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.
14 use super::{OverlapError, specializes};
16 use hir::def_id::DefId;
17 use traits::{self, Reveal};
18 use ty::{self, TyCtxt, ImplOrTraitItem, TraitDef, TypeFoldable};
19 use ty::fast_reject::{self, SimplifiedType};
20 use syntax::ast::Name;
21 use util::nodemap::{DefIdMap, FnvHashMap};
23 /// A per-trait graph of impls in specialization order. At the moment, this
24 /// graph forms a tree rooted with the trait itself, with all other nodes
25 /// representing impls, and parent-child relationships representing
28 /// The graph provides two key services:
30 /// - Construction, which implicitly checks for overlapping impls (i.e., impls
31 /// that overlap but where neither specializes the other -- an artifact of the
32 /// simple "chain" rule.
34 /// - Parent extraction. In particular, the graph can give you the *immediate*
35 /// parents of a given specializing impl, which is needed for extracting
36 /// default items amongst other thigns. In the simple "chain" rule, every impl
37 /// has at most one parent.
39 // all impls have a parent; the "root" impls have as their parent the def_id
41 parent: DefIdMap<DefId>,
43 // the "root" impls are found by looking up the trait's def_id.
44 children: DefIdMap<Children>,
47 /// Children of a given impl, grouped into blanket/non-blanket varieties as is
48 /// done in `TraitDef`.
50 // Impls of a trait (or specializations of a given impl). To allow for
51 // quicker lookup, the impls are indexed by a simplified version of their
52 // `Self` type: impls with a simplifiable `Self` are stored in
53 // `nonblanket_impls` keyed by it, while all other impls are stored in
56 // A similar division is used within `TraitDef`, but the lists there collect
57 // together *all* the impls for a trait, and are populated prior to building
58 // the specialization graph.
60 /// Impls of the trait.
61 nonblanket_impls: FnvHashMap<fast_reject::SimplifiedType, Vec<DefId>>,
63 /// Blanket impls associated with the trait.
64 blanket_impls: Vec<DefId>,
67 /// The result of attempting to insert an impl into a group of children.
69 /// The impl was inserted as a new child in this group of children.
72 /// The impl replaced an existing impl that specializes it.
75 /// The impl is a specialization of an existing child.
76 ShouldRecurseOn(DefId),
79 impl<'a, 'gcx, 'tcx> Children {
80 fn new() -> Children {
82 nonblanket_impls: FnvHashMap(),
83 blanket_impls: vec![],
87 /// Insert an impl into this set of children without comparing to any existing impls
88 fn insert_blindly(&mut self,
89 tcx: TyCtxt<'a, 'gcx, 'tcx>,
91 let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
92 if let Some(sty) = fast_reject::simplify_type(tcx, trait_ref.self_ty(), false) {
93 self.nonblanket_impls.entry(sty).or_insert(vec![]).push(impl_def_id)
95 self.blanket_impls.push(impl_def_id)
99 /// Attempt to insert an impl into this set of children, while comparing for
100 /// specialiation relationships.
102 tcx: TyCtxt<'a, 'gcx, 'tcx>,
104 simplified_self: Option<SimplifiedType>)
105 -> Result<Inserted, OverlapError>
107 for slot in match simplified_self {
108 Some(sty) => self.filtered_mut(sty),
109 None => self.iter_mut(),
111 let possible_sibling = *slot;
113 let tcx = tcx.global_tcx();
114 let (le, ge) = tcx.infer_ctxt(None, None, Reveal::ExactMatch).enter(|infcx| {
115 let overlap = traits::overlapping_impls(&infcx,
118 if let Some(impl_header) = overlap {
119 let le = specializes(tcx, impl_def_id, possible_sibling);
120 let ge = specializes(tcx, possible_sibling, impl_def_id);
123 // overlap, but no specialization; error out
124 let trait_ref = impl_header.trait_ref.unwrap();
126 with_impl: possible_sibling,
127 trait_desc: trait_ref.to_string(),
128 self_desc: trait_ref.substs.self_ty().and_then(|ty| {
129 // only report the Self type if it has at least
130 // some outer concrete shell; otherwise, it's
131 // not adding much information.
132 if ty.has_concrete_skeleton() {
148 debug!("descending as child of TraitRef {:?}",
149 tcx.impl_trait_ref(possible_sibling).unwrap());
151 // the impl specializes possible_sibling
152 return Ok(Inserted::ShouldRecurseOn(possible_sibling));
153 } else if ge && !le {
154 debug!("placing as parent of TraitRef {:?}",
155 tcx.impl_trait_ref(possible_sibling).unwrap());
157 // possible_sibling specializes the impl
159 return Ok(Inserted::Replaced(possible_sibling));
161 // no overlap (error bailed already via ?)
