1 use super::{ForeignItem, ImplItem, Item, TraitItem}; 2 3 /// The "item-like visitor" defines only the top-level methods 4 /// that can be invoked by `Crate::visit_all_item_likes()`. Whether 5 /// this trait is the right one to implement will depend on the 6 /// overall pattern you need. Here are the three available patterns, 7 /// in roughly the order of desirability: 8 /// 9 /// 1. **Shallow visit**: Get a simple callback for every item (or item-like thing) in the HIR. 10 /// - Example: find all items with a `#[foo]` attribute on them. 11 /// - How: Implement `ItemLikeVisitor` and call `tcx.hir().krate().visit_all_item_likes()`. 12 /// - Pro: Efficient; just walks the lists of item-like things, not the nodes themselves. 13 /// - Con: Don't get information about nesting 14 /// - Con: Don't have methods for specific bits of HIR, like "on 15 /// every expr, do this". 16 /// 2. **Deep visit**: Want to scan for specific kinds of HIR nodes within 17 /// an item, but don't care about how item-like things are nested 18 /// within one another. 19 /// - Example: Examine each expression to look for its type and do some check or other. 20 /// - How: Implement `intravisit::Visitor` and override the `nested_visit_map()` method 21 /// to return `NestedVisitorMap::OnlyBodies` and use 22 /// `tcx.hir().krate().visit_all_item_likes(&mut visitor.as_deep_visitor())`. Within 23 /// your `intravisit::Visitor` impl, implement methods like `visit_expr()` (don't forget 24 /// to invoke `intravisit::walk_expr()` to keep walking the subparts). 25 /// - Pro: Visitor methods for any kind of HIR node, not just item-like things. 26 /// - Pro: Integrates well into dependency tracking. 27 /// - Con: Don't get information about nesting between items 28 /// 3. **Nested visit**: Want to visit the whole HIR and you care about the nesting between 29 /// item-like things. 30 /// - Example: Lifetime resolution, which wants to bring lifetimes declared on the 31 /// impl into scope while visiting the impl-items, and then back out again. 32 /// - How: Implement `intravisit::Visitor` and override the `nested_visit_map()` method 33 /// to return `NestedVisitorMap::All`. Walk your crate with `intravisit::walk_crate()` 34 /// invoked on `tcx.hir().krate()`. 35 /// - Pro: Visitor methods for any kind of HIR node, not just item-like things. 36 /// - Pro: Preserves nesting information 37 /// - Con: Does not integrate well into dependency tracking. 38 /// 39 /// Note: the methods of `ItemLikeVisitor` intentionally have no 40 /// defaults, so that as we expand the list of item-like things, we 41 /// revisit the various visitors to see if they need to change. This 42 /// is harder to do with `intravisit::Visitor`, so when you add a new 43 /// `visit_nested_foo()` method, it is recommended that you search for 44 /// existing `fn visit_nested` methods to see where changes are 45 /// needed. 46 pub trait ItemLikeVisitor<'hir> { visit_item(&mut self, item: &'hir Item<'hir>)47 fn visit_item(&mut self, item: &'hir Item<'hir>); visit_trait_item(&mut self, trait_item: &'hir TraitItem<'hir>)48 fn visit_trait_item(&mut self, trait_item: &'hir TraitItem<'hir>); visit_impl_item(&mut self, impl_item: &'hir ImplItem<'hir>)49 fn visit_impl_item(&mut self, impl_item: &'hir ImplItem<'hir>); visit_foreign_item(&mut self, foreign_item: &'hir ForeignItem<'hir>)50 fn visit_foreign_item(&mut self, foreign_item: &'hir ForeignItem<'hir>); 51 } 52 53 /// A parallel variant of `ItemLikeVisitor`. 54 pub trait ParItemLikeVisitor<'hir> { visit_item(&self, item: &'hir Item<'hir>)55 fn visit_item(&self, item: &'hir Item<'hir>); visit_trait_item(&self, trait_item: &'hir TraitItem<'hir>)56 fn visit_trait_item(&self, trait_item: &'hir TraitItem<'hir>); visit_impl_item(&self, impl_item: &'hir ImplItem<'hir>)57 fn visit_impl_item(&self, impl_item: &'hir ImplItem<'hir>); visit_foreign_item(&self, foreign_item: &'hir ForeignItem<'hir>)58 fn visit_foreign_item(&self, foreign_item: &'hir ForeignItem<'hir>); 59 } 60