src/librustdoc/clean/auto_trait.rs

   1 // Copyright 2018 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use rustc::hir;
  12 use rustc::traits::{self, auto_trait as auto};
  13 use rustc::ty::{ToPredicate, TypeFoldable};
  14 use rustc::ty::subst::Subst;
  15 use rustc::infer::InferOk;
  16 use std::fmt::Debug;
  17 use syntax_pos::DUMMY_SP;
  18
  19 use core::DocAccessLevels;
  20
  21 use super::*;
  22
  23 pub struct AutoTraitFinder<'a, 'tcx: 'a, 'rcx: 'a> {
  24     pub cx: &'a core::DocContext<'a, 'tcx, 'rcx>,
  25     pub f: auto::AutoTraitFinder<'a, 'tcx>,
  26 }
  27
  28 impl<'a, 'tcx, 'rcx> AutoTraitFinder<'a, 'tcx, 'rcx> {
  29     pub fn new(cx: &'a core::DocContext<'a, 'tcx, 'rcx>) -> Self {
  30         let f = auto::AutoTraitFinder::new(&cx.tcx);
  31
  32         AutoTraitFinder { cx, f }
  33     }
  34
  35     pub fn get_with_def_id(&self, def_id: DefId) -> Vec<Item> {
  36         let ty = self.cx.tcx.type_of(def_id);
  37
  38         let def_ctor: fn(DefId) -> Def = match ty.sty {
  39             ty::TyAdt(adt, _) => match adt.adt_kind() {
  40                 AdtKind::Struct => Def::Struct,
  41                 AdtKind::Enum => Def::Enum,
  42                 AdtKind::Union => Def::Union,
  43             }
  44             ty::TyInt(_) |
  45             ty::TyUint(_) |
  46             ty::TyFloat(_) |
  47             ty::TyStr |
  48             ty::TyBool |
  49             ty::TyChar => return self.get_auto_trait_impls(def_id, &move |_: DefId| {
  50                 match ty.sty {
  51                     ty::TyInt(x) => Def::PrimTy(hir::TyInt(x)),
  52                     ty::TyUint(x) => Def::PrimTy(hir::TyUint(x)),
  53                     ty::TyFloat(x) => Def::PrimTy(hir::TyFloat(x)),
  54                     ty::TyStr => Def::PrimTy(hir::TyStr),
  55                     ty::TyBool => Def::PrimTy(hir::TyBool),
  56                     ty::TyChar => Def::PrimTy(hir::TyChar),
  57                     _ => unreachable!(),
  58                 }
  59             }, None),
  60             _ => {
  61                 debug!("Unexpected type {:?}", def_id);
  62                 return Vec::new()
  63             }
  64         };
  65
  66         self.get_auto_trait_impls(def_id, &def_ctor, None)
  67     }
  68
  69     pub fn get_with_node_id(&self, id: ast::NodeId, name: String) -> Vec<Item> {
  70         let item = &self.cx.tcx.hir.expect_item(id).node;
  71         let did = self.cx.tcx.hir.local_def_id(id);
  72
  73         let def_ctor = match *item {
  74             hir::ItemKind::Struct(_, _) => Def::Struct,
  75             hir::ItemKind::Union(_, _) => Def::Union,
  76             hir::ItemKind::Enum(_, _) => Def::Enum,
  77             _ => panic!("Unexpected type {:?} {:?}", item, id),
  78         };
  79
  80         self.get_auto_trait_impls(did, &def_ctor, Some(name))
  81     }
  82
  83     pub fn get_auto_trait_impls<F>(
  84         &self,
  85         def_id: DefId,
  86         def_ctor: &F,
  87         name: Option<String>,
  88     ) -> Vec<Item>
  89     where F: Fn(DefId) -> Def {
  90         if self.cx
  91             .tcx
  92             .get_attrs(def_id)
  93             .lists("doc")
  94             .has_word("hidden")
  95         {
  96             debug!(
  97                 "get_auto_trait_impls(def_id={:?}, def_ctor=...): item has doc('hidden'), \
  98                  aborting",
  99                 def_id
 100             );
 101             return Vec::new();
 102         }
 103
 104         let tcx = self.cx.tcx;
 105         let generics = self.cx.tcx.generics_of(def_id);
 106
 107         let ty = self.cx.tcx.type_of(def_id);
 108         let mut traits = Vec::new();
 109         if self.cx.crate_name != Some("core".to_string()) {
 110             if let ty::TyAdt(_adt, _) = ty.sty {
 111                 let real_name = name.clone().map(|name| Ident::from_str(&name));
 112                 let param_env = self.cx.tcx.param_env(def_id);
 113                 for &trait_def_id in self.cx.all_traits.iter() {
 114                     if !self.cx.access_levels.borrow().is_doc_reachable(trait_def_id) ||
 115                        self.cx.generated_synthetics
 116                               .borrow_mut()
 117                               .get(&(def_id, trait_def_id))
 118                               .is_some() {
 119                         continue
 120                     }
 121                     self.cx.tcx.for_each_relevant_impl(trait_def_id, ty, |impl_def_id| {
 122                         self.cx.tcx.infer_ctxt().enter(|infcx| {
 123                             let generics = infcx.tcx.generics_of(impl_def_id);
 124                             let trait_ref = infcx.tcx.impl_trait_ref(impl_def_id).unwrap();
 125
 126                             if !match infcx.tcx.type_of(impl_def_id).sty {
 127                                 ::rustc::ty::TypeVariants::TyParam(_) => true,
 128                                 _ => false,
 129                             } {
 130                                 return
 131                             }
 132
 133                             let substs = infcx.fresh_substs_for_item(DUMMY_SP, def_id);
 134                             let ty2 = ty.subst(infcx.tcx, substs);
 135                             let param_env = param_env.subst(infcx.tcx, substs);
 136
 137                             let impl_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
 138                             let trait_ref = trait_ref.subst(infcx.tcx, impl_substs);
 139
 140                             // Require the type the impl is implemented on to match
 141                             // our type, and ignore the impl if there was a mismatch.