165 // no overlap with any potential siblings, so add as a new sibling
166 debug!("placing as new sibling");
167 self.insert_blindly(tcx, impl_def_id);
168 Ok(Inserted::BecameNewSibling)
171 fn iter_mut(&'a mut self) -> Box<Iterator<Item = &'a mut DefId> + 'a> {
172 let nonblanket = self.nonblanket_impls.iter_mut().flat_map(|(_, v)| v.iter_mut());
173 Box::new(self.blanket_impls.iter_mut().chain(nonblanket))
176 fn filtered_mut(&'a mut self, sty: SimplifiedType)
177 -> Box<Iterator<Item = &'a mut DefId> + 'a> {
178 let nonblanket = self.nonblanket_impls.entry(sty).or_insert(vec![]).iter_mut();
179 Box::new(self.blanket_impls.iter_mut().chain(nonblanket))
183 impl<'a, 'gcx, 'tcx> Graph {
184 pub fn new() -> Graph {
186 parent: Default::default(),
187 children: Default::default(),
191 /// Insert a local impl into the specialization graph. If an existing impl
192 /// conflicts with it (has overlap, but neither specializes the other),
193 /// information about the area of overlap is returned in the `Err`.
194 pub fn insert(&mut self,
195 tcx: TyCtxt<'a, 'gcx, 'tcx>,
197 -> Result<(), OverlapError> {
198 assert!(impl_def_id.is_local());
200 let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
201 let trait_def_id = trait_ref.def_id;
203 debug!("insert({:?}): inserting TraitRef {:?} into specialization graph",
204 impl_def_id, trait_ref);
206 // if the reference itself contains an earlier error (e.g., due to a
207 // resolution failure), then we just insert the impl at the top level of
208 // the graph and claim that there's no overlap (in order to supress
210 if trait_ref.references_error() {
211 debug!("insert: inserting dummy node for erroneous TraitRef {:?}, \
212 impl_def_id={:?}, trait_def_id={:?}",
213 trait_ref, impl_def_id, trait_def_id);
215 self.parent.insert(impl_def_id, trait_def_id);
216 self.children.entry(trait_def_id).or_insert(Children::new())
217 .insert_blindly(tcx, impl_def_id);
221 let mut parent = trait_def_id;
222 let simplified = fast_reject::simplify_type(tcx, trait_ref.self_ty(), false);
224 // Descend the specialization tree, where `parent` is the current parent node
226 use self::Inserted::*;
228 let insert_result = self.children.entry(parent).or_insert(Children::new())
229 .insert(tcx, impl_def_id, simplified)?;
231 match insert_result {
232 BecameNewSibling => {
235 Replaced(new_child) => {
236 self.parent.insert(new_child, impl_def_id);
237 let mut new_children = Children::new();
238 new_children.insert_blindly(tcx, new_child);
239 self.children.insert(impl_def_id, new_children);
242 ShouldRecurseOn(new_parent) => {
248 self.parent.insert(impl_def_id, parent);
252 /// Insert cached metadata mapping from a child impl back to its parent.
253 pub fn record_impl_from_cstore(&mut self,
254 tcx: TyCtxt<'a, 'gcx, 'tcx>,
257 if self.parent.insert(child, parent).is_some() {
258 bug!("When recording an impl from the crate store, information about its parent \
259 was already present.");
262 self.children.entry(parent).or_insert(Children::new()).insert_blindly(tcx, child);
265 /// The parent of a given impl, which is the def id of the trait when the
266 /// impl is a "specialization root".
267 pub fn parent(&self, child: DefId) -> DefId {
268 *self.parent.get(&child).unwrap()
272 /// A node in the specialization graph is either an impl or a trait
273 /// definition; either can serve as a source of item definitions.
274 /// There is always exactly one trait definition node: the root.
275 #[derive(Debug, Copy, Clone)]
281 impl<'a, 'gcx, 'tcx> Node {
282 pub fn is_from_trait(&self) -> bool {
284 Node::Trait(..) => true,
289 /// Iterate over the items defined directly by the given (impl or trait) node.
290 pub fn items(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>) -> NodeItems<'a, 'gcx> {
292 Node::Impl(impl_def_id) => {
294 tcx: tcx.global_tcx(),
295 items: cell::Ref::map(tcx.impl_items.borrow(),
296 |impl_items| &impl_items[&impl_def_id]),
300 Node::Trait(trait_def_id) => {
302 items: tcx.trait_items(trait_def_id).clone(),
309 pub fn def_id(&self) -> DefId {
311 Node::Impl(did) => did,
312 Node::Trait(did) => did,
317 /// An iterator over the items defined within a trait or impl.
