compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs

   1 use super::OverlapError;
   2
   3 use crate::traits;
   4 use rustc_hir::def_id::DefId;
   5 use rustc_middle::ty::fast_reject::{self, SimplifiedType};
   6 use rustc_middle::ty::print::with_no_trimmed_paths;
   7 use rustc_middle::ty::{self, TyCtxt, TypeFoldable};
   8
   9 pub use rustc_middle::traits::specialization_graph::*;
  10
  11 #[derive(Copy, Clone, Debug)]
  12 pub enum FutureCompatOverlapErrorKind {
  13     Issue33140,
  14     LeakCheck,
  15 }
  16
  17 #[derive(Debug)]
  18 pub struct FutureCompatOverlapError {
  19     pub error: OverlapError,
  20     pub kind: FutureCompatOverlapErrorKind,
  21 }
  22
  23 /// The result of attempting to insert an impl into a group of children.
  24 enum Inserted {
  25     /// The impl was inserted as a new child in this group of children.
  26     BecameNewSibling(Option<FutureCompatOverlapError>),
  27
  28     /// The impl should replace existing impls [X1, ..], because the impl specializes X1, X2, etc.
  29     ReplaceChildren(Vec<DefId>),
  30
  31     /// The impl is a specialization of an existing child.
  32     ShouldRecurseOn(DefId),
  33 }
  34
  35 trait ChildrenExt {
  36     fn insert_blindly(&mut self, tcx: TyCtxt<'tcx>, impl_def_id: DefId);
  37     fn remove_existing(&mut self, tcx: TyCtxt<'tcx>, impl_def_id: DefId);
  38
  39     fn insert(
  40         &mut self,
  41         tcx: TyCtxt<'tcx>,
  42         impl_def_id: DefId,
  43         simplified_self: Option<SimplifiedType>,
  44     ) -> Result<Inserted, OverlapError>;
  45 }
  46
  47 impl ChildrenExt for Children {
  48     /// Insert an impl into this set of children without comparing to any existing impls.
  49     fn insert_blindly(&mut self, tcx: TyCtxt<'tcx>, impl_def_id: DefId) {
  50         let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
  51         if let Some(st) = fast_reject::simplify_type(tcx, trait_ref.self_ty(), false) {
  52             debug!("insert_blindly: impl_def_id={:?} st={:?}", impl_def_id, st);
  53             self.nonblanket_impls.entry(st).or_default().push(impl_def_id)
  54         } else {
  55             debug!("insert_blindly: impl_def_id={:?} st=None", impl_def_id);
  56             self.blanket_impls.push(impl_def_id)
  57         }
  58     }
  59
  60     /// Removes an impl from this set of children. Used when replacing
  61     /// an impl with a parent. The impl must be present in the list of
  62     /// children already.
  63     fn remove_existing(&mut self, tcx: TyCtxt<'tcx>, impl_def_id: DefId) {
  64         let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
  65         let vec: &mut Vec<DefId>;
  66         if let Some(st) = fast_reject::simplify_type(tcx, trait_ref.self_ty(), false) {
  67             debug!("remove_existing: impl_def_id={:?} st={:?}", impl_def_id, st);
  68             vec = self.nonblanket_impls.get_mut(&st).unwrap();
  69         } else {
  70             debug!("remove_existing: impl_def_id={:?} st=None", impl_def_id);
  71             vec = &mut self.blanket_impls;
  72         }
  73
  74         let index = vec.iter().position(|d| *d == impl_def_id).unwrap();
  75         vec.remove(index);
  76     }
  77
  78     /// Attempt to insert an impl into this set of children, while comparing for
  79     /// specialization relationships.
  80     fn insert(
  81         &mut self,
  82         tcx: TyCtxt<'tcx>,
  83         impl_def_id: DefId,
  84         simplified_self: Option<SimplifiedType>,
  85     ) -> Result<Inserted, OverlapError> {
  86         let mut last_lint = None;
  87         let mut replace_children = Vec::new();
  88
  89         debug!("insert(impl_def_id={:?}, simplified_self={:?})", impl_def_id, simplified_self,);
  90
  91         let possible_siblings = match simplified_self {
  92             Some(st) => PotentialSiblings::Filtered(filtered_children(self, st)),
  93             None => PotentialSiblings::Unfiltered(iter_children(self)),
  94         };
  95
  96         for possible_sibling in possible_siblings {
  97             debug!(
  98                 "insert: impl_def_id={:?}, simplified_self={:?}, possible_sibling={:?}",
  99                 impl_def_id, simplified_self, possible_sibling,
 100             );
 101
 102             let create_overlap_error = |overlap: traits::coherence::OverlapResult<'_>| {
 103                 let trait_ref = overlap.impl_header.trait_ref.unwrap();
 104                 let self_ty = trait_ref.self_ty();
 105
 106                 // FIXME: should postpone string formatting until we decide to actually emit.
 107                 with_no_trimmed_paths(|| OverlapError {
 108                     with_impl: possible_sibling,
 109                     trait_desc: trait_ref.print_only_trait_path().to_string(),
 110                     // Only report the `Self` type if it has at least
 111                     // some outer concrete shell; otherwise, it's
 112                     // not adding much information.
