src/librustdoc/clean/auto_trait.rs

   1 // Copyright 2018 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use rustc::hir;
  12 use rustc::traits::{self, auto_trait as auto};
  13 use rustc::ty::{ToPredicate, TypeFoldable};
  14 use rustc::ty::subst::Subst;
  15 use rustc::infer::InferOk;
  16 use std::fmt::Debug;
  17 use syntax_pos::DUMMY_SP;
  18
  19 use core::DocAccessLevels;
  20
  21 use super::*;
  22
  23 pub struct AutoTraitFinder<'a, 'tcx: 'a, 'rcx: 'a> {
  24     pub cx: &'a core::DocContext<'a, 'tcx, 'rcx>,
  25     pub f: auto::AutoTraitFinder<'a, 'tcx>,
  26 }
  27
  28 impl<'a, 'tcx, 'rcx> AutoTraitFinder<'a, 'tcx, 'rcx> {
  29     pub fn new(cx: &'a core::DocContext<'a, 'tcx, 'rcx>) -> Self {
  30         let f = auto::AutoTraitFinder::new(&cx.tcx);
  31
  32         AutoTraitFinder { cx, f }
  33     }
  34
  35     pub fn get_with_def_id(&self, def_id: DefId) -> Vec<Item> {
  36         let ty = self.cx.tcx.type_of(def_id);
  37
  38         let def_ctor: fn(DefId) -> Def = match ty.sty {
  39             ty::TyAdt(adt, _) => match adt.adt_kind() {
  40                 AdtKind::Struct => Def::Struct,
  41                 AdtKind::Enum => Def::Enum,
  42                 AdtKind::Union => Def::Union,
  43             }
  44             ty::TyInt(_) |
  45             ty::TyUint(_) |
  46             ty::TyFloat(_) |
  47             ty::TyStr |
  48             ty::TyBool |
  49             ty::TyChar => return self.get_auto_trait_impls(def_id, &move |_: DefId| {
  50                 match ty.sty {
  51                     ty::TyInt(x) => Def::PrimTy(hir::TyInt(x)),
  52                     ty::TyUint(x) => Def::PrimTy(hir::TyUint(x)),
  53                     ty::TyFloat(x) => Def::PrimTy(hir::TyFloat(x)),
  54                     ty::TyStr => Def::PrimTy(hir::TyStr),
  55                     ty::TyBool => Def::PrimTy(hir::TyBool),
  56                     ty::TyChar => Def::PrimTy(hir::TyChar),
  57                     _ => unreachable!(),
  58                 }
  59             }, None),
  60             _ => {
  61                 debug!("Unexpected type {:?}", def_id);
  62                 return Vec::new()
  63             }
  64         };
  65
  66         self.get_auto_trait_impls(def_id, &def_ctor, None)
  67     }
  68
  69     pub fn get_with_node_id(&self, id: ast::NodeId, name: String) -> Vec<Item> {
  70         let item = &self.cx.tcx.hir.expect_item(id).node;
  71         let did = self.cx.tcx.hir.local_def_id(id);
  72
  73         let def_ctor = match *item {
  74             hir::ItemKind::Struct(_, _) => Def::Struct,
  75             hir::ItemKind::Union(_, _) => Def::Union,
  76             hir::ItemKind::Enum(_, _) => Def::Enum,
  77             _ => panic!("Unexpected type {:?} {:?}", item, id),
  78         };
  79
  80         self.get_auto_trait_impls(did, &def_ctor, Some(name))
  81     }
  82
  83     pub fn get_auto_trait_impls<F>(
  84         &self,
  85         def_id: DefId,
  86         def_ctor: &F,
  87         name: Option<String>,
  88     ) -> Vec<Item>
  89     where F: Fn(DefId) -> Def {
  90         if self.cx
  91             .tcx
  92             .get_attrs(def_id)
  93             .lists("doc")
  94             .has_word("hidden")
  95         {
  96             debug!(
  97                 "get_auto_trait_impls(def_id={:?}, def_ctor=...): item has doc('hidden'), \
  98                  aborting",
  99                 def_id
 100             );
 101             return Vec::new();
 102         }
 103
 104         let tcx = self.cx.tcx;
 105         let generics = self.cx.tcx.generics_of(def_id);
 106
 107         let ty = self.cx.tcx.type_of(def_id);
 108         let mut traits = FxHashMap();
 109         if self.cx.crate_name != Some("core".to_string()) {
 110             if let ty::TyAdt(_adt, _) = ty.sty {
 111                 let param_env = self.cx.tcx.param_env(def_id);
 112                 for &trait_def_id in self.cx.all_traits.iter() {
 113                     if traits.get(&trait_def_id).is_some() ||
 114                        !self.cx.access_levels.borrow().is_doc_reachable(trait_def_id) {
 115                         continue
 116                     }
 117                     let t_name = self.cx.tcx.item_name(trait_def_id).to_string();
 118                     self.cx.tcx.for_each_relevant_impl(trait_def_id, ty, |impl_def_id| {
 119                         self.cx.tcx.infer_ctxt().enter(|infcx| {
 120                             let generics = infcx.tcx.generics_of(impl_def_id);
 121                             let trait_ref = infcx.tcx.impl_trait_ref(impl_def_id).unwrap();
 122
 123                             if !match infcx.tcx.type_of(impl_def_id).sty {
 124                                 ::rustc::ty::TypeVariants::TyParam(_) => true,
 125                                 _ => false,
 126                             } {
 127                                 return;
 128                             }
 129
 130                             let substs = infcx.fresh_substs_for_item(DUMMY_SP, def_id);
 131                             let ty2 = ty.subst(infcx.tcx, substs);
 132                             let param_env = param_env.subst(infcx.tcx, substs);
 133
 134                             let impl_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
 135                             let trait_ref = trait_ref.subst(infcx.tcx, impl_substs);
 136
 137                             // Require the type the impl is implemented on to match
 138                             // our type, and ignore the impl if there was a mismatch.
