Add some comments

compiler/rustc_interface/src/interface.rs

@@ -40,7 +40,11 @@ pub struct Compiler {
     pub sess: Session,
     pub codegen_backend: Box<dyn CodegenBackend>,
     pub(crate) override_queries: Option<fn(&Session, &mut Providers)>,
+
+    /// A reference to the current `GlobalCtxt` which we pass on to `GlobalCtxt`.
     pub(crate) current_gcx: CurrentGcx,
+
+    /// A jobserver reference which we pass on to `GlobalCtxt`.
     pub(crate) jobserver_proxy: Arc<Proxy>,
 }
 

compiler/rustc_middle/src/ty/context.rs

@@ -1440,6 +1440,7 @@ pub struct GlobalCtxt<'tcx> {
 
     current_gcx: CurrentGcx,
 
+    /// A jobserver reference used to release then acquire a token while waiting on a query.
     pub jobserver_proxy: Arc<Proxy>,
 }
 

compiler/rustc_query_system/src/query/mod.rs

@@ -152,6 +152,8 @@ pub enum QuerySideEffect {
 pub trait QueryContext: HasDepContext {
     type QueryInfo: Clone;
 
+    /// Gets a jobserver reference which is used to release then acquire
+    /// a token while waiting on a query.
     fn jobserver_proxy(&self) -> &Proxy;
 
     fn next_job_id(self) -> QueryJobId;