 113                     self_desc: if self_ty.has_concrete_skeleton() {
 114                         Some(self_ty.to_string())
 115                     } else {
 116                         None
 117                     },
 118                     intercrate_ambiguity_causes: overlap.intercrate_ambiguity_causes,
 119                     involves_placeholder: overlap.involves_placeholder,
 120                 })
 121             };
 122
 123             let report_overlap_error = |overlap: traits::coherence::OverlapResult<'_>,
 124                                         last_lint: &mut _| {
 125                 // Found overlap, but no specialization; error out or report future-compat warning.
 126
 127                 // Do we *still* get overlap if we disable the future-incompatible modes?
 128                 let should_err = traits::overlapping_impls(
 129                     tcx,
 130                     possible_sibling,
 131                     impl_def_id,
 132                     traits::SkipLeakCheck::default(),
 133                     |_| true,
 134                     || false,
 135                 );
 136
 137                 let error = create_overlap_error(overlap);
 138
 139                 if should_err {
 140                     Err(error)
 141                 } else {
 142                     *last_lint = Some(FutureCompatOverlapError {
 143                         error,
 144                         kind: FutureCompatOverlapErrorKind::LeakCheck,
 145                     });
 146
 147                     Ok((false, false))
 148                 }
 149             };
 150
 151             let last_lint_mut = &mut last_lint;
 152             let (le, ge) = traits::overlapping_impls(
 153                 tcx,
 154                 possible_sibling,
 155                 impl_def_id,
 156                 traits::SkipLeakCheck::Yes,
 157                 |overlap| {
 158                     if let Some(overlap_kind) =
 159                         tcx.impls_are_allowed_to_overlap(impl_def_id, possible_sibling)
 160                     {
 161                         match overlap_kind {
 162                             ty::ImplOverlapKind::Permitted { marker: _ } => {}
 163                             ty::ImplOverlapKind::Issue33140 => {
 164                                 *last_lint_mut = Some(FutureCompatOverlapError {
 165                                     error: create_overlap_error(overlap),
 166                                     kind: FutureCompatOverlapErrorKind::Issue33140,
 167                                 });
 168                             }
 169                         }
 170
 171                         return Ok((false, false));
 172                     }
 173
 174                     let le = tcx.specializes((impl_def_id, possible_sibling));
 175                     let ge = tcx.specializes((possible_sibling, impl_def_id));
 176
 177                     if le == ge {
 178                         report_overlap_error(overlap, last_lint_mut)
 179                     } else {
 180                         Ok((le, ge))
 181                     }
 182                 },
 183                 || Ok((false, false)),
 184             )?;
 185
 186             if le && !ge {
 187                 debug!(
 188                     "descending as child of TraitRef {:?}",
 189                     tcx.impl_trait_ref(possible_sibling).unwrap()
 190                 );
 191
 192                 // The impl specializes `possible_sibling`.
 193                 return Ok(Inserted::ShouldRecurseOn(possible_sibling));
 194             } else if ge && !le {
 195                 debug!(
 196                     "placing as parent of TraitRef {:?}",
 197                     tcx.impl_trait_ref(possible_sibling).unwrap()
 198                 );
 199
 200                 replace_children.push(possible_sibling);
 201             } else {
 202                 // Either there's no overlap, or the overlap was already reported by
 203                 // `overlap_error`.
 204             }
 205         }
 206
 207         if !replace_children.is_empty() {
 208             return Ok(Inserted::ReplaceChildren(replace_children));
 209         }
 210
 211         // No overlap with any potential siblings, so add as a new sibling.
 212         debug!("placing as new sibling");
 213         self.insert_blindly(tcx, impl_def_id);
 214         Ok(Inserted::BecameNewSibling(last_lint))
 215     }
 216 }
 217
 218 fn iter_children(children: &mut Children) -> impl Iterator<Item = DefId> + '_ {
 219     let nonblanket = children.nonblanket_impls.iter_mut().flat_map(|(_, v)| v.iter());
 220     children.blanket_impls.iter().chain(nonblanket).cloned()
 221 }
 222
 223 fn filtered_children(
 224     children: &mut Children,
 225     st: SimplifiedType,
 226 ) -> impl Iterator<Item = DefId> + '_ {
 227     let nonblanket = children.nonblanket_impls.entry(st).or_default().iter();
 228     children.blanket_impls.iter().chain(nonblanket).cloned()
 229 }
 230
 231 // A custom iterator used by Children::insert
 232 enum PotentialSiblings<I, J>
 233 where
 234     I: Iterator<Item = DefId>,
 235     J: Iterator<Item = DefId>,
 236 {
 237     Unfiltered(I),
 238     Filtered(J),
 239 }
 240
 241 impl<I, J> Iterator for PotentialSiblings<I, J>
 242 where
 243     I: Iterator<Item = DefId>,
 244     J: Iterator<Item = DefId>,
 245 {
 246     type Item = DefId;
 247
 248     fn next(&mut self) -> Option<Self::Item> {
 249         match *self {
 250             PotentialSiblings::Unfiltered(ref mut iter) => iter.next(),
 251             PotentialSiblings::Filtered(ref mut iter) => iter.next(),
 252         }
 253     }
 254 }
 255
 256 pub trait GraphExt {
 257     /// Insert a local impl into the specialization graph. If an existing impl
 258     /// conflicts with it (has overlap, but neither specializes the other),
 259     /// information about the area of overlap is returned in the `Err`.
