1 use crate::ich::{self, StableHashingContext};
2 use crate::ty::fast_reject::SimplifiedType;
3 use crate::ty::{self, TyCtxt};
4 use rustc_data_structures::fx::FxHashMap;
5 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
6 use rustc_errors::ErrorReported;
7 use rustc_hir::def_id::{DefId, DefIdMap};
8 use rustc_span::symbol::Ident;
10 /// A per-trait graph of impls in specialization order. At the moment, this
11 /// graph forms a tree rooted with the trait itself, with all other nodes
12 /// representing impls, and parent-child relationships representing
15 /// The graph provides two key services:
17 /// - Construction. This implicitly checks for overlapping impls (i.e., impls
18 /// that overlap but where neither specializes the other -- an artifact of the
19 /// simple "chain" rule.
21 /// - Parent extraction. In particular, the graph can give you the *immediate*
22 /// parents of a given specializing impl, which is needed for extracting
23 /// default items amongst other things. In the simple "chain" rule, every impl
24 /// has at most one parent.
25 #[derive(RustcEncodable, RustcDecodable, HashStable)]
27 /// All impls have a parent; the "root" impls have as their parent the `def_id`
29 pub parent: DefIdMap<DefId>,
31 /// The "root" impls are found by looking up the trait's def_id.
32 pub children: DefIdMap<Children>,
34 /// Whether an error was emitted while constructing the graph.
35 pub has_errored: bool,
39 pub fn new() -> Graph {
40 Graph { parent: Default::default(), children: Default::default(), has_errored: false }
43 /// The parent of a given impl, which is the `DefId` of the trait when the
44 /// impl is a "specialization root".
45 pub fn parent(&self, child: DefId) -> DefId {
46 *self.parent.get(&child).unwrap_or_else(|| panic!("Failed to get parent for {:?}", child))
50 /// Children of a given impl, grouped into blanket/non-blanket varieties as is
51 /// done in `TraitDef`.
52 #[derive(Default, RustcEncodable, RustcDecodable)]
54 // Impls of a trait (or specializations of a given impl). To allow for
55 // quicker lookup, the impls are indexed by a simplified version of their
56 // `Self` type: impls with a simplifiable `Self` are stored in
57 // `nonblanket_impls` keyed by it, while all other impls are stored in
60 // A similar division is used within `TraitDef`, but the lists there collect
61 // together *all* the impls for a trait, and are populated prior to building
62 // the specialization graph.
63 /// Impls of the trait.
64 pub nonblanket_impls: FxHashMap<SimplifiedType, Vec<DefId>>,
66 /// Blanket impls associated with the trait.
67 pub blanket_impls: Vec<DefId>,
70 /// A node in the specialization graph is either an impl or a trait
71 /// definition; either can serve as a source of item definitions.
72 /// There is always exactly one trait definition node: the root.
73 #[derive(Debug, Copy, Clone)]
80 pub fn is_from_trait(&self) -> bool {
82 Node::Trait(..) => true,
87 /// Iterate over the items defined directly by the given (impl or trait) node.
88 pub fn items(&self, tcx: TyCtxt<'tcx>) -> impl 'tcx + Iterator<Item = &'tcx ty::AssocItem> {
89 tcx.associated_items(self.def_id()).in_definition_order()
92 /// Finds an associated item defined in this node.
94 /// If this returns `None`, the item can potentially still be found in
95 /// parents of this node.
99 trait_item_name: Ident,
100 trait_item_kind: ty::AssocKind,
102 ) -> Option<ty::AssocItem> {
103 tcx.associated_items(self.def_id())
104 .filter_by_name_unhygienic(trait_item_name.name)
105 .find(move |impl_item| {
106 trait_item_kind == impl_item.kind
107 && tcx.hygienic_eq(impl_item.ident, trait_item_name, trait_def_id)
112 pub fn def_id(&self) -> DefId {
114 Node::Impl(did) => did,
115 Node::Trait(did) => did,
120 #[derive(Copy, Clone)]
121 pub struct Ancestors<'tcx> {
123 specialization_graph: &'tcx Graph,
124 current_source: Option<Node>,
127 impl Iterator for Ancestors<'_> {
129 fn next(&mut self) -> Option<Node> {
130 let cur = self.current_source.take();
131 if let Some(Node::Impl(cur_impl)) = cur {
132 let parent = self.specialization_graph.parent(cur_impl);
134 self.current_source = if parent == self.trait_def_id {
135 Some(Node::Trait(parent))
137 Some(Node::Impl(parent))
144 /// Information about the most specialized definition of an associated item.
146 /// The associated item described by this `LeafDef`.
147 pub item: ty::AssocItem,
149 /// The node in the specialization graph containing the definition of `item`.
150 pub defining_node: Node,
152 /// The "top-most" (ie. least specialized) specialization graph node that finalized the
153 /// definition of `item`.
162 /// impl<T> Tr for T {
163 /// default fn assoc(&self) {}
166 /// impl Tr for u8 {}
169 /// If we start the leaf definition search at `impl Tr for u8`, that impl will be the
170 /// `finalizing_node`, while `defining_node` will be the generic impl.
172 /// If the leaf definition search is started at the generic impl, `finalizing_node` will be
173 /// `None`, since the most specialized impl we found still allows overriding the method
174 /// (doesn't finalize it).
175 pub finalizing_node: Option<Node>,
179 /// Returns whether this definition is known to not be further specializable.
180 pub fn is_final(&self) -> bool {
181 self.finalizing_node.is_some()
185 impl<'tcx> Ancestors<'tcx> {
186 /// Finds the bottom-most (ie. most specialized) definition of an associated
191 trait_item_name: Ident,
192 trait_item_kind: ty::AssocKind,
193 ) -> Option<LeafDef> {
194 let trait_def_id = self.trait_def_id;
195 let mut finalizing_node = None;
197 self.find_map(|node| {
198 if let Some(item) = node.item(tcx, trait_item_name, trait_item_kind, trait_def_id) {
199 if finalizing_node.is_none() {
200 let is_specializable = item.defaultness.is_default()
201 || tcx.impl_defaultness(node.def_id()).is_default();
203 if !is_specializable {
204 finalizing_node = Some(node);
208 Some(LeafDef { item, defining_node: node, finalizing_node })
210 // Item not mentioned. This "finalizes" any defaulted item provided by an ancestor.
211 finalizing_node = Some(node);
218 /// Walk up the specialization ancestors of a given impl, starting with that
221 /// Returns `Err` if an error was reported while building the specialization
226 start_from_impl: DefId,
227 ) -> Result<Ancestors<'tcx>, ErrorReported> {
228 let specialization_graph = tcx.specialization_graph_of(trait_def_id);
229 if specialization_graph.has_errored {
234 specialization_graph,
235 current_source: Some(Node::Impl(start_from_impl)),
240 impl<'a> HashStable<StableHashingContext<'a>> for Children {
241 fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
242 let Children { ref nonblanket_impls, ref blanket_impls } = *self;
244 ich::hash_stable_trait_impls(hcx, hasher, blanket_impls, nonblanket_impls);