 139                             let cause = traits::ObligationCause::dummy();
 140                             let eq_result = infcx.at(&cause, param_env).eq(trait_ref.self_ty(), ty2);
 141                             if let Ok(InferOk { value: (), obligations }) = eq_result {
 142                                 // FIXME(eddyb) ignoring `obligations` might cause false positives.
 143                                 drop(obligations);
 144
 145                                 let may_apply = infcx.predicate_may_hold(&traits::Obligation::new(
 146                                     cause.clone(),
 147                                     param_env,
 148                                     trait_ref.to_predicate(),
 149                                 ));
 150                                 if may_apply {
 151                                     if traits.get(&trait_def_id).is_none() {
 152                                         let trait_ = hir::TraitRef {
 153                                             path: get_path_for_type(infcx.tcx, trait_def_id, hir::def::Def::Trait),
 154                                             ref_id: ast::DUMMY_NODE_ID,
 155                                         };
 156                                         let provided_trait_methods = infcx.tcx.provided_trait_methods(impl_def_id)
 157                                                                               .into_iter()
 158                                                                               .map(|meth| meth.ident.to_string())
 159                                                                               .collect();
 160                                         traits.insert(trait_def_id, Item {
 161                                             source: Span::empty(),
 162                                             name: None,
 163                                             attrs: Default::default(),
 164                                             visibility: None,
 165                                             def_id: self.next_def_id(impl_def_id.krate),
 166                                             stability: None,
 167                                             deprecation: None,
 168                                             inner: ImplItem(Impl {
 169                                                 unsafety: hir::Unsafety::Normal,
 170                                                 generics: (generics,
 171                                                            &tcx.predicates_of(impl_def_id)).clean(self.cx),
 172                                                 provided_trait_methods,
 173                                                 trait_: Some(trait_.clean(self.cx)),
 174                                                 for_: ty.clean(self.cx),
 175                                                 items: infcx.tcx.associated_items(impl_def_id).collect::<Vec<_>>().clean(self.cx),
 176                                                 polarity: None,
 177                                                 synthetic: true,
 178                                             }),
 179                                         });
 180                                     }
 181                                 }
 182                                 debug!("{:?} => {}", trait_ref, may_apply);
 183                             }
 184                         });
 185                     });
 186                 }
 187             }
 188         }
 189
 190         debug!(
 191             "get_auto_trait_impls(def_id={:?}, def_ctor=..., generics={:?}",
 192             def_id, generics
 193         );
 194         let auto_traits: Vec<_> =
 195             self.cx.send_trait
 196                           .and_then(|send_trait| {
 197                     self.get_auto_trait_impl_for(
 198                         def_id,
 199                         name.clone(),
 200                         generics.clone(),
 201                         def_ctor,
 202                         send_trait,
 203                     )
 204                 }).into_iter()
 205             .chain(self.get_auto_trait_impl_for(
 206                 def_id,
 207                 name.clone(),
 208                 generics.clone(),
 209                 def_ctor,
 210                 tcx.require_lang_item(lang_items::SyncTraitLangItem),
 211             ).into_iter())
 212             .chain(traits.into_iter().map(|(_, v)| v))
 213             .collect();
 214
 215         debug!(
 216             "get_auto_traits: type {:?} auto_traits {:?}",
 217             def_id, auto_traits
 218         );
 219         auto_traits
 220     }
 221
 222     fn get_auto_trait_impl_for<F>(
 223         &self,
 224         def_id: DefId,
 225         name: Option<String>,
 226         generics: ty::Generics,
 227         def_ctor: &F,
 228         trait_def_id: DefId,
 229     ) -> Option<Item>
 230     where F: Fn(DefId) -> Def {
 231         if !self.cx
 232             .generated_synthetics
 233             .borrow_mut()
 234             .insert((def_id, trait_def_id))
 235         {
 236             debug!(
 237                 "get_auto_trait_impl_for(def_id={:?}, generics={:?}, def_ctor=..., \
 238                  trait_def_id={:?}): already generated, aborting",
 239                 def_id, generics, trait_def_id
 240             );
 241             return None;
 242         }
 243
 244         let result = self.find_auto_trait_generics(def_id, trait_def_id, &generics);
 245
 246         if result.is_auto() {
 247             let trait_ = hir::TraitRef {
 248                 path: get_path_for_type(self.cx.tcx, trait_def_id, hir::def::Def::Trait),
 249                 ref_id: ast::DUMMY_NODE_ID,
 250             };
 251
 252             let polarity;
 253
 254             let new_generics = match result {
 255                 AutoTraitResult::PositiveImpl(new_generics) => {
 256                     polarity = None;
 257                     new_generics
 258                 }
 259                 AutoTraitResult::NegativeImpl => {
 260                     polarity = Some(ImplPolarity::Negative);
 261
 262                     // For negative impls, we use the generic params, but *not* the predicates,
 263                     // from the original type. Otherwise, the displayed impl appears to be a
 264                     // conditional negative impl, when it's really unconditional.
 265                     //
 266                     // For example, consider the struct Foo<T: Copy>(*mut T). Using
 267                     // the original predicates in our impl would cause us to generate
 268                     // `impl !Send for Foo<T: Copy>`, which makes it appear that Foo
 269                     // implements Send where T is not copy.
 270                     //
 271                     // Instead, we generate `impl !Send for Foo<T>`, which better
 272                     // expresses the fact that `Foo<T>` never implements `Send`,
 273                     // regardless of the choice of `T`.
