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_blanket_impls<F>(
 115         &self,
 116         def_id: DefId,
 117         def_ctor: &F,
 118         name: Option<String>,
 119         generics: &ty::Generics,
 120     ) -> Vec<Item>
 121     where F: Fn(DefId) -> Def {
 122         let ty = self.cx.tcx.type_of(def_id);
 123         let mut traits = Vec::new();
 124         if self.cx.access_levels.borrow().is_doc_reachable(def_id) {
 125             let real_name = name.clone().map(|name| Ident::from_str(&name));
 126             let param_env = self.cx.tcx.param_env(def_id);
 127             for &trait_def_id in self.cx.all_traits.iter() {
 128                 if !self.cx.access_levels.borrow().is_doc_reachable(trait_def_id) ||
 129                    self.cx.generated_synthetics
 130                           .borrow_mut()
 131                           .get(&(def_id, trait_def_id))
 132                           .is_some() {
 133                     continue
 134                 }
 135                 self.cx.tcx.for_each_relevant_impl(trait_def_id, ty, |impl_def_id| {
 136                     self.cx.tcx.infer_ctxt().enter(|infcx| {
 137                         let t_generics = infcx.tcx.generics_of(impl_def_id);
 138                         let trait_ref = infcx.tcx.impl_trait_ref(impl_def_id).unwrap();
 139
 140                         match infcx.tcx.type_of(impl_def_id).sty {
 141                             ::rustc::ty::TypeVariants::TyParam(_) => {},
 142                             _ => return,
 143                         }
 144
 145                         let substs = infcx.fresh_substs_for_item(DUMMY_SP, def_id);
 146                         let ty = ty.subst(infcx.tcx, substs);
 147                         let param_env = param_env.subst(infcx.tcx, substs);
 148
 149                         let impl_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
 150                         let trait_ref = trait_ref.subst(infcx.tcx, impl_substs);
 151
 152                         // Require the type the impl is implemented on to match
 153                         // our type, and ignore the impl if there was a mismatch.
 154                         let cause = traits::ObligationCause::dummy();
 155                         let eq_result = infcx.at(&cause, param_env)
 156                                              .eq(trait_ref.self_ty(), ty);
 157                         if let Ok(InferOk { value: (), obligations }) = eq_result {
 158                             // FIXME(eddyb) ignoring `obligations` might cause false positives.
 159                             drop(obligations);
 160
 161                             let may_apply = infcx.predicate_may_hold(&traits::Obligation::new(
 162                                 cause.clone(),
 163                                 param_env,
 164                                 trait_ref.to_predicate(),
 165                             ));
 166                             if !may_apply {
 167                                 return
 168                             }
 169                             self.cx.generated_synthetics.borrow_mut()
 170                                                         .insert((def_id, trait_def_id));
 171                             let trait_ = hir::TraitRef {
 172                                 path: get_path_for_type(infcx.tcx,
 173                                                         trait_def_id,
 174                                                         hir::def::Def::Trait),
 175                                 ref_id: ast::DUMMY_NODE_ID,
 176                             };
 177                             let provided_trait_methods =
 178                                 infcx.tcx.provided_trait_methods(trait_def_id)
 179                                          .into_iter()
 180                                          .map(|meth| meth.ident.to_string())
 181                                          .collect();
 182
 183                             let ty = self.get_real_ty(def_id, def_ctor, &real_name, generics);
 184                             let predicates = infcx.tcx.predicates_of(impl_def_id);
 185
 186                             traits.push(Item {
 187                                 source: infcx.tcx.def_span(impl_def_id).clean(self.cx),
 188                                 name: None,
 189                                 attrs: Default::default(),
 190                                 visibility: None,
 191                                 def_id: self.next_def_id(impl_def_id.krate),
 192                                 stability: None,
 193                                 deprecation: None,
 194                                 inner: ImplItem(Impl {
 195                                     unsafety: hir::Unsafety::Normal,
 196                                     generics: (t_generics, &predicates).clean(self.cx),
 197                                     provided_trait_methods,
 198                                     trait_: Some(trait_.clean(self.cx)),
 199                                     for_: ty.clean(self.cx),
 200                                     items: infcx.tcx.associated_items(impl_def_id)
 201                                                     .collect::<Vec<_>>()
 202                                                     .clean(self.cx),
 203                                     polarity: None,
 204                                     synthetic: false,
 205                                     blanket_impl: Some(infcx.tcx.type_of(impl_def_id)
 206                                                                 .clean(self.cx)),
 207                                 }),
 208                             });
 209                             debug!("{:?} => {}", trait_ref, may_apply);
 210                         }
 211                     });
 212                 });
 213             }
 214         }
 215         traits
 216     }
 217
 218     pub fn get_auto_trait_impls<F>(
 219         &self,
 220         def_id: DefId,
