src/librustdoc/clean/auto_trait.rs

   1 use rustc::traits::auto_trait::{self, AutoTraitResult};
   2 use rustc::ty::{self, Region, RegionVid, TypeFoldable};
   3 use rustc_data_structures::fx::FxHashSet;
   4 use rustc_hir as hir;
   5
   6 use std::fmt::Debug;
   7
   8 use super::*;
   9
  10 #[derive(Eq, PartialEq, Hash, Copy, Clone, Debug)]
  11 enum RegionTarget<'tcx> {
  12     Region(Region<'tcx>),
  13     RegionVid(RegionVid),
  14 }
  15
  16 #[derive(Default, Debug, Clone)]
  17 struct RegionDeps<'tcx> {
  18     larger: FxHashSet<RegionTarget<'tcx>>,
  19     smaller: FxHashSet<RegionTarget<'tcx>>,
  20 }
  21
  22 pub struct AutoTraitFinder<'a, 'tcx> {
  23     pub cx: &'a core::DocContext<'tcx>,
  24     pub f: auto_trait::AutoTraitFinder<'tcx>,
  25 }
  26
  27 impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> {
  28     pub fn new(cx: &'a core::DocContext<'tcx>) -> Self {
  29         let f = auto_trait::AutoTraitFinder::new(cx.tcx);
  30
  31         AutoTraitFinder { cx, f }
  32     }
  33
  34     // FIXME(eddyb) figure out a better way to pass information about
  35     // parametrization of `ty` than `param_env_def_id`.
  36     pub fn get_auto_trait_impls(&self, ty: Ty<'tcx>, param_env_def_id: DefId) -> Vec<Item> {
  37         let param_env = self.cx.tcx.param_env(param_env_def_id);
  38
  39         debug!("get_auto_trait_impls({:?})", ty);
  40         let auto_traits = self.cx.auto_traits.iter().cloned();
  41         auto_traits
  42             .filter_map(|trait_def_id| {
  43                 let trait_ref = ty::TraitRef {
  44                     def_id: trait_def_id,
  45                     substs: self.cx.tcx.mk_substs_trait(ty, &[]),
  46                 };
  47                 if !self.cx.generated_synthetics.borrow_mut().insert((ty, trait_def_id)) {
  48                     debug!("get_auto_trait_impl_for({:?}): already generated, aborting", trait_ref);
  49                     return None;
  50                 }
  51
  52                 let result =
  53                     self.f.find_auto_trait_generics(ty, param_env, trait_def_id, |infcx, info| {
  54                         let region_data = info.region_data;
  55
  56                         let names_map = self
  57                             .cx
  58                             .tcx
  59                             .generics_of(param_env_def_id)
  60                             .params
  61                             .iter()
  62                             .filter_map(|param| match param.kind {
  63                                 ty::GenericParamDefKind::Lifetime => Some(param.name.to_string()),
  64                                 _ => None,
  65                             })
  66                             .map(|name| (name.clone(), Lifetime(name)))
  67                             .collect();
  68                         let lifetime_predicates = self.handle_lifetimes(&region_data, &names_map);
  69                         let new_generics = self.param_env_to_generics(
  70                             infcx.tcx,
  71                             param_env_def_id,
  72                             info.full_user_env,
  73                             lifetime_predicates,
  74                             info.vid_to_region,
  75                         );
  76
  77                         debug!(
  78                             "find_auto_trait_generics(param_env_def_id={:?}, trait_def_id={:?}): \
  79                             finished with {:?}",
  80                             param_env_def_id, trait_def_id, new_generics
  81                         );
  82
  83                         new_generics
  84                     });
  85
  86                 let polarity;
  87                 let new_generics = match result {
  88                     AutoTraitResult::PositiveImpl(new_generics) => {
  89                         polarity = None;
  90                         new_generics
  91                     }
  92                     AutoTraitResult::NegativeImpl => {
  93                         polarity = Some(ImplPolarity::Negative);
  94
  95                         // For negative impls, we use the generic params, but *not* the predicates,
  96                         // from the original type. Otherwise, the displayed impl appears to be a
  97                         // conditional negative impl, when it's really unconditional.
