Rollup merge of #80765 - petrochenkov:traitsinscope, r=matthewjasper

resolve: Simplify collection of traits in scope

"Traits in scope" for a given location are collected by walking all scopes in type namespace, collecting traits in them and pruning traits that don't have an associated item with the given name and namespace.

Previously we tried to prune traits using some kind of hygienic resolution for associated items, but that was complex and likely incorrect, e.g. in #80762 correction to visibilites of trait items caused some traits to not be in scope anymore.
I previously had some comments and concerns about this in https://github.com/rust-lang/rust/pull/65351.

In this PR we are doing some much simpler pruning based on `Symbol` and `Namespace` comparisons, it should be enough to throw away 99.9% of unnecessary traits.
It is not necessary for pruning to be precise because for trait aliases, for example, we don't do any pruning at all, and precise hygienic resolution for associated items needs to be done in typeck anyway.

The somewhat unexpected effect is that trait imports introduced by macros 2.0 now bring traits into scope due to the removed hygienic check on associated item names.
I'm not sure whether it is desirable or not, but I think it's acceptable for now.
The old check was certainly incorrect because macros 2.0 did bring trait aliases into scope.
If doing this is not desirable, then we should come up with some other way to avoid bringing traits from macros 2.0 into scope, that would accommodate for trait aliases as well.

---

The PR also contains a couple of pure refactorings
- Scope walk is done by using `visit_scopes` instead of a hand-rolled version.
- Code is restructured to accomodate for rustdoc that also wants to query traits in scope, but doesn't want to filter them by associated items at all.

r? ```@matthewjasper```

compiler/rustc_resolve/src/late.rs

@@ -14,7 +14,6 @@ use crate::{ResolutionError, Resolver, Segment, UseError};
 use rustc_ast::ptr::P;
 use rustc_ast::visit::{self, AssocCtxt, FnCtxt, FnKind, Visitor};
 use rustc_ast::*;
-use rustc_ast::{unwrap_or, walk_list};
 use rustc_ast_lowering::ResolverAstLowering;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_errors::DiagnosticId;
@@ -1911,7 +1910,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                 // it needs to be added to the trait map.
                 if ns == ValueNS {
                     let item_name = path.last().unwrap().ident;
-                    let traits = self.get_traits_containing_item(item_name, ns);
+                    let traits = self.traits_in_scope(item_name, ns);
                     self.r.trait_map.insert(id, traits);
                 }
 
@@ -2371,12 +2370,12 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                 // field, we need to add any trait methods we find that match
                 // the field name so that we can do some nice error reporting
                 // later on in typeck.
-                let traits = self.get_traits_containing_item(ident, ValueNS);
+                let traits = self.traits_in_scope(ident, ValueNS);
                 self.r.trait_map.insert(expr.id, traits);
             }
             ExprKind::MethodCall(ref segment, ..) => {
                 debug!("(recording candidate traits for expr) recording traits for {}", expr.id);
-                let traits = self.get_traits_containing_item(segment.ident, ValueNS);
+                let traits = self.traits_in_scope(segment.ident, ValueNS);
                 self.r.trait_map.insert(expr.id, traits);
             }
             _ => {
@@ -2385,64 +2384,13 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
         }
     }
 
-    fn get_traits_containing_item(
-        &mut self,
-        mut ident: Ident,
-        ns: Namespace,
-    ) -> Vec<TraitCandidate> {
-        debug!("(getting traits containing item) looking for '{}'", ident.name);
-
-        let mut found_traits = Vec::new();
-        // Look for the current trait.
-        if let Some((module, _)) = self.current_trait_ref {
-            if self
-                .r
-                .resolve_ident_in_module(
-                    ModuleOrUniformRoot::Module(module),
-                    ident,
-                    ns,
-                    &self.parent_scope,
-                    false,
-                    module.span,
-                )
-                .is_ok()
-            {
-                let def_id = module.def_id().unwrap();
-                found_traits.push(TraitCandidate { def_id, import_ids: smallvec![] });
-            }
-        }
-
-        ident.span = ident.span.normalize_to_macros_2_0();
-        let mut search_module = self.parent_scope.module;
-        loop {
-            self.r.get_traits_in_module_containing_item(
-                ident,
-                ns,
-                search_module,
-                &mut found_traits,
-                &self.parent_scope,
-            );
-            let mut span_data = ident.span.data();
-            search_module = unwrap_or!(
-                self.r.hygienic_lexical_parent(search_module, &mut span_data.ctxt),
-                break
-            );
-            ident.span = span_data.span();
-        }
-
-        if let Some(prelude) = self.r.prelude {
-            if !search_module.no_implicit_prelude {
-                self.r.get_traits_in_module_containing_item(
-                    ident,
-                    ns,
-                    prelude,
-                    &mut found_traits,
-                    &self.parent_scope,
-                );
-            }
-        }
-
-        found_traits
+    fn traits_in_scope(&mut self, ident: Ident, ns: Namespace) -> Vec<TraitCandidate> {
+        self.r.traits_in_scope(
+            self.current_trait_ref.as_ref().map(|(module, _)| *module),
+            &self.parent_scope,
+            ident.span.ctxt(),
+            Some((ident.name, ns)),
+        )
     }
 }