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                 )
 141                 .is_some();
 142
 143                 let error = create_overlap_error(overlap);
 144
 145                 if should_err {
 146                     Err(error)
 147                 } else {
 148                     *last_lint = Some(FutureCompatOverlapError {
 149                         error,
 150                         kind: FutureCompatOverlapErrorKind::LeakCheck,
 151                     });
 152
 153                     Ok((false, false))
 154                 }
 155             };
 156
 157             let last_lint_mut = &mut last_lint;
 158             let (le, ge) = traits::overlapping_impls(
 159                 tcx,
 160                 possible_sibling,
 161                 impl_def_id,
 162                 traits::SkipLeakCheck::Yes,
 163                 overlap_mode,
 164             )
 165             .map_or(Ok((false, false)), |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 { report_overlap_error(overlap, last_lint_mut) } else { Ok((le, ge)) }
 186             })?;
 187
 188             if le && !ge {
 189                 debug!(
 190                     "descending as child of TraitRef {:?}",
 191                     tcx.impl_trait_ref(possible_sibling).unwrap()
 192                 );
 193
 194                 // The impl specializes `possible_sibling`.
 195                 return Ok(Inserted::ShouldRecurseOn(possible_sibling));
 196             } else if ge && !le {
 197                 debug!(
 198                     "placing as parent of TraitRef {:?}",
 199                     tcx.impl_trait_ref(possible_sibling).unwrap()
 200                 );
 201
 202                 replace_children.push(possible_sibling);
 203             } else {
 204                 // Either there's no overlap, or the overlap was already reported by
 205                 // `overlap_error`.
 206             }
 207         }
 208
 209         if !replace_children.is_empty() {
 210             return Ok(Inserted::ReplaceChildren(replace_children));
 211         }
 212
 213         // No overlap with any potential siblings, so add as a new sibling.
 214         debug!("placing as new sibling");
 215         self.insert_blindly(tcx, impl_def_id);
 216         Ok(Inserted::BecameNewSibling(last_lint))
 217     }
 218 }
 219
 220 fn iter_children(children: &mut Children) -> impl Iterator<Item = DefId> + '_ {
 221     let nonblanket = children.non_blanket_impls.iter().flat_map(|(_, v)| v.iter());
 222     children.blanket_impls.iter().chain(nonblanket).cloned()
 223 }
 224
 225 fn filtered_children(
 226     children: &mut Children,
 227     st: SimplifiedType,
 228 ) -> impl Iterator<Item = DefId> + '_ {
 229     let nonblanket = children.non_blanket_impls.entry(st).or_default().iter();
 230     children.blanket_impls.iter().chain(nonblanket).cloned()
 231 }
 232
 233 // A custom iterator used by Children::insert
 234 enum PotentialSiblings<I, J>
 235 where
 236     I: Iterator<Item = DefId>,
 237     J: Iterator<Item = DefId>,
 238 {
 239     Unfiltered(I),
 240     Filtered(J),
 241 }
 242
 243 impl<I, J> Iterator for PotentialSiblings<I, J>
 244 where
 245     I: Iterator<Item = DefId>,
 246     J: Iterator<Item = DefId>,
 247 {
 248     type Item = DefId;
 249
 250     fn next(&mut self) -> Option<Self::Item> {
 251         match *self {
 252             PotentialSiblings::Unfiltered(ref mut iter) => iter.next(),
 253             PotentialSiblings::Filtered(ref mut iter) => iter.next(),
 254         }
 255     }
 256 }
 257
 258 pub trait GraphExt {
 259     /// Insert a local impl into the specialization graph. If an existing impl
 260     /// conflicts with it (has overlap, but neither specializes the other),
 261     /// information about the area of overlap is returned in the `Err`.
 262     fn insert(
 263         &mut self,
 264         tcx: TyCtxt<'_>,
 265         impl_def_id: DefId,
 266         overlap_mode: OverlapMode,
 267     ) -> Result<Option<FutureCompatOverlapError>, OverlapError>;
 268
 269     /// Insert cached metadata mapping from a child impl back to its parent.
