60 lines
3.5 KiB
Rust
60 lines
3.5 KiB
Rust
use super::{ForeignItem, ImplItem, Item, TraitItem};
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/// The "item-like 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.hir().visit_all_item_likes()`.
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/// - Pro: Efficient; just walks the lists of item-like things, not the nodes themselves.
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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 override the `NestedFilter` type to
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/// `nested_filter::OnlyBodies` (and implement `nested_visit_map`), and use
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/// `tcx.hir().visit_all_item_likes(&mut visitor.as_deep_visitor())`. Within your
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/// `intravisit::Visitor` impl, implement methods like `visit_expr()` (don't forget to invoke
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/// `intravisit::walk_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 `NestedFilter` type to
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/// `nested_filter::All` (and implement `nested_visit_map`). Walk your crate with
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/// `tcx.hir().walk_toplevel_module(visitor)` invoked on `tcx.hir().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<'hir>);
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fn visit_trait_item(&mut self, trait_item: &'hir TraitItem<'hir>);
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fn visit_impl_item(&mut self, impl_item: &'hir ImplItem<'hir>);
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fn visit_foreign_item(&mut self, foreign_item: &'hir ForeignItem<'hir>);
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}
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/// A parallel variant of `ItemLikeVisitor`.
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pub trait ParItemLikeVisitor<'hir> {
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fn visit_item(&self, item: &'hir Item<'hir>);
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fn visit_trait_item(&self, trait_item: &'hir TraitItem<'hir>);
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fn visit_impl_item(&self, impl_item: &'hir ImplItem<'hir>);
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fn visit_foreign_item(&self, foreign_item: &'hir ForeignItem<'hir>);
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}
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