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::Ident;
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 /// Children of a given impl, grouped into blanket/non-blanket varieties as is
50 /// done in `TraitDef`.
51 #[derive(Default, TyEncodable, TyDecodable, Debug, HashStable)]
53 // Impls of a trait (or specializations of a given impl). To allow for
54 // quicker lookup, the impls are indexed by a simplified version of their
55 // `Self` type: impls with a simplifiable `Self` are stored in
56 // `non_blanket_impls` keyed by it, while all other impls are stored in
59 // A similar division is used within `TraitDef`, but the lists there collect
60 // together *all* the impls for a trait, and are populated prior to building
61 // the specialization graph.
62 /// Impls of the trait.
63 pub non_blanket_impls: FxIndexMap<SimplifiedType, Vec<DefId>>,
65 /// Blanket impls associated with the trait.
66 pub blanket_impls: Vec<DefId>,
69 /// A node in the specialization graph is either an impl or a trait
70 /// definition; either can serve as a source of item definitions.
71 /// There is always exactly one trait definition node: the root.
72 #[derive(Debug, Copy, Clone)]
79 pub fn is_from_trait(&self) -> bool {
80 matches!(self, Node::Trait(..))
83 /// Iterate over the items defined directly by the given (impl or trait) node.
84 pub fn items(&self, tcx: TyCtxt<'tcx>) -> impl 'tcx + Iterator<Item = &'tcx ty::AssocItem> {
85 tcx.associated_items(self.def_id()).in_definition_order()
88 /// Finds an associated item defined in this node.
90 /// If this returns `None`, the item can potentially still be found in
91 /// parents of this node.
95 trait_item_name: Ident,
96 trait_item_kind: ty::AssocKind,
98 ) -> Option<ty::AssocItem> {
99 tcx.associated_items(self.def_id())
100 .filter_by_name_unhygienic(trait_item_name.name)
101 .find(move |impl_item| {
102 trait_item_kind == impl_item.kind
103 && tcx.hygienic_eq(impl_item.ident, trait_item_name, trait_def_id)
108 pub fn def_id(&self) -> DefId {
110 Node::Impl(did) => did,
111 Node::Trait(did) => did,
116 #[derive(Copy, Clone)]
117 pub struct Ancestors<'tcx> {
119 specialization_graph: &'tcx Graph,
120 current_source: Option<Node>,
123 impl Iterator for Ancestors<'_> {
125 fn next(&mut self) -> Option<Node> {
126 let cur = self.current_source.take();
127 if let Some(Node::Impl(cur_impl)) = cur {
128 let parent = self.specialization_graph.parent(cur_impl);
130 self.current_source = if parent == self.trait_def_id {
131 Some(Node::Trait(parent))
133 Some(Node::Impl(parent))
140 /// Information about the most specialized definition of an associated item.
142 /// The associated item described by this `LeafDef`.
143 pub item: ty::AssocItem,
145 /// The node in the specialization graph containing the definition of `item`.
146 pub defining_node: Node,
148 /// The "top-most" (ie. least specialized) specialization graph node that finalized the
149 /// definition of `item`.
158 /// impl<T> Tr for T {
159 /// default fn assoc(&self) {}
162 /// impl Tr for u8 {}
165 /// If we start the leaf definition search at `impl Tr for u8`, that impl will be the
166 /// `finalizing_node`, while `defining_node` will be the generic impl.
168 /// If the leaf definition search is started at the generic impl, `finalizing_node` will be
169 /// `None`, since the most specialized impl we found still allows overriding the method
170 /// (doesn't finalize it).
171 pub finalizing_node: Option<Node>,
175 /// Returns whether this definition is known to not be further specializable.
176 pub fn is_final(&self) -> bool {
177 self.finalizing_node.is_some()
181 impl<'tcx> Ancestors<'tcx> {
182 /// Finds the bottom-most (ie. most specialized) definition of an associated
187 trait_item_name: Ident,
188 trait_item_kind: ty::AssocKind,
189 ) -> Option<LeafDef> {
190 let trait_def_id = self.trait_def_id;
191 let mut finalizing_node = None;
193 self.find_map(|node| {
194 if let Some(item) = node.item(tcx, trait_item_name, trait_item_kind, trait_def_id) {
195 if finalizing_node.is_none() {
196 let is_specializable = item.defaultness.is_default()
197 || tcx.impl_defaultness(node.def_id()).is_default();
199 if !is_specializable {
200 finalizing_node = Some(node);
204 Some(LeafDef { item, defining_node: node, finalizing_node })
206 // Item not mentioned. This "finalizes" any defaulted item provided by an ancestor.
207 finalizing_node = Some(node);
214 /// Walk up the specialization ancestors of a given impl, starting with that
217 /// Returns `Err` if an error was reported while building the specialization
222 start_from_impl: DefId,
223 ) -> Result<Ancestors<'tcx>, ErrorReported> {
224 let specialization_graph = tcx.specialization_graph_of(trait_def_id);
226 if specialization_graph.has_errored || tcx.type_of(start_from_impl).references_error() {
231 specialization_graph,
232 current_source: Some(Node::Impl(start_from_impl)),