1 use crate::ty::fast_reject::SimplifiedType;
2 use crate::ty::fold::TypeFoldable;
3 use crate::ty::{self, TyCtxt};
4 use rustc_data_structures::fx::FxIndexMap;
5 use rustc_errors::ErrorReported;
6 use rustc_hir::def_id::{DefId, DefIdMap};
7 use rustc_span::symbol::sym;
9 /// A per-trait graph of impls in specialization order. At the moment, this
10 /// graph forms a tree rooted with the trait itself, with all other nodes
11 /// representing impls, and parent-child relationships representing
14 /// The graph provides two key services:
16 /// - Construction. This implicitly checks for overlapping impls (i.e., impls
17 /// that overlap but where neither specializes the other -- an artifact of the
18 /// simple "chain" rule.
20 /// - Parent extraction. In particular, the graph can give you the *immediate*
21 /// parents of a given specializing impl, which is needed for extracting
22 /// default items amongst other things. In the simple "chain" rule, every impl
23 /// has at most one parent.
24 #[derive(TyEncodable, TyDecodable, HashStable, Debug)]
26 /// All impls have a parent; the "root" impls have as their parent the `def_id`
28 pub parent: DefIdMap<DefId>,
30 /// The "root" impls are found by looking up the trait's def_id.
31 pub children: DefIdMap<Children>,
33 /// Whether an error was emitted while constructing the graph.
34 pub has_errored: bool,
38 pub fn new() -> Graph {
39 Graph { parent: Default::default(), children: Default::default(), has_errored: false }
42 /// The parent of a given impl, which is the `DefId` of the trait when the
43 /// impl is a "specialization root".
44 pub fn parent(&self, child: DefId) -> DefId {
45 *self.parent.get(&child).unwrap_or_else(|| panic!("Failed to get parent for {:?}", child))
49 /// What kind of overlap check are we doing -- this exists just for testing and feature-gating
51 #[derive(Copy, Clone, PartialEq, Eq, Hash, HashStable, Debug, TyEncodable, TyDecodable)]
52 pub enum OverlapMode {
53 /// The 1.0 rules (either types fail to unify, or where clauses are not implemented for crate-local types)
55 /// Feature-gated test: Stable, *or* there is an explicit negative impl that rules out one of the where-clauses.
57 /// Just check for negative impls, not for "where clause not implemented": used for testing.
62 pub fn get<'tcx>(tcx: TyCtxt<'tcx>, trait_id: DefId) -> OverlapMode {
63 let with_negative_coherence = tcx.features().with_negative_coherence;
64 let strict_coherence = tcx.has_attr(trait_id, sym::rustc_strict_coherence);
66 if with_negative_coherence {
67 if strict_coherence { OverlapMode::Strict } else { OverlapMode::WithNegative }
68 } else if strict_coherence {
69 bug!("To use strict_coherence you need to set with_negative_coherence feature flag");
75 pub fn use_negative_impl(&self) -> bool {
76 *self == OverlapMode::Strict || *self == OverlapMode::WithNegative
79 pub fn use_implicit_negative(&self) -> bool {
80 *self == OverlapMode::Stable || *self == OverlapMode::WithNegative
84 /// Children of a given impl, grouped into blanket/non-blanket varieties as is
85 /// done in `TraitDef`.
86 #[derive(Default, TyEncodable, TyDecodable, Debug, HashStable)]
88 // Impls of a trait (or specializations of a given impl). To allow for
89 // quicker lookup, the impls are indexed by a simplified version of their
90 // `Self` type: impls with a simplifiable `Self` are stored in
91 // `non_blanket_impls` keyed by it, while all other impls are stored in
94 // A similar division is used within `TraitDef`, but the lists there collect
95 // together *all* the impls for a trait, and are populated prior to building
96 // the specialization graph.
97 /// Impls of the trait.
98 pub non_blanket_impls: FxIndexMap<SimplifiedType, Vec<DefId>>,
100 /// Blanket impls associated with the trait.
