1 // Copyright 2012-2015 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::{Item, ImplItem, TraitItem}
;
12 use super::intravisit
::Visitor
;
14 /// The "item-like visitor" visitor defines only the top-level methods
15 /// that can be invoked by `Crate::visit_all_item_likes()`. Whether
16 /// this trait is the right one to implement will depend on the
17 /// overall pattern you need. Here are the three available patterns,
18 /// in roughly the order of desirability:
20 /// 1. **Shallow visit**: Get a simple callback for every item (or item-like thing) in the HIR.
21 /// - Example: find all items with a `#[foo]` attribute on them.
22 /// - How: Implement `ItemLikeVisitor` and call `tcx.hir.krate().visit_all_item_likes()`.
23 /// - Pro: Efficient; just walks the lists of item-like things, not the nodes themselves.
24 /// - Con: Don't get information about nesting
25 /// - Con: Don't have methods for specific bits of HIR, like "on
26 /// every expr, do this".
27 /// 2. **Deep visit**: Want to scan for specific kinds of HIR nodes within
28 /// an item, but don't care about how item-like things are nested
29 /// within one another.
30 /// - Example: Examine each expression to look for its type and do some check or other.
31 /// - How: Implement `intravisit::Visitor` and use
32 /// `tcx.hir.krate().visit_all_item_likes(visitor.as_deep_visitor())`. Within
33 /// your `intravisit::Visitor` impl, implement methods like
34 /// `visit_expr()`; don't forget to invoke
35 /// `intravisit::walk_visit_expr()` to keep walking the subparts.
36 /// - Pro: Visitor methods for any kind of HIR node, not just item-like things.
37 /// - Pro: Integrates well into dependency tracking.
38 /// - Con: Don't get information about nesting between items
39 /// 3. **Nested visit**: Want to visit the whole HIR and you care about the nesting between
41 /// - Example: Lifetime resolution, which wants to bring lifetimes declared on the
42 /// impl into scope while visiting the impl-items, and then back out again.
43 /// - How: Implement `intravisit::Visitor` and override the
44 /// `nested_visit_map()` methods to return
45 /// `NestedVisitorMap::All`. Walk your crate with
46 /// `intravisit::walk_crate()` invoked on `tcx.hir.krate()`.
47 /// - Pro: Visitor methods for any kind of HIR node, not just item-like things.
48 /// - Pro: Preserves nesting information
49 /// - Con: Does not integrate well into dependency tracking.
51 /// Note: the methods of `ItemLikeVisitor` intentionally have no
52 /// defaults, so that as we expand the list of item-like things, we
53 /// revisit the various visitors to see if they need to change. This
54 /// is harder to do with `intravisit::Visitor`, so when you add a new
55 /// `visit_nested_foo()` method, it is recommended that you search for
56 /// existing `fn visit_nested` methods to see where changes are
58 pub trait ItemLikeVisitor
<'hir
> {
59 fn visit_item(&mut self, item
: &'hir Item
);
60 fn visit_trait_item(&mut self, trait_item
: &'hir TraitItem
);
61 fn visit_impl_item(&mut self, impl_item
: &'hir ImplItem
);
64 pub struct DeepVisitor
<'v
, V
: 'v
> {
68 impl<'v
, 'hir
, V
> DeepVisitor
<'v
, V
>
69 where V
: Visitor
<'hir
> + 'v
71 pub fn new(base
: &'v
mut V
) -> Self {
72 DeepVisitor { visitor: base }
76 impl<'v
, 'hir
, V
> ItemLikeVisitor
<'hir
> for DeepVisitor
<'v
, V
>
77 where V
: Visitor
<'hir
>
79 fn visit_item(&mut self, item
: &'hir Item
) {
80 self.visitor
.visit_item(item
);
83 fn visit_trait_item(&mut self, trait_item
: &'hir TraitItem
) {
84 self.visitor
.visit_trait_item(trait_item
);
87 fn visit_impl_item(&mut self, impl_item
: &'hir ImplItem
) {
88 self.visitor
.visit_impl_item(impl_item
);