 142                             let cause = traits::ObligationCause::dummy();
 143                             let eq_result = infcx.at(&cause, param_env).eq(trait_ref.self_ty(), ty2);
 144                             if let Ok(InferOk { value: (), obligations }) = eq_result {
 145                                 // FIXME(eddyb) ignoring `obligations` might cause false positives.
 146                                 drop(obligations);
 147
 148                                 let may_apply = infcx.predicate_may_hold(&traits::Obligation::new(
 149                                     cause.clone(),
 150                                     param_env,
 151                                     trait_ref.to_predicate(),
 152                                 ));
 153                                 if !may_apply {
 154                                     return
 155                                 }
 156                                 self.cx.generated_synthetics.borrow_mut()
 157                                                             .insert((def_id, trait_def_id));
 158                                 let trait_ = hir::TraitRef {
 159                                     path: get_path_for_type(infcx.tcx, trait_def_id, hir::def::Def::Trait),
 160                                     ref_id: ast::DUMMY_NODE_ID,
 161                                 };
 162                                 let provided_trait_methods = infcx.tcx.provided_trait_methods(impl_def_id)
 163                                                                       .into_iter()
 164                                                                       .map(|meth| meth.ident.to_string())
 165                                                                       .collect();
 166
 167                                 let path = get_path_for_type(self.cx.tcx, def_id, def_ctor);
 168                                 let mut segments = path.segments.into_vec();
 169                                 let last = segments.pop().unwrap();
 170
 171                                 segments.push(hir::PathSegment::new(
 172                                     real_name.unwrap_or(last.ident),
 173                                     self.generics_to_path_params(generics.clone()),
 174                                     false,
 175                                 ));
 176
 177                                 let new_path = hir::Path {
 178                                     span: path.span,
 179                                     def: path.def,
 180                                     segments: HirVec::from_vec(segments),
 181                                 };
 182
 183                                 let ty = hir::Ty {
 184                                     id: ast::DUMMY_NODE_ID,
 185                                     node: hir::Ty_::TyPath(hir::QPath::Resolved(None, P(new_path))),
 186                                     span: DUMMY_SP,
 187                                     hir_id: hir::DUMMY_HIR_ID,
 188                                 };
 189
 190                                 traits.push(Item {
 191                                     source: Span::empty(),
 192                                     name: None,
 193                                     attrs: Default::default(),
 194                                     visibility: None,
 195                                     def_id: self.next_def_id(impl_def_id.krate),
 196                                     stability: None,
 197                                     deprecation: None,
 198                                     inner: ImplItem(Impl {
 199                                         unsafety: hir::Unsafety::Normal,
 200                                         generics: (generics,
 201                                                    &tcx.predicates_of(impl_def_id)).clean(self.cx),
 202                                         provided_trait_methods,
 203                                         trait_: Some(trait_.clean(self.cx)),
 204                                         for_: ty.clean(self.cx),
 205                                         items: infcx.tcx.associated_items(impl_def_id).collect::<Vec<_>>().clean(self.cx),
 206                                         polarity: None,
 207                                         synthetic: true,
 208                                     }),
 209                                 });
 210                                 debug!("{:?} => {}", trait_ref, may_apply);
 211                             }
 212                         });
 213                     });
 214                 }
 215             }
 216         }
 217
 218         debug!(
 219             "get_auto_trait_impls(def_id={:?}, def_ctor=..., generics={:?}",
 220             def_id, generics
 221         );
 222         let auto_traits: Vec<_> =
 223             self.cx.send_trait
 224                           .and_then(|send_trait| {
 225                     self.get_auto_trait_impl_for(
 226                         def_id,
 227                         name.clone(),
 228                         generics.clone(),
 229                         def_ctor,
 230                         send_trait,
 231                     )
 232                 }).into_iter()
 233             .chain(self.get_auto_trait_impl_for(
 234                 def_id,
 235                 name.clone(),
 236                 generics.clone(),
 237                 def_ctor,
 238                 tcx.require_lang_item(lang_items::SyncTraitLangItem),
 239             ).into_iter())
 240             .chain(traits.into_iter())
 241             .collect();
 242
 243         debug!(
 244             "get_auto_traits: type {:?} auto_traits {:?}",
 245             def_id, auto_traits
 246         );
 247         auto_traits
 248     }
 249
 250     fn get_auto_trait_impl_for<F>(
 251         &self,
 252         def_id: DefId,
 253         name: Option<String>,
 254         generics: ty::Generics,
 255         def_ctor: &F,
 256         trait_def_id: DefId,
 257     ) -> Option<Item>
 258     where F: Fn(DefId) -> Def {
 259         if !self.cx
 260             .generated_synthetics
 261             .borrow_mut()
 262             .insert((def_id, trait_def_id))
 263         {
 264             debug!(
 265                 "get_auto_trait_impl_for(def_id={:?}, generics={:?}, def_ctor=..., \
 266                  trait_def_id={:?}): already generated, aborting",
 267                 def_id, generics, trait_def_id
 268             );
 269             return None;
 270         }
 271
 272         let result = self.find_auto_trait_generics(def_id, trait_def_id, &generics);
 273
 274         if result.is_auto() {
 275             let trait_ = hir::TraitRef {
 276                 path: get_path_for_type(self.cx.tcx, trait_def_id, hir::def::Def::Trait),
 277                 ref_id: ast::DUMMY_NODE_ID,
 278             };
 279
 280             let polarity;
 281
 282             let new_generics = match result {
 283                 AutoTraitResult::PositiveImpl(new_generics) => {
 284                     polarity = None;
 285                     new_generics
 286                 }
 287                 AutoTraitResult::NegativeImpl => {
 288                     polarity = Some(ImplPolarity::Negative);
 289
 290                     // For negative impls, we use the generic params, but *not* the predicates,
 291                     // from the original type. Otherwise, the displayed impl appears to be a
 292                     // conditional negative impl, when it's really unconditional.