  98                         //
  99                         // For example, consider the struct Foo<T: Copy>(*mut T). Using
 100                         // the original predicates in our impl would cause us to generate
 101                         // `impl !Send for Foo<T: Copy>`, which makes it appear that Foo
 102                         // implements Send where T is not copy.
 103                         //
 104                         // Instead, we generate `impl !Send for Foo<T>`, which better
 105                         // expresses the fact that `Foo<T>` never implements `Send`,
 106                         // regardless of the choice of `T`.
 107                         let params = (
 108                             self.cx.tcx.generics_of(param_env_def_id),
 109                             ty::GenericPredicates::default(),
 110                         )
 111                             .clean(self.cx)
 112                             .params;
 113
 114                         Generics { params, where_predicates: Vec::new() }
 115                     }
 116                     AutoTraitResult::ExplicitImpl => return None,
 117                 };
 118
 119                 Some(Item {
 120                     source: Span::empty(),
 121                     name: None,
 122                     attrs: Default::default(),
 123                     visibility: Inherited,
 124                     def_id: self.cx.next_def_id(param_env_def_id.krate),
 125                     stability: None,
 126                     deprecation: None,
 127                     inner: ImplItem(Impl {
 128                         unsafety: hir::Unsafety::Normal,
 129                         generics: new_generics,
 130                         provided_trait_methods: Default::default(),
 131                         trait_: Some(trait_ref.clean(self.cx).get_trait_type().unwrap()),
 132                         for_: ty.clean(self.cx),
 133                         items: Vec::new(),
 134                         polarity,
 135                         synthetic: true,
 136                         blanket_impl: None,
 137                     }),
 138                 })
 139             })
 140             .collect()
 141     }
 142
 143     fn get_lifetime(
 144         &self,
 145         region: Region<'_>,
 146         names_map: &FxHashMap<String, Lifetime>,
 147     ) -> Lifetime {
 148         self.region_name(region)
 149             .map(|name| {
 150                 names_map.get(&name).unwrap_or_else(|| {
 151                     panic!("Missing lifetime with name {:?} for {:?}", name, region)
 152                 })
 153             })
 154             .unwrap_or(&Lifetime::statik())
 155             .clone()
 156     }
 157
 158     fn region_name(&self, region: Region<'_>) -> Option<String> {
 159         match region {
 160             &ty::ReEarlyBound(r) => Some(r.name.to_string()),
 161             _ => None,
 162         }
 163     }
 164
 165     // This method calculates two things: Lifetime constraints of the form 'a: 'b,
 166     // and region constraints of the form ReVar: 'a
 167     //
 168     // This is essentially a simplified version of lexical_region_resolve. However,
 169     // handle_lifetimes determines what *needs be* true in order for an impl to hold.
 170     // lexical_region_resolve, along with much of the rest of the compiler, is concerned
 171     // with determining if a given set up constraints/predicates *are* met, given some
 172     // starting conditions (e.g., user-provided code). For this reason, it's easier
 173     // to perform the calculations we need on our own, rather than trying to make
 174     // existing inference/solver code do what we want.
 175     fn handle_lifetimes<'cx>(
 176         &self,
 177         regions: &RegionConstraintData<'cx>,
 178         names_map: &FxHashMap<String, Lifetime>,
 179     ) -> Vec<WherePredicate> {
 180         // Our goal is to 'flatten' the list of constraints by eliminating
 181         // all intermediate RegionVids. At the end, all constraints should
 182         // be between Regions (aka region variables). This gives us the information
 183         // we need to create the Generics.
 184         let mut finished: FxHashMap<_, Vec<_>> = Default::default();
 185
 186         let mut vid_map: FxHashMap<RegionTarget<'_>, RegionDeps<'_>> = Default::default();
 187
 188         // Flattening is done in two parts. First, we insert all of the constraints
 189         // into a map. Each RegionTarget (either a RegionVid or a Region) maps
 190         // to its smaller and larger regions. Note that 'larger' regions correspond
 191         // to sub-regions in Rust code (e.g., in 'a: 'b, 'a is the larger region).
