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, TreatParams};
   6 use rustc_middle::ty::print::with_no_trimmed_paths;
   7 use rustc_middle::ty::{self, TyCtxt, TypeVisitable};
   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<'tcx> {
  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         overlap_mode: OverlapMode,
  45     ) -> Result<Inserted, OverlapError>;
  46 }
  47
  48 impl ChildrenExt<'_> for Children {
  49     /// Insert an impl into this set of children without comparing to any existing impls.
  50     fn insert_blindly(&mut self, tcx: TyCtxt<'_>, impl_def_id: DefId) {
  51         let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
  52         if let Some(st) = fast_reject::simplify_type(tcx, trait_ref.self_ty(), TreatParams::AsInfer)
  53         {
  54             debug!("insert_blindly: impl_def_id={:?} st={:?}", impl_def_id, st);
  55             self.non_blanket_impls.entry(st).or_default().push(impl_def_id)
  56         } else {
  57             debug!("insert_blindly: impl_def_id={:?} st=None", impl_def_id);
  58             self.blanket_impls.push(impl_def_id)
  59         }
  60     }
  61
  62     /// Removes an impl from this set of children. Used when replacing
  63     /// an impl with a parent. The impl must be present in the list of
  64     /// children already.
  65     fn remove_existing(&mut self, tcx: TyCtxt<'_>, impl_def_id: DefId) {
  66         let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
  67         let vec: &mut Vec<DefId>;
  68         if let Some(st) = fast_reject::simplify_type(tcx, trait_ref.self_ty(), TreatParams::AsInfer)
  69         {
  70             debug!("remove_existing: impl_def_id={:?} st={:?}", impl_def_id, st);
  71             vec = self.non_blanket_impls.get_mut(&st).unwrap();
  72         } else {
  73             debug!("remove_existing: impl_def_id={:?} st=None", impl_def_id);
  74             vec = &mut self.blanket_impls;
  75         }
  76
  77         let index = vec.iter().position(|d| *d == impl_def_id).unwrap();
  78         vec.remove(index);
  79     }
  80
  81     /// Attempt to insert an impl into this set of children, while comparing for
  82     /// specialization relationships.
  83     fn insert(
  84         &mut self,
  85         tcx: TyCtxt<'_>,
  86         impl_def_id: DefId,
  87         simplified_self: Option<SimplifiedType>,
  88         overlap_mode: OverlapMode,
  89     ) -> Result<Inserted, OverlapError> {
  90         let mut last_lint = None;
  91         let mut replace_children = Vec::new();
  92
  93         debug!("insert(impl_def_id={:?}, simplified_self={:?})", impl_def_id, simplified_self,);
  94
  95         let possible_siblings = match simplified_self {
  96             Some(st) => PotentialSiblings::Filtered(filtered_children(self, st)),
  97             None => PotentialSiblings::Unfiltered(iter_children(self)),
  98         };
  99
 100         for possible_sibling in possible_siblings {
 101             debug!(
 102                 "insert: impl_def_id={:?}, simplified_self={:?}, possible_sibling={:?}",
 103                 impl_def_id, simplified_self, possible_sibling,
 104             );
 105
 106             let create_overlap_error = |overlap: traits::coherence::OverlapResult<'_>| {
 107                 let trait_ref = overlap.impl_header.trait_ref.unwrap();
 108                 let self_ty = trait_ref.self_ty();
 109
 110                 // FIXME: should postpone string formatting until we decide to actually emit.
 111                 with_no_trimmed_paths!({
 112                     OverlapError {
 113                         with_impl: possible_sibling,
 114                         trait_desc: trait_ref.print_only_trait_path().to_string(),
 115                         // Only report the `Self` type if it has at least
 116                         // some outer concrete shell; otherwise, it's
 117                         // not adding much information.
 118                         self_desc: if self_ty.has_concrete_skeleton() {
 119                             Some(self_ty.to_string())
 120                         } else {
 121                             None
 122                         },
 123                         intercrate_ambiguity_causes: overlap.intercrate_ambiguity_causes,
 124                         involves_placeholder: overlap.involves_placeholder,
 125                     }
 126                 })
 127             };
 128
 129             let report_overlap_error = |overlap: traits::coherence::OverlapResult<'_>,
 130                                         last_lint: &mut _| {
 131                 // Found overlap, but no specialization; error out or report future-compat warning.
 132
 133                 // Do we *still* get overlap if we disable the future-incompatible modes?
