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::{self, 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     fn get_real_ty<F>(&self,
  84                       def_id: DefId,
  85                       def_ctor: &F,
  86                       real_name: &Option<Ident>,
  87                       generics: &ty::Generics,
  88     ) -> hir::Ty
  89     where F: Fn(DefId) -> Def {
  90         let path = get_path_for_type(self.cx.tcx, def_id, def_ctor);
  91         let mut segments = path.segments.into_vec();
  92         let last = segments.pop().unwrap();
  93
  94         segments.push(hir::PathSegment::new(
  95             real_name.unwrap_or(last.ident),
  96             self.generics_to_path_params(generics.clone()),
  97             false,
  98         ));
  99
 100         let new_path = hir::Path {
 101             span: path.span,
 102             def: path.def,
 103             segments: HirVec::from_vec(segments),
 104         };
 105
 106         hir::Ty {
 107             id: ast::DUMMY_NODE_ID,
 108             node: hir::TyKind::Path(hir::QPath::Resolved(None, P(new_path))),
 109             span: DUMMY_SP,
 110             hir_id: hir::DUMMY_HIR_ID,
 111         }
 112     }
 113
 114     pub fn get_auto_trait_impls<F>(
 115         &self,
 116         def_id: DefId,
 117         def_ctor: &F,
 118         name: Option<String>,
 119     ) -> Vec<Item>
 120     where F: Fn(DefId) -> Def {
 121         if self.cx
 122             .tcx
 123             .get_attrs(def_id)
 124             .lists("doc")
 125             .has_word("hidden")
 126         {
 127             debug!(
 128                 "get_auto_trait_impls(def_id={:?}, def_ctor=...): item has doc('hidden'), \
 129                  aborting",
 130                 def_id
 131             );
 132             return Vec::new();
 133         }
 134
 135         let tcx = self.cx.tcx;
 136         let generics = self.cx.tcx.generics_of(def_id);
 137
 138         let ty = self.cx.tcx.type_of(def_id);
 139         let mut traits = Vec::new();
 140         if self.cx.crate_name != Some("core".to_string()) &&
 141            self.cx.access_levels.borrow().is_doc_reachable(def_id) {
 142             let real_name = name.clone().map(|name| Ident::from_str(&name));
 143             let param_env = self.cx.tcx.param_env(def_id);
 144             for &trait_def_id in self.cx.all_traits.iter() {
 145                 if !self.cx.access_levels.borrow().is_doc_reachable(trait_def_id) ||
 146                    self.cx.generated_synthetics
 147                           .borrow_mut()
 148                           .get(&(def_id, trait_def_id))
 149                           .is_some() {
 150                     continue
 151                 }
 152                 self.cx.tcx.for_each_relevant_impl(trait_def_id, ty, |impl_def_id| {
 153                     self.cx.tcx.infer_ctxt().enter(|infcx| {
 154                         let t_generics = infcx.tcx.generics_of(impl_def_id);
 155                         let trait_ref = infcx.tcx.impl_trait_ref(impl_def_id).unwrap();
 156
 157                         match infcx.tcx.type_of(impl_def_id).sty {
 158                             ::rustc::ty::TypeVariants::TyParam(_) => {},
 159                             _ => return,
 160                         }
 161
 162                         let substs = infcx.fresh_substs_for_item(DUMMY_SP, def_id);
 163                         let ty = ty.subst(infcx.tcx, substs);
 164                         let param_env = param_env.subst(infcx.tcx, substs);
 165
 166                         let impl_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
 167                         let trait_ref = trait_ref.subst(infcx.tcx, impl_substs);
 168
 169                         // Require the type the impl is implemented on to match
 170                         // our type, and ignore the impl if there was a mismatch.
 171                         let cause = traits::ObligationCause::dummy();
 172                         let eq_result = infcx.at(&cause, param_env)
 173                                              .eq(trait_ref.self_ty(), ty);
 174                         if let Ok(InferOk { value: (), obligations }) = eq_result {
 175                             // FIXME(eddyb) ignoring `obligations` might cause false positives.