 192         for constraint in regions.constraints.keys() {
 193             match constraint {
 194                 &Constraint::VarSubVar(r1, r2) => {
 195                     {
 196                         let deps1 = vid_map.entry(RegionTarget::RegionVid(r1)).or_default();
 197                         deps1.larger.insert(RegionTarget::RegionVid(r2));
 198                     }
 199
 200                     let deps2 = vid_map.entry(RegionTarget::RegionVid(r2)).or_default();
 201                     deps2.smaller.insert(RegionTarget::RegionVid(r1));
 202                 }
 203                 &Constraint::RegSubVar(region, vid) => {
 204                     let deps = vid_map.entry(RegionTarget::RegionVid(vid)).or_default();
 205                     deps.smaller.insert(RegionTarget::Region(region));
 206                 }
 207                 &Constraint::VarSubReg(vid, region) => {
 208                     let deps = vid_map.entry(RegionTarget::RegionVid(vid)).or_default();
 209                     deps.larger.insert(RegionTarget::Region(region));
 210                 }
 211                 &Constraint::RegSubReg(r1, r2) => {
 212                     // The constraint is already in the form that we want, so we're done with it
 213                     // Desired order is 'larger, smaller', so flip then
 214                     if self.region_name(r1) != self.region_name(r2) {
 215                         finished
 216                             .entry(self.region_name(r2).expect("no region_name found"))
 217                             .or_default()
 218                             .push(r1);
 219                     }
 220                 }
 221             }
 222         }
 223
 224         // Here, we 'flatten' the map one element at a time.
 225         // All of the element's sub and super regions are connected
 226         // to each other. For example, if we have a graph that looks like this:
 227         //
 228         // (A, B) - C - (D, E)
 229         // Where (A, B) are subregions, and (D,E) are super-regions
 230         //
 231         // then after deleting 'C', the graph will look like this:
 232         //  ... - A - (D, E ...)
 233         //  ... - B - (D, E, ...)
 234         //  (A, B, ...) - D - ...
 235         //  (A, B, ...) - E - ...
 236         //
 237         //  where '...' signifies the existing sub and super regions of an entry
 238         //  When two adjacent ty::Regions are encountered, we've computed a final
 239         //  constraint, and add it to our list. Since we make sure to never re-add
 240         //  deleted items, this process will always finish.
 241         while !vid_map.is_empty() {
 242             let target = *vid_map.keys().next().expect("Keys somehow empty");
 243             let deps = vid_map.remove(&target).expect("Entry somehow missing");
 244
 245             for smaller in deps.smaller.iter() {
 246                 for larger in deps.larger.iter() {
 247                     match (smaller, larger) {
 248                         (&RegionTarget::Region(r1), &RegionTarget::Region(r2)) => {
 249                             if self.region_name(r1) != self.region_name(r2) {
 250                                 finished
 251                                     .entry(self.region_name(r2).expect("no region name found"))
 252                                     .or_default()
 253                                     .push(r1) // Larger, smaller
 254                             }
 255                         }
 256                         (&RegionTarget::RegionVid(_), &RegionTarget::Region(_)) => {
 257                             if let Entry::Occupied(v) = vid_map.entry(*smaller) {
 258                                 let smaller_deps = v.into_mut();
 259                                 smaller_deps.larger.insert(*larger);
 260                                 smaller_deps.larger.remove(&target);
 261                             }
 262                         }
 263                         (&RegionTarget::Region(_), &RegionTarget::RegionVid(_)) => {
 264                             if let Entry::Occupied(v) = vid_map.entry(*larger) {
 265                                 let deps = v.into_mut();
 266                                 deps.smaller.insert(*smaller);
 267                                 deps.smaller.remove(&target);
 268                             }
 269                         }
 270                         (&RegionTarget::RegionVid(_), &RegionTarget::RegionVid(_)) => {
 271                             if let Entry::Occupied(v) = vid_map.entry(*smaller) {
 272                                 let smaller_deps = v.into_mut();
 273                                 smaller_deps.larger.insert(*larger);
 274                                 smaller_deps.larger.remove(&target);
 275                             }
 276
 277                             if let Entry::Occupied(v) = vid_map.entry(*larger) {
 278                                 let larger_deps = v.into_mut();