 221         def_ctor: &F,
 222         name: Option<String>,
 223     ) -> Vec<Item>
 224     where F: Fn(DefId) -> Def {
 225         if self.cx
 226             .tcx
 227             .get_attrs(def_id)
 228             .lists("doc")
 229             .has_word("hidden")
 230         {
 231             debug!(
 232                 "get_auto_trait_impls(def_id={:?}, def_ctor=...): item has doc('hidden'), \
 233                  aborting",
 234                 def_id
 235             );
 236             return Vec::new();
 237         }
 238
 239         let tcx = self.cx.tcx;
 240         let generics = self.cx.tcx.generics_of(def_id);
 241
 242         debug!(
 243             "get_auto_trait_impls(def_id={:?}, def_ctor=..., generics={:?}",
 244             def_id, generics
 245         );
 246         let auto_traits: Vec<_> = self.cx
 247             .send_trait
 248             .and_then(|send_trait| {
 249                 self.get_auto_trait_impl_for(
 250                     def_id,
 251                     name.clone(),
 252                     generics.clone(),
 253                     def_ctor,
 254                     send_trait,
 255                 )
 256             })
 257             .into_iter()
 258             .chain(self.get_auto_trait_impl_for(
 259                 def_id,
 260                 name.clone(),
 261                 generics.clone(),
 262                 def_ctor,
 263                 tcx.require_lang_item(lang_items::SyncTraitLangItem),
 264             ).into_iter())
 265             .chain(self.get_blanket_impls(def_id, def_ctor, name, &generics).into_iter())
 266             .collect();
 267
 268         debug!(
 269             "get_auto_traits: type {:?} auto_traits {:?}",
 270             def_id, auto_traits
 271         );
 272         auto_traits
 273     }
 274
 275     fn get_auto_trait_impl_for<F>(
 276         &self,
 277         def_id: DefId,
 278         name: Option<String>,
 279         generics: ty::Generics,
 280         def_ctor: &F,
 281         trait_def_id: DefId,
 282     ) -> Option<Item>
 283     where F: Fn(DefId) -> Def {
 284         if !self.cx
 285             .generated_synthetics
 286             .borrow_mut()
 287             .insert((def_id, trait_def_id))
 288         {
 289             debug!(
 290                 "get_auto_trait_impl_for(def_id={:?}, generics={:?}, def_ctor=..., \
 291                  trait_def_id={:?}): already generated, aborting",
 292                 def_id, generics, trait_def_id
 293             );
 294             return None;
 295         }
 296
 297         let result = self.find_auto_trait_generics(def_id, trait_def_id, &generics);
 298
 299         if result.is_auto() {
 300             let trait_ = hir::TraitRef {
 301                 path: get_path_for_type(self.cx.tcx, trait_def_id, hir::def::Def::Trait),
 302                 ref_id: ast::DUMMY_NODE_ID,
 303             };
 304
 305             let polarity;
 306
 307             let new_generics = match result {
 308                 AutoTraitResult::PositiveImpl(new_generics) => {
 309                     polarity = None;
 310                     new_generics
 311                 }
 312                 AutoTraitResult::NegativeImpl => {
 313                     polarity = Some(ImplPolarity::Negative);
 314
 315                     // For negative impls, we use the generic params, but *not* the predicates,
 316                     // from the original type. Otherwise, the displayed impl appears to be a
 317                     // conditional negative impl, when it's really unconditional.
 318                     //
 319                     // For example, consider the struct Foo<T: Copy>(*mut T). Using
 320                     // the original predicates in our impl would cause us to generate
 321                     // `impl !Send for Foo<T: Copy>`, which makes it appear that Foo
 322                     // implements Send where T is not copy.
 323                     //
 324                     // Instead, we generate `impl !Send for Foo<T>`, which better
 325                     // expresses the fact that `Foo<T>` never implements `Send`,
 326                     // regardless of the choice of `T`.
 327                     let real_generics = (&generics, &Default::default());
 328
 329                     // Clean the generics, but ignore the '?Sized' bounds generated
 330                     // by the `Clean` impl
 331                     let clean_generics = real_generics.clean(self.cx);
 332
 333                     Generics {
 334                         params: clean_generics.params,
 335                         where_predicates: Vec::new(),
 336                     }
 337                 }
 338                 _ => unreachable!(),
 339             };
 340             let real_name = name.map(|name| Ident::from_str(&name));
 341             let ty = self.get_real_ty(def_id, def_ctor, &real_name, &generics);
 342
 343             return Some(Item {
 344                 source: Span::empty(),
 345                 name: None,
 346                 attrs: Default::default(),
 347                 visibility: None,
 348                 def_id: self.next_def_id(def_id.krate),
 349                 stability: None,
 350                 deprecation: None,
 351                 inner: ImplItem(Impl {
 352                     unsafety: hir::Unsafety::Normal,
 353                     generics: new_generics,
 354                     provided_trait_methods: FxHashSet(),
 355                     trait_: Some(trait_.clean(self.cx)),
 356                     for_: ty.clean(self.cx),
 357                     items: Vec::new(),
 358                     polarity,
 359                     synthetic: true,
 360                     blanket_impl: None,
 361                 }),
 362             });
 363         }
 364         None
 365     }
 366
 367     fn generics_to_path_params(&self, generics: ty::Generics) -> hir::GenericArgs {
 368         let mut args = vec![];
 369
 370         for param in generics.params.iter() {