 176                             drop(obligations);
 177
 178                             let may_apply = infcx.predicate_may_hold(&traits::Obligation::new(
 179                                 cause.clone(),
 180                                 param_env,
 181                                 trait_ref.to_predicate(),
 182                             ));
 183                             if !may_apply {
 184                                 return
 185                             }
 186                             self.cx.generated_synthetics.borrow_mut()
 187                                                         .insert((def_id, trait_def_id));
 188                             let trait_ = hir::TraitRef {
 189                                 path: get_path_for_type(infcx.tcx,
 190                                                         trait_def_id,
 191                                                         hir::def::Def::Trait),
 192                                 ref_id: ast::DUMMY_NODE_ID,
 193                             };
 194                             let provided_trait_methods =
 195                                 infcx.tcx.provided_trait_methods(trait_def_id)
 196                                          .into_iter()
 197                                          .map(|meth| meth.ident.to_string())
 198                                          .collect();
 199
 200                             let ty = self.get_real_ty(def_id, def_ctor, &real_name, generics);
 201                             let predicates = infcx.tcx.predicates_of(def_id);
 202
 203                             traits.push(Item {
 204                                 source: infcx.tcx.def_span(impl_def_id).clean(self.cx),
 205                                 name: None,
 206                                 attrs: Default::default(),
 207                                 visibility: None,
 208                                 def_id: self.next_def_id(impl_def_id.krate),
 209                                 stability: None,
 210                                 deprecation: None,
 211                                 inner: ImplItem(Impl {
 212                                     unsafety: hir::Unsafety::Normal,
 213                                     generics: (t_generics, &predicates).clean(self.cx),
 214                                     provided_trait_methods,
 215                                     trait_: Some(trait_.clean(self.cx)),
 216                                     for_: ty.clean(self.cx),
 217                                     items: infcx.tcx.associated_items(impl_def_id)
 218                                                     .collect::<Vec<_>>()
 219                                                     .clean(self.cx),
 220                                     polarity: None,
 221                                     synthetic: true,
 222                                 }),
 223                             });
 224                             debug!("{:?} => {}", trait_ref, may_apply);
 225                         }
 226                     });
 227                 });
 228             }
 229         }
 230
 231         debug!(
 232             "get_auto_trait_impls(def_id={:?}, def_ctor=..., generics={:?}",
 233             def_id, generics
 234         );
 235         let auto_traits: Vec<_> =
 236             self.cx.send_trait
 237                           .and_then(|send_trait| {
 238                     self.get_auto_trait_impl_for(
 239                         def_id,
 240                         name.clone(),
 241                         generics.clone(),
 242                         def_ctor,
 243                         send_trait,
 244                     )
 245                 }).into_iter()
 246             .chain(self.get_auto_trait_impl_for(
 247                 def_id,
 248                 name.clone(),
 249                 generics.clone(),
 250                 def_ctor,
 251                 tcx.require_lang_item(lang_items::SyncTraitLangItem),
 252             ).into_iter())
 253             .chain(traits.into_iter())
 254             .collect();
 255
 256         debug!(
 257             "get_auto_traits: type {:?} auto_traits {:?}",
 258             def_id, auto_traits
 259         );
 260         auto_traits
 261     }
 262
 263     fn get_auto_trait_impl_for<F>(
 264         &self,
 265         def_id: DefId,
 266         name: Option<String>,
 267         generics: ty::Generics,
 268         def_ctor: &F,
 269         trait_def_id: DefId,
 270     ) -> Option<Item>
 271     where F: Fn(DefId) -> Def {
 272         if !self.cx
 273             .generated_synthetics
 274             .borrow_mut()
 275             .insert((def_id, trait_def_id))
 276         {
 277             debug!(
 278                 "get_auto_trait_impl_for(def_id={:?}, generics={:?}, def_ctor=..., \
 279                  trait_def_id={:?}): already generated, aborting",
 280                 def_id, generics, trait_def_id
 281             );
 282             return None;
 283         }
 284
 285         let result = self.find_auto_trait_generics(def_id, trait_def_id, &generics);
 286
 287         if result.is_auto() {
 288             let trait_ = hir::TraitRef {
 289                 path: get_path_for_type(self.cx.tcx, trait_def_id, hir::def::Def::Trait),
 290                 ref_id: ast::DUMMY_NODE_ID,
 291             };
 292
 293             let polarity;
 294
 295             let new_generics = match result {
 296                 AutoTraitResult::PositiveImpl(new_generics) => {
 297                     polarity = None;
 298                     new_generics
 299                 }
 300                 AutoTraitResult::NegativeImpl => {
 301                     polarity = Some(ImplPolarity::Negative);
 302
 303                     // For negative impls, we use the generic params, but *not* the predicates,
 304                     // from the original type. Otherwise, the displayed impl appears to be a
 305                     // conditional negative impl, when it's really unconditional.
 306                     //
 307                     // For example, consider the struct Foo<T: Copy>(*mut T). Using
 308                     // the original predicates in our impl would cause us to generate
 309                     // `impl !Send for Foo<T: Copy>`, which makes it appear that Foo
 310                     // implements Send where T is not copy.
 311                     //
 312                     // Instead, we generate `impl !Send for Foo<T>`, which better
 313                     // expresses the fact that `Foo<T>` never implements `Send`,
 314                     // regardless of the choice of `T`.
 315                     let real_generics = (&generics, &Default::default());
 316
 317                     // Clean the generics, but ignore the '?Sized' bounds generated
 318                     // by the `Clean` impl
 319                     let clean_generics = real_generics.clean(self.cx);
 320
 321                     Generics {
 322                         params: clean_generics.params,
 323                         where_predicates: Vec::new(),
 324                     }
 325                 }
 326                 _ => unreachable!(),
 327             };
 328             let real_name = name.map(|name| Ident::from_str(&name));
 329             let ty = self.get_real_ty(def_id, def_ctor, &real_name, &generics);
 330
 331             return Some(Item {
 332                 source: Span::empty(),
 333                 name: None,
 334                 attrs: Default::default(),
 335                 visibility: None,
 336                 def_id: self.next_def_id(def_id.krate),
 337                 stability: None,
 338                 deprecation: None,
 339                 inner: ImplItem(Impl {
 340                     unsafety: hir::Unsafety::Normal,
 341                     generics: new_generics,
 342                     provided_trait_methods: FxHashSet(),
 343                     trait_: Some(trait_.clean(self.cx)),
 344                     for_: ty.clean(self.cx),
 345                     items: Vec::new(),
 346                     polarity,
 347                     synthetic: true,
 348                 }),
 349             });
 350         }
 351         None
 352     }
 353
 354     fn generics_to_path_params(&self, generics: ty::Generics) -> hir::GenericArgs {
 355         let mut args = vec![];
 356
 357         for param in generics.params.iter() {
 358             match param.kind {
 359                 ty::GenericParamDefKind::Lifetime => {
 360                     let name = if param.name == "" {
 361                         hir::ParamName::Plain(keywords::StaticLifetime.ident())
 362                     } else {
 363                         hir::ParamName::Plain(ast::Ident::from_interned_str(param.name))
 364                     };
 365
 366                     args.push(hir::GenericArg::Lifetime(hir::Lifetime {
 367                         id: ast::DUMMY_NODE_ID,
 368                         span: DUMMY_SP,
 369                         name: hir::LifetimeName::Param(name),
 370                     }));
 371                 }
 372                 ty::GenericParamDefKind::Type {..} => {
 373                     args.push(hir::GenericArg::Type(self.ty_param_to_ty(param.clone())));
 374                 }
 375             }
 376         }
 377
 378         hir::GenericArgs {
 379             args: HirVec::from_vec(args),
 380             bindings: HirVec::new(),
 381             parenthesized: false,
 382         }
 383     }
 384
 385     fn ty_param_to_ty(&self, param: ty::GenericParamDef) -> hir::Ty {
 386         debug!("ty_param_to_ty({:?}) {:?}", param, param.def_id);
 387         hir::Ty {
 388             id: ast::DUMMY_NODE_ID,
 389             node: hir::TyKind::Path(hir::QPath::Resolved(
 390                 None,
 391                 P(hir::Path {
 392                     span: DUMMY_SP,
 393                     def: Def::TyParam(param.def_id),
 394                     segments: HirVec::from_vec(vec![
 395                         hir::PathSegment::from_ident(Ident::from_interned_str(param.name))
 396                     ]),
 397                 }),
 398             )),
 399             span: DUMMY_SP,
 400             hir_id: hir::DUMMY_HIR_ID,
 401         }
 402     }
 403
 404     fn find_auto_trait_generics(
 405         &self,
 406         did: DefId,
 407         trait_did: DefId,
 408         generics: &ty::Generics,
 409     ) -> AutoTraitResult {
 410         match self.f.find_auto_trait_generics(did, trait_did, generics,
 411                 |infcx, mut info| {
 412                     let region_data = info.region_data;
 413                     let names_map =
 414                         info.names_map
 415                             .drain()
 416                             .map(|name| (name.clone(), Lifetime(name)))
 417                             .collect();
 418                     let lifetime_predicates =
 419                         self.handle_lifetimes(&region_data, &names_map);
 420                     let new_generics = self.param_env_to_generics(
 421                         infcx.tcx,
 422                         did,
 423                         info.full_user_env,
 424                         generics.clone(),
 425                         lifetime_predicates,
 426                         info.vid_to_region,
 427                     );
 428
 429                     debug!(
 430                         "find_auto_trait_generics(did={:?}, trait_did={:?}, generics={:?}): \
 431                          finished with {:?}",
 432                         did, trait_did, generics, new_generics
 433                     );
 434
 435                     new_generics
 436                 }) {
 437             auto::AutoTraitResult::ExplicitImpl => AutoTraitResult::ExplicitImpl,
 438             auto::AutoTraitResult::NegativeImpl => AutoTraitResult::NegativeImpl,
 439             auto::AutoTraitResult::PositiveImpl(res) => AutoTraitResult::PositiveImpl(res),
 440         }
 441     }
 442
 443     fn get_lifetime(&self, region: Region, names_map: &FxHashMap<String, Lifetime>) -> Lifetime {
 444         self.region_name(region)
 445             .map(|name| {
 446                 names_map.get(&name).unwrap_or_else(|| {
 447                     panic!("Missing lifetime with name {:?} for {:?}", name, region)
 448                 })
 449             })
 450             .unwrap_or(&Lifetime::statik())
 451             .clone()
 452     }
 453
 454     fn region_name(&self, region: Region) -> Option<String> {
 455         match region {
 456             &ty::ReEarlyBound(r) => Some(r.name.to_string()),
 457             _ => None,
 458         }
 459     }
 460
 461     // This method calculates two things: Lifetime constraints of the form 'a: 'b,
 462     // and region constraints of the form ReVar: 'a
 463     //
 464     // This is essentially a simplified version of lexical_region_resolve. However,
 465     // handle_lifetimes determines what *needs be* true in order for an impl to hold.
 466     // lexical_region_resolve, along with much of the rest of the compiler, is concerned
 467     // with determining if a given set up constraints/predicates *are* met, given some
 468     // starting conditions (e.g. user-provided code). For this reason, it's easier
 469     // to perform the calculations we need on our own, rather than trying to make
 470     // existing inference/solver code do what we want.
 471     fn handle_lifetimes<'cx>(
 472         &self,
 473         regions: &RegionConstraintData<'cx>,
 474         names_map: &FxHashMap<String, Lifetime>,
 475     ) -> Vec<WherePredicate> {
 476         // Our goal is to 'flatten' the list of constraints by eliminating
 477         // all intermediate RegionVids. At the end, all constraints should
 478         // be between Regions (aka region variables). This gives us the information
 479         // we need to create the Generics.
 480         let mut finished = FxHashMap();
 481
 482         let mut vid_map: FxHashMap<RegionTarget, RegionDeps> = FxHashMap();
 483
 484         // Flattening is done in two parts. First, we insert all of the constraints
 485         // into a map. Each RegionTarget (either a RegionVid or a Region) maps
 486         // to its smaller and larger regions. Note that 'larger' regions correspond
 487         // to sub-regions in Rust code (e.g. in 'a: 'b, 'a is the larger region).
 488         for constraint in regions.constraints.keys() {
 489             match constraint {
 490                 &Constraint::VarSubVar(r1, r2) => {
 491                     {
 492                         let deps1 = vid_map
 493                             .entry(RegionTarget::RegionVid(r1))
 494                             .or_insert_with(|| Default::default());
 495                         deps1.larger.insert(RegionTarget::RegionVid(r2));
 496                     }
 497
 498                     let deps2 = vid_map
 499                         .entry(RegionTarget::RegionVid(r2))
 500                         .or_insert_with(|| Default::default());
 501                     deps2.smaller.insert(RegionTarget::RegionVid(r1));
 502                 }
 503                 &Constraint::RegSubVar(region, vid) => {
 504                     let deps = vid_map
 505                         .entry(RegionTarget::RegionVid(vid))
 506                         .or_insert_with(|| Default::default());
 507                     deps.smaller.insert(RegionTarget::Region(region));
 508                 }
 509                 &Constraint::VarSubReg(vid, region) => {
 510                     let deps = vid_map
 511                         .entry(RegionTarget::RegionVid(vid))
 512                         .or_insert_with(|| Default::default());
 513                     deps.larger.insert(RegionTarget::Region(region));
 514                 }
 515                 &Constraint::RegSubReg(r1, r2) => {
 516                     // The constraint is already in the form that we want, so we're done with it
 517                     // Desired order is 'larger, smaller', so flip then
 518                     if self.region_name(r1) != self.region_name(r2) {
 519                         finished
 520                             .entry(self.region_name(r2).unwrap())
 521                             .or_insert_with(|| Vec::new())
 522                             .push(r1);
 523                     }
 524                 }
 525             }
 526         }
 527
 528         // Here, we 'flatten' the map one element at a time.
 529         // All of the element's sub and super regions are connected
 530         // to each other. For example, if we have a graph that looks like this:
 531         //
 532         // (A, B) - C - (D, E)
 533         // Where (A, B) are subregions, and (D,E) are super-regions
 534         //
 535         // then after deleting 'C', the graph will look like this:
 536         //  ... - A - (D, E ...)
 537         //  ... - B - (D, E, ...)
 538         //  (A, B, ...) - D - ...
 539         //  (A, B, ...) - E - ...
 540         //
 541         //  where '...' signifies the existing sub and super regions of an entry
 542         //  When two adjacent ty::Regions are encountered, we've computed a final
 543         //  constraint, and add it to our list. Since we make sure to never re-add
 544         //  deleted items, this process will always finish.
 545         while !vid_map.is_empty() {
 546             let target = vid_map.keys().next().expect("Keys somehow empty").clone();
 547             let deps = vid_map.remove(&target).expect("Entry somehow missing");
 548
 549             for smaller in deps.smaller.iter() {
 550                 for larger in deps.larger.iter() {
 551                     match (smaller, larger) {
 552                         (&RegionTarget::Region(r1), &RegionTarget::Region(r2)) => {
 553                             if self.region_name(r1) != self.region_name(r2) {
 554                                 finished
 555                                     .entry(self.region_name(r2).unwrap())
 556                                     .or_insert_with(|| Vec::new())
 557                                     .push(r1) // Larger, smaller
 558                             }
 559                         }
 560                         (&RegionTarget::RegionVid(_), &RegionTarget::Region(_)) => {
 561                             if let Entry::Occupied(v) = vid_map.entry(*smaller) {
 562                                 let smaller_deps = v.into_mut();
 563                                 smaller_deps.larger.insert(*larger);
 564                                 smaller_deps.larger.remove(&target);
 565                             }
 566                         }
 567                         (&RegionTarget::Region(_), &RegionTarget::RegionVid(_)) => {
 568                             if let Entry::Occupied(v) = vid_map.entry(*larger) {
 569                                 let deps = v.into_mut();
 570                                 deps.smaller.insert(*smaller);
 571                                 deps.smaller.remove(&target);
 572                             }
 573                         }
 574                         (&RegionTarget::RegionVid(_), &RegionTarget::RegionVid(_)) => {
 575                             if let Entry::Occupied(v) = vid_map.entry(*smaller) {
 576                                 let smaller_deps = v.into_mut();
 577                                 smaller_deps.larger.insert(*larger);
 578                                 smaller_deps.larger.remove(&target);
 579                             }
 580
 581                             if let Entry::Occupied(v) = vid_map.entry(*larger) {
 582                                 let larger_deps = v.into_mut();
 583                                 larger_deps.smaller.insert(*smaller);
 584                                 larger_deps.smaller.remove(&target);
 585                             }
 586                         }
 587                     }
 588                 }
 589             }
 590         }
 591
 592         let lifetime_predicates = names_map
 593             .iter()
 594             .flat_map(|(name, lifetime)| {
 595                 let empty = Vec::new();
 596                 let bounds: FxHashSet<GenericBound> = finished.get(name).unwrap_or(&empty).iter()
 597                     .map(|region| GenericBound::Outlives(self.get_lifetime(region, names_map)))
 598                     .collect();
 599
 600                 if bounds.is_empty() {
 601                     return None;
 602                 }
 603                 Some(WherePredicate::RegionPredicate {
 604                     lifetime: lifetime.clone(),
 605                     bounds: bounds.into_iter().collect(),
 606                 })
 607             })
 608             .collect();
 609
 610         lifetime_predicates
 611     }
 612
 613     fn extract_for_generics<'b, 'c, 'd>(
 614         &self,
 615         tcx: TyCtxt<'b, 'c, 'd>,
 616         pred: ty::Predicate<'d>,
 617     ) -> FxHashSet<GenericParamDef> {
 618         pred.walk_tys()
 619             .flat_map(|t| {
 620                 let mut regions = FxHashSet();
 621                 tcx.collect_regions(&t, &mut regions);
 622
 623                 regions.into_iter().flat_map(|r| {
 624                     match r {
 625                         // We only care about late bound regions, as we need to add them
 626                         // to the 'for<>' section
 627                         &ty::ReLateBound(_, ty::BoundRegion::BrNamed(_, name)) => {
 628                             Some(GenericParamDef {
 629                                 name: name.to_string(),
 630                                 kind: GenericParamDefKind::Lifetime,
 631                             })
 632                         }
 633                         &ty::ReVar(_) | &ty::ReEarlyBound(_) => None,
 634                         _ => panic!("Unexpected region type {:?}", r),
 635                     }
 636                 })
 637             })
 638             .collect()
 639     }
 640
 641     fn make_final_bounds<'b, 'c, 'cx>(
 642         &self,
 643         ty_to_bounds: FxHashMap<Type, FxHashSet<GenericBound>>,
 644         ty_to_fn: FxHashMap<Type, (Option<PolyTrait>, Option<Type>)>,
 645         lifetime_to_bounds: FxHashMap<Lifetime, FxHashSet<GenericBound>>,
 646     ) -> Vec<WherePredicate> {
 647         ty_to_bounds
 648             .into_iter()
 649             .flat_map(|(ty, mut bounds)| {
 650                 if let Some(data) = ty_to_fn.get(&ty) {
 651                     let (poly_trait, output) =
 652                         (data.0.as_ref().unwrap().clone(), data.1.as_ref().cloned());
 653                     let new_ty = match &poly_trait.trait_ {
 654                         &Type::ResolvedPath {
 655                             ref path,
 656                             ref typarams,
 657                             ref did,
 658                             ref is_generic,
 659                         } => {
 660                             let mut new_path = path.clone();
 661                             let last_segment = new_path.segments.pop().unwrap();
 662
 663                             let (old_input, old_output) = match last_segment.args {
 664                                 GenericArgs::AngleBracketed { types, .. } => (types, None),
 665                                 GenericArgs::Parenthesized { inputs, output, .. } => {
 666                                     (inputs, output)
 667                                 }
 668                             };
 669
 670                             if old_output.is_some() && old_output != output {
 671                                 panic!(
 672                                     "Output mismatch for {:?} {:?} {:?}",
 673                                     ty, old_output, data.1
 674                                 );
 675                             }
 676
 677                             let new_params = GenericArgs::Parenthesized {
 678                                 inputs: old_input,
 679                                 output,
 680                             };
 681
 682                             new_path.segments.push(PathSegment {
 683                                 name: last_segment.name,
 684                                 args: new_params,
 685                             });
 686
 687                             Type::ResolvedPath {
 688                                 path: new_path,
 689                                 typarams: typarams.clone(),
 690                                 did: did.clone(),
 691                                 is_generic: *is_generic,
 692                             }
 693                         }
 694                         _ => panic!("Unexpected data: {:?}, {:?}", ty, data),
 695                     };
 696                     bounds.insert(GenericBound::TraitBound(
 697                         PolyTrait {
 698                             trait_: new_ty,
 699                             generic_params: poly_trait.generic_params,
 700                         },
 701                         hir::TraitBoundModifier::None,
 702                     ));
 703                 }
 704                 if bounds.is_empty() {
 705                     return None;
 706                 }
 707
 708                 let mut bounds_vec = bounds.into_iter().collect();
 709                 self.sort_where_bounds(&mut bounds_vec);
 710
 711                 Some(WherePredicate::BoundPredicate {
 712                     ty,
 713                     bounds: bounds_vec,
 714                 })
 715             })
 716             .chain(
 717                 lifetime_to_bounds
 718                     .into_iter()
 719                     .filter(|&(_, ref bounds)| !bounds.is_empty())
 720                     .map(|(lifetime, bounds)| {
 721                         let mut bounds_vec = bounds.into_iter().collect();
 722                         self.sort_where_bounds(&mut bounds_vec);
 723                         WherePredicate::RegionPredicate {
 724                             lifetime,
 725                             bounds: bounds_vec,
 726                         }
 727                     }),
 728             )
 729             .collect()
 730     }
 731
 732     // Converts the calculated ParamEnv and lifetime information to a clean::Generics, suitable for
 733     // display on the docs page. Cleaning the Predicates produces sub-optimal WherePredicate's,
 734     // so we fix them up:
 735     //
 736     // * Multiple bounds for the same type are coalesced into one: e.g. 'T: Copy', 'T: Debug'
 737     // becomes 'T: Copy + Debug'
 738     // * Fn bounds are handled specially - instead of leaving it as 'T: Fn(), <T as Fn::Output> =
 739     // K', we use the dedicated syntax 'T: Fn() -> K'
 740     // * We explcitly add a '?Sized' bound if we didn't find any 'Sized' predicates for a type
 741     fn param_env_to_generics<'b, 'c, 'cx>(
 742         &self,
 743         tcx: TyCtxt<'b, 'c, 'cx>,
 744         did: DefId,
 745         param_env: ty::ParamEnv<'cx>,
 746         type_generics: ty::Generics,
 747         mut existing_predicates: Vec<WherePredicate>,
 748         vid_to_region: FxHashMap<ty::RegionVid, ty::Region<'cx>>,
 749     ) -> Generics {
 750         debug!(
 751             "param_env_to_generics(did={:?}, param_env={:?}, type_generics={:?}, \
 752              existing_predicates={:?})",
 753             did, param_env, type_generics, existing_predicates
 754         );
 755
 756         // The `Sized` trait must be handled specially, since we only only display it when
 757         // it is *not* required (i.e. '?Sized')
 758         let sized_trait = self.cx
 759             .tcx
 760             .require_lang_item(lang_items::SizedTraitLangItem);
 761
 762         let mut replacer = RegionReplacer {
 763             vid_to_region: &vid_to_region,
 764             tcx,
 765         };
 766
 767         let orig_bounds: FxHashSet<_> = self.cx.tcx.param_env(did).caller_bounds.iter().collect();
 768         let clean_where_predicates = param_env
 769             .caller_bounds
 770             .iter()
 771             .filter(|p| {
 772                 !orig_bounds.contains(p) || match p {
