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`.

6 files changed, 16 insertions, 16 deletions

diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
index e96db885131..396a0cbc889 100644
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@@ -2606,8 +2606,8 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
 impl<'tcx> Visitor<'tcx> for CheckAttrVisitor<'tcx> {
     type NestedFilter = nested_filter::OnlyBodies;
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.tcx
     }
 
     fn visit_item(&mut self, item: &'tcx Item<'tcx>) {
diff --git a/compiler/rustc_passes/src/hir_id_validator.rs b/compiler/rustc_passes/src/hir_id_validator.rs
index 34d60d90be5..43f2f892e77 100644
--- a/compiler/rustc_passes/src/hir_id_validator.rs
+++ b/compiler/rustc_passes/src/hir_id_validator.rs
@@ -105,8 +105,8 @@ impl<'a, 'hir> HirIdValidator<'a, 'hir> {
 impl<'a, 'hir> intravisit::Visitor<'hir> for HirIdValidator<'a, 'hir> {
     type NestedFilter = nested_filter::OnlyBodies;
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.tcx
     }
 
     fn visit_nested_item(&mut self, id: hir::ItemId) {
diff --git a/compiler/rustc_passes/src/lib_features.rs b/compiler/rustc_passes/src/lib_features.rs
index 600c46eb3d0..09d59e1f717 100644
--- a/compiler/rustc_passes/src/lib_features.rs
+++ b/compiler/rustc_passes/src/lib_features.rs
@@ -129,8 +129,8 @@ impl<'tcx> LibFeatureCollector<'tcx> {
 impl<'tcx> Visitor<'tcx> for LibFeatureCollector<'tcx> {
     type NestedFilter = nested_filter::All;
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.tcx
     }
 
     fn visit_attribute(&mut self, attr: &'tcx Attribute) {
diff --git a/compiler/rustc_passes/src/loops.rs b/compiler/rustc_passes/src/loops.rs
index 6eef0b926a1..0fd980af0b5 100644
--- a/compiler/rustc_passes/src/loops.rs
+++ b/compiler/rustc_passes/src/loops.rs
@@ -87,8 +87,8 @@ pub(crate) fn provide(providers: &mut Providers) {
 impl<'hir> Visitor<'hir> for CheckLoopVisitor<'hir> {
     type NestedFilter = nested_filter::OnlyBodies;
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.tcx
     }
 
     fn visit_anon_const(&mut self, c: &'hir hir::AnonConst) {
diff --git a/compiler/rustc_passes/src/naked_functions.rs b/compiler/rustc_passes/src/naked_functions.rs
index 23322be8f55..cb17b0f6cf5 100644
--- a/compiler/rustc_passes/src/naked_functions.rs
+++ b/compiler/rustc_passes/src/naked_functions.rs
@@ -259,8 +259,8 @@ struct CheckNakedAsmInNakedFn<'tcx> {
 impl<'tcx> Visitor<'tcx> for CheckNakedAsmInNakedFn<'tcx> {
     type NestedFilter = OnlyBodies;
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.tcx
     }
 
     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
diff --git a/compiler/rustc_passes/src/stability.rs b/compiler/rustc_passes/src/stability.rs
index fd30d0d4867..d045e61d1d4 100644
--- a/compiler/rustc_passes/src/stability.rs
+++ b/compiler/rustc_passes/src/stability.rs
@@ -394,8 +394,8 @@ impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
     /// deep-walking.
     type NestedFilter = nested_filter::All;
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.tcx
     }
 
     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
@@ -616,8 +616,8 @@ impl<'tcx> MissingStabilityAnnotations<'tcx> {
 impl<'tcx> Visitor<'tcx> for MissingStabilityAnnotations<'tcx> {
     type NestedFilter = nested_filter::OnlyBodies;
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.tcx
     }
 
     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
@@ -756,8 +756,8 @@ impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
     /// Because stability levels are scoped lexically, we want to walk
     /// nested items in the context of the outer item, so enable
     /// deep-walking.
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.tcx
     }
 
     fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {