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