 134                 let should_err = traits::overlapping_impls(
 135                     tcx,
 136                     possible_sibling,
 137                     impl_def_id,
 138                     traits::SkipLeakCheck::default(),
 139                     overlap_mode,
 140                     |_| true,
 141                     || false,
 142                 );
 143
 144                 let error = create_overlap_error(overlap);
 145
 146                 if should_err {
 147                     Err(error)
 148                 } else {
 149                     *last_lint = Some(FutureCompatOverlapError {
 150                         error,
 151                         kind: FutureCompatOverlapErrorKind::LeakCheck,
 152                     });
 153
 154                     Ok((false, false))
 155                 }
 156             };
 157
 158             let last_lint_mut = &mut last_lint;
 159             let (le, ge) = traits::overlapping_impls(
 160                 tcx,
 161                 possible_sibling,
 162                 impl_def_id,
 163                 traits::SkipLeakCheck::Yes,
 164                 overlap_mode,
 165                 |overlap| {
 166                     if let Some(overlap_kind) =
 167                         tcx.impls_are_allowed_to_overlap(impl_def_id, possible_sibling)
 168                     {
 169                         match overlap_kind {
 170                             ty::ImplOverlapKind::Permitted { marker: _ } => {}
 171                             ty::ImplOverlapKind::Issue33140 => {
 172                                 *last_lint_mut = Some(FutureCompatOverlapError {
 173                                     error: create_overlap_error(overlap),
 174                                     kind: FutureCompatOverlapErrorKind::Issue33140,
 175                                 });
 176                             }
 177                         }
 178
 179                         return Ok((false, false));
 180                     }
 181
 182                     let le = tcx.specializes((impl_def_id, possible_sibling));
 183                     let ge = tcx.specializes((possible_sibling, impl_def_id));
 184
 185                     if le == ge {
 186                         report_overlap_error(overlap, last_lint_mut)
 187                     } else {
 188                         Ok((le, ge))
 189                     }
 190                 },
 191                 || Ok((false, false)),
 192             )?;
 193
 194             if le && !ge {
 195                 debug!(
 196                     "descending as child of TraitRef {:?}",
 197                     tcx.impl_trait_ref(possible_sibling).unwrap()
 198                 );
 199
 200                 // The impl specializes `possible_sibling`.
 201                 return Ok(Inserted::ShouldRecurseOn(possible_sibling));
 202             } else if ge && !le {
 203                 debug!(
 204                     "placing as parent of TraitRef {:?}",
 205                     tcx.impl_trait_ref(possible_sibling).unwrap()
 206                 );
 207
 208                 replace_children.push(possible_sibling);
 209             } else {
 210                 // Either there's no overlap, or the overlap was already reported by
 211                 // `overlap_error`.
 212             }
 213         }
 214
 215         if !replace_children.is_empty() {
 216             return Ok(Inserted::ReplaceChildren(replace_children));
 217         }
 218
 219         // No overlap with any potential siblings, so add as a new sibling.
 220         debug!("placing as new sibling");
 221         self.insert_blindly(tcx, impl_def_id);
 222         Ok(Inserted::BecameNewSibling(last_lint))
 223     }
 224 }
 225
 226 fn iter_children(children: &mut Children) -> impl Iterator<Item = DefId> + '_ {
 227     let nonblanket = children.non_blanket_impls.iter().flat_map(|(_, v)| v.iter());
 228     children.blanket_impls.iter().chain(nonblanket).cloned()
 229 }
 230
 231 fn filtered_children(
 232     children: &mut Children,
 233     st: SimplifiedType,
 234 ) -> impl Iterator<Item = DefId> + '_ {
 235     let nonblanket = children.non_blanket_impls.entry(st).or_default().iter();
 236     children.blanket_impls.iter().chain(nonblanket).cloned()
 237 }
 238
 239 // A custom iterator used by Children::insert
 240 enum PotentialSiblings<I, J>
 241 where
 242     I: Iterator<Item = DefId>,
 243     J: Iterator<Item = DefId>,
 244 {
 245     Unfiltered(I),
 246     Filtered(J),
 247 }
 248
 249 impl<I, J> Iterator for PotentialSiblings<I, J>
 250 where
 251     I: Iterator<Item = DefId>,
 252     J: Iterator<Item = DefId>,
 253 {
 254     type Item = DefId;
 255
 256     fn next(&mut self) -> Option<Self::Item> {
 257         match *self {
 258             PotentialSiblings::Unfiltered(ref mut iter) => iter.next(),
 259             PotentialSiblings::Filtered(ref mut iter) => iter.next(),
 260         }
 261     }
 262 }
 263
 264 pub trait GraphExt {
 265     /// Insert a local impl into the specialization graph. If an existing impl
 266     /// conflicts with it (has overlap, but neither specializes the other),
 267     /// information about the area of overlap is returned in the `Err`.
