rustc_lint: Enforce rustc::potential_query_instability lint

Stop allowing `rustc::potential_query_instability` on all of
`rustc_lint` and instead allow it on a case-by-case basis if it is safe
to do so. In this particular crate, all lints were safe to allow.

compiler/rustc_lint/src/context.rs

@@ -430,6 +430,8 @@ impl LintStore {
         // Note: find_best_match_for_name depends on the sort order of its input vector.
         // To ensure deterministic output, sort elements of the lint_groups hash map.
         // Also, never suggest deprecated lint groups.
+        // We will soon sort, so the initial order does not matter.
+        #[allow(rustc::potential_query_instability)]
         let mut groups: Vec<_> = self
             .lint_groups
             .iter()

compiler/rustc_lint/src/context/diagnostics.rs

@@ -197,6 +197,8 @@ pub(super) fn builtin(
                 if let Some(ExpectedValues::Some(best_match_values)) =
                     sess.parse_sess.check_config.expecteds.get(&best_match)
                 {
+                    // We will soon sort, so the initial order does not matter.
+                    #[allow(rustc::potential_query_instability)]
                     let mut possibilities =
                         best_match_values.iter().flatten().map(Symbol::as_str).collect::<Vec<_>>();
                     possibilities.sort();
@@ -298,6 +300,9 @@ pub(super) fn builtin(
                 );
             };
             let mut have_none_possibility = false;
+            // We later sort possibilities if it is not empty, so the
+            // order here does not matter.
+            #[allow(rustc::potential_query_instability)]
             let possibilities: Vec<Symbol> = values
                 .iter()
                 .inspect(|a| have_none_possibility |= a.is_none())

compiler/rustc_lint/src/lib.rs

@@ -25,7 +25,6 @@
 //!
 //! This API is completely unstable and subject to change.
 
-#![allow(rustc::potential_query_instability)]
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(rustdoc_internals)]

compiler/rustc_lint/src/non_ascii_idents.rs

@@ -174,6 +174,8 @@ impl EarlyLintPass for NonAsciiIdents {
 
         // Sort by `Span` so that error messages make sense with respect to the
         // order of identifier locations in the code.
+        // We will soon sort, so the initial order does not matter.
+        #[allow(rustc::potential_query_instability)]
         let mut symbols: Vec<_> = symbols.iter().collect();
         symbols.sort_by_key(|k| k.1);
 
@@ -287,6 +289,8 @@ impl EarlyLintPass for NonAsciiIdents {
             }
 
             if has_suspicious {
+                // The end result is put in `lint_reports` which is sorted.
+                #[allow(rustc::potential_query_instability)]
                 let verified_augmented_script_sets = script_states
                     .iter()
                     .flat_map(|(k, v)| match v {
@@ -299,6 +303,8 @@ impl EarlyLintPass for NonAsciiIdents {
                 let mut lint_reports: BTreeMap<(Span, Vec<char>), AugmentedScriptSet> =
                     BTreeMap::new();
 
+                // The end result is put in `lint_reports` which is sorted.
+                #[allow(rustc::potential_query_instability)]
                 'outerloop: for (augment_script_set, usage) in script_states {
                     let ScriptSetUsage::Suspicious(mut ch_list, sp) = usage else { continue };