 274                     let real_generics = (&generics, &Default::default());
 275
 276                     // Clean the generics, but ignore the '?Sized' bounds generated
 277                     // by the `Clean` impl
 278                     let clean_generics = real_generics.clean(self.cx);
 279
 280                     Generics {
 281                         params: clean_generics.params,
 282                         where_predicates: Vec::new(),
 283                     }
 284                 }
 285                 _ => unreachable!(),
 286             };
 287
 288             let path = get_path_for_type(self.cx.tcx, def_id, def_ctor);
 289             let mut segments = path.segments.into_vec();
 290             let last = segments.pop().unwrap();
 291
 292             let real_name = name.map(|name| Ident::from_str(&name));
 293
 294             segments.push(hir::PathSegment::new(
 295                 real_name.unwrap_or(last.ident),
 296                 self.generics_to_path_params(generics.clone()),
 297                 false,
 298             ));
 299
 300             let new_path = hir::Path {
 301                 span: path.span,
 302                 def: path.def,
 303                 segments: HirVec::from_vec(segments),
 304             };
 305
 306             let ty = hir::Ty {
 307                 id: ast::DUMMY_NODE_ID,
 308                 node: hir::TyKind::Path(hir::QPath::Resolved(None, P(new_path))),
 309                 span: DUMMY_SP,
 310                 hir_id: hir::DUMMY_HIR_ID,
 311             };
 312
 313             return Some(Item {
 314                 source: Span::empty(),
 315                 name: None,
 316                 attrs: Default::default(),
 317                 visibility: None,
 318                 def_id: self.next_def_id(def_id.krate),
 319                 stability: None,
 320                 deprecation: None,
 321                 inner: ImplItem(Impl {
 322                     unsafety: hir::Unsafety::Normal,
 323                     generics: new_generics,
 324                     provided_trait_methods: FxHashSet(),
 325                     trait_: Some(trait_.clean(self.cx)),
 326                     for_: ty.clean(self.cx),
 327                     items: Vec::new(),
 328                     polarity,
 329                     synthetic: true,
 330                 }),
 331             });
 332         }
 333         None
 334     }
 335
 336     fn generics_to_path_params(&self, generics: ty::Generics) -> hir::GenericArgs {
 337         let mut args = vec![];
 338
 339         for param in generics.params.iter() {
 340             match param.kind {
 341                 ty::GenericParamDefKind::Lifetime => {
 342                     let name = if param.name == "" {
 343                         hir::ParamName::Plain(keywords::StaticLifetime.ident())
 344                     } else {
 345                         hir::ParamName::Plain(ast::Ident::from_interned_str(param.name))
 346                     };
 347
 348                     args.push(hir::GenericArg::Lifetime(hir::Lifetime {
 349                         id: ast::DUMMY_NODE_ID,
 350                         span: DUMMY_SP,
 351                         name: hir::LifetimeName::Param(name),
 352                     }));
 353                 }
 354                 ty::GenericParamDefKind::Type {..} => {
 355                     args.push(hir::GenericArg::Type(self.ty_param_to_ty(param.clone())));
 356                 }
 357             }
 358         }
 359
 360         hir::GenericArgs {
 361             args: HirVec::from_vec(args),
 362             bindings: HirVec::new(),
 363             parenthesized: false,
 364         }
 365     }
 366
 367     fn ty_param_to_ty(&self, param: ty::GenericParamDef) -> hir::Ty {
 368         debug!("ty_param_to_ty({:?}) {:?}", param, param.def_id);
 369         hir::Ty {
 370             id: ast::DUMMY_NODE_ID,
 371             node: hir::TyKind::Path(hir::QPath::Resolved(
 372                 None,
 373                 P(hir::Path {
 374                     span: DUMMY_SP,
 375                     def: Def::TyParam(param.def_id),
 376                     segments: HirVec::from_vec(vec![
 377                         hir::PathSegment::from_ident(Ident::from_interned_str(param.name))
 378                     ]),
 379                 }),
 380             )),
 381             span: DUMMY_SP,
 382             hir_id: hir::DUMMY_HIR_ID,
 383         }
 384     }
 385
 386     fn find_auto_trait_generics(
 387         &self,
 388         did: DefId,
 389         trait_did: DefId,
 390         generics: &ty::Generics,
 391     ) -> AutoTraitResult {
 392         match self.f.find_auto_trait_generics(did, trait_did, generics,
 393                 |infcx, mut info| {
 394                     let region_data = info.region_data;
 395                     let names_map =
 396                         info.names_map
 397                             .drain()
 398                             .map(|name| (name.clone(), Lifetime(name)))
 399                             .collect();
 400                     let lifetime_predicates =
 401                         self.handle_lifetimes(&region_data, &names_map);
 402                     let new_generics = self.param_env_to_generics(
 403                         infcx.tcx,
 404                         did,
 405                         info.full_user_env,
 406                         generics.clone(),
 407                         lifetime_predicates,
 408                         info.vid_to_region,
 409                     );
 410
 411                     debug!(
 412                         "find_auto_trait_generics(did={:?}, trait_did={:?}, generics={:?}): \
 413                          finished with {:?}",
 414                         did, trait_did, generics, new_generics
 415                     );
 416
 417                     new_generics
 418                 }) {
 419             auto::AutoTraitResult::ExplicitImpl => AutoTraitResult::ExplicitImpl,
 420             auto::AutoTraitResult::NegativeImpl => AutoTraitResult::NegativeImpl,
 421             auto::AutoTraitResult::PositiveImpl(res) => AutoTraitResult::PositiveImpl(res),
 422         }
 423     }
 424
 425     fn get_lifetime(&self, region: Region, names_map: &FxHashMap<String, Lifetime>) -> Lifetime {
 426         self.region_name(region)
 427             .map(|name| {
 428                 names_map.get(&name).unwrap_or_else(|| {
 429                     panic!("Missing lifetime with name {:?} for {:?}", name, region)
 430                 })
 431             })
 432             .unwrap_or(&Lifetime::statik())
 433             .clone()
 434     }
 435
 436     fn region_name(&self, region: Region) -> Option<String> {
 437         match region {
 438             &ty::ReEarlyBound(r) => Some(r.name.to_string()),
 439             _ => None,
 440         }
 441     }
 442
 443     // This method calculates two things: Lifetime constraints of the form 'a: 'b,
 444     // and region constraints of the form ReVar: 'a
 445     //
 446     // This is essentially a simplified version of lexical_region_resolve. However,
 447     // handle_lifetimes determines what *needs be* true in order for an impl to hold.