 371             match param.kind {
 372                 ty::GenericParamDefKind::Lifetime => {
 373                     let name = if param.name == "" {
 374                         hir::ParamName::Plain(keywords::StaticLifetime.ident())
 375                     } else {
 376                         hir::ParamName::Plain(ast::Ident::from_interned_str(param.name))
 377                     };
 378
 379                     args.push(hir::GenericArg::Lifetime(hir::Lifetime {
 380                         id: ast::DUMMY_NODE_ID,
 381                         span: DUMMY_SP,
 382                         name: hir::LifetimeName::Param(name),
 383                     }));
 384                 }
 385                 ty::GenericParamDefKind::Type {..} => {
 386                     args.push(hir::GenericArg::Type(self.ty_param_to_ty(param.clone())));
 387                 }
 388             }
 389         }
 390
 391         hir::GenericArgs {
 392             args: HirVec::from_vec(args),
 393             bindings: HirVec::new(),
 394             parenthesized: false,
 395         }
 396     }
 397
 398     fn ty_param_to_ty(&self, param: ty::GenericParamDef) -> hir::Ty {
 399         debug!("ty_param_to_ty({:?}) {:?}", param, param.def_id);
 400         hir::Ty {
 401             id: ast::DUMMY_NODE_ID,
 402             node: hir::TyKind::Path(hir::QPath::Resolved(
 403                 None,
 404                 P(hir::Path {
 405                     span: DUMMY_SP,
 406                     def: Def::TyParam(param.def_id),
 407                     segments: HirVec::from_vec(vec![
 408                         hir::PathSegment::from_ident(Ident::from_interned_str(param.name))
 409                     ]),
 410                 }),
 411             )),
 412             span: DUMMY_SP,
 413             hir_id: hir::DUMMY_HIR_ID,
 414         }
 415     }
 416
 417     fn find_auto_trait_generics(
 418         &self,
 419         did: DefId,
 420         trait_did: DefId,
 421         generics: &ty::Generics,
 422     ) -> AutoTraitResult {
 423         match self.f.find_auto_trait_generics(did, trait_did, generics,
 424                 |infcx, mut info| {
 425                     let region_data = info.region_data;
 426                     let names_map =
 427                         info.names_map
 428                             .drain()
 429                             .map(|name| (name.clone(), Lifetime(name)))
 430                             .collect();
 431                     let lifetime_predicates =
 432                         self.handle_lifetimes(&region_data, &names_map);
 433                     let new_generics = self.param_env_to_generics(
 434                         infcx.tcx,
 435                         did,
 436                         info.full_user_env,
 437                         generics.clone(),
 438                         lifetime_predicates,
 439                         info.vid_to_region,
 440                     );
 441
 442                     debug!(
 443                         "find_auto_trait_generics(did={:?}, trait_did={:?}, generics={:?}): \
 444                          finished with {:?}",
 445                         did, trait_did, generics, new_generics
 446                     );
 447
 448                     new_generics
 449                 }) {
 450             auto::AutoTraitResult::ExplicitImpl => AutoTraitResult::ExplicitImpl,
 451             auto::AutoTraitResult::NegativeImpl => AutoTraitResult::NegativeImpl,
 452             auto::AutoTraitResult::PositiveImpl(res) => AutoTraitResult::PositiveImpl(res),
 453         }
 454     }
 455
 456     fn get_lifetime(&self, region: Region, names_map: &FxHashMap<String, Lifetime>) -> Lifetime {
 457         self.region_name(region)
 458             .map(|name| {
 459                 names_map.get(&name).unwrap_or_else(|| {
 460                     panic!("Missing lifetime with name {:?} for {:?}", name, region)
 461                 })
 462             })
 463             .unwrap_or(&Lifetime::statik())
 464             .clone()
 465     }
 466
 467     fn region_name(&self, region: Region) -> Option<String> {
 468         match region {
 469             &ty::ReEarlyBound(r) => Some(r.name.to_string()),
 470             _ => None,
 471         }
 472     }
 473
 474     // This method calculates two things: Lifetime constraints of the form 'a: 'b,
 475     // and region constraints of the form ReVar: 'a
 476     //
 477     // This is essentially a simplified version of lexical_region_resolve. However,
 478     // handle_lifetimes determines what *needs be* true in order for an impl to hold.
 479     // lexical_region_resolve, along with much of the rest of the compiler, is concerned
 480     // with determining if a given set up constraints/predicates *are* met, given some
 481     // starting conditions (e.g. user-provided code). For this reason, it's easier
 482     // to perform the calculations we need on our own, rather than trying to make
 483     // existing inference/solver code do what we want.
 484     fn handle_lifetimes<'cx>(
 485         &self,
 486         regions: &RegionConstraintData<'cx>,
 487         names_map: &FxHashMap<String, Lifetime>,
 488     ) -> Vec<WherePredicate> {
 489         // Our goal is to 'flatten' the list of constraints by eliminating
 490         // all intermediate RegionVids. At the end, all constraints should
 491         // be between Regions (aka region variables). This gives us the information
 492         // we need to create the Generics.
 493         let mut finished = FxHashMap();
 494
 495         let mut vid_map: FxHashMap<RegionTarget, RegionDeps> = FxHashMap();
 496
 497         // Flattening is done in two parts. First, we insert all of the constraints
 498         // into a map. Each RegionTarget (either a RegionVid or a Region) maps
 499         // to its smaller and larger regions. Note that 'larger' regions correspond
 500         // to sub-regions in Rust code (e.g. in 'a: 'b, 'a is the larger region).