 268     fn insert(
 269         &mut self,
 270         tcx: TyCtxt<'_>,
 271         impl_def_id: DefId,
 272         overlap_mode: OverlapMode,
 273     ) -> Result<Option<FutureCompatOverlapError>, OverlapError>;
 274
 275     /// Insert cached metadata mapping from a child impl back to its parent.
 276     fn record_impl_from_cstore(&mut self, tcx: TyCtxt<'_>, parent: DefId, child: DefId);
 277 }
 278
 279 impl GraphExt for Graph {
 280     /// Insert a local impl into the specialization graph. If an existing impl
 281     /// conflicts with it (has overlap, but neither specializes the other),
 282     /// information about the area of overlap is returned in the `Err`.
 283     fn insert(
 284         &mut self,
 285         tcx: TyCtxt<'_>,
 286         impl_def_id: DefId,
 287         overlap_mode: OverlapMode,
 288     ) -> Result<Option<FutureCompatOverlapError>, OverlapError> {
 289         assert!(impl_def_id.is_local());
 290
 291         let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
 292         let trait_def_id = trait_ref.def_id;
 293
 294         debug!(
 295             "insert({:?}): inserting TraitRef {:?} into specialization graph",
 296             impl_def_id, trait_ref
 297         );
 298
 299         // If the reference itself contains an earlier error (e.g., due to a
 300         // resolution failure), then we just insert the impl at the top level of
 301         // the graph and claim that there's no overlap (in order to suppress
 302         // bogus errors).
 303         if trait_ref.references_error() {
 304             debug!(
 305                 "insert: inserting dummy node for erroneous TraitRef {:?}, \
 306                  impl_def_id={:?}, trait_def_id={:?}",
 307                 trait_ref, impl_def_id, trait_def_id
 308             );
 309
 310             self.parent.insert(impl_def_id, trait_def_id);
 311             self.children.entry(trait_def_id).or_default().insert_blindly(tcx, impl_def_id);
 312             return Ok(None);
 313         }
 314
 315         let mut parent = trait_def_id;
 316         let mut last_lint = None;
 317         let simplified = fast_reject::simplify_type(tcx, trait_ref.self_ty(), TreatParams::AsInfer);
 318
 319         // Descend the specialization tree, where `parent` is the current parent node.
 320         loop {
 321             use self::Inserted::*;
 322
 323             let insert_result = self.children.entry(parent).or_default().insert(
 324                 tcx,
 325                 impl_def_id,
 326                 simplified,
 327                 overlap_mode,
 328             )?;
 329
 330             match insert_result {
 331                 BecameNewSibling(opt_lint) => {
 332                     last_lint = opt_lint;
 333                     break;
 334                 }
 335                 ReplaceChildren(grand_children_to_be) => {
 336                     // We currently have
 337                     //
 338                     //     P
 339                     //     |
 340                     //     G
 341                     //
 342                     // and we are inserting the impl N. We want to make it:
 343                     //
 344                     //     P
 345                     //     |
 346                     //     N
 347                     //     |
 348                     //     G
 349
 350                     // Adjust P's list of children: remove G and then add N.
 351                     {
 352                         let siblings = self.children.get_mut(&parent).unwrap();
 353                         for &grand_child_to_be in &grand_children_to_be {
 354                             siblings.remove_existing(tcx, grand_child_to_be);
 355                         }
 356                         siblings.insert_blindly(tcx, impl_def_id);
 357                     }
 358
 359                     // Set G's parent to N and N's parent to P.
 360                     for &grand_child_to_be in &grand_children_to_be {
 361                         self.parent.insert(grand_child_to_be, impl_def_id);
 362                     }
 363                     self.parent.insert(impl_def_id, parent);
 364
 365                     // Add G as N's child.
 366                     for &grand_child_to_be in &grand_children_to_be {
 367                         self.children
 368                             .entry(impl_def_id)
 369                             .or_default()
 370                             .insert_blindly(tcx, grand_child_to_be);
 371                     }
 372                     break;
 373                 }
 374                 ShouldRecurseOn(new_parent) => {
 375                     parent = new_parent;
 376                 }
 377             }
 378         }
 379
 380         self.parent.insert(impl_def_id, parent);
 381         Ok(last_lint)
 382     }
 383
 384     /// Insert cached metadata mapping from a child impl back to its parent.
 385     fn record_impl_from_cstore(&mut self, tcx: TyCtxt<'_>, parent: DefId, child: DefId) {
 386         if self.parent.insert(child, parent).is_some() {
 387             bug!(
 388                 "When recording an impl from the crate store, information about its parent \
 389                  was already present."
 390             );
 391         }
 392
 393         self.children.entry(parent).or_default().insert_blindly(tcx, child);
 394     }
 395 }