1 // Copyright 2016 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 use super::{OverlapError, specializes};
13 use hir::def_id::DefId;
14 use traits::{self, Reveal};
15 use ty::{self, TyCtxt, TraitDef, TypeFoldable};
16 use ty::fast_reject::{self, SimplifiedType};
17 use syntax::ast::Name;
18 use util::nodemap::{DefIdMap, FxHashMap};
20 /// A per-trait graph of impls in specialization order. At the moment, this
21 /// graph forms a tree rooted with the trait itself, with all other nodes
22 /// representing impls, and parent-child relationships representing
25 /// The graph provides two key services:
27 /// - Construction, which implicitly checks for overlapping impls (i.e., impls
28 /// that overlap but where neither specializes the other -- an artifact of the
29 /// simple "chain" rule.
31 /// - Parent extraction. In particular, the graph can give you the *immediate*
32 /// parents of a given specializing impl, which is needed for extracting
33 /// default items amongst other thigns. In the simple "chain" rule, every impl
34 /// has at most one parent.
36 // all impls have a parent; the "root" impls have as their parent the def_id
38 parent: DefIdMap<DefId>,
40 // the "root" impls are found by looking up the trait's def_id.
41 children: DefIdMap<Children>,
44 /// Children of a given impl, grouped into blanket/non-blanket varieties as is
45 /// done in `TraitDef`.
47 // Impls of a trait (or specializations of a given impl). To allow for
48 // quicker lookup, the impls are indexed by a simplified version of their
49 // `Self` type: impls with a simplifiable `Self` are stored in
50 // `nonblanket_impls` keyed by it, while all other impls are stored in
53 // A similar division is used within `TraitDef`, but the lists there collect
54 // together *all* the impls for a trait, and are populated prior to building
55 // the specialization graph.
57 /// Impls of the trait.
58 nonblanket_impls: FxHashMap<fast_reject::SimplifiedType, Vec<DefId>>,
60 /// Blanket impls associated with the trait.
61 blanket_impls: Vec<DefId>,
64 /// The result of attempting to insert an impl into a group of children.
66 /// The impl was inserted as a new child in this group of children.
69 /// The impl replaced an existing impl that specializes it.
72 /// The impl is a specialization of an existing child.
73 ShouldRecurseOn(DefId),
76 impl<'a, 'gcx, 'tcx> Children {
77 fn new() -> Children {
79 nonblanket_impls: FxHashMap(),
80 blanket_impls: vec![],
84 /// Insert an impl into this set of children without comparing to any existing impls
85 fn insert_blindly(&mut self,
86 tcx: TyCtxt<'a, 'gcx, 'tcx>,
88 let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
89 if let Some(sty) = fast_reject::simplify_type(tcx, trait_ref.self_ty(), false) {
90 self.nonblanket_impls.entry(sty).or_insert(vec![]).push(impl_def_id)
92 self.blanket_impls.push(impl_def_id)
96 /// Attempt to insert an impl into this set of children, while comparing for
97 /// specialiation relationships.
99 tcx: TyCtxt<'a, 'gcx, 'tcx>,
101 simplified_self: Option<SimplifiedType>)
102 -> Result<Inserted, OverlapError>
104 for slot in match simplified_self {
105 Some(sty) => self.filtered_mut(sty),
106 None => self.iter_mut(),
108 let possible_sibling = *slot;
110 let tcx = tcx.global_tcx();
111 let (le, ge) = tcx.infer_ctxt((), Reveal::UserFacing).enter(|infcx| {
112 let overlap = traits::overlapping_impls(&infcx,
115 if let Some(impl_header) = overlap {
116 let le = specializes(tcx, impl_def_id, possible_sibling);
117 let ge = specializes(tcx, possible_sibling, impl_def_id);
120 // overlap, but no specialization; error out
121 let trait_ref = impl_header.trait_ref.unwrap();
122 let self_ty = trait_ref.self_ty();
124 with_impl: possible_sibling,
125 trait_desc: trait_ref.to_string(),
126 // only report the Self type if it has at least
127 // some outer concrete shell; otherwise, it's
128 // not adding much information.
129 self_desc: if self_ty.has_concrete_skeleton() {
130 Some(self_ty.to_string())
144 debug!("descending as child of TraitRef {:?}",
145 tcx.impl_trait_ref(possible_sibling).unwrap());
147 // the impl specializes possible_sibling
148 return Ok(Inserted::ShouldRecurseOn(possible_sibling));
149 } else if ge && !le {
150 debug!("placing as parent of TraitRef {:?}",
151 tcx.impl_trait_ref(possible_sibling).unwrap());
153 // possible_sibling specializes the impl
155 return Ok(Inserted::Replaced(possible_sibling));
157 // no overlap (error bailed already via ?)
161 // no overlap with any potential siblings, so add as a new sibling
162 debug!("placing as new sibling");
163 self.insert_blindly(tcx, impl_def_id);
164 Ok(Inserted::BecameNewSibling)
167 fn iter_mut(&'a mut self) -> Box<Iterator<Item = &'a mut DefId> + 'a> {
168 let nonblanket = self.nonblanket_impls.iter_mut().flat_map(|(_, v)| v.iter_mut());
169 Box::new(self.blanket_impls.iter_mut().chain(nonblanket))
172 fn filtered_mut(&'a mut self, sty: SimplifiedType)
173 -> Box<Iterator<Item = &'a mut DefId> + 'a> {
174 let nonblanket = self.nonblanket_impls.entry(sty).or_insert(vec![]).iter_mut();
175 Box::new(self.blanket_impls.iter_mut().chain(nonblanket))
179 impl<'a, 'gcx, 'tcx> Graph {
180 pub fn new() -> Graph {
182 parent: Default::default(),
183 children: Default::default(),
187 /// Insert a local impl into the specialization graph. If an existing impl
188 /// conflicts with it (has overlap, but neither specializes the other),
189 /// information about the area of overlap is returned in the `Err`.