 260     fn insert(
 261         &mut self,
 262         tcx: TyCtxt<'tcx>,
 263         impl_def_id: DefId,
 264     ) -> Result<Option<FutureCompatOverlapError>, OverlapError>;
 265
 266     /// Insert cached metadata mapping from a child impl back to its parent.
 267     fn record_impl_from_cstore(&mut self, tcx: TyCtxt<'tcx>, parent: DefId, child: DefId);
 268 }
 269
 270 impl GraphExt for Graph {
 271     /// Insert a local impl into the specialization graph. If an existing impl
 272     /// conflicts with it (has overlap, but neither specializes the other),
 273     /// information about the area of overlap is returned in the `Err`.
 274     fn insert(
 275         &mut self,
 276         tcx: TyCtxt<'tcx>,
 277         impl_def_id: DefId,
 278     ) -> Result<Option<FutureCompatOverlapError>, OverlapError> {
 279         assert!(impl_def_id.is_local());
 280
 281         let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
 282         let trait_def_id = trait_ref.def_id;
 283
 284         debug!(
 285             "insert({:?}): inserting TraitRef {:?} into specialization graph",
 286             impl_def_id, trait_ref
 287         );
 288
 289         // If the reference itself contains an earlier error (e.g., due to a
 290         // resolution failure), then we just insert the impl at the top level of
 291         // the graph and claim that there's no overlap (in order to suppress
 292         // bogus errors).
 293         if trait_ref.references_error() {
 294             debug!(
 295                 "insert: inserting dummy node for erroneous TraitRef {:?}, \
 296                  impl_def_id={:?}, trait_def_id={:?}",
 297                 trait_ref, impl_def_id, trait_def_id
 298             );
 299
 300             self.parent.insert(impl_def_id, trait_def_id);
 301             self.children.entry(trait_def_id).or_default().insert_blindly(tcx, impl_def_id);
 302             return Ok(None);
 303         }
 304
 305         let mut parent = trait_def_id;
 306         let mut last_lint = None;
 307         let simplified = fast_reject::simplify_type(tcx, trait_ref.self_ty(), false);
 308
 309         // Descend the specialization tree, where `parent` is the current parent node.
 310         loop {
 311             use self::Inserted::*;
 312
 313             let insert_result =
 314                 self.children.entry(parent).or_default().insert(tcx, impl_def_id, simplified)?;
 315
 316             match insert_result {
 317                 BecameNewSibling(opt_lint) => {
 318                     last_lint = opt_lint;
 319                     break;
 320                 }
 321                 ReplaceChildren(grand_children_to_be) => {
 322                     // We currently have
 323                     //
 324                     //     P
 325                     //     |
 326                     //     G
 327                     //
 328                     // and we are inserting the impl N. We want to make it:
 329                     //
 330                     //     P
 331                     //     |
 332                     //     N
 333                     //     |
 334                     //     G
 335
 336                     // Adjust P's list of children: remove G and then add N.
 337                     {
 338                         let siblings = self.children.get_mut(&parent).unwrap();
 339                         for &grand_child_to_be in &grand_children_to_be {
 340                             siblings.remove_existing(tcx, grand_child_to_be);
 341                         }
 342                         siblings.insert_blindly(tcx, impl_def_id);
 343                     }
 344
 345                     // Set G's parent to N and N's parent to P.
 346                     for &grand_child_to_be in &grand_children_to_be {
 347                         self.parent.insert(grand_child_to_be, impl_def_id);
 348                     }
 349                     self.parent.insert(impl_def_id, parent);
 350
 351                     // Add G as N's child.
 352                     for &grand_child_to_be in &grand_children_to_be {
 353                         self.children
 354                             .entry(impl_def_id)
 355                             .or_default()
 356                             .insert_blindly(tcx, grand_child_to_be);
 357                     }
 358                     break;
 359                 }
 360                 ShouldRecurseOn(new_parent) => {
 361                     parent = new_parent;
 362                 }
 363             }
 364         }
 365
 366         self.parent.insert(impl_def_id, parent);
 367         Ok(last_lint)
 368     }
 369
 370     /// Insert cached metadata mapping from a child impl back to its parent.
 371     fn record_impl_from_cstore(&mut self, tcx: TyCtxt<'tcx>, parent: DefId, child: DefId) {
 372         if self.parent.insert(child, parent).is_some() {
 373             bug!(
 374                 "When recording an impl from the crate store, information about its parent \
 375                  was already present."
 376             );
 377         }
 378
 379         self.children.entry(parent).or_default().insert_blindly(tcx, child);
 380     }
 381 }