Move lint_store from GlobalCtxt to Session.

This was made possible by the removal of plugin support, which
simplified lint store creation.

This simplifies the places in rustc and rustdoc that call
`describe_lints`, which are early on. The lint store is now built before
those places, so they don't have to create their own lint store for
temporary use, they can just use the main one.

compiler/rustc_session/src/session.rs

@@ -16,7 +16,9 @@ use rustc_data_structures::flock;
 use rustc_data_structures::fx::{FxHashMap, FxIndexSet};
 use rustc_data_structures::jobserver::{self, Client};
 use rustc_data_structures::profiling::{SelfProfiler, SelfProfilerRef};
-use rustc_data_structures::sync::{AtomicU64, Lock, Lrc, OneThread, Ordering::SeqCst};
+use rustc_data_structures::sync::{
+    AtomicU64, DynSend, DynSync, Lock, Lrc, OneThread, Ordering::SeqCst,
+};
 use rustc_errors::annotate_snippet_emitter_writer::AnnotateSnippetEmitterWriter;
 use rustc_errors::emitter::{DynEmitter, EmitterWriter, HumanReadableErrorType};
 use rustc_errors::json::JsonEmitter;
@@ -37,6 +39,7 @@ use rustc_target::spec::{
     DebuginfoKind, SanitizerSet, SplitDebuginfo, StackProtector, Target, TargetTriple, TlsModel,
 };
 
+use std::any::Any;
 use std::cell::{self, RefCell};
 use std::env;
 use std::fmt;
@@ -167,6 +170,15 @@ pub struct Session {
     /// false positives about a job server in our environment.
     pub jobserver: Client,
 
+    /// This only ever stores a `LintStore` but we don't want a dependency on that type here.
+    ///
+    /// FIXME(Centril): consider `dyn LintStoreMarker` once
+    /// we can upcast to `Any` for some additional type safety.
+    pub lint_store: Option<Lrc<dyn Any + DynSync + DynSend>>,
+
+    /// Should be set if any lints are registered in `lint_store`.
+    pub registered_lints: bool,
+
     /// Cap lint level specified by a driver specifically.
     pub driver_lint_caps: FxHashMap<lint::LintId, lint::Level>,
 
@@ -1483,6 +1495,8 @@ pub fn build_session(
         optimization_fuel,
         print_fuel,
         jobserver: jobserver::client(),
+        lint_store: None,
+        registered_lints: false,
         driver_lint_caps,
         ctfe_backtrace,
         miri_unleashed_features: Lock::new(Default::default()),