 279                                 larger_deps.smaller.insert(*smaller);
 280                                 larger_deps.smaller.remove(&target);
 281                             }
 282                         }
 283                     }
 284                 }
 285             }
 286         }
 287
 288         let lifetime_predicates = names_map
 289             .iter()
 290             .flat_map(|(name, lifetime)| {
 291                 let empty = Vec::new();
 292                 let bounds: FxHashSet<GenericBound> = finished
 293                     .get(name)
 294                     .unwrap_or(&empty)
 295                     .iter()
 296                     .map(|region| GenericBound::Outlives(self.get_lifetime(region, names_map)))
 297                     .collect();
 298
 299                 if bounds.is_empty() {
 300                     return None;
 301                 }
 302                 Some(WherePredicate::RegionPredicate {
 303                     lifetime: lifetime.clone(),
 304                     bounds: bounds.into_iter().collect(),
 305                 })
 306             })
 307             .collect();
 308
 309         lifetime_predicates
 310     }
 311
 312     fn extract_for_generics(
 313         &self,
 314         tcx: TyCtxt<'tcx>,
 315         pred: ty::Predicate<'tcx>,
 316     ) -> FxHashSet<GenericParamDef> {
 317         pred.walk_tys()
 318             .flat_map(|t| {
 319                 let mut regions = FxHashSet::default();
 320                 tcx.collect_regions(&t, &mut regions);
 321
 322                 regions.into_iter().flat_map(|r| {
 323                     match r {
 324                         // We only care about late bound regions, as we need to add them
 325                         // to the 'for<>' section
 326                         &ty::ReLateBound(_, ty::BoundRegion::BrNamed(_, name)) => {
 327                             Some(GenericParamDef {
 328                                 name: name.to_string(),
 329                                 kind: GenericParamDefKind::Lifetime,
 330                             })
 331                         }
 332                         &ty::ReVar(_) | &ty::ReEarlyBound(_) | &ty::ReStatic => None,
 333                         _ => panic!("Unexpected region type {:?}", r),
 334                     }
 335                 })
 336             })
 337             .collect()
 338     }
 339
 340     fn make_final_bounds(
 341         &self,
 342         ty_to_bounds: FxHashMap<Type, FxHashSet<GenericBound>>,
 343         ty_to_fn: FxHashMap<Type, (Option<PolyTrait>, Option<Type>)>,
 344         lifetime_to_bounds: FxHashMap<Lifetime, FxHashSet<GenericBound>>,
 345     ) -> Vec<WherePredicate> {
 346         ty_to_bounds
 347             .into_iter()
 348             .flat_map(|(ty, mut bounds)| {
 349                 if let Some(data) = ty_to_fn.get(&ty) {
 350                     let (poly_trait, output) =
 351                         (data.0.as_ref().expect("as_ref failed").clone(), data.1.as_ref().cloned());
 352                     let new_ty = match &poly_trait.trait_ {
 353                         &Type::ResolvedPath {
 354                             ref path,
 355                             ref param_names,
 356                             ref did,
 357                             ref is_generic,
 358                         } => {
 359                             let mut new_path = path.clone();
 360                             let last_segment =
 361                                 new_path.segments.pop().expect("segments were empty");
 362
 363                             let (old_input, old_output) = match last_segment.args {
 364                                 GenericArgs::AngleBracketed { args, .. } => {
 365                                     let types = args
 366                                         .iter()
 367                                         .filter_map(|arg| match arg {
 368                                             GenericArg::Type(ty) => Some(ty.clone()),
 369                                             _ => None,
 370                                         })
 371                                         .collect();
 372                                     (types, None)
 373                                 }
 374                                 GenericArgs::Parenthesized { inputs, output, .. } => {
 375                                     (inputs, output)
 376                                 }
 377                             };
 378
 379                             if old_output.is_some() && old_output != output {
 380                                 panic!(
 381                                     "Output mismatch for {:?} {:?} {:?}",
 382                                     ty, old_output, data.1
 383                                 );
 384                             }
 385
 386                             let new_params =
 387                                 GenericArgs::Parenthesized { inputs: old_input, output };
 388
 389                             new_path