101 pub blanket_impls: Vec<DefId>,
104 /// A node in the specialization graph is either an impl or a trait
105 /// definition; either can serve as a source of item definitions.
106 /// There is always exactly one trait definition node: the root.
107 #[derive(Debug, Copy, Clone)]
114 pub fn is_from_trait(&self) -> bool {
115 matches!(self, Node::Trait(..))
118 /// Trys to find the associated item that implements `trait_item_def_id`
119 /// defined in this node.
121 /// If this returns `None`, the item can potentially still be found in
122 /// parents of this node.
126 trait_item_def_id: DefId,
127 ) -> Option<&'tcx ty::AssocItem> {
129 Node::Trait(_) => Some(tcx.associated_item(trait_item_def_id)),
130 Node::Impl(impl_def_id) => {
131 let id = tcx.impl_item_implementor_ids(impl_def_id).get(&trait_item_def_id)?;
132 Some(tcx.associated_item(*id))
137 pub fn def_id(&self) -> DefId {
139 Node::Impl(did) => did,
140 Node::Trait(did) => did,
145 #[derive(Copy, Clone)]
146 pub struct Ancestors<'tcx> {
148 specialization_graph: &'tcx Graph,
149 current_source: Option<Node>,
152 impl Iterator for Ancestors<'_> {
154 fn next(&mut self) -> Option<Node> {
155 let cur = self.current_source.take();
156 if let Some(Node::Impl(cur_impl)) = cur {
157 let parent = self.specialization_graph.parent(cur_impl);
159 self.current_source = if parent == self.trait_def_id {
160 Some(Node::Trait(parent))
162 Some(Node::Impl(parent))
169 /// Information about the most specialized definition of an associated item.
171 /// The associated item described by this `LeafDef`.
172 pub item: ty::AssocItem,
174 /// The node in the specialization graph containing the definition of `item`.
175 pub defining_node: Node,
177 /// The "top-most" (ie. least specialized) specialization graph node that finalized the
178 /// definition of `item`.
187 /// impl<T> Tr for T {
188 /// default fn assoc(&self) {}
191 /// impl Tr for u8 {}
194 /// If we start the leaf definition search at `impl Tr for u8`, that impl will be the
195 /// `finalizing_node`, while `defining_node` will be the generic impl.
197 /// If the leaf definition search is started at the generic impl, `finalizing_node` will be
198 /// `None`, since the most specialized impl we found still allows overriding the method
199 /// (doesn't finalize it).
200 pub finalizing_node: Option<Node>,
204 /// Returns whether this definition is known to not be further specializable.
205 pub fn is_final(&self) -> bool {
206 self.finalizing_node.is_some()
210 impl<'tcx> Ancestors<'tcx> {
211 /// Finds the bottom-most (ie. most specialized) definition of an associated
213 pub fn leaf_def(mut self, tcx: TyCtxt<'tcx>, trait_item_def_id: DefId) -> Option<LeafDef> {
214 let mut finalizing_node = None;
216 self.find_map(|node| {
217 if let Some(item) = node.item(tcx, trait_item_def_id) {
218 if finalizing_node.is_none() {
219 let is_specializable = item.defaultness.is_default()
220 || tcx.impl_defaultness(node.def_id()).is_default();
222 if !is_specializable {
223 finalizing_node = Some(node);
227 Some(LeafDef { item: *item, defining_node: node, finalizing_node })
229 // Item not mentioned. This "finalizes" any defaulted item provided by an ancestor.
230 finalizing_node = Some(node);
237 /// Walk up the specialization ancestors of a given impl, starting with that
240 /// Returns `Err` if an error was reported while building the specialization
242 pub fn ancestors<'tcx>(
245 start_from_impl: DefId,
246 ) -> Result<Ancestors<'tcx>, ErrorReported> {
247 let specialization_graph = tcx.specialization_graph_of(trait_def_id);
249 if specialization_graph.has_errored || tcx.type_of(start_from_impl).references_error() {
254 specialization_graph,
255 current_source: Some(Node::Impl(start_from_impl)),