rustc_session: implement latent TODO

compiler/rustc_lint/src/context.rs

@@ -36,7 +36,7 @@ use rustc_middle::ty::{self, print::Printer, GenericArg, RegisteredTools, Ty, Ty
 use rustc_session::config::ExpectedValues;
 use rustc_session::lint::{BuiltinLintDiagnostics, LintExpectationId};
 use rustc_session::lint::{FutureIncompatibleInfo, Level, Lint, LintBuffer, LintId};
-use rustc_session::Session;
+use rustc_session::{LintStoreMarker, Session};
 use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::{BytePos, Span};
@@ -77,6 +77,8 @@ pub struct LintStore {
     lint_groups: FxHashMap<&'static str, LintGroup>,
 }
 
+impl LintStoreMarker for LintStore {}
+
 /// The target of the `by_name` map, which accounts for renaming/deprecation.
 #[derive(Debug)]
 enum TargetLint {

compiler/rustc_lint/src/late.rs

@@ -30,8 +30,9 @@ use rustc_span::Span;
 use std::any::Any;
 use std::cell::Cell;
 
-/// Extract the `LintStore` from the query context.
-/// This function exists because we've erased `LintStore` as `dyn Any` in the session.
+/// Extract the [`LintStore`] from [`Session`].
+///
+/// This function exists because [`Session::lint_store`] is type-erased.
 pub fn unerased_lint_store(sess: &Session) -> &LintStore {
     let store: &Lrc<_> = sess.lint_store.as_ref().unwrap();
     let store: &dyn Any = &**store;

compiler/rustc_lint/src/lib.rs

@@ -39,6 +39,7 @@
 #![feature(min_specialization)]
 #![feature(never_type)]
 #![feature(rustc_attrs)]
+#![cfg_attr(bootstrap, feature(trait_upcasting))]
 #![recursion_limit = "256"]
 #![deny(rustc::untranslatable_diagnostic)]
 #![deny(rustc::diagnostic_outside_of_impl)]