 390                                 .segments
 391                                 .push(PathSegment { name: last_segment.name, args: new_params });
 392
 393                             Type::ResolvedPath {
 394                                 path: new_path,
 395                                 param_names: param_names.clone(),
 396                                 did: did.clone(),
 397                                 is_generic: *is_generic,
 398                             }
 399                         }
 400                         _ => panic!("Unexpected data: {:?}, {:?}", ty, data),
 401                     };
 402                     bounds.insert(GenericBound::TraitBound(
 403                         PolyTrait { trait_: new_ty, generic_params: poly_trait.generic_params },
 404                         hir::TraitBoundModifier::None,
 405                     ));
 406                 }
 407                 if bounds.is_empty() {
 408                     return None;
 409                 }
 410
 411                 let mut bounds_vec = bounds.into_iter().collect();
 412                 self.sort_where_bounds(&mut bounds_vec);
 413
 414                 Some(WherePredicate::BoundPredicate { ty, bounds: bounds_vec })
 415             })
 416             .chain(
 417                 lifetime_to_bounds.into_iter().filter(|&(_, ref bounds)| !bounds.is_empty()).map(
 418                     |(lifetime, bounds)| {
 419                         let mut bounds_vec = bounds.into_iter().collect();
 420                         self.sort_where_bounds(&mut bounds_vec);
 421                         WherePredicate::RegionPredicate { lifetime, bounds: bounds_vec }
 422                     },
 423                 ),
 424             )
 425             .collect()
 426     }
 427
 428     // Converts the calculated ParamEnv and lifetime information to a clean::Generics, suitable for
 429     // display on the docs page. Cleaning the Predicates produces sub-optimal WherePredicate's,
 430     // so we fix them up:
 431     //
 432     // * Multiple bounds for the same type are coalesced into one: e.g., 'T: Copy', 'T: Debug'
 433     // becomes 'T: Copy + Debug'
 434     // * Fn bounds are handled specially - instead of leaving it as 'T: Fn(), <T as Fn::Output> =
 435     // K', we use the dedicated syntax 'T: Fn() -> K'
 436     // * We explcitly add a '?Sized' bound if we didn't find any 'Sized' predicates for a type
 437     fn param_env_to_generics(
 438         &self,
 439         tcx: TyCtxt<'tcx>,
 440         param_env_def_id: DefId,
 441         param_env: ty::ParamEnv<'tcx>,
 442         mut existing_predicates: Vec<WherePredicate>,
 443         vid_to_region: FxHashMap<ty::RegionVid, ty::Region<'tcx>>,
 444     ) -> Generics {
 445         debug!(
 446             "param_env_to_generics(param_env_def_id={:?}, param_env={:?}, \
 447              existing_predicates={:?})",
 448             param_env_def_id, param_env, existing_predicates
 449         );
 450
 451         // The `Sized` trait must be handled specially, since we only display it when
 452         // it is *not* required (i.e., '?Sized')
 453         let sized_trait = self.cx.tcx.require_lang_item(lang_items::SizedTraitLangItem, None);
 454
 455         let mut replacer = RegionReplacer { vid_to_region: &vid_to_region, tcx };
 456
 457         let orig_bounds: FxHashSet<_> =
 458             self.cx.tcx.param_env(param_env_def_id).caller_bounds.iter().collect();
 459         let clean_where_predicates = param_env
 460             .caller_bounds
 461             .iter()
 462             .filter(|p| {
 463                 !orig_bounds.contains(p)
 464                     || match p {
 465                         ty::Predicate::Trait(pred, _) => pred.def_id() == sized_trait,
 466                         _ => false,
 467                     }
 468             })
 469             .map(|p| {
 470                 let replaced = p.fold_with(&mut replacer);
 471                 (replaced.clone(), replaced.clean(self.cx))
 472             });
 473
 474         let mut generic_params =
 475             (tcx.generics_of(param_env_def_id), tcx.explicit_predicates_of(param_env_def_id))
 476                 .clean(self.cx)
 477                 .params;
 478
 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();
 483
 484         let mut ty_to_fn: FxHashMap<Type, (Option<PolyTrait>, Option<Type>)> = Default::default();
 485
 486         for (orig_p, p) in clean_where_predicates {
 487             if p.is_none() {
 488                 continue;
 489             }
 490             let p = p.unwrap();
 491             match p {
 492                 WherePredicate::BoundPredicate { ty, mut bounds } => {
 493                     // Writing a projection trait bound of the form
 494                     // <T as Trait>::Name : ?Sized
 495                     // is illegal, because ?Sized bounds can only
 496                     // be written in the (here, nonexistant) definition
 497                     // of the type.
