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1 | // Copyright 2012-2014 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. | |
4 | // | |
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. | |
10 | ||
11 | //! This pass enforces various "well-formedness constraints" on impls. | |
12 | //! Logically, it is part of wfcheck -- but we do it early so that we | |
13 | //! can stop compilation afterwards, since part of the trait matching | |
14 | //! infrastructure gets very grumpy if these conditions don't hold. In | |
15 | //! particular, if there are type parameters that are not part of the | |
16 | //! impl, then coherence will report strange inference ambiguity | |
17 | //! errors; if impls have duplicate items, we get misleading | |
18 | //! specialization errors. These things can (and probably should) be | |
19 | //! fixed, but for the moment it's easier to do these checks early. | |
20 | ||
21 | use constrained_type_params as ctp; | |
476ff2be SL |
22 | use rustc::hir; |
23 | use rustc::hir::itemlikevisit::ItemLikeVisitor; | |
24 | use rustc::hir::def_id::DefId; | |
8bb4bdeb | 25 | use rustc::ty::{self, TyCtxt}; |
476ff2be SL |
26 | use rustc::util::nodemap::{FxHashMap, FxHashSet}; |
27 | use std::collections::hash_map::Entry::{Occupied, Vacant}; | |
28 | ||
29 | use syntax_pos::Span; | |
30 | ||
476ff2be SL |
31 | /// Checks that all the type/lifetime parameters on an impl also |
32 | /// appear in the trait ref or self-type (or are constrained by a | |
33 | /// where-clause). These rules are needed to ensure that, given a | |
34 | /// trait ref like `<T as Trait<U>>`, we can derive the values of all | |
35 | /// parameters on the impl (which is needed to make specialization | |
36 | /// possible). | |
37 | /// | |
38 | /// However, in the case of lifetimes, we only enforce these rules if | |
39 | /// the lifetime parameter is used in an associated type. This is a | |
40 | /// concession to backwards compatibility; see comment at the end of | |
41 | /// the fn for details. | |
42 | /// | |
43 | /// Example: | |
44 | /// | |
45 | /// ``` | |
46 | /// impl<T> Trait<Foo> for Bar { ... } | |
47 | /// ^ T does not appear in `Foo` or `Bar`, error! | |
48 | /// | |
49 | /// impl<T> Trait<Foo<T>> for Bar { ... } | |
50 | /// ^ T appears in `Foo<T>`, ok. | |
51 | /// | |
52 | /// impl<T> Trait<Foo> for Bar where Bar: Iterator<Item=T> { ... } | |
53 | /// ^ T is bound to `<Bar as Iterator>::Item`, ok. | |
54 | /// | |
55 | /// impl<'a> Trait<Foo> for Bar { } | |
56 | /// ^ 'a is unused, but for back-compat we allow it | |
57 | /// | |
58 | /// impl<'a> Trait<Foo> for Bar { type X = &'a i32; } | |
59 | /// ^ 'a is unused and appears in assoc type, error | |
60 | /// ``` | |
8bb4bdeb | 61 | pub fn impl_wf_check<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) { |
476ff2be SL |
62 | // We will tag this as part of the WF check -- logically, it is, |
63 | // but it's one that we must perform earlier than the rest of | |
64 | // WfCheck. | |
cc61c64b | 65 | tcx.hir.krate().visit_all_item_likes(&mut ImplWfCheck { tcx: tcx }); |
476ff2be SL |
66 | } |
67 | ||
68 | struct ImplWfCheck<'a, 'tcx: 'a> { | |
8bb4bdeb | 69 | tcx: TyCtxt<'a, 'tcx, 'tcx>, |
476ff2be SL |
70 | } |
71 | ||
72 | impl<'a, 'tcx> ItemLikeVisitor<'tcx> for ImplWfCheck<'a, 'tcx> { | |
73 | fn visit_item(&mut self, item: &'tcx hir::Item) { | |
74 | match item.node { | |
75 | hir::ItemImpl(.., ref generics, _, _, ref impl_item_refs) => { | |
8bb4bdeb XL |
76 | let impl_def_id = self.tcx.hir.local_def_id(item.id); |
77 | enforce_impl_params_are_constrained(self.tcx, | |
476ff2be SL |
78 | generics, |
79 | impl_def_id, | |
80 | impl_item_refs); | |
8bb4bdeb | 81 | enforce_impl_items_are_distinct(self.tcx, impl_item_refs); |
476ff2be SL |
82 | } |
83 | _ => { } | |
84 | } | |
85 | } | |
86 | ||
32a655c1 SL |
87 | fn visit_trait_item(&mut self, _trait_item: &'tcx hir::TraitItem) { } |
88 | ||
476ff2be SL |
89 | fn visit_impl_item(&mut self, _impl_item: &'tcx hir::ImplItem) { } |
90 | } | |
91 | ||
8bb4bdeb | 92 | fn enforce_impl_params_are_constrained<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, |
476ff2be SL |
93 | impl_hir_generics: &hir::Generics, |
94 | impl_def_id: DefId, | |
95 | impl_item_refs: &[hir::ImplItemRef]) | |
96 | { | |
97 | // Every lifetime used in an associated type must be constrained. | |
7cac9316 XL |
98 | let impl_self_ty = tcx.type_of(impl_def_id); |
99 | let impl_generics = tcx.generics_of(impl_def_id); | |
