80 lines
3.7 KiB
Rust
80 lines
3.7 KiB
Rust
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// Copyright 2012-2015 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use super::Item;
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use super::intravisit::Visitor;
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/// The "item-like visitor" visitor defines only the top-level methods
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/// that can be invoked by `Crate::visit_all_item_likes()`. Whether
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/// this trait is the right one to implement will depend on the
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/// overall pattern you need. Here are the three available patterns,
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/// in roughly the order of desirability:
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///
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/// 1. **Shallow visit**: Get a simple callback for every item (or item-like thing) in the HIR.
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/// - Example: find all items with a `#[foo]` attribute on them.
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/// - How: Implement `ItemLikeVisitor` and call `tcx.visit_all_item_likes_in_krate()`.
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/// - Pro: Efficient; just walks the lists of item-like things, not the nodes themselves.
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/// - Pro: Integrates well into dependency tracking.
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/// - Con: Don't get information about nesting
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/// - Con: Don't have methods for specific bits of HIR, like "on
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/// every expr, do this".
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/// 2. **Deep visit**: Want to scan for specific kinds of HIR nodes within
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/// an item, but don't care about how item-like things are nested
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/// within one another.
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/// - Example: Examine each expression to look for its type and do some check or other.
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/// - How: Implement `intravisit::Visitor` and use
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/// `tcx.visit_all_item_likes_in_krate(visitor.as_deep_visitor())`. Within
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/// your `intravisit::Visitor` impl, implement methods like
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/// `visit_expr()`; don't forget to invoke
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/// `intravisit::walk_visit_expr()` to keep walking the subparts.
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/// - Pro: Visitor methods for any kind of HIR node, not just item-like things.
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/// - Pro: Integrates well into dependency tracking.
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/// - Con: Don't get information about nesting between items
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/// 3. **Nested visit**: Want to visit the whole HIR and you care about the nesting between
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/// item-like things.
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/// - Example: Lifetime resolution, which wants to bring lifetimes declared on the
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/// impl into scope while visiting the impl-items, and then back out again.
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/// - How: Implement `intravisit::Visitor` and override the `visit_nested_foo()` foo methods
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/// as needed. Walk your crate with `intravisit::walk_crate()` invoked on `tcx.map.krate()`.
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/// - Pro: Visitor methods for any kind of HIR node, not just item-like things.
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/// - Pro: Preserves nesting information
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/// - Con: Does not integrate well into dependency tracking.
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///
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/// Note: the methods of `ItemLikeVisitor` intentionally have no
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/// defaults, so that as we expand the list of item-like things, we
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/// revisit the various visitors to see if they need to change. This
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/// is harder to do with `intravisit::Visitor`, so when you add a new
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/// `visit_nested_foo()` method, it is recommended that you search for
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/// existing `fn visit_nested` methods to see where changes are
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/// needed.
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pub trait ItemLikeVisitor<'hir> {
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fn visit_item(&mut self, item: &'hir Item);
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}
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pub struct DeepVisitor<'v, V: 'v> {
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visitor: &'v mut V,
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}
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impl<'v, 'hir, V> DeepVisitor<'v, V>
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where V: Visitor<'hir> + 'v
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{
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pub fn new(base: &'v mut V) -> Self {
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DeepVisitor { visitor: base }
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}
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}
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impl<'v, 'hir, V> ItemLikeVisitor<'hir> for DeepVisitor<'v, V>
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where V: Visitor<'hir>
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{
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fn visit_item(&mut self, item: &'hir Item) {
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self.visitor.visit_item(item);
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}
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}
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