Move maybe_lint_level_root_bounded.

From `TyCtxt` to the MIR `Builder`. This will allow us to add a cache to
`Builder` and use it from `maybe_lint_level_root_bounded`.

Author: nnethercote

compiler/rustc_middle/src/lint.rs

@@ -169,26 +169,6 @@ impl TyCtxt<'_> {
     pub fn lint_level_at_node(self, lint: &'static Lint, id: HirId) -> (Level, LintLevelSource) {
         self.shallow_lint_levels_on(id.owner).lint_level_id_at_node(self, LintId::of(lint), id)
     }
-
-    /// Walks upwards from `id` to find a node which might change lint levels with attributes.
-    /// It stops at `bound` and just returns it if reached.
-    pub fn maybe_lint_level_root_bounded(self, mut id: HirId, bound: HirId) -> HirId {
-        let hir = self.hir();
-        loop {
-            if id == bound {
-                return bound;
-            }
-
-            if hir.attrs(id).iter().any(|attr| Level::from_attr(attr).is_some()) {
-                return id;
-            }
-            let next = hir.parent_id(id);
-            if next == id {
-                bug!("lint traversal reached the root of the crate");
-            }
-            id = next;
-        }
-    }
 }
 
 /// This struct represents a lint expectation and holds all required information

compiler/rustc_mir_build/src/build/scope.rs

@@ -90,8 +90,8 @@ use rustc_index::{IndexSlice, IndexVec};
 use rustc_middle::middle::region;
 use rustc_middle::mir::*;
 use rustc_middle::thir::{Expr, LintLevel};
-
 use rustc_middle::ty::Ty;
+use rustc_session::lint::Level;
 use rustc_span::{Span, DUMMY_SP};
 
 #[derive(Debug)]
@@ -773,8 +773,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 // to avoid adding Hir dependencies on our parents.
                 // We estimate the true lint roots here to avoid creating a lot of source scopes.
                 (
-                    self.tcx.maybe_lint_level_root_bounded(current_id, self.hir_id),
-                    self.tcx.maybe_lint_level_root_bounded(parent_id, self.hir_id),
+                    self.maybe_lint_level_root_bounded(current_id, self.hir_id),
+                    self.maybe_lint_level_root_bounded(parent_id, self.hir_id),
                 )
             };
 
@@ -784,6 +784,27 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         }
     }
 
+    /// Walks upwards from `id` to find a node which might change lint levels with attributes.
+    /// It stops at `bound` and just returns it if reached.
+    fn maybe_lint_level_root_bounded(&self, mut id: HirId, bound: HirId) -> HirId {
+        let hir = self.tcx.hir();
+        loop {
+            if id == bound {
+                return bound;
+            }
+
+            if hir.attrs(id).iter().any(|attr| Level::from_attr(attr).is_some()) {
+                return id;
+            }
+
+            let next = hir.parent_id(id);
+            if next == id {
+                bug!("lint traversal reached the root of the crate");
+            }
+            id = next;
+        }
+    }
+
     /// Creates a new source scope, nested in the current one.
     pub(crate) fn new_source_scope(
         &mut self,