 501         for constraint in regions.constraints.keys() {
 502             match constraint {
 503                 &Constraint::VarSubVar(r1, r2) => {
 504                     {
 505                         let deps1 = vid_map
 506                             .entry(RegionTarget::RegionVid(r1))
 507                             .or_insert_with(|| Default::default());
 508                         deps1.larger.insert(RegionTarget::RegionVid(r2));
 509                     }
 510
 511                     let deps2 = vid_map
 512                         .entry(RegionTarget::RegionVid(r2))
 513                         .or_insert_with(|| Default::default());
 514                     deps2.smaller.insert(RegionTarget::RegionVid(r1));
 515                 }
 516                 &Constraint::RegSubVar(region, vid) => {
 517                     let deps = vid_map
 518                         .entry(RegionTarget::RegionVid(vid))
 519                         .or_insert_with(|| Default::default());
 520                     deps.smaller.insert(RegionTarget::Region(region));
 521                 }
 522                 &Constraint::VarSubReg(vid, region) => {
 523                     let deps = vid_map
 524                         .entry(RegionTarget::RegionVid(vid))
 525                         .or_insert_with(|| Default::default());
 526                     deps.larger.insert(RegionTarget::Region(region));
 527                 }
 528                 &Constraint::RegSubReg(r1, r2) => {
 529                     // The constraint is already in the form that we want, so we're done with it
 530                     // Desired order is 'larger, smaller', so flip then
 531                     if self.region_name(r1) != self.region_name(r2) {
 532                         finished
 533                             .entry(self.region_name(r2).unwrap())
 534                             .or_insert_with(|| Vec::new())
 535                             .push(r1);
 536                     }
 537                 }
 538             }
 539         }
 540
 541         // Here, we 'flatten' the map one element at a time.
 542         // All of the element's sub and super regions are connected
 543         // to each other. For example, if we have a graph that looks like this:
 544         //
 545         // (A, B) - C - (D, E)
 546         // Where (A, B) are subregions, and (D,E) are super-regions
 547         //
 548         // then after deleting 'C', the graph will look like this:
 549         //  ... - A - (D, E ...)
 550         //  ... - B - (D, E, ...)
 551         //  (A, B, ...) - D - ...
 552         //  (A, B, ...) - E - ...
 553         //
 554         //  where '...' signifies the existing sub and super regions of an entry
 555         //  When two adjacent ty::Regions are encountered, we've computed a final
 556         //  constraint, and add it to our list. Since we make sure to never re-add
 557         //  deleted items, this process will always finish.
 558         while !vid_map.is_empty() {
 559             let target = vid_map.keys().next().expect("Keys somehow empty").clone();
 560             let deps = vid_map.remove(&target).expect("Entry somehow missing");
 561
 562             for smaller in deps.smaller.iter() {
 563                 for larger in deps.larger.iter() {
 564                     match (smaller, larger) {
 565                         (&RegionTarget::Region(r1), &RegionTarget::Region(r2)) => {
 566                             if self.region_name(r1) != self.region_name(r2) {
 567                                 finished
 568                                     .entry(self.region_name(r2).unwrap())
 569                                     .or_insert_with(|| Vec::new())
 570                                     .push(r1) // Larger, smaller
 571                             }
 572                         }
 573                         (&RegionTarget::RegionVid(_), &RegionTarget::Region(_)) => {
 574                             if let Entry::Occupied(v) = vid_map.entry(*smaller) {
 575                                 let smaller_deps = v.into_mut();
 576                                 smaller_deps.larger.insert(*larger);
 577                                 smaller_deps.larger.remove(&target);
 578                             }
 579                         }
 580                         (&RegionTarget::Region(_), &RegionTarget::RegionVid(_)) => {
 581                             if let Entry::Occupied(v) = vid_map.entry(*larger) {
 582                                 let deps = v.into_mut();
 583                                 deps.smaller.insert(*smaller);
 584                                 deps.smaller.remove(&target);
 585                             }
 586                         }
 587                         (&RegionTarget::RegionVid(_), &RegionTarget::RegionVid(_)) => {
 588                             if let Entry::Occupied(v) = vid_map.entry(*smaller) {
 589                                 let smaller_deps = v.into_mut();
 590                                 smaller_deps.larger.insert(*larger);
 591                                 smaller_deps.larger.remove(&target);
 592                             }
 593
 594                             if let Entry::Occupied(v) = vid_map.entry(*larger) {
 595                                 let larger_deps = v.into_mut();
 596                                 larger_deps.smaller.insert(*smaller);
 597                                 larger_deps.smaller.remove(&target);
 598                             }
 599                         }
 600                     }
 601                 }
 602             }
 603         }
 604
 605         let lifetime_predicates = names_map
 606             .iter()
 607             .flat_map(|(name, lifetime)| {
 608                 let empty = Vec::new();
 609                 let bounds: FxHashSet<GenericBound> = finished.get(name).unwrap_or(&empty).iter()
 610                     .map(|region| GenericBound::Outlives(self.get_lifetime(region, names_map)))
 611                     .collect();
 612
 613                 if bounds.is_empty() {
 614                     return None;
 615                 }
 616                 Some(WherePredicate::RegionPredicate {
 617                     lifetime: lifetime.clone(),
 618                     bounds: bounds.into_iter().collect(),
 619                 })
 620             })
 621             .collect();
 622
 623         lifetime_predicates
 624     }
 625
 626     fn extract_for_generics<'b, 'c, 'd>(
 627         &self,
 628         tcx: TyCtxt<'b, 'c, 'd>,
 629         pred: ty::Predicate<'d>,
 630     ) -> FxHashSet<GenericParamDef> {
 631         pred.walk_tys()
 632             .flat_map(|t| {
 633                 let mut regions = FxHashSet();
 634                 tcx.collect_regions(&t, &mut regions);
 635
 636                 regions.into_iter().flat_map(|r| {
 637                     match r {
 638                         // We only care about late bound regions, as we need to add them
