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`.

clippy_lints/src/derive.rs

@@ -437,8 +437,8 @@ impl<'tcx> Visitor<'tcx> for UnsafeVisitor<'_, 'tcx> {
         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
     }
 }
 

clippy_lints/src/doc/mod.rs

@@ -1079,8 +1079,8 @@ impl<'tcx> Visitor<'tcx> for FindPanicUnwrap<'_, 'tcx> {
     // Panics in const blocks will cause compilation to fail.
     fn visit_anon_const(&mut self, _: &'tcx AnonConst) {}
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.cx.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.cx.tcx
     }
 }
 

clippy_lints/src/extra_unused_type_parameters.rs

@@ -241,8 +241,8 @@ impl<'tcx> Visitor<'tcx> for TypeWalker<'_, 'tcx> {
         }
     }
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.cx.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.cx.tcx
     }
 }
 

clippy_lints/src/from_over_into.rs

@@ -134,8 +134,8 @@ impl<'tcx> Visitor<'tcx> for SelfFinder<'_, 'tcx> {
     type Result = ControlFlow<()>;
     type NestedFilter = 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_path(&mut self, path: &Path<'tcx>, _id: HirId) -> Self::Result {

clippy_lints/src/implicit_hasher.rs

@@ -363,7 +363,7 @@ impl<'tcx> Visitor<'tcx> for ImplicitHasherConstructorVisitor<'_, '_, 'tcx> {
         walk_expr(self, e);
     }
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.cx.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.cx.tcx
     }
 }

clippy_lints/src/index_refutable_slice.rs

@@ -223,8 +223,8 @@ struct SliceIndexLintingVisitor<'a, 'tcx> {
 impl<'tcx> Visitor<'tcx> for SliceIndexLintingVisitor<'_, '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 hir::Expr<'tcx>) {

clippy_lints/src/lifetimes.rs

@@ -19,8 +19,8 @@ use rustc_hir::{
     WherePredicateKind, lang_items,
 };
 use rustc_lint::{LateContext, LateLintPass, LintContext};
-use rustc_middle::hir::map::Map;
 use rustc_middle::hir::nested_filter as middle_nested_filter;
+use rustc_middle::ty::TyCtxt;
 use rustc_session::impl_lint_pass;
 use rustc_span::Span;
 use rustc_span::def_id::LocalDefId;
@@ -582,7 +582,7 @@ impl<'tcx, F> Visitor<'tcx> for LifetimeChecker<'_, 'tcx, F>
 where
     F: NestedFilter<'tcx>,
 {
-    type Map = Map<'tcx>;
+    type MaybeTyCtxt = TyCtxt<'tcx>;
     type NestedFilter = F;
 
     // for lifetimes as parameters of generics
@@ -628,8 +628,8 @@ where
         self.lifetime_elision_impossible = false;
     }
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.cx.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.cx.tcx
     }
 }
 

clippy_lints/src/loops/utils.rs

@@ -240,8 +240,8 @@ impl<'tcx> Visitor<'tcx> for InitializeVisitor<'_, 'tcx> {
         }
     }
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.cx.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.cx.tcx
     }
 }
 

clippy_lints/src/loops/while_let_on_iterator.rs

@@ -245,8 +245,8 @@ fn needs_mutable_borrow(cx: &LateContext<'_>, iter_expr: &IterExpr, loop_expr: &
     impl<'tcx> Visitor<'tcx> for AfterLoopVisitor<'_, '_, 'tcx> {
         type NestedFilter = OnlyBodies;
         type Result = ControlFlow<()>;
-        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, e: &'tcx Expr<'_>) -> Self::Result {
@@ -288,8 +288,8 @@ fn needs_mutable_borrow(cx: &LateContext<'_>, iter_expr: &IterExpr, loop_expr: &
     }
     impl<'tcx> Visitor<'tcx> for NestedLoopVisitor<'_, '_, 'tcx> {
         type NestedFilter = 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_local(&mut self, l: &'tcx LetStmt<'_>) {

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
     }
 }
 

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
     }
 }

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>) {

clippy_lints/src/mutable_debug_assertion.rs

@@ -119,7 +119,7 @@ impl<'tcx> Visitor<'tcx> for MutArgVisitor<'_, 'tcx> {
         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
     }
 }

clippy_lints/src/ptr.rs

@@ -583,8 +583,8 @@ fn check_ptr_arg_usage<'tcx>(cx: &LateContext<'tcx>, body: &Body<'tcx>, args: &[
     }
     impl<'tcx> Visitor<'tcx> for V<'_, '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_anon_const(&mut self, _: &'tcx AnonConst) {}

clippy_lints/src/redundant_closure_call.rs

@@ -241,8 +241,8 @@ impl<'tcx> LateLintPass<'tcx> for RedundantClosureCall {
                     hir_visit::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
                 }
             }
             let mut closure_usage_count = ClosureUsageCount { cx, path, count: 0 };