 773                     &&ty::Predicate::Trait(pred) => pred.def_id() == sized_trait,
 774                     _ => false,
 775                 }
 776             })
 777             .map(|p| {
 778                 let replaced = p.fold_with(&mut replacer);
 779                 (replaced.clone(), replaced.clean(self.cx))
 780             });
 781
 782         let full_generics = (&type_generics, &tcx.predicates_of(did));
 783         let Generics {
 784             params: mut generic_params,
 785             ..
 786         } = full_generics.clean(self.cx);
 787
 788         let mut has_sized = FxHashSet();
 789         let mut ty_to_bounds = FxHashMap();
 790         let mut lifetime_to_bounds = FxHashMap();
 791         let mut ty_to_traits: FxHashMap<Type, FxHashSet<Type>> = FxHashMap();
 792
 793         let mut ty_to_fn: FxHashMap<Type, (Option<PolyTrait>, Option<Type>)> = FxHashMap();
 794
 795         for (orig_p, p) in clean_where_predicates {
 796             match p {
 797                 WherePredicate::BoundPredicate { ty, mut bounds } => {
 798                     // Writing a projection trait bound of the form
 799                     // <T as Trait>::Name : ?Sized
 800                     // is illegal, because ?Sized bounds can only
 801                     // be written in the (here, nonexistant) definition
 802                     // of the type.
 803                     // Therefore, we make sure that we never add a ?Sized
 804                     // bound for projections
 805                     match &ty {
 806                         &Type::QPath { .. } => {
 807                             has_sized.insert(ty.clone());
 808                         }
 809                         _ => {}
 810                     }
 811
 812                     if bounds.is_empty() {
 813                         continue;
 814                     }
 815
 816                     let mut for_generics = self.extract_for_generics(tcx, orig_p.clone());
 817
 818                     assert!(bounds.len() == 1);
 819                     let mut b = bounds.pop().unwrap();
 820
 821                     if b.is_sized_bound(self.cx) {
 822                         has_sized.insert(ty.clone());
 823                     } else if !b.get_trait_type()
 824                         .and_then(|t| {
 825                             ty_to_traits
 826                                 .get(&ty)
 827                                 .map(|bounds| bounds.contains(&strip_type(t.clone())))
 828                         })
 829                         .unwrap_or(false)
 830                     {
 831                         // If we've already added a projection bound for the same type, don't add
 832                         // this, as it would be a duplicate
 833
 834                         // Handle any 'Fn/FnOnce/FnMut' bounds specially,
 835                         // as we want to combine them with any 'Output' qpaths
 836                         // later
 837
 838                         let is_fn = match &mut b {
 839                             &mut GenericBound::TraitBound(ref mut p, _) => {
 840                                 // Insert regions into the for_generics hash map first, to ensure
 841                                 // that we don't end up with duplicate bounds (e.g. for<'b, 'b>)
 842                                 for_generics.extend(p.generic_params.clone());
 843                                 p.generic_params = for_generics.into_iter().collect();
 844                                 self.is_fn_ty(&tcx, &p.trait_)
 845                             }
 846                             _ => false,
 847                         };
 848
 849                         let poly_trait = b.get_poly_trait().unwrap();
 850
 851                         if is_fn {
 852                             ty_to_fn
 853                                 .entry(ty.clone())
 854                                 .and_modify(|e| *e = (Some(poly_trait.clone()), e.1.clone()))
 855                                 .or_insert(((Some(poly_trait.clone())), None));
 856
 857                             ty_to_bounds
 858                                 .entry(ty.clone())
 859                                 .or_insert_with(|| FxHashSet());
 860                         } else {
 861                             ty_to_bounds
 862                                 .entry(ty.clone())
 863                                 .or_insert_with(|| FxHashSet())
 864                                 .insert(b.clone());
 865                         }
 866                     }
 867                 }
 868                 WherePredicate::RegionPredicate { lifetime, bounds } => {
 869                     lifetime_to_bounds
 870                         .entry(lifetime)
 871                         .or_insert_with(|| FxHashSet())
 872                         .extend(bounds);
 873                 }
 874                 WherePredicate::EqPredicate { lhs, rhs } => {
 875                     match &lhs {
 876                         &Type::QPath {
 877                             name: ref left_name,
 878                             ref self_type,
 879                             ref trait_,
 880                         } => {
 881                             let ty = &*self_type;
 882                             match **trait_ {
 883                                 Type::ResolvedPath {
 884                                     path: ref trait_path,
 885                                     ref typarams,
 886                                     ref did,
 887                                     ref is_generic,
 888                                 } => {
 889                                     let mut new_trait_path = trait_path.clone();
 890
 891                                     if self.is_fn_ty(&tcx, trait_) && left_name == FN_OUTPUT_NAME {
 892                                         ty_to_fn
 893                                             .entry(*ty.clone())
 894                                             .and_modify(|e| *e = (e.0.clone(), Some(rhs.clone())))
 895                                             .or_insert((None, Some(rhs)));
 896                                         continue;
 897                                     }
 898
 899                                     // FIXME: Remove this scope when NLL lands
 900                                     {
 901                                         let args =
 902                                             &mut new_trait_path.segments.last_mut().unwrap().args;
 903
 904                                         match args {
 905                                             // Convert somethiung like '<T as Iterator::Item> = u8'
 906                                             // to 'T: Iterator<Item=u8>'
 907                                             &mut GenericArgs::AngleBracketed {
 908                                                 ref mut bindings,
 909                                                 ..