 639                         // to the 'for<>' section
 640                         &ty::ReLateBound(_, ty::BoundRegion::BrNamed(_, name)) => {
 641                             Some(GenericParamDef {
 642                                 name: name.to_string(),
 643                                 kind: GenericParamDefKind::Lifetime,
 644                             })
 645                         },
 646                         &ty::ReVar(_) | &ty::ReEarlyBound(_) | &ty::ReStatic => None,
 647                         _ => panic!("Unexpected region type {:?}", r),
 648                     }
 649                 })
 650             })
 651             .collect()
 652     }
 653
 654     fn make_final_bounds<'b, 'c, 'cx>(
 655         &self,
 656         ty_to_bounds: FxHashMap<Type, FxHashSet<GenericBound>>,
 657         ty_to_fn: FxHashMap<Type, (Option<PolyTrait>, Option<Type>)>,
 658         lifetime_to_bounds: FxHashMap<Lifetime, FxHashSet<GenericBound>>,
 659     ) -> Vec<WherePredicate> {
 660         ty_to_bounds
 661             .into_iter()
 662             .flat_map(|(ty, mut bounds)| {
 663                 if let Some(data) = ty_to_fn.get(&ty) {
 664                     let (poly_trait, output) =
 665                         (data.0.as_ref().unwrap().clone(), data.1.as_ref().cloned());
 666                     let new_ty = match &poly_trait.trait_ {
 667                         &Type::ResolvedPath {
 668                             ref path,
 669                             ref typarams,
 670                             ref did,
 671                             ref is_generic,
 672                         } => {
 673                             let mut new_path = path.clone();
 674                             let last_segment = new_path.segments.pop().unwrap();
 675
 676                             let (old_input, old_output) = match last_segment.args {
 677                                 GenericArgs::AngleBracketed { types, .. } => (types, None),
 678                                 GenericArgs::Parenthesized { inputs, output, .. } => {
 679                                     (inputs, output)
 680                                 }
 681                             };
 682
 683                             if old_output.is_some() && old_output != output {
 684                                 panic!(
 685                                     "Output mismatch for {:?} {:?} {:?}",
 686                                     ty, old_output, data.1
 687                                 );
 688                             }
 689
 690                             let new_params = GenericArgs::Parenthesized {
 691                                 inputs: old_input,
 692                                 output,
 693                             };
 694
 695                             new_path.segments.push(PathSegment {
 696                                 name: last_segment.name,
 697                                 args: new_params,
 698                             });
 699
 700                             Type::ResolvedPath {
 701                                 path: new_path,
 702                                 typarams: typarams.clone(),
 703                                 did: did.clone(),
 704                                 is_generic: *is_generic,
 705                             }
 706                         }
 707                         _ => panic!("Unexpected data: {:?}, {:?}", ty, data),
 708                     };
 709                     bounds.insert(GenericBound::TraitBound(
 710                         PolyTrait {
 711                             trait_: new_ty,
 712                             generic_params: poly_trait.generic_params,
 713                         },
 714                         hir::TraitBoundModifier::None,
 715                     ));
 716                 }
 717                 if bounds.is_empty() {
 718                     return None;
 719                 }
 720
 721                 let mut bounds_vec = bounds.into_iter().collect();
 722                 self.sort_where_bounds(&mut bounds_vec);
 723
 724                 Some(WherePredicate::BoundPredicate {
 725                     ty,
 726                     bounds: bounds_vec,
 727                 })
 728             })
 729             .chain(
 730                 lifetime_to_bounds
 731                     .into_iter()
 732                     .filter(|&(_, ref bounds)| !bounds.is_empty())
 733                     .map(|(lifetime, bounds)| {
 734                         let mut bounds_vec = bounds.into_iter().collect();
 735                         self.sort_where_bounds(&mut bounds_vec);
 736                         WherePredicate::RegionPredicate {
 737                             lifetime,
 738                             bounds: bounds_vec,
 739                         }
 740                     }),
 741             )
 742             .collect()
 743     }
 744
 745     // Converts the calculated ParamEnv and lifetime information to a clean::Generics, suitable for
 746     // display on the docs page. Cleaning the Predicates produces sub-optimal WherePredicate's,
 747     // so we fix them up:
 748     //
 749     // * Multiple bounds for the same type are coalesced into one: e.g. 'T: Copy', 'T: Debug'
 750     // becomes 'T: Copy + Debug'
 751     // * Fn bounds are handled specially - instead of leaving it as 'T: Fn(), <T as Fn::Output> =
 752     // K', we use the dedicated syntax 'T: Fn() -> K'
 753     // * We explcitly add a '?Sized' bound if we didn't find any 'Sized' predicates for a type
 754     fn param_env_to_generics<'b, 'c, 'cx>(
 755         &self,
 756         tcx: TyCtxt<'b, 'c, 'cx>,
 757         did: DefId,
 758         param_env: ty::ParamEnv<'cx>,
 759         type_generics: ty::Generics,
 760         mut existing_predicates: Vec<WherePredicate>,
 761         vid_to_region: FxHashMap<ty::RegionVid, ty::Region<'cx>>,
 762     ) -> Generics {
 763         debug!(
 764             "param_env_to_generics(did={:?}, param_env={:?}, type_generics={:?}, \
 765              existing_predicates={:?})",
 766             did, param_env, type_generics, existing_predicates
 767         );
 768
 769         // The `Sized` trait must be handled specially, since we only only display it when
 770         // it is *not* required (i.e. '?Sized')
 771         let sized_trait = self.cx
 772             .tcx
 773             .require_lang_item(lang_items::SizedTraitLangItem);
 774
 775         let mut replacer = RegionReplacer {
 776             vid_to_region: &vid_to_region,
 777             tcx,
 778         };
 779
 780         let orig_bounds: FxHashSet<_> = self.cx.tcx.param_env(did).caller_bounds.iter().collect();
 781         let clean_where_predicates = param_env
 782             .caller_bounds
 783             .iter()
 784             .filter(|p| {
 785                 !orig_bounds.contains(p) || match p {