clippy_lints/src/unconditional_recursion.rs

@@ -9,7 +9,6 @@ use rustc_hir::intravisit::{FnKind, Visitor, walk_body, walk_expr};
 use rustc_hir::{Body, Expr, ExprKind, FnDecl, HirId, Item, ItemKind, Node, QPath, TyKind};
 use rustc_hir_analysis::lower_ty;
 use rustc_lint::{LateContext, LateLintPass};
-use rustc_middle::hir::map::Map;
 use rustc_middle::hir::nested_filter;
 use rustc_middle::ty::{self, AssocKind, Ty, TyCtxt};
 use rustc_session::impl_lint_pass;
@@ -275,7 +274,6 @@ fn is_default_method_on_current_ty<'tcx>(tcx: TyCtxt<'tcx>, qpath: QPath<'tcx>,
 
 struct CheckCalls<'a, 'tcx> {
     cx: &'a LateContext<'tcx>,
-    map: Map<'tcx>,
     implemented_ty_id: DefId,
     method_span: Span,
 }
@@ -287,8 +285,8 @@ where
     type NestedFilter = nested_filter::OnlyBodies;
     type Result = ControlFlow<()>;
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.map
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.cx.tcx
     }
 
     fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) -> ControlFlow<()> {
@@ -380,7 +378,6 @@ impl UnconditionalRecursion {
         {
             let mut c = CheckCalls {
                 cx,
-                map: cx.tcx.hir(),
                 implemented_ty_id,
                 method_span,
             };

clippy_lints/src/unused_async.rs

@@ -101,8 +101,8 @@ impl<'tcx> Visitor<'tcx> for AsyncFnVisitor<'_, 'tcx> {
         }
     }
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.cx.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.cx.tcx
     }
 }
 

clippy_lints/src/unused_peekable.rs

@@ -112,8 +112,8 @@ impl<'tcx> Visitor<'tcx> for PeekableVisitor<'_, 'tcx> {
     type NestedFilter = OnlyBodies;
     type Result = ControlFlow<()>;
 
-    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, ex: &'tcx Expr<'tcx>) -> ControlFlow<()> {

clippy_lints/src/unwrap.rs

@@ -374,8 +374,8 @@ impl<'tcx> Visitor<'tcx> for UnwrappableVariablesVisitor<'_, 'tcx> {
         }
     }
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.cx.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.cx.tcx
     }
 }
 

clippy_lints/src/utils/internal_lints/lint_without_lint_pass.rs

@@ -277,7 +277,7 @@ impl<'tcx> Visitor<'tcx> for LintCollector<'_, 'tcx> {
         }
     }
 
-    fn nested_visit_map(&mut self) -> Self::Map {
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
         self.cx.tcx.hir()
     }
 }

clippy_lints/src/zombie_processes.rs

@@ -249,8 +249,8 @@ impl<'tcx> Visitor<'tcx> for WaitFinder<'_, 'tcx> {
         walk_expr(self, ex)
     }
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.cx.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.cx.tcx
     }
 }
 

clippy_utils/src/lib.rs

@@ -1370,8 +1370,8 @@ impl<'tcx> Visitor<'tcx> for ContainsName<'_, 'tcx> {
         }
     }
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.cx.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.cx.tcx
     }
 }
 

clippy_utils/src/usage.rs

@@ -133,8 +133,8 @@ impl<'tcx> Visitor<'tcx> for BindingUsageFinder<'_, 'tcx> {
         ControlFlow::Continue(())
     }
 
-    fn nested_visit_map(&mut self) -> Self::Map {
-        self.cx.tcx.hir()
+    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
+        self.cx.tcx
     }
 }
 

clippy_utils/src/visitors.rs

@@ -154,8 +154,8 @@ pub fn for_each_expr<'tcx, B, C: Continue>(
         type NestedFilter = nested_filter::OnlyBodies;
         type Result = ControlFlow<B>;
 
-        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, e: &'tcx Expr<'tcx>) -> Self::Result {
@@ -412,8 +412,8 @@ pub fn is_expr_unsafe<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) -> bool {
         type NestedFilter = nested_filter::OnlyBodies;
         type Result = ControlFlow<()>;
 
-        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, e: &'tcx Expr<'_>) -> Self::Result {
             match e.kind {
@@ -477,8 +477,8 @@ pub fn contains_unsafe_block<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'tcx>)
     impl<'tcx> Visitor<'tcx> for V<'_, 'tcx> {
         type Result = ControlFlow<()>;
         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_block(&mut self, b: &'tcx Block<'_>) -> Self::Result {
@@ -544,8 +544,8 @@ pub fn for_each_local_use_after_expr<'tcx, B>(
     }
     impl<'tcx, F: FnMut(&'tcx Expr<'tcx>) -> ControlFlow<B>, B> Visitor<'tcx> for V<'_, 'tcx, F, B> {
         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, e: &'tcx Expr<'tcx>) {
@@ -729,8 +729,8 @@ pub fn for_each_local_assignment<'tcx, B>(
     }
     impl<'tcx, F: FnMut(&'tcx Expr<'tcx>) -> ControlFlow<B>, B> Visitor<'tcx> for V<'_, 'tcx, F, B> {
         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, e: &'tcx Expr<'tcx>) {