318 pub enum NodeItems<'a, 'tcx: 'a> {
320 tcx: TyCtxt<'a, 'tcx, 'tcx>,
321 items: cell::Ref<'a, Vec<ty::ImplOrTraitItemId>>,
325 items: Rc<Vec<ImplOrTraitItem<'tcx>>>,
330 impl<'a, 'tcx> Iterator for NodeItems<'a, 'tcx> {
331 type Item = ImplOrTraitItem<'tcx>;
332 fn next(&mut self) -> Option<ImplOrTraitItem<'tcx>> {
334 NodeItems::Impl { tcx, ref items, ref mut idx } => {
335 let items_table = tcx.impl_or_trait_items.borrow();
336 if *idx < items.len() {
337 let item_def_id = items[*idx].def_id();
338 let item = items_table[&item_def_id].clone();
345 NodeItems::Trait { ref items, ref mut idx } => {
346 if *idx < items.len() {
347 let item = items[*idx].clone();
358 pub struct Ancestors<'a, 'tcx: 'a> {
359 trait_def: &'a TraitDef<'tcx>,
360 current_source: Option<Node>,
363 impl<'a, 'tcx> Iterator for Ancestors<'a, 'tcx> {
365 fn next(&mut self) -> Option<Node> {
366 let cur = self.current_source.take();
367 if let Some(Node::Impl(cur_impl)) = cur {
368 let parent = self.trait_def.specialization_graph.borrow().parent(cur_impl);
369 if parent == self.trait_def.def_id() {
370 self.current_source = Some(Node::Trait(parent));
372 self.current_source = Some(Node::Impl(parent));
379 pub struct NodeItem<T> {
384 impl<T> NodeItem<T> {
385 pub fn map<U, F: FnOnce(T) -> U>(self, f: F) -> NodeItem<U> {
393 pub struct TypeDefs<'a, 'tcx: 'a> {
394 // generally only invoked once or twice, so the box doesn't hurt
395 iter: Box<Iterator<Item = NodeItem<Rc<ty::AssociatedType<'tcx>>>> + 'a>,
398 impl<'a, 'tcx> Iterator for TypeDefs<'a, 'tcx> {
399 type Item = NodeItem<Rc<ty::AssociatedType<'tcx>>>;
400 fn next(&mut self) -> Option<Self::Item> {
405 pub struct FnDefs<'a, 'tcx: 'a> {
406 // generally only invoked once or twice, so the box doesn't hurt
407 iter: Box<Iterator<Item = NodeItem<Rc<ty::Method<'tcx>>>> + 'a>,
410 impl<'a, 'tcx> Iterator for FnDefs<'a, 'tcx> {
411 type Item = NodeItem<Rc<ty::Method<'tcx>>>;
412 fn next(&mut self) -> Option<Self::Item> {
417 pub struct ConstDefs<'a, 'tcx: 'a> {
418 // generally only invoked once or twice, so the box doesn't hurt
419 iter: Box<Iterator<Item = NodeItem<Rc<ty::AssociatedConst<'tcx>>>> + 'a>,
422 impl<'a, 'tcx> Iterator for ConstDefs<'a, 'tcx> {
423 type Item = NodeItem<Rc<ty::AssociatedConst<'tcx>>>;
424 fn next(&mut self) -> Option<Self::Item> {
429 impl<'a, 'gcx, 'tcx> Ancestors<'a, 'tcx> {
430 /// Search the items from the given ancestors, returning each type definition
431 /// with the given name.
432 pub fn type_defs(self, tcx: TyCtxt<'a, 'gcx, 'tcx>, name: Name) -> TypeDefs<'a, 'gcx> {
433 let iter = self.flat_map(move |node| {
435 .filter_map(move |item| {
436 if let ty::TypeTraitItem(assoc_ty) = item {
437 if assoc_ty.name == name {
438 return Some(NodeItem {
448 TypeDefs { iter: Box::new(iter) }
451 /// Search the items from the given ancestors, returning each fn definition
452 /// with the given name.
453 pub fn fn_defs(self, tcx: TyCtxt<'a, 'gcx, 'tcx>, name: Name) -> FnDefs<'a, 'gcx> {
454 let iter = self.flat_map(move |node| {
456 .filter_map(move |item| {
457 if let ty::MethodTraitItem(method) = item {
458 if method.name == name {
459 return Some(NodeItem {
469 FnDefs { iter: Box::new(iter) }
472 /// Search the items from the given ancestors, returning each const
473 /// definition with the given name.
474 pub fn const_defs(self, tcx: TyCtxt<'a, 'gcx, 'tcx>, name: Name) -> ConstDefs<'a, 'gcx> {
475 let iter = self.flat_map(move |node| {
477 .filter_map(move |item| {
478 if let ty::ConstTraitItem(konst) = item {
479 if konst.name == name {
480 return Some(NodeItem {
490 ConstDefs { iter: Box::new(iter) }
494 /// Walk up the specialization ancestors of a given impl, starting with that
496 pub fn ancestors<'a, 'tcx>(trait_def: &'a TraitDef<'tcx>,
497 start_from_impl: DefId)
498 -> Ancestors<'a, 'tcx> {
500 trait_def: trait_def,
501 current_source: Some(Node::Impl(start_from_impl)),