 786                     &&ty::Predicate::Trait(pred) => pred.def_id() == sized_trait,
 787                     _ => false,
 788                 }
 789             })
 790             .map(|p| {
 791                 let replaced = p.fold_with(&mut replacer);
 792                 (replaced.clone(), replaced.clean(self.cx))
 793             });
 794
 795         let full_generics = (&type_generics, &tcx.predicates_of(did));
 796         let Generics {
 797             params: mut generic_params,
 798             ..
 799         } = full_generics.clean(self.cx);
 800
 801         let mut has_sized = FxHashSet();
 802         let mut ty_to_bounds = FxHashMap();
 803         let mut lifetime_to_bounds = FxHashMap();
 804         let mut ty_to_traits: FxHashMap<Type, FxHashSet<Type>> = FxHashMap();
 805
 806         let mut ty_to_fn: FxHashMap<Type, (Option<PolyTrait>, Option<Type>)> = FxHashMap();
 807
 808         for (orig_p, p) in clean_where_predicates {
 809             match p {
 810                 WherePredicate::BoundPredicate { ty, mut bounds } => {
 811                     // Writing a projection trait bound of the form
 812                     // <T as Trait>::Name : ?Sized
 813                     // is illegal, because ?Sized bounds can only
 814                     // be written in the (here, nonexistant) definition
 815                     // of the type.
 816                     // Therefore, we make sure that we never add a ?Sized
 817                     // bound for projections
 818                     match &ty {
 819                         &Type::QPath { .. } => {
 820                             has_sized.insert(ty.clone());
 821                         }
 822                         _ => {}
 823                     }
 824
 825                     if bounds.is_empty() {
 826                         continue;
 827                     }
 828
 829                     let mut for_generics = self.extract_for_generics(tcx, orig_p.clone());
 830
 831                     assert!(bounds.len() == 1);
 832                     let mut b = bounds.pop().unwrap();
 833
 834                     if b.is_sized_bound(self.cx) {
 835                         has_sized.insert(ty.clone());
 836                     } else if !b.get_trait_type()
 837                         .and_then(|t| {
 838                             ty_to_traits
 839                                 .get(&ty)
 840                                 .map(|bounds| bounds.contains(&strip_type(t.clone())))
 841                         })
 842                         .unwrap_or(false)
 843                     {
 844                         // If we've already added a projection bound for the same type, don't add
 845                         // this, as it would be a duplicate
 846
 847                         // Handle any 'Fn/FnOnce/FnMut' bounds specially,
 848                         // as we want to combine them with any 'Output' qpaths
 849                         // later
 850
 851                         let is_fn = match &mut b {
 852                             &mut GenericBound::TraitBound(ref mut p, _) => {
 853                                 // Insert regions into the for_generics hash map first, to ensure
 854                                 // that we don't end up with duplicate bounds (e.g. for<'b, 'b>)
 855                                 for_generics.extend(p.generic_params.clone());
 856                                 p.generic_params = for_generics.into_iter().collect();
 857                                 self.is_fn_ty(&tcx, &p.trait_)
 858                             }
 859                             _ => false,
 860                         };
 861
 862                         let poly_trait = b.get_poly_trait().unwrap();
 863
 864                         if is_fn {
 865                             ty_to_fn
 866                                 .entry(ty.clone())
 867                                 .and_modify(|e| *e = (Some(poly_trait.clone()), e.1.clone()))
 868                                 .or_insert(((Some(poly_trait.clone())), None));
 869
 870                             ty_to_bounds
 871                                 .entry(ty.clone())
 872                                 .or_insert_with(|| FxHashSet());
 873                         } else {
 874                             ty_to_bounds
 875                                 .entry(ty.clone())
 876                                 .or_insert_with(|| FxHashSet())
 877                                 .insert(b.clone());
 878                         }
 879                     }
 880                 }
 881                 WherePredicate::RegionPredicate { lifetime, bounds } => {
 882                     lifetime_to_bounds
 883                         .entry(lifetime)
 884                         .or_insert_with(|| FxHashSet())
 885                         .extend(bounds);
 886                 }
 887                 WherePredicate::EqPredicate { lhs, rhs } => {
 888                     match &lhs {
 889                         &Type::QPath {
 890                             name: ref left_name,
 891                             ref self_type,
 892                             ref trait_,
 893                         } => {
 894                             let ty = &*self_type;
 895                             match **trait_ {
 896                                 Type::ResolvedPath {
 897                                     path: ref trait_path,
 898                                     ref typarams,
 899                                     ref did,
 900                                     ref is_generic,
 901                                 } => {
 902                                     let mut new_trait_path = trait_path.clone();
 903
 904                                     if self.is_fn_ty(&tcx, trait_) && left_name == FN_OUTPUT_NAME {
 905                                         ty_to_fn
 906                                             .entry(*ty.clone())
 907                                             .and_modify(|e| *e = (e.0.clone(), Some(rhs.clone())))
 908                                             .or_insert((None, Some(rhs)));
 909                                         continue;
 910                                     }
 911
 912                                     // FIXME: Remove this scope when NLL lands
 913                                     {
 914                                         let args =
 915                                             &mut new_trait_path.segments.last_mut().unwrap().args;
 916
 917                                         match args {
 918                                             // Convert somethiung like '<T as Iterator::Item> = u8'
 919                                             // to 'T: Iterator<Item=u8>'
 920                                             &mut GenericArgs::AngleBracketed {
 921                                                 ref mut bindings,
 922                                                 ..
