1 // Copyright 2013 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.
13 // Terms are structured as a straightforward tree. Rather than rely on
14 // GC, we allocate terms out of a bounded arena (the lifetime of this
15 // arena is the lifetime 'a that is threaded around).
17 // We assign a unique index to each type/region parameter whose variance
18 // is to be inferred. We refer to such variables as "inferreds". An
19 // `InferredIndex` is a newtype'd int representing the index of such
22 use arena::TypedArena;
23 use dep_graph::DepTrackingMapConfig;
24 use rustc::ty::{self, TyCtxt};
25 use rustc::ty::maps::ItemVariances;
30 use rustc::hir::intravisit::Visitor;
31 use util::nodemap::NodeMap;
33 use self::VarianceTerm::*;
35 pub type VarianceTermPtr<'a> = &'a VarianceTerm<'a>;
37 #[derive(Copy, Clone, Debug)]
38 pub struct InferredIndex(pub usize);
40 #[derive(Copy, Clone)]
41 pub enum VarianceTerm<'a> {
42 ConstantTerm(ty::Variance),
43 TransformTerm(VarianceTermPtr<'a>, VarianceTermPtr<'a>),
44 InferredTerm(InferredIndex),
47 impl<'a> fmt::Debug for VarianceTerm<'a> {
48 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
50 ConstantTerm(c1) => write!(f, "{:?}", c1),
51 TransformTerm(v1, v2) => write!(f, "({:?} \u{00D7} {:?})", v1, v2),
52 InferredTerm(id) => write!(f, "[{}]", { let InferredIndex(i) = id; i })
57 // The first pass over the crate simply builds up the set of inferreds.
59 pub struct TermsContext<'a, 'tcx: 'a> {
60 pub tcx: TyCtxt<'a, 'tcx, 'tcx>,
61 pub arena: &'a TypedArena<VarianceTerm<'a>>,
63 pub empty_variances: Rc<Vec<ty::Variance>>,
65 // For marker types, UnsafeCell, and other lang items where
66 // variance is hardcoded, records the item-id and the hardcoded
68 pub lang_items: Vec<(ast::NodeId, Vec<ty::Variance>)>,
70 // Maps from the node id of a type/generic parameter to the
71 // corresponding inferred index.
72 pub inferred_map: NodeMap<InferredIndex>,
74 // Maps from an InferredIndex to the info for that variable.
75 pub inferred_infos: Vec<InferredInfo<'a>> ,
78 pub struct InferredInfo<'a> {
79 pub item_id: ast::NodeId,
81 pub param_id: ast::NodeId,
82 pub term: VarianceTermPtr<'a>,
84 // Initial value to use for this parameter when inferring
85 // variance. For most parameters, this is Bivariant. But for lang
86 // items and input type parameters on traits, it is different.
87 pub initial_variance: ty::Variance,
90 pub fn determine_parameters_to_be_inferred<'a, 'tcx>(
91 tcx: TyCtxt<'a, 'tcx, 'tcx>,
92 arena: &'a mut TypedArena<VarianceTerm<'a>>)
93 -> TermsContext<'a, 'tcx>
95 let mut terms_cx = TermsContext {
98 inferred_map: NodeMap(),
99 inferred_infos: Vec::new(),
101 lang_items: lang_items(tcx),
103 // cache and share the variance struct used for items with
104 // no type/region parameters
105 empty_variances: Rc::new(vec![])
108 // See README.md for a discussion on dep-graph management.