100 | let impl_predicates = tcx.predicates_of(impl_def_id); | |
8bb4bdeb | 101 | let impl_trait_ref = tcx.impl_trait_ref(impl_def_id); |
476ff2be SL |
102 | |
103 | let mut input_parameters = ctp::parameters_for_impl(impl_self_ty, impl_trait_ref); | |
104 | ctp::identify_constrained_type_params( | |
105 | &impl_predicates.predicates.as_slice(), impl_trait_ref, &mut input_parameters); | |
106 | ||
107 | // Disallow ANY unconstrained type parameters. | |
108 | for (ty_param, param) in impl_generics.types.iter().zip(&impl_hir_generics.ty_params) { | |
109 | let param_ty = ty::ParamTy::for_def(ty_param); | |
110 | if !input_parameters.contains(&ctp::Parameter::from(param_ty)) { | |
8bb4bdeb | 111 | report_unused_parameter(tcx, param.span, "type", ¶m_ty.to_string()); |
476ff2be SL |
112 | } |
113 | } | |
114 | ||
115 | // Disallow unconstrained lifetimes, but only if they appear in assoc types. | |
116 | let lifetimes_in_associated_types: FxHashSet<_> = impl_item_refs.iter() | |
8bb4bdeb | 117 | .map(|item_ref| tcx.hir.local_def_id(item_ref.id.node_id)) |
476ff2be | 118 | .filter(|&def_id| { |
8bb4bdeb | 119 | let item = tcx.associated_item(def_id); |
476ff2be SL |
120 | item.kind == ty::AssociatedKind::Type && item.defaultness.has_value() |
121 | }) | |
122 | .flat_map(|def_id| { | |
7cac9316 | 123 | ctp::parameters_for(&tcx.type_of(def_id), true) |
476ff2be SL |
124 | }).collect(); |
125 | for (ty_lifetime, lifetime) in impl_generics.regions.iter() | |
126 | .zip(&impl_hir_generics.lifetimes) | |
127 | { | |
128 | let param = ctp::Parameter::from(ty_lifetime.to_early_bound_region_data()); | |
129 | ||
130 | if | |
131 | lifetimes_in_associated_types.contains(¶m) && // (*) | |
132 | !input_parameters.contains(¶m) | |
133 | { | |
8bb4bdeb | 134 | report_unused_parameter(tcx, lifetime.lifetime.span, |
476ff2be SL |
135 | "lifetime", &lifetime.lifetime.name.to_string()); |
136 | } | |
137 | } | |
138 | ||
139 | // (*) This is a horrible concession to reality. I think it'd be | |
140 | // better to just ban unconstrianed lifetimes outright, but in | |
141 | // practice people do non-hygenic macros like: | |
142 | // | |
143 | // ``` | |
144 | // macro_rules! __impl_slice_eq1 { | |
145 | // ($Lhs: ty, $Rhs: ty, $Bound: ident) => { | |
146 | // impl<'a, 'b, A: $Bound, B> PartialEq<$Rhs> for $Lhs where A: PartialEq<B> { | |
147 | // .... | |
148 | // } | |
149 | // } | |
150 | // } | |
151 | // ``` | |
152 | // | |
153 | // In a concession to backwards compatbility, we continue to | |
154 | // permit those, so long as the lifetimes aren't used in | |
155 | // associated types. I believe this is sound, because lifetimes | |
156 | // used elsewhere are not projected back out. | |
157 | } | |
158 | ||
8bb4bdeb | 159 | fn report_unused_parameter(tcx: TyCtxt, |
476ff2be SL |
160 | span: Span, |
161 | kind: &str, | |
162 | name: &str) | |
163 | { | |
164 | struct_span_err!( | |
8bb4bdeb | 165 | tcx.sess, span, E0207, |
476ff2be SL |
166 | "the {} parameter `{}` is not constrained by the \ |
167 | impl trait, self type, or predicates", | |
168 | kind, name) | |
7cac9316 | 169 | .span_label(span, format!("unconstrained {} parameter", kind)) |
476ff2be SL |
170 | .emit(); |
171 | } | |
172 | ||
173 | /// Enforce that we do not have two items in an impl with the same name. | |
8bb4bdeb | 174 | fn enforce_impl_items_are_distinct<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, |
476ff2be SL |
175 | impl_item_refs: &[hir::ImplItemRef]) |
176 | { | |
476ff2be SL |
177 | let mut seen_type_items = FxHashMap(); |
178 | let mut seen_value_items = FxHashMap(); | |
179 | for impl_item_ref in impl_item_refs { | |
32a655c1 | 180 | let impl_item = tcx.hir.impl_item(impl_item_ref.id); |
476ff2be SL |
181 | let seen_items = match impl_item.node { |
182 | hir::ImplItemKind::Type(_) => &mut seen_type_items, | |
183 | _ => &mut seen_value_items, | |
184 | }; | |
185 | match seen_items.entry(impl_item.name) { | |
186 | Occupied(entry) => { | |
187 | let mut err = struct_span_err!(tcx.sess, impl_item.span, E0201, | |
188 | "duplicate definitions with name `{}`:", | |
189 | impl_item.name); | |
190 | err.span_label(*entry.get(), | |
7cac9316 | 191 | format!("previous definition of `{}` here", |
476ff2be | 192 | impl_item.name)); |
7cac9316 | 193 | err.span_label(impl_item.span, "duplicate definition"); |
476ff2be SL |
194 | err.emit(); |
195 | } | |
196 | Vacant(entry) => { | |
197 | entry.insert(impl_item.span); | |
198 | } | |
199 | } | |
200 | } | |
201 | } |