 923                                             } => {
 924                                                 bindings.push(TypeBinding {
 925                                                     name: left_name.clone(),
 926                                                     ty: rhs,
 927                                                 });
 928                                             }
 929                                             &mut GenericArgs::Parenthesized { .. } => {
 930                                                 existing_predicates.push(
 931                                                     WherePredicate::EqPredicate {
 932                                                         lhs: lhs.clone(),
 933                                                         rhs,
 934                                                     },
 935                                                 );
 936                                                 continue; // If something other than a Fn ends up
 937                                                           // with parenthesis, leave it alone
 938                                             }
 939                                         }
 940                                     }
 941
 942                                     let bounds = ty_to_bounds
 943                                         .entry(*ty.clone())
 944                                         .or_insert_with(|| FxHashSet());
 945
 946                                     bounds.insert(GenericBound::TraitBound(
 947                                         PolyTrait {
 948                                             trait_: Type::ResolvedPath {
 949                                                 path: new_trait_path,
 950                                                 typarams: typarams.clone(),
 951                                                 did: did.clone(),
 952                                                 is_generic: *is_generic,
 953                                             },
 954                                             generic_params: Vec::new(),
 955                                         },
 956                                         hir::TraitBoundModifier::None,
 957                                     ));
 958
 959                                     // Remove any existing 'plain' bound (e.g. 'T: Iterator`) so
 960                                     // that we don't see a
 961                                     // duplicate bound like `T: Iterator + Iterator<Item=u8>`
 962                                     // on the docs page.
 963                                     bounds.remove(&GenericBound::TraitBound(
 964                                         PolyTrait {
 965                                             trait_: *trait_.clone(),
 966                                             generic_params: Vec::new(),
 967                                         },
 968                                         hir::TraitBoundModifier::None,
 969                                     ));
 970                                     // Avoid creating any new duplicate bounds later in the outer
 971                                     // loop
 972                                     ty_to_traits
 973                                         .entry(*ty.clone())
 974                                         .or_insert_with(|| FxHashSet())
 975                                         .insert(*trait_.clone());
 976                                 }
 977                                 _ => panic!("Unexpected trait {:?} for {:?}", trait_, did),
 978                             }
 979                         }
 980                         _ => panic!("Unexpected LHS {:?} for {:?}", lhs, did),
 981                     }
 982                 }
 983             };
 984         }
 985
 986         let final_bounds = self.make_final_bounds(ty_to_bounds, ty_to_fn, lifetime_to_bounds);
 987
 988         existing_predicates.extend(final_bounds);
 989
 990         for param in generic_params.iter_mut() {
 991             match param.kind {
 992                 GenericParamDefKind::Type { ref mut default, ref mut bounds, .. } => {
 993                     // We never want something like `impl<T=Foo>`.
 994                     default.take();
 995                     let generic_ty = Type::Generic(param.name.clone());
 996                     if !has_sized.contains(&generic_ty) {
 997                         bounds.insert(0, GenericBound::maybe_sized(self.cx));
 998                     }
 999                 }
1000                 GenericParamDefKind::Lifetime => {}
1001             }
1002         }
1003
1004         self.sort_where_predicates(&mut existing_predicates);
1005
1006         Generics {
1007             params: generic_params,
1008             where_predicates: existing_predicates,
1009         }
1010     }
1011
1012     // Ensure that the predicates are in a consistent order. The precise
1013     // ordering doesn't actually matter, but it's important that
1014     // a given set of predicates 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_predicates(&self, mut predicates: &mut Vec<WherePredicate>) {
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 predicates);
1023     }
1024
1025     // Ensure that the bounds are in a consistent order. The precise
1026     // ordering doesn't actually matter, but it's important that
1027     // a given set of bounds always appears in the same order -
1028     // both for visual consistency between 'rustdoc' runs, and to
1029     // make writing tests much easier
1030     #[inline]
1031     fn sort_where_bounds(&self, mut bounds: &mut Vec<GenericBound>) {
1032         // We should never have identical bounds - and if we do,
1033         // they're visually identical as well. Therefore, using
1034         // an unstable sort is fine.