 498                     // Therefore, we make sure that we never add a ?Sized
 499                     // bound for projections
 500                     match &ty {
 501                         &Type::QPath { .. } => {
 502                             has_sized.insert(ty.clone());
 503                         }
 504                         _ => {}
 505                     }
 506
 507                     if bounds.is_empty() {
 508                         continue;
 509                     }
 510
 511                     let mut for_generics = self.extract_for_generics(tcx, orig_p.clone());
 512
 513                     assert!(bounds.len() == 1);
 514                     let mut b = bounds.pop().expect("bounds were empty");
 515
 516                     if b.is_sized_bound(self.cx) {
 517                         has_sized.insert(ty.clone());
 518                     } else if !b
 519                         .get_trait_type()
 520                         .and_then(|t| {
 521                             ty_to_traits
 522                                 .get(&ty)
 523                                 .map(|bounds| bounds.contains(&strip_type(t.clone())))
 524                         })
 525                         .unwrap_or(false)
 526                     {
 527                         // If we've already added a projection bound for the same type, don't add
 528                         // this, as it would be a duplicate
 529
 530                         // Handle any 'Fn/FnOnce/FnMut' bounds specially,
 531                         // as we want to combine them with any 'Output' qpaths
 532                         // later
 533
 534                         let is_fn = match &mut b {
 535                             &mut GenericBound::TraitBound(ref mut p, _) => {
 536                                 // Insert regions into the for_generics hash map first, to ensure
 537                                 // that we don't end up with duplicate bounds (e.g., for<'b, 'b>)
 538                                 for_generics.extend(p.generic_params.clone());
 539                                 p.generic_params = for_generics.into_iter().collect();
 540                                 self.is_fn_ty(tcx, &p.trait_)
 541                             }
 542                             _ => false,
 543                         };
 544
 545                         let poly_trait = b.get_poly_trait().expect("Cannot get poly trait");
 546
 547                         if is_fn {
 548                             ty_to_fn
 549                                 .entry(ty.clone())
 550                                 .and_modify(|e| *e = (Some(poly_trait.clone()), e.1.clone()))
 551                                 .or_insert(((Some(poly_trait.clone())), None));
 552
 553                             ty_to_bounds.entry(ty.clone()).or_default();
 554                         } else {
 555                             ty_to_bounds.entry(ty.clone()).or_default().insert(b.clone());
 556                         }
 557                     }
 558                 }
 559                 WherePredicate::RegionPredicate { lifetime, bounds } => {
 560                     lifetime_to_bounds.entry(lifetime).or_default().extend(bounds);
 561                 }
 562                 WherePredicate::EqPredicate { lhs, rhs } => {
 563                     match lhs {
 564                         Type::QPath { name: ref left_name, ref self_type, ref trait_ } => {
 565                             let ty = &*self_type;
 566                             match **trait_ {
 567                                 Type::ResolvedPath {
 568                                     path: ref trait_path,
 569                                     ref param_names,
 570                                     ref did,
 571                                     ref is_generic,
 572                                 } => {
 573                                     let mut new_trait_path = trait_path.clone();
 574
 575                                     if self.is_fn_ty(tcx, trait_) && left_name == FN_OUTPUT_NAME {
 576                                         ty_to_fn
 577                                             .entry(*ty.clone())
 578                                             .and_modify(|e| *e = (e.0.clone(), Some(rhs.clone())))
 579                                             .or_insert((None, Some(rhs)));
 580                                         continue;
 581                                     }
 582
 583                                     let args = &mut new_trait_path
 584                                         .segments
 585                                         .last_mut()
 586                                         .expect("segments were empty")
 587                                         .args;
 588
 589                                     match args {
 590                                         // Convert somethiung like '<T as Iterator::Item> = u8'
 591                                         // to 'T: Iterator<Item=u8>'
 592                                         GenericArgs::AngleBracketed {
 593                                             ref mut bindings, ..