 293                     //
 294                     // For example, consider the struct Foo<T: Copy>(*mut T). Using
 295                     // the original predicates in our impl would cause us to generate
 296                     // `impl !Send for Foo<T: Copy>`, which makes it appear that Foo
 297                     // implements Send where T is not copy.
 298                     //
 299                     // Instead, we generate `impl !Send for Foo<T>`, which better
 300                     // expresses the fact that `Foo<T>` never implements `Send`,
 301                     // regardless of the choice of `T`.
 302                     let real_generics = (&generics, &Default::default());
 303
 304                     // Clean the generics, but ignore the '?Sized' bounds generated
 305                     // by the `Clean` impl
 306                     let clean_generics = real_generics.clean(self.cx);
 307
 308                     Generics {
 309                         params: clean_generics.params,
 310                         where_predicates: Vec::new(),
 311                     }
 312                 }
 313                 _ => unreachable!(),
 314             };
 315
 316             let path = get_path_for_type(self.cx.tcx, def_id, def_ctor);
 317             let mut segments = path.segments.into_vec();
 318             let last = segments.pop().unwrap();
 319
 320             let real_name = name.map(|name| Ident::from_str(&name));
 321
 322             segments.push(hir::PathSegment::new(
 323                 real_name.unwrap_or(last.ident),
 324                 self.generics_to_path_params(generics.clone()),
 325                 false,
 326             ));
 327
 328             let new_path = hir::Path {
 329                 span: path.span,
 330                 def: path.def,
 331                 segments: HirVec::from_vec(segments),
 332             };
 333
 334             let ty = hir::Ty {
 335                 id: ast::DUMMY_NODE_ID,
 336                 node: hir::TyKind::Path(hir::QPath::Resolved(None, P(new_path))),
 337                 span: DUMMY_SP,
 338                 hir_id: hir::DUMMY_HIR_ID,
 339             };
 340
 341             return Some(Item {
 342                 source: Span::empty(),
 343                 name: None,
 344                 attrs: Default::default(),
 345                 visibility: None,
 346                 def_id: self.next_def_id(def_id.krate),
 347                 stability: None,
 348                 deprecation: None,
 349                 inner: ImplItem(Impl {
 350                     unsafety: hir::Unsafety::Normal,
 351                     generics: new_generics,
 352                     provided_trait_methods: FxHashSet(),
 353                     trait_: Some(trait_.clean(self.cx)),
 354                     for_: ty.clean(self.cx),
 355                     items: Vec::new(),
 356                     polarity,
 357                     synthetic: true,
 358                 }),
 359             });
 360         }
 361         None
 362     }
 363
 364     fn generics_to_path_params(&self, generics: ty::Generics) -> hir::GenericArgs {
 365         let mut args = vec![];
 366
 367         for param in generics.params.iter() {
 368             match param.kind {
 369                 ty::GenericParamDefKind::Lifetime => {
 370                     let name = if param.name == "" {
 371                         hir::ParamName::Plain(keywords::StaticLifetime.ident())
 372                     } else {
 373                         hir::ParamName::Plain(ast::Ident::from_interned_str(param.name))
 374                     };
 375
 376                     args.push(hir::GenericArg::Lifetime(hir::Lifetime {
 377                         id: ast::DUMMY_NODE_ID,
 378                         span: DUMMY_SP,
 379                         name: hir::LifetimeName::Param(name),
 380                     }));
 381                 }
 382                 ty::GenericParamDefKind::Type {..} => {
 383                     args.push(hir::GenericArg::Type(self.ty_param_to_ty(param.clone())));
 384                 }
 385             }
 386         }
 387
 388         hir::GenericArgs {
 389             args: HirVec::from_vec(args),
 390             bindings: HirVec::new(),
 391             parenthesized: false,
 392         }
 393     }
 394
 395     fn ty_param_to_ty(&self, param: ty::GenericParamDef) -> hir::Ty {
 396         debug!("ty_param_to_ty({:?}) {:?}", param, param.def_id);
 397         hir::Ty {
 398             id: ast::DUMMY_NODE_ID,
 399             node: hir::TyKind::Path(hir::QPath::Resolved(
 400                 None,
 401                 P(hir::Path {
 402                     span: DUMMY_SP,
 403                     def: Def::TyParam(param.def_id),
 404                     segments: HirVec::from_vec(vec![
 405                         hir::PathSegment::from_ident(Ident::from_interned_str(param.name))
 406                     ]),
 407                 }),
 408             )),
 409             span: DUMMY_SP,
 410             hir_id: hir::DUMMY_HIR_ID,
 411         }
 412     }
 413
 414     fn find_auto_trait_generics(
 415         &self,
 416         did: DefId,
 417         trait_did: DefId,
 418         generics: &ty::Generics,
 419     ) -> AutoTraitResult {
 420         match self.f.find_auto_trait_generics(did, trait_did, generics,
 421                 |infcx, mut info| {
 422                     let region_data = info.region_data;
 423                     let names_map =
 424                         info.names_map
 425                             .drain()
 426                             .map(|name| (name.clone(), Lifetime(name)))
 427                             .collect();
 428                     let lifetime_predicates =
 429                         self.handle_lifetimes(&region_data, &names_map);
 430                     let new_generics = self.param_env_to_generics(
 431                         infcx.tcx,
 432                         did,
 433                         info.full_user_env,
 434                         generics.clone(),
 435                         lifetime_predicates,
 436                         info.vid_to_region,
 437                     );
 438
 439                     debug!(
 440                         "find_auto_trait_generics(did={:?}, trait_did={:?}, generics={:?}): \
 441                          finished with {:?}",
 442                         did, trait_did, generics, new_generics
 443                     );
 444
 445                     new_generics
 446                 }) {
 447             auto::AutoTraitResult::ExplicitImpl => AutoTraitResult::ExplicitImpl,
 448             auto::AutoTraitResult::NegativeImpl => AutoTraitResult::NegativeImpl,
 449             auto::AutoTraitResult::PositiveImpl(res) => AutoTraitResult::PositiveImpl(res),
 450         }
 451     }
 452
 453     fn get_lifetime(&self, region: Region, names_map: &FxHashMap<String, Lifetime>) -> Lifetime {
 454         self.region_name(region)
 455             .map(|name| {
 456                 names_map.get(&name).unwrap_or_else(|| {
 457                     panic!("Missing lifetime with name {:?} for {:?}", name, region)
 458                 })
 459             })
 460             .unwrap_or(&Lifetime::statik())
 461             .clone()
 462     }
 463
 464     fn region_name(&self, region: Region) -> Option<String> {
 465         match region {
 466             &ty::ReEarlyBound(r) => Some(r.name.to_string()),
 467             _ => None,
 468         }
 469     }
 470
 471     // This method calculates two things: Lifetime constraints of the form 'a: 'b,
 472     // and region constraints of the form ReVar: 'a
 473     //
 474     // This is essentially a simplified version of lexical_region_resolve. However,
 475     // handle_lifetimes determines what *needs be* true in order for an impl to hold.