 270     fn record_impl_from_cstore(&mut self, tcx: TyCtxt<'_>, parent: DefId, child: DefId);
 271 }
 272
 273 impl GraphExt for Graph {
 274     /// Insert a local impl into the specialization graph. If an existing impl
 275     /// conflicts with it (has overlap, but neither specializes the other),
 276     /// information about the area of overlap is returned in the `Err`.
 277     fn insert(
 278         &mut self,
 279         tcx: TyCtxt<'_>,
 280         impl_def_id: DefId,
 281         overlap_mode: OverlapMode,
 282     ) -> Result<Option<FutureCompatOverlapError>, OverlapError> {
 283         assert!(impl_def_id.is_local());
 284
 285         let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
 286         let trait_def_id = trait_ref.def_id;
 287
 288         debug!(
 289             "insert({:?}): inserting TraitRef {:?} into specialization graph",
 290             impl_def_id, trait_ref
 291         );
 292
 293         // If the reference itself contains an earlier error (e.g., due to a
 294         // resolution failure), then we just insert the impl at the top level of
 295         // the graph and claim that there's no overlap (in order to suppress
 296         // bogus errors).
 297         if trait_ref.references_error() {
 298             debug!(
 299                 "insert: inserting dummy node for erroneous TraitRef {:?}, \
 300                  impl_def_id={:?}, trait_def_id={:?}",
 301                 trait_ref, impl_def_id, trait_def_id
 302             );
 303
 304             self.parent.insert(impl_def_id, trait_def_id);
 305             self.children.entry(trait_def_id).or_default().insert_blindly(tcx, impl_def_id);
 306             return Ok(None);
 307         }
 308
 309         let mut parent = trait_def_id;
 310         let mut last_lint = None;
 311         let simplified = fast_reject::simplify_type(tcx, trait_ref.self_ty(), TreatParams::AsInfer);
 312
 313         // Descend the specialization tree, where `parent` is the current parent node.
 314         loop {
 315             use self::Inserted::*;
 316
 317             let insert_result = self.children.entry(parent).or_default().insert(
 318                 tcx,
 319                 impl_def_id,
 320                 simplified,
 321                 overlap_mode,
 322             )?;
 323
 324             match insert_result {
 325                 BecameNewSibling(opt_lint) => {
 326                     last_lint = opt_lint;
 327                     break;
 328                 }
 329                 ReplaceChildren(grand_children_to_be) => {
 330                     // We currently have
 331                     //
 332                     //     P
 333                     //     |
 334                     //     G
 335                     //
 336                     // and we are inserting the impl N. We want to make it:
 337                     //
 338                     //     P
 339                     //     |
 340                     //     N
 341                     //     |
 342                     //     G
 343
 344                     // Adjust P's list of children: remove G and then add N.
 345                     {
 346                         let siblings = self.children.get_mut(&parent).unwrap();
 347                         for &grand_child_to_be in &grand_children_to_be {
 348                             siblings.remove_existing(tcx, grand_child_to_be);
 349                         }
 350                         siblings.insert_blindly(tcx, impl_def_id);
 351                     }
 352
 353                     // Set G's parent to N and N's parent to P.
 354                     for &grand_child_to_be in &grand_children_to_be {
 355                         self.parent.insert(grand_child_to_be, impl_def_id);
 356                     }
 357                     self.parent.insert(impl_def_id, parent);
 358
 359                     // Add G as N's child.
 360                     for &grand_child_to_be in &grand_children_to_be {
 361                         self.children
 362                             .entry(impl_def_id)
 363                             .or_default()
 364                             .insert_blindly(tcx, grand_child_to_be);
 365                     }
 366                     break;
 367                 }
 368                 ShouldRecurseOn(new_parent) => {
 369                     parent = new_parent;
 370                 }
 371             }
 372         }
 373
 374         self.parent.insert(impl_def_id, parent);
 375         Ok(last_lint)
 376     }
 377
 378     /// Insert cached metadata mapping from a child impl back to its parent.
 379     fn record_impl_from_cstore(&mut self, tcx: TyCtxt<'_>, parent: DefId, child: DefId) {
 380         if self.parent.insert(child, parent).is_some() {
 381             bug!(
 382                 "When recording an impl from the crate store, information about its parent \
 383                  was already present."
 384             );
 385         }
 386
 387         self.children.entry(parent).or_default().insert_blindly(tcx, child);
 388     }
 389 }