 594                                         } => {
 595                                             bindings.push(TypeBinding {
 596                                                 name: left_name.clone(),
 597                                                 kind: TypeBindingKind::Equality { ty: rhs },
 598                                             });
 599                                         }
 600                                         GenericArgs::Parenthesized { .. } => {
 601                                             existing_predicates.push(WherePredicate::EqPredicate {
 602                                                 lhs: lhs.clone(),
 603                                                 rhs,
 604                                             });
 605                                             continue; // If something other than a Fn ends up
 606                                             // with parenthesis, leave it alone
 607                                         }
 608                                     }
 609
 610                                     let bounds = ty_to_bounds.entry(*ty.clone()).or_default();
 611
 612                                     bounds.insert(GenericBound::TraitBound(
 613                                         PolyTrait {
 614                                             trait_: Type::ResolvedPath {
 615                                                 path: new_trait_path,
 616                                                 param_names: param_names.clone(),
 617                                                 did: did.clone(),
 618                                                 is_generic: *is_generic,
 619                                             },
 620                                             generic_params: Vec::new(),
 621                                         },
 622                                         hir::TraitBoundModifier::None,
 623                                     ));
 624
 625                                     // Remove any existing 'plain' bound (e.g., 'T: Iterator`) so
 626                                     // that we don't see a
 627                                     // duplicate bound like `T: Iterator + Iterator<Item=u8>`
 628                                     // on the docs page.
 629                                     bounds.remove(&GenericBound::TraitBound(
 630                                         PolyTrait {
 631                                             trait_: *trait_.clone(),
 632                                             generic_params: Vec::new(),
 633                                         },
 634                                         hir::TraitBoundModifier::None,
 635                                     ));
 636                                     // Avoid creating any new duplicate bounds later in the outer
 637                                     // loop
 638                                     ty_to_traits
 639                                         .entry(*ty.clone())
 640                                         .or_default()
 641                                         .insert(*trait_.clone());
 642                                 }
 643                                 _ => panic!(
 644                                     "Unexpected trait {:?} for {:?}",
 645                                     trait_, param_env_def_id,
 646                                 ),
 647                             }
 648                         }
 649                         _ => panic!("Unexpected LHS {:?} for {:?}", lhs, param_env_def_id),
 650                     }
 651                 }
 652             };
 653         }
 654
 655         let final_bounds = self.make_final_bounds(ty_to_bounds, ty_to_fn, lifetime_to_bounds);
 656
 657         existing_predicates.extend(final_bounds);
 658
 659         for param in generic_params.iter_mut() {
 660             match param.kind {
 661                 GenericParamDefKind::Type { ref mut default, ref mut bounds, .. } => {
 662                     // We never want something like `impl<T=Foo>`.
 663                     default.take();
 664                     let generic_ty = Type::Generic(param.name.clone());
 665                     if !has_sized.contains(&generic_ty) {
 666                         bounds.insert(0, GenericBound::maybe_sized(self.cx));
 667                     }
 668                 }
 669                 GenericParamDefKind::Lifetime => {}
 670                 GenericParamDefKind::Const { .. } => {}
 671             }
 672         }
 673
 674         self.sort_where_predicates(&mut existing_predicates);
 675
 676         Generics { params: generic_params, where_predicates: existing_predicates }
 677     }
 678
 679     // Ensure that the predicates are in a consistent order. The precise
 680     // ordering doesn't actually matter, but it's important that
 681     // a given set of predicates always appears in the same order -
 682     // both for visual consistency between 'rustdoc' runs, and to
 683     // make writing tests much easier
 684     #[inline]
 685     fn sort_where_predicates(&self, mut predicates: &mut Vec<WherePredicate>) {
 686         // We should never have identical bounds - and if we do,
 687         // they're visually identical as well. Therefore, using
 688         // an unstable sort is fine.