 476     // lexical_region_resolve, along with much of the rest of the compiler, is concerned
 477     // with determining if a given set up constraints/predicates *are* met, given some
 478     // starting conditions (e.g. user-provided code). For this reason, it's easier
 479     // to perform the calculations we need on our own, rather than trying to make
 480     // existing inference/solver code do what we want.
 481     fn handle_lifetimes<'cx>(
 482         &self,
 483         regions: &RegionConstraintData<'cx>,
 484         names_map: &FxHashMap<String, Lifetime>,
 485     ) -> Vec<WherePredicate> {
 486         // Our goal is to 'flatten' the list of constraints by eliminating
 487         // all intermediate RegionVids. At the end, all constraints should
 488         // be between Regions (aka region variables). This gives us the information
 489         // we need to create the Generics.
 490         let mut finished = FxHashMap();
 491
 492         let mut vid_map: FxHashMap<RegionTarget, RegionDeps> = FxHashMap();
 493
 494         // Flattening is done in two parts. First, we insert all of the constraints
 495         // into a map. Each RegionTarget (either a RegionVid or a Region) maps
 496         // to its smaller and larger regions. Note that 'larger' regions correspond
 497         // to sub-regions in Rust code (e.g. in 'a: 'b, 'a is the larger region).
 498         for constraint in regions.constraints.keys() {
 499             match constraint {
 500                 &Constraint::VarSubVar(r1, r2) => {
 501                     {
 502                         let deps1 = vid_map
 503                             .entry(RegionTarget::RegionVid(r1))
 504                             .or_insert_with(|| Default::default());
 505                         deps1.larger.insert(RegionTarget::RegionVid(r2));
 506                     }
 507
 508                     let deps2 = vid_map
 509                         .entry(RegionTarget::RegionVid(r2))
 510                         .or_insert_with(|| Default::default());
 511                     deps2.smaller.insert(RegionTarget::RegionVid(r1));
 512                 }
 513                 &Constraint::RegSubVar(region, vid) => {
 514                     let deps = vid_map
 515                         .entry(RegionTarget::RegionVid(vid))
 516                         .or_insert_with(|| Default::default());
 517                     deps.smaller.insert(RegionTarget::Region(region));
 518                 }
 519                 &Constraint::VarSubReg(vid, region) => {
 520                     let deps = vid_map
 521                         .entry(RegionTarget::RegionVid(vid))
 522                         .or_insert_with(|| Default::default());
 523                     deps.larger.insert(RegionTarget::Region(region));
 524                 }
 525                 &Constraint::RegSubReg(r1, r2) => {
 526                     // The constraint is already in the form that we want, so we're done with it
 527                     // Desired order is 'larger, smaller', so flip then
 528                     if self.region_name(r1) != self.region_name(r2) {
 529                         finished
 530                             .entry(self.region_name(r2).unwrap())
 531                             .or_insert_with(|| Vec::new())
 532                             .push(r1);
 533                     }
 534                 }
 535             }
 536         }
 537
 538         // Here, we 'flatten' the map one element at a time.
 539         // All of the element's sub and super regions are connected
 540         // to each other. For example, if we have a graph that looks like this:
 541         //
 542         // (A, B) - C - (D, E)
 543         // Where (A, B) are subregions, and (D,E) are super-regions
 544         //
 545         // then after deleting 'C', the graph will look like this:
 546         //  ... - A - (D, E ...)
 547         //  ... - B - (D, E, ...)
 548         //  (A, B, ...) - D - ...
 549         //  (A, B, ...) - E - ...
 550         //
 551         //  where '...' signifies the existing sub and super regions of an entry
 552         //  When two adjacent ty::Regions are encountered, we've computed a final
 553         //  constraint, and add it to our list. Since we make sure to never re-add
 554         //  deleted items, this process will always finish.
