Trait rustc_hir::itemlikevisit::ItemLikeVisitor[−][src]

pub trait ItemLikeVisitor<'hir> {
    fn visit_item(&mut self, item: &'hir Item<'hir>);

    fn visit_trait_item(&mut self, trait_item: &'hir TraitItem<'hir>);

    fn visit_impl_item(&mut self, impl_item: &'hir ImplItem<'hir>);

    fn visit_foreign_item(&mut self, foreign_item: &'hir ForeignItem<'hir>);
}
Expand description

The “item-like visitor” defines only the top-level methods that can be invoked by Crate::visit_all_item_likes(). Whether this trait is the right one to implement will depend on the overall pattern you need. Here are the three available patterns, in roughly the order of desirability:

  1. Shallow visit: Get a simple callback for every item (or item-like thing) in the HIR.
    • Example: find all items with a #[foo] attribute on them.
    • How: Implement ItemLikeVisitor and call tcx.hir().krate().visit_all_item_likes().
    • Pro: Efficient; just walks the lists of item-like things, not the nodes themselves.
    • Con: Don’t get information about nesting
    • Con: Don’t have methods for specific bits of HIR, like “on every expr, do this”.
  2. Deep visit: Want to scan for specific kinds of HIR nodes within an item, but don’t care about how item-like things are nested within one another.
    • Example: Examine each expression to look for its type and do some check or other.
    • How: Implement intravisit::Visitor and override the nested_visit_map() method to return NestedVisitorMap::OnlyBodies and use tcx.hir().krate().visit_all_item_likes(&mut visitor.as_deep_visitor()). Within your intravisit::Visitor impl, implement methods like visit_expr() (don’t forget to invoke intravisit::walk_expr() to keep walking the subparts).
    • Pro: Visitor methods for any kind of HIR node, not just item-like things.
    • Pro: Integrates well into dependency tracking.
    • Con: Don’t get information about nesting between items
  3. Nested visit: Want to visit the whole HIR and you care about the nesting between item-like things.
    • Example: Lifetime resolution, which wants to bring lifetimes declared on the impl into scope while visiting the impl-items, and then back out again.
    • How: Implement intravisit::Visitor and override the nested_visit_map() method to return NestedVisitorMap::All. Walk your crate with intravisit::walk_crate() invoked on tcx.hir().krate().
    • Pro: Visitor methods for any kind of HIR node, not just item-like things.
    • Pro: Preserves nesting information
    • Con: Does not integrate well into dependency tracking.

Note: the methods of ItemLikeVisitor intentionally have no defaults, so that as we expand the list of item-like things, we revisit the various visitors to see if they need to change. This is harder to do with intravisit::Visitor, so when you add a new visit_nested_foo() method, it is recommended that you search for existing fn visit_nested methods to see where changes are needed.

Required methods

Implementors