 910                                             } => {
 911                                                 bindings.push(TypeBinding {
 912                                                     name: left_name.clone(),
 913                                                     ty: rhs,
 914                                                 });
 915                                             }
 916                                             &mut GenericArgs::Parenthesized { .. } => {
 917                                                 existing_predicates.push(
 918                                                     WherePredicate::EqPredicate {
 919                                                         lhs: lhs.clone(),
 920                                                         rhs,
 921                                                     },
 922                                                 );
 923                                                 continue; // If something other than a Fn ends up
 924                                                           // with parenthesis, leave it alone
 925                                             }
 926                                         }
 927                                     }
 928
 929                                     let bounds = ty_to_bounds
 930                                         .entry(*ty.clone())
 931                                         .or_insert_with(|| FxHashSet());
 932
 933                                     bounds.insert(GenericBound::TraitBound(
 934                                         PolyTrait {
 935                                             trait_: Type::ResolvedPath {
 936                                                 path: new_trait_path,
 937                                                 typarams: typarams.clone(),
 938                                                 did: did.clone(),
 939                                                 is_generic: *is_generic,
 940                                             },
 941                                             generic_params: Vec::new(),
 942                                         },
 943                                         hir::TraitBoundModifier::None,
 944                                     ));
 945
 946                                     // Remove any existing 'plain' bound (e.g. 'T: Iterator`) so
 947                                     // that we don't see a
 948                                     // duplicate bound like `T: Iterator + Iterator<Item=u8>`
 949                                     // on the docs page.
 950                                     bounds.remove(&GenericBound::TraitBound(
 951                                         PolyTrait {
 952                                             trait_: *trait_.clone(),
 953                                             generic_params: Vec::new(),
 954                                         },
 955                                         hir::TraitBoundModifier::None,
 956                                     ));
 957                                     // Avoid creating any new duplicate bounds later in the outer
 958                                     // loop
 959                                     ty_to_traits
 960                                         .entry(*ty.clone())
 961                                         .or_insert_with(|| FxHashSet())
 962                                         .insert(*trait_.clone());
 963                                 }
 964                                 _ => panic!("Unexpected trait {:?} for {:?}", trait_, did),
 965                             }
 966                         }
 967                         _ => panic!("Unexpected LHS {:?} for {:?}", lhs, did),
 968                     }
 969                 }
 970             };
 971         }
 972
 973         let final_bounds = self.make_final_bounds(ty_to_bounds, ty_to_fn, lifetime_to_bounds);
 974
 975         existing_predicates.extend(final_bounds);
 976
 977         for param in generic_params.iter_mut() {
 978             match param.kind {
 979                 GenericParamDefKind::Type { ref mut default, ref mut bounds, .. } => {
 980                     // We never want something like `impl<T=Foo>`.
 981                     default.take();
 982                     let generic_ty = Type::Generic(param.name.clone());
 983                     if !has_sized.contains(&generic_ty) {
 984                         bounds.insert(0, GenericBound::maybe_sized(self.cx));
 985                     }
 986                 }
 987                 GenericParamDefKind::Lifetime => {}
 988             }
 989         }
 990
 991         self.sort_where_predicates(&mut existing_predicates);
 992
 993         Generics {
 994             params: generic_params,
 995             where_predicates: existing_predicates,
 996         }
 997     }
 998
 999     // Ensure that the predicates are in a consistent order. The precise
1000     // ordering doesn't actually matter, but it's important that
1001     // a given set of predicates always appears in the same order -
1002     // both for visual consistency between 'rustdoc' runs, and to
1003     // make writing tests much easier
1004     #[inline]
1005     fn sort_where_predicates(&self, mut predicates: &mut Vec<WherePredicate>) {
1006         // We should never have identical bounds - and if we do,
1007         // they're visually identical as well. Therefore, using
1008         // an unstable sort is fine.