 555         while !vid_map.is_empty() {
 556             let target = vid_map.keys().next().expect("Keys somehow empty").clone();
 557             let deps = vid_map.remove(&target).expect("Entry somehow missing");
 558
 559             for smaller in deps.smaller.iter() {
 560                 for larger in deps.larger.iter() {
 561                     match (smaller, larger) {
 562                         (&RegionTarget::Region(r1), &RegionTarget::Region(r2)) => {
 563                             if self.region_name(r1) != self.region_name(r2) {
 564                                 finished
 565                                     .entry(self.region_name(r2).unwrap())
 566                                     .or_insert_with(|| Vec::new())
 567                                     .push(r1) // Larger, smaller
 568                             }
 569                         }
 570                         (&RegionTarget::RegionVid(_), &RegionTarget::Region(_)) => {
 571                             if let Entry::Occupied(v) = vid_map.entry(*smaller) {
 572                                 let smaller_deps = v.into_mut();
 573                                 smaller_deps.larger.insert(*larger);
 574                                 smaller_deps.larger.remove(&target);
 575                             }
 576                         }
 577                         (&RegionTarget::Region(_), &RegionTarget::RegionVid(_)) => {
 578                             if let Entry::Occupied(v) = vid_map.entry(*larger) {
 579                                 let deps = v.into_mut();
 580                                 deps.smaller.insert(*smaller);
 581                                 deps.smaller.remove(&target);
 582                             }
 583                         }
 584                         (&RegionTarget::RegionVid(_), &RegionTarget::RegionVid(_)) => {
 585                             if let Entry::Occupied(v) = vid_map.entry(*smaller) {
 586                                 let smaller_deps = v.into_mut();
 587                                 smaller_deps.larger.insert(*larger);
 588                                 smaller_deps.larger.remove(&target);
 589                             }
 590
 591                             if let Entry::Occupied(v) = vid_map.entry(*larger) {
 592                                 let larger_deps = v.into_mut();
 593                                 larger_deps.smaller.insert(*smaller);
 594                                 larger_deps.smaller.remove(&target);
 595                             }
 596                         }
 597                     }
 598                 }
 599             }
 600         }
 601
 602         let lifetime_predicates = names_map
 603             .iter()
 604             .flat_map(|(name, lifetime)| {
 605                 let empty = Vec::new();
 606                 let bounds: FxHashSet<GenericBound> = finished.get(name).unwrap_or(&empty).iter()
 607                     .map(|region| GenericBound::Outlives(self.get_lifetime(region, names_map)))
 608                     .collect();
 609
 610                 if bounds.is_empty() {
 611                     return None;
 612                 }
 613                 Some(WherePredicate::RegionPredicate {
 614                     lifetime: lifetime.clone(),
 615                     bounds: bounds.into_iter().collect(),
 616                 })
 617             })
 618             .collect();
 619
 620         lifetime_predicates
 621     }
 622
 623     fn extract_for_generics<'b, 'c, 'd>(
 624         &self,
 625         tcx: TyCtxt<'b, 'c, 'd>,
 626         pred: ty::Predicate<'d>,
 627     ) -> FxHashSet<GenericParamDef> {
 628         pred.walk_tys()
 629             .flat_map(|t| {
 630                 let mut regions = FxHashSet();
 631                 tcx.collect_regions(&t, &mut regions);
 632
 633                 regions.into_iter().flat_map(|r| {
 634                     match r {
 635                         // We only care about late bound regions, as we need to add them
 636                         // to the 'for<>' section
 637                         &ty::ReLateBound(_, ty::BoundRegion::BrNamed(_, name)) => {
 638                             Some(GenericParamDef {
 639                                 name: name.to_string(),
 640                                 kind: GenericParamDefKind::Lifetime,
 641                             })
 642                         }
 643                         &ty::ReVar(_) | &ty::ReEarlyBound(_) => None,
 644                         _ => panic!("Unexpected region type {:?}", r),
 645                     }
 646                 })
 647             })
 648             .collect()
 649     }
 650
 651     fn make_final_bounds<'b, 'c, 'cx>(
 652         &self,
 653         ty_to_bounds: FxHashMap<Type, FxHashSet<GenericBound>>,
 654         ty_to_fn: FxHashMap<Type, (Option<PolyTrait>, Option<Type>)>,
 655         lifetime_to_bounds: FxHashMap<Lifetime, FxHashSet<GenericBound>>,
 656     ) -> Vec<WherePredicate> {
 657         ty_to_bounds
 658             .into_iter()
 659             .flat_map(|(ty, mut bounds)| {
 660                 if let Some(data) = ty_to_fn.get(&ty) {
 661                     let (poly_trait, output) =
 662                         (data.0.as_ref().unwrap().clone(), data.1.as_ref().cloned());
 663                     let new_ty = match &poly_trait.trait_ {
 664                         &Type::ResolvedPath {
 665                             ref path,
 666                             ref typarams,
 667                             ref did,
 668                             ref is_generic,
 669                         } => {
 670                             let mut new_path = path.clone();
 671                             let last_segment = new_path.segments.pop().unwrap();
 672
 673                             let (old_input, old_output) = match last_segment.args {
 674                                 GenericArgs::AngleBracketed { types, .. } => (types, None),
 675                                 GenericArgs::Parenthesized { inputs, output, .. } => {
 676                                     (inputs, output)
 677                                 }
 678                             };
 679
 680                             if old_output.is_some() && old_output != output {
 681                                 panic!(
 682                                     "Output mismatch for {:?} {:?} {:?}",
 683                                     ty, old_output, data.1
 684                                 );
 685                             }
 686
 687                             let new_params = GenericArgs::Parenthesized {
 688                                 inputs: old_input,
 689                                 output,
 690                             };
 691
 692                             new_path.segments.push(PathSegment {
 693                                 name: last_segment.name,
 694                                 args: new_params,
 695                             });
 696
 697                             Type::ResolvedPath {
 698                                 path: new_path,
 699                                 typarams: typarams.clone(),
 700                                 did: did.clone(),
 701                                 is_generic: *is_generic,
 702                             }
 703                         }
 704                         _ => panic!("Unexpected data: {:?}, {:?}", ty, data),
 705                     };
 706                     bounds.insert(GenericBound::TraitBound(
 707                         PolyTrait {
 708                             trait_: new_ty,
 709                             generic_params: poly_trait.generic_params,
 710                         },
 711                         hir::TraitBoundModifier::None,