1035         self.unstable_debug_sort(&mut bounds);
1036     }
1037
1038     // This might look horrendously hacky, but it's actually not that bad.
1039     //
1040     // For performance reasons, we use several different FxHashMaps
1041     // in the process of computing the final set of where predicates.
1042     // However, the iteration order of a HashMap is completely unspecified.
1043     // In fact, the iteration of an FxHashMap can even vary between platforms,
1044     // since FxHasher has different behavior for 32-bit and 64-bit platforms.
1045     //
1046     // Obviously, it's extremely undesireable for documentation rendering
1047     // to be depndent on the platform it's run on. Apart from being confusing
1048     // to end users, it makes writing tests much more difficult, as predicates
1049     // can appear in any order in the final result.
1050     //
1051     // To solve this problem, we sort WherePredicates and GenericBounds
1052     // by their Debug string. The thing to keep in mind is that we don't really
1053     // care what the final order is - we're synthesizing an impl or bound
1054     // ourselves, so any order can be considered equally valid. By sorting the
1055     // predicates and bounds, however, we ensure that for a given codebase, all
1056     // auto-trait impls always render in exactly the same way.
1057     //
1058     // Using the Debug impementation for sorting prevents us from needing to
1059     // write quite a bit of almost entirely useless code (e.g. how should two
1060     // Types be sorted relative to each other). It also allows us to solve the
1061     // problem for both WherePredicates and GenericBounds at the same time. This
1062     // approach is probably somewhat slower, but the small number of items
1063     // involved (impls rarely have more than a few bounds) means that it
1064     // shouldn't matter in practice.
1065     fn unstable_debug_sort<T: Debug>(&self, vec: &mut Vec<T>) {
1066         vec.sort_by_cached_key(|x| format!("{:?}", x))
1067     }
1068
1069     fn is_fn_ty(&self, tcx: &TyCtxt, ty: &Type) -> bool {
1070         match &ty {
1071             &&Type::ResolvedPath { ref did, .. } => {
1072                 *did == tcx.require_lang_item(lang_items::FnTraitLangItem)
1073                     || *did == tcx.require_lang_item(lang_items::FnMutTraitLangItem)
1074                     || *did == tcx.require_lang_item(lang_items::FnOnceTraitLangItem)
1075             }
1076             _ => false,
1077         }
1078     }
1079
1080     // This is an ugly hack, but it's the simplest way to handle synthetic impls without greatly
1081     // refactoring either librustdoc or librustc. In particular, allowing new DefIds to be
1082     // registered after the AST is constructed would require storing the defid mapping in a
1083     // RefCell, decreasing the performance for normal compilation for very little gain.
1084     //
1085     // Instead, we construct 'fake' def ids, which start immediately after the last DefId in
1086     // DefIndexAddressSpace::Low. In the Debug impl for clean::Item, we explicitly check for fake
1087     // def ids, as we'll end up with a panic if we use the DefId Debug impl for fake DefIds
1088     fn next_def_id(&self, crate_num: CrateNum) -> DefId {
1089         let start_def_id = {
1090             let next_id = if crate_num == LOCAL_CRATE {
1091                 self.cx
1092                     .tcx
1093                     .hir
1094                     .definitions()
1095                     .def_path_table()
1096                     .next_id(DefIndexAddressSpace::Low)
1097             } else {
1098                 self.cx
1099                     .cstore
1100                     .def_path_table(crate_num)
1101                     .next_id(DefIndexAddressSpace::Low)
1102             };
1103
1104             DefId {
1105                 krate: crate_num,
1106                 index: next_id,
1107             }
1108         };
1109
1110         let mut fake_ids = self.cx.fake_def_ids.borrow_mut();
1111
1112         let def_id = fake_ids.entry(crate_num).or_insert(start_def_id).clone();
1113         fake_ids.insert(
1114             crate_num,
1115             DefId {
1116                 krate: crate_num,
1117                 index: DefIndex::from_array_index(
1118                     def_id.index.as_array_index() + 1,
1119                     def_id.index.address_space(),
1120                 ),
1121             },
1122         );
1123
1124         MAX_DEF_ID.with(|m| {
1125             m.borrow_mut()
1126                 .entry(def_id.krate.clone())
1127                 .or_insert(start_def_id);
1128         });
1129
1130         self.cx.all_fake_def_ids.borrow_mut().insert(def_id);
1131
1132         def_id.clone()
1133     }
1134 }
1135
1136 // Replaces all ReVars in a type with ty::Region's, using the provided map
1137 struct RegionReplacer<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
1138     vid_to_region: &'a FxHashMap<ty::RegionVid, ty::Region<'tcx>>,
1139     tcx: TyCtxt<'a, 'gcx, 'tcx>,
1140 }
1141
1142 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for RegionReplacer<'a, 'gcx, 'tcx> {
1143     fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> {
1144         self.tcx
1145     }
1146
1147     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
1148         (match r {
1149             &ty::ReVar(vid) => self.vid_to_region.get(&vid).cloned(),
1150             _ => None,
1151         }).unwrap_or_else(|| r.super_fold_with(self))
1152     }
1153 }