109 tcx.visit_all_items_in_krate(|def_id| ItemVariances::to_dep_node(&def_id),
115 fn lang_items(tcx: TyCtxt) -> Vec<(ast::NodeId,Vec<ty::Variance>)> {
117 (tcx.lang_items.phantom_data(), vec![ty::Covariant]),
118 (tcx.lang_items.unsafe_cell_type(), vec![ty::Invariant]),
121 (tcx.lang_items.covariant_type(), vec![ty::Covariant]),
122 (tcx.lang_items.contravariant_type(), vec![ty::Contravariant]),
123 (tcx.lang_items.invariant_type(), vec![ty::Invariant]),
124 (tcx.lang_items.covariant_lifetime(), vec![ty::Covariant]),
125 (tcx.lang_items.contravariant_lifetime(), vec![ty::Contravariant]),
126 (tcx.lang_items.invariant_lifetime(), vec![ty::Invariant]),
130 all.into_iter() // iterating over (Option<DefId>, Variance)
131 .filter(|&(ref d,_)| d.is_some())
132 .map(|(d, v)| (d.unwrap(), v)) // (DefId, Variance)
133 .filter_map(|(d, v)| tcx.map.as_local_node_id(d).map(|n| (n, v))) // (NodeId, Variance)
137 impl<'a, 'tcx> TermsContext<'a, 'tcx> {
138 fn add_inferreds_for_item(&mut self,
139 item_id: ast::NodeId,
141 generics: &hir::Generics)
144 * Add "inferreds" for the generic parameters declared on this
145 * item. This has a lot of annoying parameters because we are
146 * trying to drive this from the AST, rather than the
147 * ty::Generics, so that we can get span info -- but this
148 * means we must accommodate syntactic distinctions.
151 // NB: In the code below for writing the results back into the
152 // tcx, we rely on the fact that all inferreds for a particular
153 // item are assigned continuous indices.
155 let inferreds_on_entry = self.num_inferred();
158 self.add_inferred(item_id, 0, item_id);
161 for (i, p) in generics.lifetimes.iter().enumerate() {
162 let id = p.lifetime.id;
163 let i = has_self as usize + i;
164 self.add_inferred(item_id, i, id);
167 for (i, p) in generics.ty_params.iter().enumerate() {
168 let i = has_self as usize + generics.lifetimes.len() + i;
169 self.add_inferred(item_id, i, p.id);
172 // If this item has no type or lifetime parameters,
173 // then there are no variances to infer, so just
174 // insert an empty entry into the variance map.
175 // Arguably we could just leave the map empty in this
176 // case but it seems cleaner to be able to distinguish
177 // "invalid item id" from "item id with no
179 if self.num_inferred() == inferreds_on_entry {
180 let item_def_id = self.tcx.map.local_def_id(item_id);
182 self.tcx.item_variance_map.borrow_mut().insert(
184 self.empty_variances.clone()).is_none();
185 assert!(newly_added);
189 fn add_inferred(&mut self,
190 item_id: ast::NodeId,
192 param_id: ast::NodeId) {
193 let inf_index = InferredIndex(self.inferred_infos.len());
194 let term = self.arena.alloc(InferredTerm(inf_index));
195 let initial_variance = self.pick_initial_variance(item_id, index);
196 self.inferred_infos.push(InferredInfo { item_id: item_id,
200 initial_variance: initial_variance });
201 let newly_added = self.inferred_map.insert(param_id, inf_index).is_none();
202 assert!(newly_added);
204 debug!("add_inferred(item_path={}, \
209 initial_variance={:?})",
210 self.tcx.item_path_str(self.tcx.map.local_def_id(item_id)),
211 item_id, index, param_id, inf_index,
215 fn pick_initial_variance(&self,
216 item_id: ast::NodeId,
220 match self.lang_items.iter().find(|&&(n, _)| n == item_id) {
221 Some(&(_, ref variances)) => variances[index],
222 None => ty::Bivariant
226 pub fn num_inferred(&self) -> usize {
227 self.inferred_infos.len()
231 impl<'a, 'tcx, 'v> Visitor<'v> for TermsContext<'a, 'tcx> {
232 fn visit_item(&mut self, item: &hir::Item) {
233 debug!("add_inferreds for item {}", self.tcx.map.node_to_string(item.id));
236 hir::ItemEnum(_, ref generics) |
237 hir::ItemStruct(_, ref generics) => {
238 self.add_inferreds_for_item(item.id, false, generics);
240 hir::ItemTrait(_, ref generics, _, _) => {
241 // Note: all inputs for traits are ultimately
242 // constrained to be invariant. See `visit_item` in
243 // the impl for `ConstraintContext` in `constraints.rs`.
244 self.add_inferreds_for_item(item.id, true, generics);
247 hir::ItemExternCrate(_) |
249 hir::ItemDefaultImpl(..) |
251 hir::ItemStatic(..) |
255 hir::ItemForeignMod(..) |