rustc_lint: replace free function with extension trait

This is a bit more discoverable.

compiler/rustc_driver_impl/src/lib.rs

@@ -33,7 +33,7 @@ use rustc_feature::find_gated_cfg;
 use rustc_fluent_macro::fluent_messages;
 use rustc_interface::util::{self, collect_crate_types, get_codegen_backend};
 use rustc_interface::{interface, Queries};
-use rustc_lint::unerased_lint_store;
+use rustc_lint::SessionExt;
 use rustc_metadata::locator;
 use rustc_session::config::{nightly_options, CG_OPTIONS, Z_OPTIONS};
 use rustc_session::config::{ErrorOutputType, Input, OutFileName, OutputType, TrimmedDefPaths};
@@ -979,7 +979,7 @@ Available lint options:
         lints
     }
 
-    let lint_store = unerased_lint_store(sess);
+    let lint_store = sess.lint_store();
     let (loaded, builtin): (Vec<_>, _) =
         lint_store.get_lints().iter().cloned().partition(|&lint| lint.is_loaded);
     let loaded = sort_lints(sess, loaded);

compiler/rustc_interface/src/passes.rs

@@ -14,7 +14,7 @@ use rustc_expand::base::{ExtCtxt, LintStoreExpand};
 use rustc_feature::Features;
 use rustc_fs_util::try_canonicalize;
 use rustc_hir::def_id::{StableCrateId, LOCAL_CRATE};
-use rustc_lint::{unerased_lint_store, BufferedEarlyLint, EarlyCheckNode, LintStore};
+use rustc_lint::{BufferedEarlyLint, EarlyCheckNode, LintStore, SessionExt};
 use rustc_metadata::creader::CStore;
 use rustc_middle::arena::Arena;
 use rustc_middle::dep_graph::DepGraph;
@@ -127,7 +127,7 @@ fn configure_and_expand(
     let tcx = resolver.tcx();
     let sess = tcx.sess;
     let features = tcx.features();
-    let lint_store = unerased_lint_store(tcx.sess);
+    let lint_store = tcx.sess.lint_store();
     let crate_name = tcx.crate_name(LOCAL_CRATE);
     let lint_check_node = (&krate, pre_configured_attrs);
     pre_expansion_lint(
@@ -319,7 +319,7 @@ fn early_lint_checks(tcx: TyCtxt<'_>, (): ()) {
         }
     });
 
-    let lint_store = unerased_lint_store(tcx.sess);
+    let lint_store = tcx.sess.lint_store();
     rustc_lint::check_ast_node(
         sess,
         tcx.features(),

compiler/rustc_lint/src/late.rs

@@ -30,13 +30,16 @@ use rustc_span::Span;
 use std::any::Any;
 use std::cell::Cell;
 
-/// 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;
-    store.downcast_ref().unwrap()
+pub trait SessionExt {
+    fn lint_store(&self) -> &LintStore;
+}
+
+impl SessionExt for Session {
+    fn lint_store(&self) -> &LintStore {
+        let store: &Lrc<_> = self.lint_store.as_ref().unwrap();
+        let store: &dyn Any = &**store;
+        store.downcast_ref().unwrap()
+    }
 }
 
 macro_rules! lint_callback { ($cx:expr, $f:ident, $($args:expr),*) => ({
@@ -364,11 +367,8 @@ pub fn late_lint_mod<'tcx, T: LateLintPass<'tcx> + 'tcx>(
     // Note: `passes` is often empty. In that case, it's faster to run
     // `builtin_lints` directly rather than bundling it up into the
     // `RuntimeCombinedLateLintPass`.
-    let mut passes: Vec<_> = unerased_lint_store(tcx.sess)
-        .late_module_passes
-        .iter()
-        .map(|mk_pass| (mk_pass)(tcx))
-        .collect();
+    let mut passes: Vec<_> =
+        tcx.sess.lint_store().late_module_passes.iter().map(|mk_pass| (mk_pass)(tcx)).collect();
     if passes.is_empty() {
         late_lint_mod_inner(tcx, module_def_id, context, builtin_lints);
     } else {
@@ -405,7 +405,7 @@ fn late_lint_mod_inner<'tcx, T: LateLintPass<'tcx>>(
 fn late_lint_crate<'tcx>(tcx: TyCtxt<'tcx>) {
     // Note: `passes` is often empty.
     let mut passes: Vec<_> =
-        unerased_lint_store(tcx.sess).late_passes.iter().map(|mk_pass| (mk_pass)(tcx)).collect();
+        tcx.sess.lint_store().late_passes.iter().map(|mk_pass| (mk_pass)(tcx)).collect();
 
     if passes.is_empty() {
         return;

compiler/rustc_lint/src/levels.rs

@@ -7,7 +7,7 @@ use crate::{
     builtin::MISSING_DOCS,
     context::{CheckLintNameResult, LintStore},
     fluent_generated as fluent,
-    late::unerased_lint_store,
+    late::SessionExt,
     lints::{
         DeprecatedLintName, IgnoredUnlessCrateSpecified, OverruledAttributeLint, RemovedLint,
         RenamedLint, RenamedLintSuggestion, UnknownLint, UnknownLintSuggestion,
@@ -122,7 +122,7 @@ impl LintLevelSets {
 }
 
 fn lint_expectations(tcx: TyCtxt<'_>, (): ()) -> Vec<(LintExpectationId, LintExpectation)> {
-    let store = unerased_lint_store(tcx.sess);
+    let store = tcx.sess.lint_store();
 
     let mut builder = LintLevelsBuilder {
         sess: tcx.sess,
@@ -151,7 +151,7 @@ fn lint_expectations(tcx: TyCtxt<'_>, (): ()) -> Vec<(LintExpectationId, LintExp
 
 #[instrument(level = "trace", skip(tcx), ret)]
 fn shallow_lint_levels_on(tcx: TyCtxt<'_>, owner: hir::OwnerId) -> ShallowLintLevelMap {
-    let store = unerased_lint_store(tcx.sess);
+    let store = tcx.sess.lint_store();
     let attrs = tcx.hir_attrs(owner);
 
     let mut levels = LintLevelsBuilder {

compiler/rustc_lint/src/lib.rs

@@ -133,7 +133,7 @@ pub use builtin::{MissingDoc, SoftLints};
 pub use context::{CheckLintNameResult, FindLintError, LintStore};
 pub use context::{EarlyContext, LateContext, LintContext};
 pub use early::{check_ast_node, EarlyCheckNode};
-pub use late::{check_crate, late_lint_mod, unerased_lint_store};
+pub use late::{check_crate, late_lint_mod, SessionExt};
 pub use passes::{EarlyLintPass, LateLintPass};
 pub use rustc_session::lint::Level::{self, *};
 pub use rustc_session::lint::{BufferedEarlyLint, FutureIncompatibleInfo, Lint, LintId};