 689         self.unstable_debug_sort(&mut predicates);
 690     }
 691
 692     // Ensure that the bounds are in a consistent order. The precise
 693     // ordering doesn't actually matter, but it's important that
 694     // a given set of bounds always appears in the same order -
 695     // both for visual consistency between 'rustdoc' runs, and to
 696     // make writing tests much easier
 697     #[inline]
 698     fn sort_where_bounds(&self, mut bounds: &mut Vec<GenericBound>) {
 699         // We should never have identical bounds - and if we do,
 700         // they're visually identical as well. Therefore, using
 701         // an unstable sort is fine.
 702         self.unstable_debug_sort(&mut bounds);
 703     }
 704
 705     // This might look horrendously hacky, but it's actually not that bad.
 706     //
 707     // For performance reasons, we use several different FxHashMaps
 708     // in the process of computing the final set of where predicates.
 709     // However, the iteration order of a HashMap is completely unspecified.
 710     // In fact, the iteration of an FxHashMap can even vary between platforms,
 711     // since FxHasher has different behavior for 32-bit and 64-bit platforms.
 712     //
 713     // Obviously, it's extremely undesirable for documentation rendering
 714     // to be depndent on the platform it's run on. Apart from being confusing
 715     // to end users, it makes writing tests much more difficult, as predicates
 716     // can appear in any order in the final result.
 717     //
 718     // To solve this problem, we sort WherePredicates and GenericBounds
 719     // by their Debug string. The thing to keep in mind is that we don't really
 720     // care what the final order is - we're synthesizing an impl or bound
 721     // ourselves, so any order can be considered equally valid. By sorting the
 722     // predicates and bounds, however, we ensure that for a given codebase, all
 723     // auto-trait impls always render in exactly the same way.
 724     //
 725     // Using the Debug implementation for sorting prevents us from needing to
 726     // write quite a bit of almost entirely useless code (e.g., how should two
 727     // Types be sorted relative to each other). It also allows us to solve the
 728     // problem for both WherePredicates and GenericBounds at the same time. This
 729     // approach is probably somewhat slower, but the small number of items
 730     // involved (impls rarely have more than a few bounds) means that it
 731     // shouldn't matter in practice.
 732     fn unstable_debug_sort<T: Debug>(&self, vec: &mut Vec<T>) {
 733         vec.sort_by_cached_key(|x| format!("{:?}", x))
 734     }
 735
 736     fn is_fn_ty(&self, tcx: TyCtxt<'_>, ty: &Type) -> bool {
 737         match &ty {
 738             &&Type::ResolvedPath { ref did, .. } => {
 739                 *did == tcx.require_lang_item(lang_items::FnTraitLangItem, None)
 740                     || *did == tcx.require_lang_item(lang_items::FnMutTraitLangItem, None)
 741                     || *did == tcx.require_lang_item(lang_items::FnOnceTraitLangItem, None)
 742             }
 743             _ => false,
 744         }
 745     }
 746 }
 747
 748 // Replaces all ReVars in a type with ty::Region's, using the provided map
 749 struct RegionReplacer<'a, 'tcx> {
 750     vid_to_region: &'a FxHashMap<ty::RegionVid, ty::Region<'tcx>>,
 751     tcx: TyCtxt<'tcx>,
 752 }
 753
 754 impl<'a, 'tcx> TypeFolder<'tcx> for RegionReplacer<'a, 'tcx> {
 755     fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
 756         self.tcx
 757     }
 758
 759     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
 760         (match r {
 761             &ty::ReVar(vid) => self.vid_to_region.get(&vid).cloned(),
 762             _ => None,
 763         })
 764         .unwrap_or_else(|| r.super_fold_with(self))
 765     }
 766 }