Overhaul the `intravisit::Map` trait.

First of all, note that `Map` has three different relevant meanings.
- The `intravisit::Map` trait.
- The `map::Map` struct.
- The `NestedFilter::Map` associated type.

The `intravisit::Map` trait is impl'd twice.
- For `!`, where the methods are all unreachable.
- For `map::Map`, which gets HIR stuff from the `TyCtxt`.

As part of getting rid of `map::Map`, this commit changes `impl
intravisit::Map for map::Map` to `impl intravisit::Map for TyCtxt`. It's
fairly straightforward except various things are renamed, because the
existing names would no longer have made sense.

- `trait intravisit::Map` becomes `trait intravisit::HirTyCtxt`, so named
  because it gets some HIR stuff from a `TyCtxt`.
- `NestedFilter::Map` assoc type becomes `NestedFilter::MaybeTyCtxt`,
  because it's always `!` or `TyCtxt`.
- `Visitor::nested_visit_map` becomes `Visitor::maybe_tcx`.

I deliberately made the new trait and associated type names different to
avoid the old `type Map: Map` situation, which I found confusing. We now
have `type MaybeTyCtxt: HirTyCtxt`.

3 files changed, 8 insertions, 8 deletions

diff --git a/clippy_lints/src/methods/needless_collect.rs b/clippy_lints/src/methods/needless_collect.rs
index 5664ffba1a0..45f79dd44f2 100644
--- a/clippy_lints/src/methods/needless_collect.rs
+++ b/clippy_lints/src/methods/needless_collect.rs
@@ -456,8 +456,8 @@ impl<'tcx> Visitor<'tcx> for UsedCountVisitor<'_, 'tcx> {
         }
     }
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.cx.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.cx.tcx
     }
 }
 
diff --git a/clippy_lints/src/methods/option_map_unwrap_or.rs b/clippy_lints/src/methods/option_map_unwrap_or.rs
index 7c4dc4ffb20..4a8a221e8c3 100644
--- a/clippy_lints/src/methods/option_map_unwrap_or.rs
+++ b/clippy_lints/src/methods/option_map_unwrap_or.rs
@@ -143,8 +143,8 @@ impl<'tcx> Visitor<'tcx> for UnwrapVisitor<'_, 'tcx> {
         walk_path(self, path);
     }
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.cx.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.cx.tcx
     }
 }
 
@@ -174,7 +174,7 @@ impl<'tcx> Visitor<'tcx> for ReferenceVisitor<'_, 'tcx> {
         rustc_hir::intravisit::walk_expr(self, expr)
     }
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.cx.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.cx.tcx
     }
 }
diff --git a/clippy_lints/src/methods/utils.rs b/clippy_lints/src/methods/utils.rs
index 6e39e7be2c4..3611b341897 100644
--- a/clippy_lints/src/methods/utils.rs
+++ b/clippy_lints/src/methods/utils.rs
@@ -89,8 +89,8 @@ struct CloneOrCopyVisitor<'cx, 'tcx> {
 impl<'tcx> Visitor<'tcx> for CloneOrCopyVisitor<'_, 'tcx> {
     type NestedFilter = nested_filter::OnlyBodies;
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.cx.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.cx.tcx
     }
 
     fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {