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