 448     // lexical_region_resolve, along with much of the rest of the compiler, is concerned
 449     // with determining if a given set up constraints/predicates *are* met, given some
 450     // starting conditions (e.g. user-provided code). For this reason, it's easier
 451     // to perform the calculations we need on our own, rather than trying to make
 452     // existing inference/solver code do what we want.
 453     fn handle_lifetimes<'cx>(
 454         &self,
 455         regions: &RegionConstraintData<'cx>,
 456         names_map: &FxHashMap<String, Lifetime>,
 457     ) -> Vec<WherePredicate> {
 458         // Our goal is to 'flatten' the list of constraints by eliminating
 459         // all intermediate RegionVids. At the end, all constraints should
 460         // be between Regions (aka region variables). This gives us the information
 461         // we need to create the Generics.
 462         let mut finished = FxHashMap();
 463
 464         let mut vid_map: FxHashMap<RegionTarget, RegionDeps> = FxHashMap();
 465
 466         // Flattening is done in two parts. First, we insert all of the constraints
 467         // into a map. Each RegionTarget (either a RegionVid or a Region) maps
 468         // to its smaller and larger regions. Note that 'larger' regions correspond
 469         // to sub-regions in Rust code (e.g. in 'a: 'b, 'a is the larger region).
 470         for constraint in regions.constraints.keys() {
 471             match constraint {
 472                 &Constraint::VarSubVar(r1, r2) => {
 473                     {
 474                         let deps1 = vid_map
 475                             .entry(RegionTarget::RegionVid(r1))
 476                             .or_insert_with(|| Default::default());
 477                         deps1.larger.insert(RegionTarget::RegionVid(r2));
 478                     }
 479
 480                     let deps2 = vid_map
 481                         .entry(RegionTarget::RegionVid(r2))
 482                         .or_insert_with(|| Default::default());
 483                     deps2.smaller.insert(RegionTarget::RegionVid(r1));
 484                 }
 485                 &Constraint::RegSubVar(region, vid) => {
 486                     let deps = vid_map
 487                         .entry(RegionTarget::RegionVid(vid))
 488                         .or_insert_with(|| Default::default());
 489                     deps.smaller.insert(RegionTarget::Region(region));
 490                 }
 491                 &Constraint::VarSubReg(vid, region) => {
 492                     let deps = vid_map
 493                         .entry(RegionTarget::RegionVid(vid))
 494                         .or_insert_with(|| Default::default());
 495                     deps.larger.insert(RegionTarget::Region(region));
 496                 }
 497                 &Constraint::RegSubReg(r1, r2) => {
 498                     // The constraint is already in the form that we want, so we're done with it
 499                     // Desired order is 'larger, smaller', so flip then
 500                     if self.region_name(r1) != self.region_name(r2) {
 501                         finished
 502                             .entry(self.region_name(r2).unwrap())
 503                             .or_insert_with(|| Vec::new())
 504                             .push(r1);
 505                     }
 506                 }
 507             }
 508         }
 509
 510         // Here, we 'flatten' the map one element at a time.
 511         // All of the element's sub and super regions are connected
 512         // to each other. For example, if we have a graph that looks like this:
 513         //
 514         // (A, B) - C - (D, E)
 515         // Where (A, B) are subregions, and (D,E) are super-regions
 516         //
 517         // then after deleting 'C', the graph will look like this:
 518         //  ... - A - (D, E ...)
 519         //  ... - B - (D, E, ...)
 520         //  (A, B, ...) - D - ...
 521         //  (A, B, ...) - E - ...
 522         //
 523         //  where '...' signifies the existing sub and super regions of an entry
 524         //  When two adjacent ty::Regions are encountered, we've computed a final
 525         //  constraint, and add it to our list. Since we make sure to never re-add
 526         //  deleted items, this process will always finish.