1009         self.unstable_debug_sort(&mut predicates);
1010     }
1011
1012     // Ensure that the bounds are in a consistent order. The precise
1013     // ordering doesn't actually matter, but it's important that
1014     // a given set of bounds always appears in the same order -
1015     // both for visual consistency between 'rustdoc' runs, and to
1016     // make writing tests much easier
1017     #[inline]
1018     fn sort_where_bounds(&self, mut bounds: &mut Vec<GenericBound>) {
1019         // We should never have identical bounds - and if we do,
1020         // they're visually identical as well. Therefore, using
1021         // an unstable sort is fine.
1022         self.unstable_debug_sort(&mut bounds);
1023     }
1024
1025     // This might look horrendously hacky, but it's actually not that bad.
1026     //
1027     // For performance reasons, we use several different FxHashMaps
1028     // in the process of computing the final set of where predicates.
1029     // However, the iteration order of a HashMap is completely unspecified.
1030     // In fact, the iteration of an FxHashMap can even vary between platforms,
1031     // since FxHasher has different behavior for 32-bit and 64-bit platforms.
1032     //
1033     // Obviously, it's extremely undesireable for documentation rendering
1034     // to be depndent on the platform it's run on. Apart from being confusing
1035     // to end users, it makes writing tests much more difficult, as predicates
1036     // can appear in any order in the final result.
1037     //
1038     // To solve this problem, we sort WherePredicates and GenericBounds
1039     // by their Debug string. The thing to keep in mind is that we don't really
1040     // care what the final order is - we're synthesizing an impl or bound
1041     // ourselves, so any order can be considered equally valid. By sorting the
1042     // predicates and bounds, however, we ensure that for a given codebase, all
1043     // auto-trait impls always render in exactly the same way.
1044     //
1045     // Using the Debug impementation for sorting prevents us from needing to
1046     // write quite a bit of almost entirely useless code (e.g. how should two
1047     // Types be sorted relative to each other). It also allows us to solve the
1048     // problem for both WherePredicates and GenericBounds at the same time. This
1049     // approach is probably somewhat slower, but the small number of items
1050     // involved (impls rarely have more than a few bounds) means that it
1051     // shouldn't matter in practice.
1052     fn unstable_debug_sort<T: Debug>(&self, vec: &mut Vec<T>) {
1053         vec.sort_by_cached_key(|x| format!("{:?}", x))
1054     }
1055
1056     fn is_fn_ty(&self, tcx: &TyCtxt, ty: &Type) -> bool {
1057         match &ty {
1058             &&Type::ResolvedPath { ref did, .. } => {
1059                 *did == tcx.require_lang_item(lang_items::FnTraitLangItem)
1060                     || *did == tcx.require_lang_item(lang_items::FnMutTraitLangItem)
1061                     || *did == tcx.require_lang_item(lang_items::FnOnceTraitLangItem)
1062             }
1063             _ => false,
1064         }
1065     }
1066
1067     // This is an ugly hack, but it's the simplest way to handle synthetic impls without greatly
1068     // refactoring either librustdoc or librustc. In particular, allowing new DefIds to be
1069     // registered after the AST is constructed would require storing the defid mapping in a
1070     // RefCell, decreasing the performance for normal compilation for very little gain.
1071     //
1072     // Instead, we construct 'fake' def ids, which start immediately after the last DefId in
1073     // DefIndexAddressSpace::Low. In the Debug impl for clean::Item, we explicitly check for fake
1074     // def ids, as we'll end up with a panic if we use the DefId Debug impl for fake DefIds
1075     fn next_def_id(&self, crate_num: CrateNum) -> DefId {
1076         let start_def_id = {
1077             let next_id = if crate_num == LOCAL_CRATE {
1078                 self.cx
1079                     .tcx
1080                     .hir
1081                     .definitions()
1082                     .def_path_table()
1083                     .next_id(DefIndexAddressSpace::Low)
1084             } else {
1085                 self.cx
1086                     .cstore
1087                     .def_path_table(crate_num)
1088                     .next_id(DefIndexAddressSpace::Low)
1089             };
1090
1091             DefId {
1092                 krate: crate_num,
1093                 index: next_id,
1094             }
1095         };
1096
1097         let mut fake_ids = self.cx.fake_def_ids.borrow_mut();
1098
1099         let def_id = fake_ids.entry(crate_num).or_insert(start_def_id).clone();
1100         fake_ids.insert(
1101             crate_num,
1102             DefId {
1103                 krate: crate_num,
1104                 index: DefIndex::from_array_index(
1105                     def_id.index.as_array_index() + 1,
1106                     def_id.index.address_space(),
1107                 ),
1108             },
1109         );
1110
1111         MAX_DEF_ID.with(|m| {
1112             m.borrow_mut()
1113                 .entry(def_id.krate.clone())
1114                 .or_insert(start_def_id);
1115         });
1116
1117         self.cx.all_fake_def_ids.borrow_mut().insert(def_id);
1118
1119         def_id.clone()
1120     }
1121 }
1122
1123 // Replaces all ReVars in a type with ty::Region's, using the provided map
1124 struct RegionReplacer<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
1125     vid_to_region: &'a FxHashMap<ty::RegionVid, ty::Region<'tcx>>,
1126     tcx: TyCtxt<'a, 'gcx, 'tcx>,
1127 }
1128
1129 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for RegionReplacer<'a, 'gcx, 'tcx> {
1130     fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> {
1131         self.tcx
1132     }
1133
1134     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
1135         (match r {
1136             &ty::ReVar(vid) => self.vid_to_region.get(&vid).cloned(),
1137             _ => None,
1138         }).unwrap_or_else(|| r.super_fold_with(self))
1139     }
1140 }