 712                     ));
 713                 }
 714                 if bounds.is_empty() {
 715                     return None;
 716                 }
 717
 718                 let mut bounds_vec = bounds.into_iter().collect();
 719                 self.sort_where_bounds(&mut bounds_vec);
 720
 721                 Some(WherePredicate::BoundPredicate {
 722                     ty,
 723                     bounds: bounds_vec,
 724                 })
 725             })
 726             .chain(
 727                 lifetime_to_bounds
 728                     .into_iter()
 729                     .filter(|&(_, ref bounds)| !bounds.is_empty())
 730                     .map(|(lifetime, bounds)| {
 731                         let mut bounds_vec = bounds.into_iter().collect();
 732                         self.sort_where_bounds(&mut bounds_vec);
 733                         WherePredicate::RegionPredicate {
 734                             lifetime,
 735                             bounds: bounds_vec,
 736                         }
 737                     }),
 738             )
 739             .collect()
 740     }
 741
 742     // Converts the calculated ParamEnv and lifetime information to a clean::Generics, suitable for
 743     // display on the docs page. Cleaning the Predicates produces sub-optimal WherePredicate's,
 744     // so we fix them up:
 745     //
 746     // * Multiple bounds for the same type are coalesced into one: e.g. 'T: Copy', 'T: Debug'
 747     // becomes 'T: Copy + Debug'
 748     // * Fn bounds are handled specially - instead of leaving it as 'T: Fn(), <T as Fn::Output> =
 749     // K', we use the dedicated syntax 'T: Fn() -> K'
 750     // * We explcitly add a '?Sized' bound if we didn't find any 'Sized' predicates for a type
 751     fn param_env_to_generics<'b, 'c, 'cx>(
 752         &self,
 753         tcx: TyCtxt<'b, 'c, 'cx>,
 754         did: DefId,
 755         param_env: ty::ParamEnv<'cx>,
 756         type_generics: ty::Generics,
 757         mut existing_predicates: Vec<WherePredicate>,
 758         vid_to_region: FxHashMap<ty::RegionVid, ty::Region<'cx>>,
 759     ) -> Generics {
 760         debug!(
 761             "param_env_to_generics(did={:?}, param_env={:?}, type_generics={:?}, \
 762              existing_predicates={:?})",
 763             did, param_env, type_generics, existing_predicates
 764         );
 765
 766         // The `Sized` trait must be handled specially, since we only only display it when
 767         // it is *not* required (i.e. '?Sized')
 768         let sized_trait = self.cx
 769             .tcx
 770             .require_lang_item(lang_items::SizedTraitLangItem);
 771
 772         let mut replacer = RegionReplacer {
 773             vid_to_region: &vid_to_region,
 774             tcx,
 775         };
 776
 777         let orig_bounds: FxHashSet<_> = self.cx.tcx.param_env(did).caller_bounds.iter().collect();
 778         let clean_where_predicates = param_env
 779             .caller_bounds
 780             .iter()
 781             .filter(|p| {
 782                 !orig_bounds.contains(p) || match p {
 783                     &&ty::Predicate::Trait(pred) => pred.def_id() == sized_trait,
 784                     _ => false,
 785                 }
 786             })
 787             .map(|p| {
 788                 let replaced = p.fold_with(&mut replacer);
 789                 (replaced.clone(), replaced.clean(self.cx))
 790             });
 791
 792         let full_generics = (&type_generics, &tcx.predicates_of(did));
 793         let Generics {
 794             params: mut generic_params,
 795             ..
 796         } = full_generics.clean(self.cx);
 797
 798         let mut has_sized = FxHashSet();
 799         let mut ty_to_bounds = FxHashMap();
 800         let mut lifetime_to_bounds = FxHashMap();
 801         let mut ty_to_traits: FxHashMap<Type, FxHashSet<Type>> = FxHashMap();
 802
 803         let mut ty_to_fn: FxHashMap<Type, (Option<PolyTrait>, Option<Type>)> = FxHashMap();
 804
 805         for (orig_p, p) in clean_where_predicates {
 806             match p {
 807                 WherePredicate::BoundPredicate { ty, mut bounds } => {
 808                     // Writing a projection trait bound of the form
 809                     // <T as Trait>::Name : ?Sized
 810                     // is illegal, because ?Sized bounds can only
 811                     // be written in the (here, nonexistant) definition
 812                     // of the type.
 813                     // Therefore, we make sure that we never add a ?Sized
 814                     // bound for projections
 815                     match &ty {
 816                         &Type::QPath { .. } => {
 817                             has_sized.insert(ty.clone());
 818                         }
 819                         _ => {}
 820                     }
 821
 822                     if bounds.is_empty() {
 823                         continue;
 824                     }
 825
 826                     let mut for_generics = self.extract_for_generics(tcx, orig_p.clone());
 827
 828                     assert!(bounds.len() == 1);
 829                     let mut b = bounds.pop().unwrap();
 830
 831                     if b.is_sized_bound(self.cx) {
 832                         has_sized.insert(ty.clone());
 833                     } else if !b.get_trait_type()
 834                         .and_then(|t| {
 835                             ty_to_traits
 836                                 .get(&ty)
 837                                 .map(|bounds| bounds.contains(&strip_type(t.clone())))
 838                         })
 839                         .unwrap_or(false)
 840                     {
 841                         // If we've already added a projection bound for the same type, don't add
 842                         // this, as it would be a duplicate
 843
 844                         // Handle any 'Fn/FnOnce/FnMut' bounds specially,
 845                         // as we want to combine them with any 'Output' qpaths
 846                         // later
 847
 848                         let is_fn = match &mut b {
 849                             &mut GenericBound::TraitBound(ref mut p, _) => {
 850                                 // Insert regions into the for_generics hash map first, to ensure
 851                                 // that we don't end up with duplicate bounds (e.g. for<'b, 'b>)
 852                                 for_generics.extend(p.generic_params.clone());
 853                                 p.generic_params = for_generics.into_iter().collect();
 854                                 self.is_fn_ty(&tcx, &p.trait_)
 855                             }
 856                             _ => false,
 857                         };
 858
 859                         let poly_trait = b.get_poly_trait().unwrap();
 860
 861                         if is_fn {
 862                             ty_to_fn
 863                                 .entry(ty.clone())
 864                                 .and_modify(|e| *e = (Some(poly_trait.clone()), e.1.clone()))
 865                                 .or_insert(((Some(poly_trait.clone())), None));
 866
 867                             ty_to_bounds
 868                                 .entry(ty.clone())
 869                                 .or_insert_with(|| FxHashSet());
 870                         } else {
 871                             ty_to_bounds
 872                                 .entry(ty.clone())
 873                                 .or_insert_with(|| FxHashSet())
 874                                 .insert(b.clone());
 875                         }
 876                     }
 877                 }
 878                 WherePredicate::RegionPredicate { lifetime, bounds } => {
 879                     lifetime_to_bounds
 880                         .entry(lifetime)
 881                         .or_insert_with(|| FxHashSet())
 882                         .extend(bounds);
 883                 }
 884                 WherePredicate::EqPredicate { lhs, rhs } => {
 885                     match &lhs {
 886                         &Type::QPath {
 887                             name: ref left_name,
 888                             ref self_type,
 889                             ref trait_,
 890                         } => {
 891                             let ty = &*self_type;
 892                             match **trait_ {
 893                                 Type::ResolvedPath {
 894                                     path: ref trait_path,
 895                                     ref typarams,
 896                                     ref did,
 897                                     ref is_generic,
 898                                 } => {
 899                                     let mut new_trait_path = trait_path.clone();
 900
 901                                     if self.is_fn_ty(&tcx, trait_) && left_name == FN_OUTPUT_NAME {
 902                                         ty_to_fn
 903                                             .entry(*ty.clone())
 904                                             .and_modify(|e| *e = (e.0.clone(), Some(rhs.clone())))
 905                                             .or_insert((None, Some(rhs)));
 906                                         continue;
 907                                     }
 908
 909                                     // FIXME: Remove this scope when NLL lands
 910                                     {
 911                                         let args =
 912                                             &mut new_trait_path.segments.last_mut().unwrap().args;
 913
 914                                         match args {
 915                                             // Convert somethiung like '<T as Iterator::Item> = u8'
 916                                             // to 'T: Iterator<Item=u8>'
 917                                             &mut GenericArgs::AngleBracketed {
 918                                                 ref mut bindings,
 919                                                 ..
 920                                             } => {
 921                                                 bindings.push(TypeBinding {
 922                                                     name: left_name.clone(),
 923                                                     ty: rhs,
 924                                                 });
 925                                             }
 926                                             &mut GenericArgs::Parenthesized { .. } => {
 927                                                 existing_predicates.push(
 928                                                     WherePredicate::EqPredicate {
 929                                                         lhs: lhs.clone(),
 930                                                         rhs,
 931                                                     },
 932                                                 );
 933                                                 continue; // If something other than a Fn ends up
 934                                                           // with parenthesis, leave it alone
 935                                             }
 936                                         }
 937                                     }
 938
 939                                     let bounds = ty_to_bounds
 940                                         .entry(*ty.clone())
 941                                         .or_insert_with(|| FxHashSet());
 942
 943                                     bounds.insert(GenericBound::TraitBound(
 944                                         PolyTrait {
 945                                             trait_: Type::ResolvedPath {
 946                                                 path: new_trait_path,
 947                                                 typarams: typarams.clone(),
 948                                                 did: did.clone(),
 949                                                 is_generic: *is_generic,
 950                                             },
 951                                             generic_params: Vec::new(),
 952                                         },
 953                                         hir::TraitBoundModifier::None,
 954                                     ));
 955
 956                                     // Remove any existing 'plain' bound (e.g. 'T: Iterator`) so
 957                                     // that we don't see a
 958                                     // duplicate bound like `T: Iterator + Iterator<Item=u8>`
 959                                     // on the docs page.
 960                                     bounds.remove(&GenericBound::TraitBound(
 961                                         PolyTrait {
 962                                             trait_: *trait_.clone(),
 963                                             generic_params: Vec::new(),
 964                                         },
 965                                         hir::TraitBoundModifier::None,
 966                                     ));
 967                                     // Avoid creating any new duplicate bounds later in the outer
 968                                     // loop
 969                                     ty_to_traits
 970                                         .entry(*ty.clone())
 971                                         .or_insert_with(|| FxHashSet())
 972                                         .insert(*trait_.clone());
 973                                 }
 974                                 _ => panic!("Unexpected trait {:?} for {:?}", trait_, did),
 975                             }
 976                         }
 977                         _ => panic!("Unexpected LHS {:?} for {:?}", lhs, did),
 978                     }
 979                 }
 980             };
 981         }
 982
 983         let final_bounds = self.make_final_bounds(ty_to_bounds, ty_to_fn, lifetime_to_bounds);
 984
 985         existing_predicates.extend(final_bounds);
 986
 987         for param in generic_params.iter_mut() {
 988             match param.kind {
 989                 GenericParamDefKind::Type { ref mut default, ref mut bounds, .. } => {
 990                     // We never want something like `impl<T=Foo>`.
 991                     default.take();
 992                     let generic_ty = Type::Generic(param.name.clone());
 993                     if !has_sized.contains(&generic_ty) {
 994                         bounds.insert(0, GenericBound::maybe_sized(self.cx));
 995                     }
 996                 }
 997                 GenericParamDefKind::Lifetime => {}
 998             }
 999         }
1000
1001         self.sort_where_predicates(&mut existing_predicates);
1002
1003         Generics {
1004             params: generic_params,
1005             where_predicates: existing_predicates,
1006         }
1007     }
1008
1009     // Ensure that the predicates are in a consistent order. The precise
1010     // ordering doesn't actually matter, but it's important that
1011     // a given set of predicates always appears in the same order -
1012     // both for visual consistency between 'rustdoc' runs, and to
1013     // make writing tests much easier
1014     #[inline]
1015     fn sort_where_predicates(&self, mut predicates: &mut Vec<WherePredicate>) {
1016         // We should never have identical bounds - and if we do,
1017         // they're visually identical as well. Therefore, using
1018         // an unstable sort is fine.
1019         self.unstable_debug_sort(&mut predicates);
1020     }
1021
1022     // Ensure that the bounds are in a consistent order. The precise
1023     // ordering doesn't actually matter, but it's important that
1024     // a given set of bounds always appears in the same order -
1025     // both for visual consistency between 'rustdoc' runs, and to
1026     // make writing tests much easier
1027     #[inline]
1028     fn sort_where_bounds(&self, mut bounds: &mut Vec<GenericBound>) {
1029         // We should never have identical bounds - and if we do,
1030         // they're visually identical as well. Therefore, using
1031         // an unstable sort is fine.
1032         self.unstable_debug_sort(&mut bounds);
1033     }
1034
1035     // This might look horrendously hacky, but it's actually not that bad.
1036     //
1037     // For performance reasons, we use several different FxHashMaps
1038     // in the process of computing the final set of where predicates.
1039     // However, the iteration order of a HashMap is completely unspecified.
1040     // In fact, the iteration of an FxHashMap can even vary between platforms,
1041     // since FxHasher has different behavior for 32-bit and 64-bit platforms.
1042     //
1043     // Obviously, it's extremely undesireable for documentation rendering
1044     // to be depndent on the platform it's run on. Apart from being confusing
1045     // to end users, it makes writing tests much more difficult, as predicates
1046     // can appear in any order in the final result.
1047     //
1048     // To solve this problem, we sort WherePredicates and GenericBounds
1049     // by their Debug string. The thing to keep in mind is that we don't really
1050     // care what the final order is - we're synthesizing an impl or bound
1051     // ourselves, so any order can be considered equally valid. By sorting the
1052     // predicates and bounds, however, we ensure that for a given codebase, all
1053     // auto-trait impls always render in exactly the same way.
1054     //
1055     // Using the Debug impementation for sorting prevents us from needing to
1056     // write quite a bit of almost entirely useless code (e.g. how should two
1057     // Types be sorted relative to each other). It also allows us to solve the
1058     // problem for both WherePredicates and GenericBounds at the same time. This
1059     // approach is probably somewhat slower, but the small number of items
1060     // involved (impls rarely have more than a few bounds) means that it
1061     // shouldn't matter in practice.
1062     fn unstable_debug_sort<T: Debug>(&self, vec: &mut Vec<T>) {
1063         vec.sort_by_cached_key(|x| format!("{:?}", x))
1064     }
1065
1066     fn is_fn_ty(&self, tcx: &TyCtxt, ty: &Type) -> bool {
1067         match &ty {
1068             &&Type::ResolvedPath { ref did, .. } => {
1069                 *did == tcx.require_lang_item(lang_items::FnTraitLangItem)
1070                     || *did == tcx.require_lang_item(lang_items::FnMutTraitLangItem)
1071                     || *did == tcx.require_lang_item(lang_items::FnOnceTraitLangItem)
1072             }
1073             _ => false,
1074         }
1075     }
1076
1077     // This is an ugly hack, but it's the simplest way to handle synthetic impls without greatly
1078     // refactoring either librustdoc or librustc. In particular, allowing new DefIds to be
1079     // registered after the AST is constructed would require storing the defid mapping in a
1080     // RefCell, decreasing the performance for normal compilation for very little gain.
1081     //
1082     // Instead, we construct 'fake' def ids, which start immediately after the last DefId in
1083     // DefIndexAddressSpace::Low. In the Debug impl for clean::Item, we explicitly check for fake
1084     // def ids, as we'll end up with a panic if we use the DefId Debug impl for fake DefIds
1085     fn next_def_id(&self, crate_num: CrateNum) -> DefId {
1086         let start_def_id = {
1087             let next_id = if crate_num == LOCAL_CRATE {
1088                 self.cx
1089                     .tcx
1090                     .hir
1091                     .definitions()
1092                     .def_path_table()
1093                     .next_id(DefIndexAddressSpace::Low)
1094             } else {
1095                 self.cx
1096                     .cstore
1097                     .def_path_table(crate_num)
1098                     .next_id(DefIndexAddressSpace::Low)
1099             };
1100
1101             DefId {
1102                 krate: crate_num,
1103                 index: next_id,
1104             }
1105         };
1106
1107         let mut fake_ids = self.cx.fake_def_ids.borrow_mut();
1108
1109         let def_id = fake_ids.entry(crate_num).or_insert(start_def_id).clone();
1110         fake_ids.insert(
1111             crate_num,
1112             DefId {
1113                 krate: crate_num,
1114                 index: DefIndex::from_array_index(
1115                     def_id.index.as_array_index() + 1,
1116                     def_id.index.address_space(),
1117                 ),
1118             },
1119         );
1120
1121         MAX_DEF_ID.with(|m| {
1122             m.borrow_mut()
1123                 .entry(def_id.krate.clone())
1124                 .or_insert(start_def_id);
1125         });
1126
1127         self.cx.all_fake_def_ids.borrow_mut().insert(def_id);
1128
1129         def_id.clone()
1130     }
1131 }
1132
1133 // Replaces all ReVars in a type with ty::Region's, using the provided map
1134 struct RegionReplacer<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
1135     vid_to_region: &'a FxHashMap<ty::RegionVid, ty::Region<'tcx>>,
1136     tcx: TyCtxt<'a, 'gcx, 'tcx>,
1137 }
1138
1139 impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for RegionReplacer<'a, 'gcx, 'tcx> {
1140     fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> {
1141         self.tcx
1142     }
1143
1144     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
1145         (match r {
1146             &ty::ReVar(vid) => self.vid_to_region.get(&vid).cloned(),
1147             _ => None,
1148         }).unwrap_or_else(|| r.super_fold_with(self))
1149     }
1150 }