } => {}
655 GenericParamDefKind::Const { ref mut default, .. } => {
656 // We never want something like `impl<const N: usize = 10>`
662 self.sort_where_predicates(&mut existing_predicates);
664 Generics { params: generic_params, where_predicates: existing_predicates }
667 // Ensure that the predicates are in a consistent order. The precise
668 // ordering doesn't actually matter, but it's important that
669 // a given set of predicates always appears in the same order -
670 // both for visual consistency between 'rustdoc' runs, and to
671 // make writing tests much easier
673 fn sort_where_predicates(&self, mut predicates: &mut Vec<WherePredicate>) {
674 // We should never have identical bounds - and if we do,
675 // they're visually identical as well. Therefore, using
676 // an unstable sort is fine.
677 self.unstable_debug_sort(&mut predicates);
680 // Ensure that the bounds are in a consistent order. The precise
681 // ordering doesn't actually matter, but it's important that
682 // a given set of bounds always appears in the same order -
683 // both for visual consistency between 'rustdoc' runs, and to
684 // make writing tests much easier
686 fn sort_where_bounds(&self, mut bounds: &mut Vec<GenericBound>) {
687 // We should never have identical bounds - and if we do,
688 // they're visually identical as well. Therefore, using
689 // an unstable sort is fine.
690 self.unstable_debug_sort(&mut bounds);
693 // This might look horrendously hacky, but it's actually not that bad.
695 // For performance reasons, we use several different FxHashMaps
696 // in the process of computing the final set of where predicates.
697 // However, the iteration order of a HashMap is completely unspecified.
698 // In fact, the iteration of an FxHashMap can even vary between platforms,
699 // since FxHasher has different behavior for 32-bit and 64-bit platforms.
701 // Obviously, it's extremely undesirable for documentation rendering
702 // to be dependent on the platform it's run on. Apart from being confusing
703 // to end users, it makes writing tests much more difficult, as predicates
704 // can appear in any order in the final result.
706 // To solve this problem, we sort WherePredicates and GenericBounds
707 // by their Debug string. The thing to keep in mind is that we don't really
708 // care what the final order is - we're synthesizing an impl or bound
709 // ourselves, so any order can be considered equally valid. By sorting the
710 // predicates and bounds, however, we ensure that for a given codebase, all
711 // auto-trait impls always render in exactly the same way.
713 // Using the Debug implementation for sorting prevents us from needing to
714 // write quite a bit of almost entirely useless code (e.g., how should two
715 // Types be sorted relative to each other). It also allows us to solve the
716 // problem for both WherePredicates and GenericBounds at the same time. This
717 // approach is probably somewhat slower, but the small number of items
718 // involved (impls rarely have more than a few bounds) means that it
719 // shouldn't matter in practice.
720 fn unstable_debug_sort<T: Debug>(&self, vec: &mut Vec<T>) {
721 vec.sort_by_cached_key(|x| format!("{:?}", x))
724 fn is_fn_ty(&self, ty: &Type) -> bool {
725 let tcx = self.cx.tcx;
727 &Type::ResolvedPath { did, .. } => {
728 did == tcx.require_lang_item(LangItem::Fn, None)
729 || did == tcx.require_lang_item(LangItem::FnMut, None)
730 || did == tcx.require_lang_item(LangItem::FnOnce, None)
737 fn region_name(region: Region<'_>) -> Option<Symbol> {
739 &ty::ReEarlyBound(r) => Some(r.name),
744 // Replaces all ReVars in a type with ty::Region's, using the provided map
745 struct RegionReplacer<'a, 'tcx> {
746 vid_to_region: &'a FxHashMap<ty::RegionVid, ty::Region<'tcx>>,
750 impl<'a, 'tcx> TypeFolder<'tcx> for RegionReplacer<'a, 'tcx> {
751 fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
755 fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
757 &ty::ReVar(vid) => self.vid_to_region.get(&vid).cloned(),
760 .unwrap_or_else(|| r.super_fold_with(self))