 527         while !vid_map.is_empty() {
 528             let target = vid_map.keys().next().expect("Keys somehow empty").clone();
 529             let deps = vid_map.remove(&target).expect("Entry somehow missing");
 530
 531             for smaller in deps.smaller.iter() {
 532                 for larger in deps.larger.iter() {
 533                     match (smaller, larger) {
 534                         (&RegionTarget::Region(r1), &RegionTarget::Region(r2)) => {
 535                             if self.region_name(r1) != self.region_name(r2) {
 536                                 finished
 537                                     .entry(self.region_name(r2).unwrap())
 538                                     .or_insert_with(|| Vec::new())
 539                                     .push(r1) // Larger, smaller
 540                             }
 541                         }
 542                         (&RegionTarget::RegionVid(_), &RegionTarget::Region(_)) => {
 543                             if let Entry::Occupied(v) = vid_map.entry(*smaller) {
 544                                 let smaller_deps = v.into_mut();
 545                                 smaller_deps.larger.insert(*larger);
 546                                 smaller_deps.larger.remove(&target);
 547                             }
 548                         }
 549                         (&RegionTarget::Region(_), &RegionTarget::RegionVid(_)) => {
 550                             if let Entry::Occupied(v) = vid_map.entry(*larger) {
 551                                 let deps = v.into_mut();
 552                                 deps.smaller.insert(*smaller);
 553                                 deps.smaller.remove(&target);
 554                             }
 555                         }
 556                         (&RegionTarget::RegionVid(_), &RegionTarget::RegionVid(_)) => {
 557                             if let Entry::Occupied(v) = vid_map.entry(*smaller) {
 558                                 let smaller_deps = v.into_mut();
 559                                 smaller_deps.larger.insert(*larger);
 560                                 smaller_deps.larger.remove(&target);
 561                             }
 562
 563                             if let Entry::Occupied(v) = vid_map.entry(*larger) {
 564                                 let larger_deps = v.into_mut();
 565                                 larger_deps.smaller.insert(*smaller);
 566                                 larger_deps.smaller.remove(&target);
 567                             }
 568                         }
 569                     }
 570                 }
 571             }
 572         }
 573
 574         let lifetime_predicates = names_map
 575             .iter()
 576             .flat_map(|(name, lifetime)| {
 577                 let empty = Vec::new();
 578                 let bounds: FxHashSet<GenericBound> = finished.get(name).unwrap_or(&empty).iter()
 579                     .map(|region| GenericBound::Outlives(self.get_lifetime(region, names_map)))
 580                     .collect();
 581
 582                 if bounds.is_empty() {
 583                     return None;
 584                 }
 585                 Some(WherePredicate::RegionPredicate {
 586                     lifetime: lifetime.clone(),
 587                     bounds: bounds.into_iter().collect(),
 588                 })
 589             })
 590             .collect();
 591
 592         lifetime_predicates
 593     }
 594
 595     fn extract_for_generics<'b, 'c, 'd>(
 596         &self,
 597         tcx: TyCtxt<'b, 'c, 'd>,
 598         pred: ty::Predicate<'d>,
 599     ) -> FxHashSet<GenericParamDef> {
 600         pred.walk_tys()
 601             .flat_map(|t| {
 602                 let mut regions = FxHashSet();
 603                 tcx.collect_regions(&t, &mut regions);
 604
 605                 regions.into_iter().flat_map(|r| {
 606                     match r {
 607                         // We only care about late bound regions, as we need to add them
 608                         // to the 'for<>' section
 609                         &ty::ReLateBound(_, ty::BoundRegion::BrNamed(_, name)) => {
 610                             Some(GenericParamDef {
 611                                 name: name.to_string(),
 612                                 kind: GenericParamDefKind::Lifetime,
 613                             })
 614                         }
 615                         &ty::ReVar(_) | &ty::ReEarlyBound(_) => None,
 616                         _ => panic!("Unexpected region type {:?}", r),
 617                     }
 618                 })
 619             })
 620             .collect()
 621     }
 622
 623     fn make_final_bounds<'b, 'c, 'cx>(
 624         &self,
 625         ty_to_bounds: FxHashMap<Type, FxHashSet<GenericBound>>,
 626         ty_to_fn: FxHashMap<Type, (Option<PolyTrait>, Option<Type>)>,
 627         lifetime_to_bounds: FxHashMap<Lifetime, FxHashSet<GenericBound>>,
 628     ) -> Vec<WherePredicate> {
 629         ty_to_bounds
 630             .into_iter()
 631             .flat_map(|(ty, mut bounds)| {
 632                 if let Some(data) = ty_to_fn.get(&ty) {
 633                     let (poly_trait, output) =
 634                         (data.0.as_ref().unwrap().clone(), data.1.as_ref().cloned());
 635                     let new_ty = match &poly_trait.trait_ {
 636                         &Type::ResolvedPath {
 637                             ref path,
 638                             ref typarams,
 639                             ref did,
 640                             ref is_generic,
 641                         } => {
 642                             let mut new_path = path.clone();
 643                             let last_segment = new_path.segments.pop().unwrap();
 644
 645                             let (old_input, old_output) = match last_segment.args {
 646                                 GenericArgs::AngleBracketed { types, .. } => (types, None),
 647                                 GenericArgs::Parenthesized { inputs, output, .. } => {
 648                                     (inputs, output)
 649                                 }
 650                             };
 651
 652                             if old_output.is_some() && old_output != output {
 653                                 panic!(
 654                                     "Output mismatch for {:?} {:?} {:?}",
 655                                     ty, old_output, data.1
 656                                 );
 657                             }
 658
 659                             let new_params = GenericArgs::Parenthesized {
 660                                 inputs: old_input,
 661                                 output,
 662                             };
 663
 664                             new_path.segments.push(PathSegment {
 665                                 name: last_segment.name,
 666                                 args: new_params,
 667                             });
 668
 669                             Type::ResolvedPath {
 670                                 path: new_path,
 671                                 typarams: typarams.clone(),
 672                                 did: did.clone(),
 673                                 is_generic: *is_generic,
 674                             }
 675                         }
 676                         _ => panic!("Unexpected data: {:?}, {:?}", ty, data),
 677                     };
 678                     bounds.insert(GenericBound::TraitBound(
 679                         PolyTrait {
 680                             trait_: new_ty,
 681                             generic_params: poly_trait.generic_params,
 682                         },
 683                         hir::TraitBoundModifier::None,
