rustc_session: Address all rustc::potential_query_instability lints

Instead of allowing `rustc::potential_query_instability` on the whole
crate we go over each lint and allow it individually if it is safe to
do. Turns out all instances were safe to allow in this crate.

compiler/rustc_session/src/code_stats.rs

@@ -132,6 +132,8 @@ impl CodeStats {
 
     pub fn print_type_sizes(&self) {
         let type_sizes = self.type_sizes.borrow();
+        // We will soon sort, so the initial order does not matter.
+        #[allow(rustc::potential_query_instability)]
         let mut sorted: Vec<_> = type_sizes.iter().collect();
 
         // Primary sort: large-to-small.
@@ -227,6 +229,8 @@ impl CodeStats {
     }
 
     pub fn print_vtable_sizes(&self, crate_name: Symbol) {
+        // We will soon sort, so the initial order does not matter.
+        #[allow(rustc::potential_query_instability)]
         let mut infos =
             std::mem::take(&mut *self.vtable_sizes.lock()).into_values().collect::<Vec<_>>();
 

compiler/rustc_session/src/lib.rs

@@ -6,7 +6,6 @@
 #![feature(map_many_mut)]
 #![feature(iter_intersperse)]
 #![recursion_limit = "256"]
-#![allow(rustc::potential_query_instability)]
 #![deny(rustc::untranslatable_diagnostic)]
 #![deny(rustc::diagnostic_outside_of_impl)]
 #![allow(internal_features)]

compiler/rustc_session/src/parse.rs

@@ -51,6 +51,9 @@ impl GatedSpans {
     /// Prepend the given set of `spans` onto the set in `self`.
     pub fn merge(&self, mut spans: FxHashMap<Symbol, Vec<Span>>) {
         let mut inner = self.spans.borrow_mut();
+        // The entries will be moved to another map so the drain order does not
+        // matter.
+        #[allow(rustc::potential_query_instability)]
         for (gate, mut gate_spans) in inner.drain() {
             spans.entry(gate).or_default().append(&mut gate_spans);
         }