190 pub fn insert(&mut self,
191 tcx: TyCtxt<'a, 'gcx, 'tcx>,
193 -> Result<(), OverlapError> {
194 assert!(impl_def_id.is_local());
196 let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
197 let trait_def_id = trait_ref.def_id;
199 debug!("insert({:?}): inserting TraitRef {:?} into specialization graph",
200 impl_def_id, trait_ref);
202 // if the reference itself contains an earlier error (e.g., due to a
203 // resolution failure), then we just insert the impl at the top level of
204 // the graph and claim that there's no overlap (in order to supress
206 if trait_ref.references_error() {
207 debug!("insert: inserting dummy node for erroneous TraitRef {:?}, \
208 impl_def_id={:?}, trait_def_id={:?}",
209 trait_ref, impl_def_id, trait_def_id);
211 self.parent.insert(impl_def_id, trait_def_id);
212 self.children.entry(trait_def_id).or_insert(Children::new())
213 .insert_blindly(tcx, impl_def_id);
217 let mut parent = trait_def_id;
218 let simplified = fast_reject::simplify_type(tcx, trait_ref.self_ty(), false);
220 // Descend the specialization tree, where `parent` is the current parent node
222 use self::Inserted::*;
224 let insert_result = self.children.entry(parent).or_insert(Children::new())
225 .insert(tcx, impl_def_id, simplified)?;
227 match insert_result {
228 BecameNewSibling => {
231 Replaced(new_child) => {
232 self.parent.insert(new_child, impl_def_id);
233 let mut new_children = Children::new();
234 new_children.insert_blindly(tcx, new_child);
235 self.children.insert(impl_def_id, new_children);
238 ShouldRecurseOn(new_parent) => {
244 self.parent.insert(impl_def_id, parent);
248 /// Insert cached metadata mapping from a child impl back to its parent.
249 pub fn record_impl_from_cstore(&mut self,
250 tcx: TyCtxt<'a, 'gcx, 'tcx>,
253 if self.parent.insert(child, parent).is_some() {
254 bug!("When recording an impl from the crate store, information about its parent \
255 was already present.");
258 self.children.entry(parent).or_insert(Children::new()).insert_blindly(tcx, child);
261 /// The parent of a given impl, which is the def id of the trait when the
262 /// impl is a "specialization root".
263 pub fn parent(&self, child: DefId) -> DefId {
264 *self.parent.get(&child).unwrap()
268 /// A node in the specialization graph is either an impl or a trait
269 /// definition; either can serve as a source of item definitions.
270 /// There is always exactly one trait definition node: the root.
271 #[derive(Debug, Copy, Clone)]
277 impl<'a, 'gcx, 'tcx> Node {
278 pub fn is_from_trait(&self) -> bool {
280 Node::Trait(..) => true,
285 /// Iterate over the items defined directly by the given (impl or trait) node.
286 #[inline] // FIXME(#35870) Avoid closures being unexported due to impl Trait.
287 pub fn items(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>)
288 -> impl Iterator<Item = ty::AssociatedItem> + 'a {
289 tcx.associated_items(self.def_id())
292 pub fn def_id(&self) -> DefId {
294 Node::Impl(did) => did,
295 Node::Trait(did) => did,
300 pub struct Ancestors<'a> {
301 trait_def: &'a TraitDef,
302 current_source: Option<Node>,
305 impl<'a> Iterator for Ancestors<'a> {
307 fn next(&mut self) -> Option<Node> {
308 let cur = self.current_source.take();
309 if let Some(Node::Impl(cur_impl)) = cur {
310 let parent = self.trait_def.specialization_graph.borrow().parent(cur_impl);
311 if parent == self.trait_def.def_id {
312 self.current_source = Some(Node::Trait(parent));
314 self.current_source = Some(Node::Impl(parent));
321 pub struct NodeItem<T> {
326 impl<T> NodeItem<T> {
327 pub fn map<U, F: FnOnce(T) -> U>(self, f: F) -> NodeItem<U> {
335 impl<'a, 'gcx, 'tcx> Ancestors<'a> {
336 /// Search the items from the given ancestors, returning each definition
337 /// with the given name and the given kind.
338 #[inline] // FIXME(#35870) Avoid closures being unexported due to impl Trait.
339 pub fn defs(self, tcx: TyCtxt<'a, 'gcx, 'tcx>, name: Name, kind: ty::AssociatedKind)
340 -> impl Iterator<Item = NodeItem<ty::AssociatedItem>> + 'a {
341 self.flat_map(move |node| {
342 node.items(tcx).filter(move |item| item.kind == kind && item.name == name)
343 .map(move |item| NodeItem { node: node, item: item })
348 /// Walk up the specialization ancestors of a given impl, starting with that
350 pub fn ancestors<'a>(trait_def: &'a TraitDef, start_from_impl: DefId) -> Ancestors<'a> {
352 trait_def: trait_def,
353 current_source: Some(Node::Impl(start_from_impl)),