 684                     ));
 685                 }
 686                 if bounds.is_empty() {
 687                     return None;
 688                 }
 689
 690                 let mut bounds_vec = bounds.into_iter().collect();
 691                 self.sort_where_bounds(&mut bounds_vec);
 692
 693                 Some(WherePredicate::BoundPredicate {
 694                     ty,
 695                     bounds: bounds_vec,
 696                 })
 697             })
 698             .chain(
 699                 lifetime_to_bounds
 700                     .into_iter()
 701                     .filter(|&(_, ref bounds)| !bounds.is_empty())
 702                     .map(|(lifetime, bounds)| {
 703                         let mut bounds_vec = bounds.into_iter().collect();
 704                         self.sort_where_bounds(&mut bounds_vec);
 705                         WherePredicate::RegionPredicate {
 706                             lifetime,
 707                             bounds: bounds_vec,
 708                         }
 709                     }),
 710             )
 711             .collect()
 712     }
 713
 714     // Converts the calculated ParamEnv and lifetime information to a clean::Generics, suitable for
 715     // display on the docs page. Cleaning the Predicates produces sub-optimal WherePredicate's,
 716     // so we fix them up:
 717     //
 718     // * Multiple bounds for the same type are coalesced into one: e.g. 'T: Copy', 'T: Debug'
 719     // becomes 'T: Copy + Debug'
 720     // * Fn bounds are handled specially - instead of leaving it as 'T: Fn(), <T as Fn::Output> =
 721     // K', we use the dedicated syntax 'T: Fn() -> K'
 722     // * We explcitly add a '?Sized' bound if we didn't find any 'Sized' predicates for a type
 723     fn param_env_to_generics<'b, 'c, 'cx>(
 724         &self,
 725         tcx: TyCtxt<'b, 'c, 'cx>,
 726         did: DefId,
 727         param_env: ty::ParamEnv<'cx>,
 728         type_generics: ty::Generics,
 729         mut existing_predicates: Vec<WherePredicate>,
 730         vid_to_region: FxHashMap<ty::RegionVid, ty::Region<'cx>>,
 731     ) -> Generics {
 732         debug!(
 733             "param_env_to_generics(did={:?}, param_env={:?}, type_generics={:?}, \
 734              existing_predicates={:?})",
 735             did, param_env, type_generics, existing_predicates
 736         );
 737
 738         // The `Sized` trait must be handled specially, since we only only display it when
 739         // it is *not* required (i.e. '?Sized')
 740         let sized_trait = self.cx
 741             .tcx
 742             .require_lang_item(lang_items::SizedTraitLangItem);
 743
 744         let mut replacer = RegionReplacer {
 745             vid_to_region: &vid_to_region,
 746             tcx,
 747         };
 748
 749         let orig_bounds: FxHashSet<_> = self.cx.tcx.param_env(did).caller_bounds.iter().collect();
 750         let clean_where_predicates = param_env
 751             .caller_bounds
 752             .iter()
 753             .filter(|p| {
 754                 !orig_bounds.contains(p) || match p {
 755                     &&ty::Predicate::Trait(pred) => pred.def_id() == sized_trait,
 756                     _ => false,
 757                 }
 758             })
 759             .map(|p| {
 760                 let replaced = p.fold_with(&mut replacer);
 761                 (replaced.clone(), replaced.clean(self.cx))
 762             });
 763
 764         let full_generics = (&type_generics, &tcx.predicates_of(did));
 765         let Generics {
 766             params: mut generic_params,
 767             ..
 768         } = full_generics.clean(self.cx);
 769
 770         let mut has_sized = FxHashSet();
 771         let mut ty_to_bounds = FxHashMap();
 772         let mut lifetime_to_bounds = FxHashMap();
 773         let mut ty_to_traits: FxHashMap<Type, FxHashSet<Type>> = FxHashMap();
 774
 775         let mut ty_to_fn: FxHashMap<Type, (Option<PolyTrait>, Option<Type>)> = FxHashMap();
 776
 777         for (orig_p, p) in clean_where_predicates {
 778             match p {
 779                 WherePredicate::BoundPredicate { ty, mut bounds } => {
 780                     // Writing a projection trait bound of the form
 781                     // <T as Trait>::Name : ?Sized
 782                     // is illegal, because ?Sized bounds can only
 783                     // be written in the (here, nonexistant) definition
 784                     // of the type.
 785                     // Therefore, we make sure that we never add a ?Sized
 786                     // bound for projections
 787                     match &ty {
 788                         &Type::QPath { .. } => {
 789                             has_sized.insert(ty.clone());
 790                         }
 791                         _ => {}
 792                     }
 793
 794                     if bounds.is_empty() {
 795                         continue;
 796                     }
 797
 798                     let mut for_generics = self.extract_for_generics(tcx, orig_p.clone());
 799
 800                     assert!(bounds.len() == 1);
 801                     let mut b = bounds.pop().unwrap();
 802
 803                     if b.is_sized_bound(self.cx) {
 804                         has_sized.insert(ty.clone());
 805                     } else if !b.get_trait_type()
 806                         .and_then(|t| {
 807                             ty_to_traits
 808                                 .get(&ty)
 809                                 .map(|bounds| bounds.contains(&strip_type(t.clone())))
 810                         })
 811                         .unwrap_or(false)
 812                     {
 813                         // If we've already added a projection bound for the same type, don't add
 814                         // this, as it would be a duplicate
 815
 816                         // Handle any 'Fn/FnOnce/FnMut' bounds specially,
 817                         // as we want to combine them with any 'Output' qpaths
 818                         // later
 819
 820                         let is_fn = match &mut b {
 821                             &mut GenericBound::TraitBound(ref mut p, _) => {
 822                                 // Insert regions into the for_generics hash map first, to ensure
 823                                 // that we don't end up with duplicate bounds (e.g. for<'b, 'b>)
 824                                 for_generics.extend(p.generic_params.clone());
 825                                 p.generic_params = for_generics.into_iter().collect();
 826                                 self.is_fn_ty(&tcx, &p.trait_)
 827                             }
 828                             _ => false,
 829                         };
 830
 831                         let poly_trait = b.get_poly_trait().unwrap();
 832
 833                         if is_fn {
 834                             ty_to_fn
 835                                 .entry(ty.clone())
 836                                 .and_modify(|e| *e = (Some(poly_trait.clone()), e.1.clone()))
 837                                 .or_insert(((Some(poly_trait.clone())), None));
 838
 839                             ty_to_bounds
 840                                 .entry(ty.clone())
 841                                 .or_insert_with(|| FxHashSet());
 842                         } else {
 843                             ty_to_bounds
 844                                 .entry(ty.clone())
 845                                 .or_insert_with(|| FxHashSet())
 846                                 .insert(b.clone());
 847                         }
 848                     }
 849                 }
 850                 WherePredicate::RegionPredicate { lifetime, bounds } => {
 851                     lifetime_to_bounds
 852                         .entry(lifetime)
 853                         .or_insert_with(|| FxHashSet())
 854                         .extend(bounds);
 855                 }
 856                 WherePredicate::EqPredicate { lhs, rhs } => {
 857                     match &lhs {
 858                         &Type::QPath {
 859                             name: ref left_name,
 860                             ref self_type,
 861                             ref trait_,
 862                         } => {
 863                             let ty = &*self_type;
 864                             match **trait_ {
 865                                 Type::ResolvedPath {
 866                                     path: ref trait_path,
 867                                     ref typarams,
 868                                     ref did,
 869                                     ref is_generic,
 870                                 } => {
 871                                     let mut new_trait_path = trait_path.clone();
 872
 873                                     if self.is_fn_ty(&tcx, trait_) && left_name == FN_OUTPUT_NAME {
 874                                         ty_to_fn
 875                                             .entry(*ty.clone())
 876                                             .and_modify(|e| *e = (e.0.clone(), Some(rhs.clone())))
 877                                             .or_insert((None, Some(rhs)));
 878                                         continue;
 879                                     }
 880
 881                                     // FIXME: Remove this scope when NLL lands
 882                                     {
 883                                         let args =
 884                                             &mut new_trait_path.segments.last_mut().unwrap().args;
 885
 886                                         match args {
 887                                             // Convert somethiung like '<T as Iterator::Item> = u8'
 888                                             // to 'T: Iterator<Item=u8>'
 889                                             &mut GenericArgs::AngleBracketed {
 890                                                 ref mut bindings,
 891                                                 ..
 892                                             } => {
 893                                                 bindings.push(TypeBinding {
 894                                                     name: left_name.clone(),
 895                                                     ty: rhs,
 896                                                 });
 897                                             }
 898                                             &mut GenericArgs::Parenthesized { .. } => {
 899                                                 existing_predicates.push(
 900                                                     WherePredicate::EqPredicate {
 901                                                         lhs: lhs.clone(),
 902                                                         rhs,
 903                                                     },
 904                                                 );
 905                                                 continue; // If something other than a Fn ends up
 906                                                           // with parenthesis, leave it alone
 907                                             }
 908                                         }
 909                                     }
 910
 911                                     let bounds = ty_to_bounds
 912                                         .entry(*ty.clone())
 913                                         .or_insert_with(|| FxHashSet());
 914
 915                                     bounds.insert(GenericBound::TraitBound(
 916                                         PolyTrait {
 917                                             trait_: Type::ResolvedPath {
 918                                                 path: new_trait_path,
 919                                                 typarams: typarams.clone(),
 920                                                 did: did.clone(),
 921                                                 is_generic: *is_generic,
 922                                             },
 923                                             generic_params: Vec::new(),
 924                                         },
 925                                         hir::TraitBoundModifier::None,
 926                                     ));
 927
 928                                     // Remove any existing 'plain' bound (e.g. 'T: Iterator`) so
 929                                     // that we don't see a
 930                                     // duplicate bound like `T: Iterator + Iterator<Item=u8>`
 931                                     // on the docs page.
 932                                     bounds.remove(&GenericBound::TraitBound(
 933                                         PolyTrait {
 934                                             trait_: *trait_.clone(),
 935                                             generic_params: Vec::new(),
 936                                         },
 937                                         hir::TraitBoundModifier::None,
 938                                     ));
 939                                     // Avoid creating any new duplicate bounds later in the outer
 940                                     // loop
 941                                     ty_to_traits
 942                                         .entry(*ty.clone())
 943                                         .or_insert_with(|| FxHashSet())
 944                                         .insert(*trait_.clone());
 945                                 }
 946                                 _ => panic!("Unexpected trait {:?} for {:?}", trait_, did),
 947                             }
 948                         }
 949                         _ => panic!("Unexpected LHS {:?} for {:?}", lhs, did),
 950                     }
 951                 }
 952             };
 953         }
 954
 955         let final_bounds = self.make_final_bounds(ty_to_bounds, ty_to_fn, lifetime_to_bounds);
 956
 957         existing_predicates.extend(final_bounds);
 958
 959         for param in generic_params.iter_mut() {
 960             match param.kind {
 961                 GenericParamDefKind::Type { ref mut default, ref mut bounds, .. } => {
 962                     // We never want something like `impl<T=Foo>`.
 963                     default.take();
 964                     let generic_ty = Type::Generic(param.name.clone());
 965                     if !has_sized.contains(&generic_ty) {
 966                         bounds.insert(0, GenericBound::maybe_sized(self.cx));
 967                     }
 968                 }
 969                 GenericParamDefKind::Lifetime => {}
 970             }
 971         }
 972
 973         self.sort_where_predicates(&mut existing_predicates);
 974
 975         Generics {
 976             params: generic_params,
 977             where_predicates: existing_predicates,
 978         }
 979     }
 980
 981     // Ensure that the predicates are in a consistent order. The precise
 982     // ordering doesn't actually matter, but it's important that
 983     // a given set of predicates always appears in the same order -
 984     // both for visual consistency between 'rustdoc' runs, and to
 985     // make writing tests much easier
 986     #[inline]
 987     fn sort_where_predicates(&self, mut predicates: &mut Vec<WherePredicate>) {
 988         // We should never have identical bounds - and if we do,
 989         // they're visually identical as well. Therefore, using
 990         // an unstable sort is fine.
 991         self.unstable_debug_sort(&mut predicates);
 992     }
 993
 994     // Ensure that the bounds are in a consistent order. The precise
 995     // ordering doesn't actually matter, but it's important that
 996     // a given set of bounds always appears in the same order -
 997     // both for visual consistency between 'rustdoc' runs, and to
 998     // make writing tests much easier
 999     #[inline]
1000     fn sort_where_bounds(&self, mut bounds: &mut Vec<GenericBound>) {
1001         // We should never have identical bounds - and if we do,
1002         // they're visually identical as well. Therefore, using
1003         // an unstable sort is fine.
1004         self.unstable_debug_sort(&mut bounds);
1005     }
1006
1007     // This might look horrendously hacky, but it's actually not that bad.
1008     //
1009     // For performance reasons, we use several different FxHashMaps
1010     // in the process of computing the final set of where predicates.
1011     // However, the iteration order of a HashMap is completely unspecified.
1012     // In fact, the iteration of an FxHashMap can even vary between platforms,
1013     // since FxHasher has different behavior for 32-bit and 64-bit platforms.
1014     //
1015     // Obviously, it's extremely undesireable for documentation rendering
1016     // to be depndent on the platform it's run on. Apart from being confusing
1017     // to end users, it makes writing tests much more difficult, as predicates
1018     // can appear in any order in the final result.
1019     //
1020     // To solve this problem, we sort WherePredicates and GenericBounds
1021     // by their Debug string. The thing to keep in mind is that we don't really
1022     // care what the final order is - we're synthesizing an impl or bound
1023     // ourselves, so any order can be considered equally valid. By sorting the
1024     // predicates and bounds, however, we ensure that for a given codebase, all
1025     // auto-trait impls always render in exactly the same way.
1026     //
1027     // Using the Debug impementation for sorting prevents us from needing to
1028     // write quite a bit of almost entirely useless code (e.g. how should two
1029     // Types be sorted relative to each other). It also allows us to solve the
1030     // problem for both WherePredicates and GenericBounds at the same time. This
1031     // approach is probably somewhat slower, but the small number of items
1032     // involved (impls rarely have more than a few bounds) means that it
1033     // shouldn't matter in practice.
1034     fn unstable_debug_sort<T: Debug>(&self, vec: &mut Vec<T>) {
1035         vec.sort_by_cached_key(|x| format!("{:?}", x))
1036     }
1037
1038     fn is_fn_ty(&self, tcx: &TyCtxt, ty: &Type) -> bool {
1039         match &ty {
1040             &&Type::ResolvedPath { ref did, .. } => {
1041                 *did == tcx.require_lang_item(lang_items::FnTraitLangItem)
1042                     || *did == tcx.require_lang_item(lang_items::FnMutTraitLangItem)
1043                     || *did == tcx.require_lang_item(lang_items::FnOnceTraitLangItem)
1044             }
1045             _ => false,
1046         }
1047     }
1048
1049     // This is an ugly hack, but it's the simplest way to handle synthetic impls without greatly
1050     // refactoring either librustdoc or librustc. In particular, allowing new DefIds to be
1051     // registered after the AST is constructed would require storing the defid mapping in a
1052     // RefCell, decreasing the performance for normal compilation for very little gain.
1053     //
1054     // Instead, we construct 'fake' def ids, which start immediately after the last DefId in
1055     // DefIndexAddressSpace::Low. In the Debug impl for clean::Item, we explicitly check for fake
1056     // def ids, as we'll end up with a panic if we use the DefId Debug impl for fake DefIds
1057     fn next_def_id(&self, crate_num: CrateNum) -> DefId {
1058         let start_def_id = {
1059             let next_id = if crate_num == LOCAL_CRATE {
1060                 self.cx
1061                     .tcx
1062                     .hir
1063                     .definitions()
1064                     .def_path_table()
1065                     .next_id(DefIndexAddressSpace::Low)
1066             } else {
1067                 self.cx
1068                     .cstore
1069                     .def_path_table(crate_num)
1070                     .next_id(DefIndexAddressSpace::Low)
1071             };
1072
1073             DefId {
1074                 krate: crate_num,
1075                 index: next_id,
1076             }
1077         };
1078
1079         let mut fake_ids = self.cx.fake_def_ids.borrow_mut();
1080
1081         let def_id = fake_ids.entry(crate_num).or_insert(start_def_id).clone();
1082         fake_ids.insert(
1083             crate_num,
1084             DefId {
1085                 krate: crate_num,
1086                 index: DefIndex::from_array_index(
1087                     def_id.index.as_array_index() + 1,
1088                     def_id.index.address_space(),
1089                 ),
1090             },
1091         );
1092
1093         MAX_DEF_ID.with(|m| {
1094             m.borrow_mut()
1095                 .entry(def_id.krate.clone())
1096                 .or_insert(start_def_id);
1097         });
1098
1099         self.cx.all_fake_def_ids.borrow_mut().insert(def_id);
1100
1101         def_id.clone()
1102     }
1103 }
1104
1105 // Replaces all ReVars in a type with ty::Region's, using the provided map
1106 struct RegionReplacer<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
1107     vid_to_region: &'a FxHashMap<ty::RegionVid, ty::Region<'tcx>>,
1108     tcx: TyCtxt<'a, 'gcx, 'tcx>,
1109 }
1110
1111 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for RegionReplacer<'a, 'gcx, 'tcx> {
1112     fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> {
1113         self.tcx
1114     }
1115
1116     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
1117         (match r {
1118             &ty::ReVar(vid) => self.vid_to_region.get(&vid).cloned(),
1119             _ => None,
1120         }).unwrap_or_else(|| r.super_fold_with(self))
1121     }
1122 }